\ Management of PONDEROSA PINE IN THE SOUTHWEST Agriculture Monograph No. 6 : UNITED STATES DEPARTMENT OF AGRICULTURE Forest Service Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. ye ae is a MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST As Developed by Research and Experimental Practice By G. A. PEARSON, Silviculturist Southwestern Forest and Range Experiment Station Agriculture Monograph No. 6 U. 8. DEPARTMENT OF AGRICULTURE FOREST SERVICE For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D. C. — Price 50 cents pol ; ey ts ACKNOWLEDGMENTS Acknowledgment is given to the many associates who have helped at one time or another to carry forward the ponderosa pine research program in the Southwest. Raphael Zon and S. T. Dana, as chief and assistant chief, respectively, of silvical inves- tigations in the Forest Service, and T. S. Woolsey, Jr., assistant regional forester in charge of timber management, took an active part in early planning. Other individuals who have rendered more than routine service are, in chronological order, H. D. Burrall, Enoch W. Nelson, C. F. Korstian, S. S. VanBoskirk, Hermann Krauch, Emanuel Fritz, F. W. Haasis, B. R. Lexen, EK. M. Horni- brook, F. H. Wadsworth, Edward C. Martin, Geraldine Peterson, and George Meagher. Following the author’s death in January 1949, the manuscript was completed by George Meagher, Forester, Southwestern Forest and Range Experiment Station. PREFACE Ponderosa pine, from the very beginning of the conservation movement, has figured as a leading timber species. In 1908 G. A. Pearson, a year out of forest school, was sent to Arizona to study natural regeneration of this tree, then called western yellow pine. Commercial logging was in full swing on both private and public lands. In the national forests, despite measures that seemed adequate for natural reforestation, seedlings started sparingly after cutting. To provide information on natural regeneration as well as on other phases of ponderosa pine management, the Forest Service established the Fort Valley Forest Experiment Station in 1909. The research field covered Arizona and New Mexico, but work was concentrated largely in what is now the Fort Valley Experimental Forest, a branch of the Southwestern Forest and Range Experiment Station. A long-range attack on such problems as natural restocking, growth, mortality, and methods of cutting took concrete form in the creation of a series of so-called permanent sample plots. These are essentially experimental management areas on which all trees were numbered and measured periodically. The findings presented are derived not only from academic studies and small plot records, but also from experimental practice and record on areas sufficiently large to permit commercial operations. They cover the five broad phases of ponderosa pine silviculture: (1) Removal of mature, declining, or inferior members; (2) improv- ing growth and quality of less mature stems; (3) training pole and sapling classes with an eye toward future form; (4) re- generation; and (5) protection of all age classes. While these five phases deal with the forest from seedling to sawlog, the sequence here is in a different order, because management usually begins with logging followed by treatment of younger age classes already in the stand; actual regeneration often is deferred until several decades after the first cutting. In a well-managed ponderosa pine forest, all five of these measures must go on simultaneously. Neglect of any one will adversely affect the program as a whole. Although this work presents findings over a period of 40 years, it aims to leave conclusions open to modification in the light of further experience. Tree records, many of which are now over 30 years old, should be continued. Each remeasurement brings new phases into view and each cutting virtually institutes a new set of records. Intensive management has barely begun. Not until individual areas have gone through the entire rotation from seedling to sawlog under management and record can such an experiment be regarded as finished. Several large areas in the Fort Valley Experimental Forest are unique in that they have undergone almost complete restocking since the first cutting, and the young stands are now approaching the pole stage. V vi PREFACE When the western national forests were first created, millions of acres of wild forest were placed under the jurisdiction of a handful of foresters. Forest-management application was neces- sarily crude and was focused on the protection of forests from fire, and the removal of mature and declining trees through com- mercial timber sales. Basic silvicultural information was lacking and desirable forest practices were often subordinated to economic demands. Now, after 40 years, the stage is set for a new era in western forestry. Studies such as those at Fort Valley have made available a large array of timber-growing information. Improved transpor- tation facilities have removed many of the economic barriers to the practice of good silviculture, and trained personnel is available to do the job. Western foresters can now look forward to a period of more scientific and more intensive forest management. Perpetuation of the lumber industry demands large volumes of usable raw wood material in strategic places. The national econ- omy further demands that long before the dwindling old reserves are exhausted, cut-over forests be placed in a highly productive condition. We must depend upon the ponderosa pine forests of western United States in large part to maintain softwood timber supplies in the immediate future. They contain large bodies of virgin timber and of conservatively logged stands which can be put under management with reasonable effort. Under makeshift management their yields will be low and quality lower; but under scientific management the yield in both volume and quality can be increased several fold. CONTENTS Page Page The place of ponderosa pine in Silvicultural foundations American forestry ..-..... 1 (continued) Area and geographic range 1 Tree classifications in rela- Botanical varieties of pon- tion {to ero wthnnc 5 40 derosawpine yc aati. 3 Position in the crown Timber and other resources canopy. 6. ae Al of the ponderosa pine Age-and-vigor classes Al forest 356.0 0:66-0:06 s0s0. COL ONaCGO 4 Position on the ground 43 Properties of ponderosa A comparison of DINE ee a aa ci 4 ground space and Products of ponderosa pine 5 crown vigor ...... 44 Lumber ............ 5 Use and limitations of Railroad ties ....... 6 tree classifications . A6 Mine timbers .>.. 3: af Guth . ee ea Utility poles ........ 7 Cutting in virgin stands...... AT KNuelowG0ds oe. 8 Methods tested at Fort Relation to the national Valley ceo. Bove ene yel'e cous AT timber supply ........ 8 Group selection <>... . AT Ponderosa pine research in the Light selection ...... 53 SouthWest. 06. 6 orks 9 Scattered seed tree Experimental management CULLING ee 4. o4 Sample plots ........ 9 Favoring dominants : 54 Application of Southwest- Salvage cutting ..... 56 ern findings sor. 13 Maturity selection ... o7 Silvicultural foundations ..... 15 Improvement selection 59 Climatic characteristics .. 15 Growth after partial cutting. . 66 Temperature and mois- Diameter growth ........ 66 ture limiting factors 145) Diameter growth af- Temperature and pre- fected by cutting.. 66 cipitation in the Montaltya oka ee 70 southwest 1.4 3.24% 16 Mortality in virgin and Growth periods of pon- cut-over stands 70 derosa pine ...:... 18 Mortality in relation Light and moisture re- to time after cutting 70 quirements) is4 505. : 19 Causes of mortality. . 74 Experiments in light Mortality in relation requirement ...... 21 to size and age.... 76 Soil requirements ....... 26 Mortality in relation Stochkinea ain. so eoc ns 27 to method of cutting 7 Space requirement ... 27 Replacement. s.ic 0. 06% TT ORI ene eae 5 Saco Wins me 33 Advance reproduction eee Highs taper. yes. 33 Redistribution of di- Abnormal branching . 33 ameter classes Forked boles ........ 34 through growth ... 78 Crooked or leaning Volume increment of stands i) DOlES eet ein Siete. 36 Increment in relation INO ClASSES Hh, aut Gc Gn 36 to volume and char- Balanced gradation of acter of growing age classes ....... 38 Stocks ceca cee 81 Rotations 2.255 sh ese. 40 Increment on large Site quality 65 (Gos 40 cut-over areas .... 82 Vili Growth after partial cutting Volume increment of stands (continued) Increment on _ small, well-stocked plots .. Increment in relation to time since cutting Reasons for decline of increment 2.55. Original trees and new LYCCS eae. re ee: Increment of large CVCES oe ee eee ee Increment on _ small cutting plots in New Mexico. eae To keep the forest SLOWING; can eS new silvicultural PROSVAM os eee Prediction of yield... Regeneration—natural and ar- CHI Cia ee acetate oee Natural regeneration .... Seed supply Seedbed Climatic factors in re- lation to germina- tion and survival... Relations between cut- ee) 0 -e-,e e120) e ting practice and regeneration ...... Protection of young SNOW Ne tee. os, here ee Present status of pine reproduction in Southwest -.2. 2... Artificial reforestation ... Limitations of ponde- rosa pine reforesta- tion Results of reforesta- tion in the South- west exe’ 8) se) le ee) es'one VeLie.le le eal eerie oie! 10) a) ae ei-. Seasons for planting... Seasons for seeding. . Planting stock Source and character of seed The planting or seed- ing operation Spacing Relative advantages of planting and _ seed SPOUS Sie sins serene Protection and care of plantations The place of artificial reforestation ...... Control of damaging agents... Wind mec e" 9. <9 le ie Wy @awie. oe CONTENTS Page 142 142 143 143 Control of damaging agents (continued) Snow. damage: 3.2 PIPES Se ee eee ee Control of fires by re- duction of fuel.... Rodents Small-rodents: 4... Rabbits - Porcupines TNSC CES reich ee eee Bark beetles 32 Cone beetles Root grubs Aipiemoths 7-2 eases Browsing animals ....... Control of browsing damage Mistletoe Mistletoe control .... Fungus diseases Western red rot...... Paintbrush blister rust Root. rot... eee Stagnation Total loss due to control- lable agents © Ye elie e).0) 0, @ e-= ©) 0).e e>2 -e eo), a), ebie) a) 6) os 0 We oe! 'e ie) ete @ \0' oe (eo ele e« Timber stand improvement... Objects and procedure.... Thinning the stand... Improvement cutting . Pruning Financial aspects of stand improvement .......... Costs Financing Returns on the invest- ment Stand improvement in ex- tensive practice Selection of areas.... Intensity of operation a 0s) 2) e-\8/ vee 0)re) ee see ee we Management of cut-over stands Second cuttings in Fort Valley Experimental Wing Mountain sample plot—after the first and the sec- ond cuttings se. e Economic aspects of ponderosa pine management e) ele Ge.) we eer e Silviculture lowers produc- LION COStS*S2..4. Se eee Values in relation to log grades The economic future of ponderosa pine lands... The business of timber growing a) sce, etree) Bie) 0, 85a ee ge A program for better ponderosa pine management .......... 144 Literature cited = .: 2 tases Page 145 145 145 151 151 153 153 154 154 155 156 156 157 160 162 165 165 165 167 168 168 168 170 170 170 171 176 180 180 182 182. 183 183 183 187 188 188 200 200 201 205 206 208 213 | | | The Place of Ponderosa Pine in American Forestry AREA AND GEOGRAPHIC RANGE Ponderosa pine (Pinus ponderosa) is the most widely dis- tributed conifer in North America, and one of the most valuable. Commercial stands of the species are found in all of the 15 States which lie wholly or in part west of the 102d meridian, and in all but one it ranks among the most important lumber producers (fig. 1). In the Southwest, ponderosa pine is of particular im- portance since this one species makes up 88 percent of the Se at saw-timber volume in the two States of Arizona and New eX1Co. In this treatise, distinction is made between the ‘“‘interior”’ ponderosa pine type and the ‘“‘mixed” type where ponderosa pine is associated with other species. The latter type occurs in zones of high precipitation, mainly near the Pacific coast where pon- derosa pine is associated with sugar pine, incense cedar, hemlock, and fir. Smaller areas of the mixed type are found throughout the Rocky Mountain region in the transition zone where pon- derosa pine merges with the Douglas-fir-white fir type at higher elevations. In both cases increased soil moisture and lower tem- perature favor species which by virtue of lower demands on light and heat are able to reproduce under ponderosa pine and thus gain dominance in the next generation. Under these circum- stances, even though the present stand may carry a heavy volume of ponderosa pine, the permanence of this species is not assured. The interior ponderosa pine type, characterized by pure or nearly pure stands of ponderosa pine, occupies middle elevations in a belt about 800 miles wide beginning 150-200 miles inland from the Pacific coast, reaching eastward into the Dakotas, northern Nebraska, and western Texas, and extending clear across the United States from north to south. Commercial stands also occur in Canada and Mexico. The interior type generally receives an annual precipitation of less than 25 inches and in some localities less than 20 inches. This work deals exclusively with the interior or pure ponderosa pine type and is concerned primarily with the interior type as it occurs in the Southwest. The total area occupied by the interior ponderosa pine type in the United States is estimated at 37 million acres. Distribu- 1 Because of the intermingling with other types and the many ownerships involved, exact figures are not available. 1 2 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 cs *WYOMINGS ¥ FIGURE 1.—Geographic range of ponderosa pine in western United States. (After Sudworth.) tion is approximately as follows: Northwest, including eastern Oregon, eastern Washington, Idaho, and Montana, 18 million acres; California, east of the Sierras, 4 million acres; the central Rocky Mountains, including Colorado, Wyoming, South Dakota, Utah, and Nevada, 7 million acres; and Arizona and New Mexico, 8 million acres. Of the 8 million acres of interior ponderosa pine in the Southwest, roughly one-third is at present commercially inaccessible or withdrawn from timber growing use. About one- half of the accessible land has now been logged. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 3 BOTANICAL VARIETIES OF PONDEROSA PINE The United States Forest Service (89) ? recognizes, in addi- tion to the type species Pinus ponderosa Laws., two varieties: scopulorum Engelm. and arizonica (Engelm.) Shaw. Pinus ponderosa Laws. ranges from near the Pacific coast east- ward through California, Oregon, Washington, Idaho, and into western Montana. The variety scopulorum, commonly called the Rocky Mountain form, extends clear through the Rocky Mountain region eastward to the Black Hills and south into central Arizona and New Mexico. The other variety, arizonica, whose real home is Mexico, occurs on isolated mountains in southern Arizona and southern New Mexico. All three forms are found in the interior ponderosa pine type. Differences which have given rise to distinctions in nomen- clature are both morphological and physiological. The ‘true’ ponderosa is a larger tree than scopulorum. In the interior region this appears to be due to greater longevity rather than faster growth. Longer needles, larger seeds, and slower germination characterize ponderosa as compared with scopulorum. Korstian (34) has pointed out that the Black Hills pine beetle (Dendrocto- nus ponderosae Hopk.) confines its activity to scopulorum, giving way to the species D. brevicomis within the range of ponderosa. It should be noted, however, that although the Black Hills beetle has attained epidemic proportions on the north side of the Grand Canyon of Arizona it is not known to have occurred in the great pine belt extending from the south rim clear across the State and well into New Mexico. Korstian also calls attention to differences in leaf structure and chemical composition of the oleoresin (33). Weidman (97) has made an exhaustive study of leaf characteristics and growth habits of various geographic races. Scopulorum is by no means a tree of ,fixed characteristics. According to the textbooks it has two or three needles in a bundle, but in Arizona the number is uniformly three. In the Black Hills, Colorado, and northern New Mexico there are either two or three needles. The Black Hills tree is generally smaller than its Arizona kin; it also has shorter needles, of a yellowish green color in contrast to the bluish green in Arizona, and no- ticeably smaller seeds. Seedlings grown from Black Hills and Arizona seed in the nursery at Fort Valley have exhibited the same difference in length and color of needles; the Black Hills seedlings were also smaller and had more compact crowns than those grown from local seed. Another characteristic of the Black Hills seedlings was their habit of forming definite terminal buds in their third year, whereas the progeny of Arizona seed do not form terminal buds until several years older. Seedlings propa- gated from Colorado and Utah seed were intermediate between Black Hills and Arizona types, though more like the former. The variety arizonica differs from the Arizona form of scopu- lorum mainly in having five needles in a bundle instead of three. 2 Italic numbers in parentheses refer to Literature Cited, pages 213 to 218, 4 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 The needles are more slender than those of scopulorum and they fall in their third year, whereas those of scopulorum persist until their fourth or fifth year. TIMBER AND OTHER RESOURCES OF THE PONDEROSA PINE FOREST As compared with forests in humid regions, interior ponderosa pine yields are light, ranging generally from 5,000 to 15,000 board feet per acre though occasionally exceeding 20,000 feet. Less sig- nificance is attached to the volume of timber than to its distri- bution and location. Ponderosa pine may be thought of as the near-desert timber tree of the United States. It is not, strictly speaking, a desert tree but it grows on elevated plateaus rising out of the vast semiarid region known as the Great American Desert. In mountain regions it inhabits the lowest of the zones in which trees attain a stature suitable for lumber. Although too cold for most field crops, the area characterized by the pon- derosa pine type does support some agriculture and a large amount of summer grazing. Because of relatively high accessi- bility, ponderosa pine forests are the main source of lumber and fuel for local consumption within a million square miles of ter- ritory. Lumber manufacture is an important industry in hundreds of communities. The pine forests, correctly managed, provide an excellent cover for millions of acres of watershed. They pro- vide summer recreational grounds which rank among the finest in the country. © The low yields of ponderosa pine are in a measure compensated by other features. The tree produces a wood which ranks among the best for all-round use, and it is able to grow on sites generally too dry to support other saw-timber species. One of the distinct advantages of interior ponderosa pine, as compared with some other forests, is that the key species succeeds itself from gen- eration to generation. Another advantage is that fires are more controllable because the crown canopy is more open than that of the heavier stands, so that the forest is less subject to crown fires. According to present standards, much of the interior pon- derosa pine type is likely, because of low production or inaccessi- bility, to remain under an extensive form of management, or multiple use. On the other hand, intensive management can im- prove this situation by growing heavier stands of superior qual- ity. It is estimated that half of the total acreage would justify intensive management with timber as the major crop. PROPERTIES OF PONDEROSA PINE Botanically, Pinus ponderosa belongs to the yellow pine group, but the wood resembles more closely the white pines. The heart- wood is reddish brown, and the sapwood pale yellow or almost white. In trees under 200 years old, the wood is nearly all sap- wood, and if such trees have been well grown the product is a beautiful soft white material comparable to white pine. Old MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 3 trees contain a larger proportion of the darker heartwood, which is usually heavier, harder, and stronger than the sapwood. Since the heartwood occupies the central core of the bole, produced while the tree was young, it usually has wider annual rings and contains more knots and resin than are found in the sapwood produced later in life. In slow-growing trees, such as generally occur in dense stands or on dry sites, the sapwood is of very fine and even grain, in contrast to the coarse or variable grain of the fast-growing trees in open stands or on moist sites. According to Betts (&) ponderosa pine ranks moderately high in paintability, being rated above Douglas-fir and the southern pines, but below the commercial white pines. It does not split easily in nailing, but neither does it hold nails as well as some other woods. In contact with the soil, it is said to decay more readily than the white pines; this, however, may not be true of the heartwood which is much more resistant than the sapwood. Both heartwood and sapwood take preservative treatment readily. Compared with Douglas-fir and longleaf pine, ponderosa pine is lighter in weight, weaker, softer, and more easily worked. A fact which should always be borne in mind in dealing with ponderosa pine is that the wood is extremely variable, according to the conditions under which it has grown. The qualities which place ponderosa pine lumber in the high-value class, namely regular grain and a relatively soft, even textured, and readily workable wood, are attained only by trees grown under condi- tions which produce clear boles and maintain a uniform rate of growth. Open-grown trees are always limby, and while the boles may become smooth after attaining great size the interior is al- ways knotty. Small, firm knots, produced by small limbs which die and shed quickly, are far less objectionable than the large, loose knots formed when limbs are allowed to grow to large diam- eter. As will be explained later, both natural clearing of boles and width of annual rings can be controlled by regulating the density of stands. And, fortunately, the measures which induce the development of high quality also make for high yields. PRODUCTS OF PONDEROSA PINE Ponderosa pine is adapted to a variety of uses but at present the most important markets are for lumber and railroad ties. In some regions, notably the Black Hills, large quantities of ponderosa pine go into mine props and stulls; the mines promise to take increasing quantities in other regions. Naval stores are a possibility which has been explored in Arizona with results which are not wholly unfavorable (7). Ponderosa pine fuel finds exten- sive local use throughout the region. Lumber Ponderosa pine lumber ranks high among western conifers, commanding prices exceeded in general markets only by Cali- fornia sugar pine and western white pine. In the two States of 6 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 Arizona and New Mexico, annual production of ponderosa pine lumber has, since 1925, varied from a high of 345 million board feet in 1946 to a low of 118 million in 1932. Southwestern forests furnish about 10 percent of the national production of ponderosa pine lumber. Large quantities are absorbed by the building trades which employ intermediate grades for framework, sheathing, and sub- flooring, the better grades for siding, and the highest grades for window sash, doors, and interior finish. In recent years, knotty pine has become popular for interior paneling. The knots in this class of material must be firm and not excessively large, thus again calling for timber which has grown in close stands. Pon- derosa pine is too soft for good flooring. In addition to that used by the building trades, the fruit and vegetable industry is now absorbing immense quantities of lum- ber which is remanufactured into boxes and crates. According to statistics by the U. S. Forest Service (88), the volume of ponderosa pine used for “boxes, baskets, and crating’’ in 1940 was 29,593,000 board feet in Arizona and 7,580,000 board feet in New Mexico.* During the same year California and Oregon each used over 300 million board feet and Washington 126 million. In all of the Rocky Mountain and Pacific Coast States except Idaho, ponderosa pine exceeded by a wide margin the total of all other woods used for these purposes. i An acute lumber shortage during the war brought many sug- gestions for replacement of wooden boxes with fiber cartons. Pro- posed substitutions encountered many limitations, notably in the transportation of heavy materials, such as ammunition, and pro- duce which tends to exude moisture, such as fruits and vegetables. Railroad Ties Next to lumber, the greatest industrial use of ponderosa pine throughout the West is for railroad ties. Ponderosa pine makes a good tie because, along with other desirable qualities, it responds well to preservative treatment. Railroad ties are cut from trees of about the same minimum diameter and quality that is required for good lumber. They must be free of large knots in the section where the spikes are driven, while loose knots and rot are pro- hibited generally. Ties are of two broad classes: sawn and hewn. Sawn ties.—Sawn ties are made from medium grades of saw- logs with a minimum diameter of 11 inches inside the bark at the small end. Operations combining production of sawn ties with lumber result in less waste than if ties alone are sawn. One ob- jection to such a combination, however, is that standard ties are now 9 feet long while standard logs are 16 feet, thus yielding one tie plus 7 feet, which is an odd length in lumber. This should °In southern Arizona, the cost of box shook used in packing the crop from a single acre of grapefruit in full bearing amounted to from $60 to $80 in normal times, and twice those figures since the war. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST a not prove to be an unsurmountable difficulty if production of lumber and ties in the same operation is otherwise practicable. Hewn ties.—Tie hewing is a hand operation whose main jus- tification is that it furnishes employment to low-income groups in remote rural communities. In sections of northern New Mexico, Spanish-American farmers formerly depended on tie cutting as a supplemental source of income. A standard 7- x 9-inch tie requires a minimum diameter at breast height (d. b. h.) outside bark of about 12 inches, and in order to avoid excessive waste of labor and wood, the. diameter should not be much over 14 inches. The waste in tops is usually greater than in a sawlog operation. Unless prolific regeneration is the rule, a straight hewn-tie rotation is silviculturally impractical. If, as in most regions, relatively large trees are required as a seed source, and if regeneration is difficult, the only logical course for hewn- tie management is in combination with sawlogs, employing hewn- tie operations for purposes of stand improvement. In recent years hewn ties have been replaced almost entirely by the sawn product. Mine Timbers Mine props and stulls* offer silvicultural opportunities in con- nection with saw-timber management because they afford a com- mercial outlet for material unsuitable as either railroad ties or sawlogs. In the Southwest props may be as small as 5 inches inside bark at the top, and stulls as large as 18 inches, the length in feet equaling the top diameter in inches. Live knots and mod- erate crook are not objectionable, and therefore these products can utilize stems which will not qualify as sawlogs or ties. At present, the market is inadequate to absorb more than a small fraction of the supply of prop and stull material that should be removed in the near future. In Arizona this is partly because of a pref- erence on the part of copper miners for Douglas-fir in heavy timbers requiring great strength. With a large number of pro- ducing mines in the interior ponderosa pine region, cultivation es me market affords an opportunity which should not be over- ooked. Converter poles —Another commodity which imposes low re- strictions as to form or size is converter poles used in copper smelters. Already several small sales have been made in the Southwest to supply this market. Utility Poles Having good form and receptiveness to preservatives, ponderosa pine stems are well adapted for use as treated poles. This species is now admitted for use as utility poles under the specifications of the American Standards Association. Since 1946, the numbers of ponderosa pine poles treated in the Northern Rocky Mountain 4Props go to coal mines, stulls to metal mines. Some metal mines take round ponderosa pine lagging. 8 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 and Pacific Coast States have steadily increased. This develop- ment has been retarded in the Southwest because the region lacks wood preservation plants or facilities. Since pole material brings prices equal to or exceeding that of sawlogs, this type of utilization offers distinct possibilities for future development. Fuel Wood Fuel wood, though not rated high commercially, is neverthe- less of great local importance throughout the 12 States which embrace the main ponderosa pine region. Ponderosa pine makes an excellent fuel where quick, hot fires are required. Cull logs, limb wood, and mill blocks are used in quantity both in rural communities and in the larger towns and cities. RELATION TO THE NATIONAL TIMBER SUPPLY At the present time ponderosa pine supplies a substantial por- tion of the lumber used in all of the States west of the Mississippi River. Large quantities of the better grades are shipped farther east for use by millwork concerns. In saw-timber volume, it ranks second in the United States, exceeded only by Douglas-fir (79). How long ponderosa pine will be able to hold this position depends upon how rapidly intensive management is applied, because the present large volume is accounted for mainly by virgin stands. Growth in the extensive interior type will always be slow. Without intensive management, yields and quality will fall to such a level that, notwithstanding the vast acreage of this type, its contribu- tion to the total timber supply of the country will be insignifi- cant. Even if the object is only to supply local consumption in the western States in which ponderosa pine is the predominant species, management must be placed on a much higher plane than has been attained heretofore on any considerable areas. -A favorable aspect of the timber situation in the Southwest is the fact that approximately four-fifths of the acreage and nine- tenths of the volume in the ponderosa pine type is in some form of public ownership, mainly Federal. Several million acres still remain untouched by the saw and some 2 million acres have been logged under some system of partial cutting. There are in the region probably 4 to 5 million acres of commercially accessible ponderosa pine that could within 50 years, if placed under inten- sive management, be made to yield an annual increment of 100 to 200 board feet per acre. e Ponderosa Pine Research in the Southwest EXPERIMENTAL MANAGEMENT Ponderosa pine research in the Southwest began at Fort Valley near Flagstaff, Ariz., in 1908. Early investigations were made in the national forests of Arizona and New Mexico wherever suitable conditions were found. Cut-over areas came in for major attention. As early as 1909, selected areas designated as “‘sample plots” were withdrawn from such administrative use as might interfere with permanent records of natural reproduction and tree growth. Other areas were set aside for experiments in ar- tificial reforestation. Research on these areas was directed from the Fort Valley Experiment Station, now a branch of the South- western Forest and Range Experiment Station. In 1931, the Fort Valley Experimental Forest was created by linking together the large sample plots and planting plots nearest the Fort Valley headquarters. Also included were several thousand acres of timberland used since then for new cutting experiments, timber stand improvement, and mistletoe control experiments. Later, several more distant sample plots were added. Figure 2 shows the location of the five units now constituting the Fort Valley Experimental Forest, and figure 3 the headquarters as seen in 1916 and 1942. Other experimental areas, mainly in New Mexico, though not a part of the Fort Valley Experimental Forest, have supplied data used in this monograph. Sample Plots Records of growth, mortality, periodic and average annual increment, progress of reproduction, and numbers of trees per acre by diameter, age, and crown classes are furnished by a series of sample plots, the oldest of which date back to 1909. All trees are numbered with metal tags, on some plots down through the 4-inch diameter class, on others through the 8-inch class. Diam- eters, and in some cases heights, are measured at 5-year inter- vals. In total, long-time records on 2,000 acres of sample plots, containing 75,000 tagged trees, are available for study. Sample plots are of two broad classes—large or ‘‘extensive”’ and small or “intensive.’”’ Extensive plots range in size from 72 to 480 acres, intensive ones from 3 to 14 acres. In many cases, the intensive plots are merely subdivisions of extensive ones, selected for detailed record. Originally, the trees on extensive 9 10 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 ) SYA St (\ 22San* Francisco ‘TENS €= Z | FigurRE 2.—Location of Fort Valley Experimental Forest and nearby experimental areas. plots were not tagged and diameters were merely tallied; begin- ning in 1924 (1913 on the S5 series and 1915 on S6), all trees down to 38.6 inches were tagged; since 1939, the minimum limit for tagging and measuring has been 7.6 inches. Intensive plots were all tagged at the beginning; heights as well as diameters were measured; notes have been made on the crown class and condition of each tree; and seedling records have been kept on supplementary small plots. Most of the intensive plots have been mapped on a scale of 1 inch to the chain, showing the location of individual trees, stumps, down trees, and groups of reproduc- ae This type of map is illustrated in earlier publications (54, 59). MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST dpa Ze F-44925, 449255 FIGURE 3.—Headquarters of the Fort Valley Experimental Forest, near Flagstaff, Ariz. Upper view in 1916, lower view from near the same point in 1942. The young trees are of natural regeneration. Arizona Plots All but one of the Arizona plots are within what is now the Fort Valley Experimental Forest. Their location by unit numbers and smaller subdivisions is shown in table 1 and figure 2. As may be seen, they are not in one continuous tract, but are widely separated over an area approximately 18 miles square. All are pure ponderosa pine stands except one (S4) which, lying near the lower border of the type, contains a few specimens of pinyon and juniper. I U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 TABLE 1.—Ponderosa pine sample plots in Arizona and New Mexico National forest : Year and Beene estab- atest | Location and local name State on | lished e |(S1-A 1909 | 8 |\Fort Valley Experimental Forest ||S1-B 1909 | 8 | nit 2. 1|S2-A | 1909 | 8 |\Fort Valley Experimental Forest ||S2-B 1909 | Satpce Umitet: $31 1909 | 480 Fort Valley Experimental Forest | Unit 8, Wing Mt. S41 | 1909 | 320 | Fort Valley Experimental Forest Unit 4, Cinder area. 11S5-1 1 | : ee Re | ee | re Fort Valley Experimental Forest Carano ee es 3 | 4913 | 127 || Unit 5, Coulter Ranch. 11 S6 2 1925 | 160 | Fort Valley Experimental Forest || (- Uimt 2; \|\S6-A | 1940} 80 | Do. |S6-B | 1940 |. 72 | Do. \1S7 1925 | 160 | Do. 1188 1926 8 | 4 mi. south of Flagstaff. 11S9 1941 85 | Fort Valley Experimental Forest || | tS atinite.- ||S10 | 1942 | 76 Fort Valley Experimental Forest | Unit 1, Corey Pasture. New Mexico: Carson____.___.._|f Amole | 1914 3 | Amole Canyon. \ Cienega! 1915 4 | Near former Cienega R.S. |(S1-A 1910 | 6 | Point-o’-Rocks Canyon. Cibola__________|{S1-B | 1910 6 | Point-o’-Rocks Canyon. | (S2-A 1910 14 | Ranch Supply Canyon. Giles 2 eee £9E2 5] 6 | Pinos Altos. Santa Fe: | | Jemez ((S1-A | 1911 | 6 | Los Alamos. Division___ |= eee eee Se A co cee Pe ins aol 41 6.4 LOTS ene ee (OS ca pe oe ee re eye Se | 88 9.4 AQ?) 3S Se eee See cower ie Pen et Pea eae Reet, 156 12.5 219 OS)| at teeters 1 | ee oe nels ee Le ra 243 SG VIO. 6: sea 1 Ua ge Sa ann gM eee ty ae 348 nS 125.0 4,600 UPA es oe a eltccehe 474 21.8 91.9 7,500 NGe ies es ee re asc 619 24.9 70.4 10,800 IG Set ee eae yee atest | 783 28.0 55.6 14,400 Oe oe oe eG a hatag wt an | 967 31.1 45.0 17,500 IN aide EOE Sth Oe coe | ea Era) 34.2 3H) 2 20,400 7 eas, iG el ha aS Sst | 1,393 37.3 31.3 23,000 LG ete ett Oe Deeg nee eee eg erway) 1,634 40.4 26.6 25,300 PR NRO is Sek GP Ee ree 1,896 43.5 23.0 26, 900 2} | ened a res eS Pet ioe | 2,193 46.8 1929 28,500 a Paap get remem. eter 4 | 2,476 49.8 126 29 , 600 SY WS, becciaae a pee tine eae Sk sabe ag! 2,796 52.9 526 30,700 SOne Aes es Gee | 3,185 56.0 13.9 31,000 Doe ee Sadie as TU sealer | 3,493 59 1 1 2) 31,500 AN ein, eSB a 2 epee ate | 3, 870 6222 1G 31,600 | SERS Sees AR ne 5s ON ee a gR | 4,268 65.3 10.2 31,600 Ye Co ee ne Santer pe tei seg Ane | 4,684 68.4 9.3 31,700 AGW Pen CSc EA ae Mgr ene ae | 5,120 71.6 8.5 31,200 7 Ses Rs ab cae Oy a eee | 5,575 (aa 7.8 31,000 1 (Reet Sra oR Scr aet l 6,050 77.8 Nez, 30,900 1 Based on 100-percent cruise of 640 acres on the Long Valley Experimental Forest. 2 Assuming a rectangular space. Actually, the space occupied is irregular. Regulation of Spacing Application of spacing rules is difficult where trees of different sizes are intermingled, or where the stand is grouped as is the prevailing habit of ponderosa pine. Densely stocked groups man- age to carry on by sending their roots 50 or more feet outside the group, provided they do not encounter too much competition from neighboring groups. As a rule, it is the interior members of the group that suffer most from moisture or light deficiency. They can be relieved either by thinning within the group or by cutting some of the outside members, thus allowing the roots to reach out into formerly occupied territory. Dominants are able to grow in dense stands by robbing their smaller neighbors, which eventually be- come suppressed. Natural thinnings made in this way are costly, especially if the dominant is of inferior timber quality. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 29 Dense stocking is desirable in young stands.—During the pole stage, when the stems are shaping up, diameter growth is sec- ondary to form and natural pruning. Dense stocking should be the rule. Overstocking in this stage is preferable to understocking, be- cause in the former case, dominants usually assert themselves. If, as a last resort, thinning becomes necessary, removal of only enough stems to encourage the development of dominants will break the deadlock. If pole stands are too widely spaced, pruning provides a partial remedy. Progress of natural pruning provides an excellent criterion as to proper density of young stands. Spacing guides must be flexible-——The guides in table 6 are for application in princ-ple rather than in letter, because the stands must be taken as found and remedies must be sought in modifica- tion rather than reconstruction. In overdense sapling or pole groups, the cost of artificial thinning is usually prohibitive, ex- cept to the extent of releasing a limited number of selected stems designated as crop trees. As poles approach the 12-inch diameter, thought should be given to utilization. Often the solution may be to wait until occasional stems become large enough to yield a log, a railroad tie, or a mine prop, then cut them, thus automatically releasing the nearest neighbors. In practice, only part of a young stand will have optimum spac- ing. Some portions may be too dense and others too open. Under intensive management the answer might be uniform thinning in one instance and planting in the other, but neither of these correc- tives is now feasible on a large scale. A practical and economical means of opening up thickets is to poison (63) dominants of poor form here.and there and depend on the resulting breaks in the canopy to encourage desirable stems to gain dominance. In spots of wide spacing, early pruning will insure a clear butt log, and since trees in these situations grow rapidly they can be left to at- tain large size. This subject is discussed further under Stand Im- provement. Thinning in Seedling and Sapling Stands Although overdense sapling stands are rather common, thin- nings are not considered feasible or necessary in the Southwest. Although correctly timed and executed thinnings might be ex- pected to increase the growth rate, the cost under present con- ditions would be far out of proportion to the benefits. Moreover, dominants generally make their appearance in the sapling thickets, and once they gain the lead, they hold and increase it. Even the densest stands seldom stagnate as they do in some other regions. A thinning experiment on the Sitgreaves National Forest illus- trates the foregoing observations. Large areas in the Decker Wash district became densely stocked with ponderosa pine in 1914. In 1926, when the seedlings were mostly between 2 and 3 feet tall, five plots of 50 x 125 feet were thinned to different densities, as shown in figure 8 and table 7. Density of stocking before thinning varied within plots from 10,000 to 50,000 per acre. Measurements were made at 5-year intervals on a 5 x 125-foot strip in each plot, 2 at ra AY ¥ <4 F-333108-330508-330507 FIGURE 8.—Thinning plots on the Sitgreaves National Forest in 1936. Re- production started in 1914, was thinned in 1926. A, No thinning; note uneven contour of top line, indicating the development of dominants. B, Thinned to 20-24 inches. C, 20-24 inch thinning, showing uneven heights, a most desirable feature. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 31 F—330509-330515 FIGURE 8 continued.—D, 30-36 inch thinning, complete needle cover. E, Thinned to 10 x 10 feet, grass cover almost complete. 32 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 except that the entire plot in the 10 x 10-foot spacing was meas- ured. Differentiation in height was already noticeable in the first measurement and became more and more striking with succeeding measurements. It soon became apparent that the relative merits of the several degrees of thinning would be determined not by the average height growth but by extremes, in other words the ap- pearance of relatively few exceptionally tall stems capable of dom- inating the rank and file. TABLE 7.—Number of trees by height classes above 6 feet on 5 x 125-foot strips in 1941, on Decker Wash plots, Sitgreaves National Forest, thinned in 1926 Number of trees in each height class (feet) Thinning treatment Under 7 a 8 9 10 11 IN(Omt linn oe oe ee eels 47 14 1 0 0 20—24 inch spacing______| 300 34 8 1 0 0 30-36 inch spacing______ ae JUG} 23 20 24 7 0 40-48 inch spacing. ___ __ 152 17 10 tf 3 5 10 x 10 foot spacing 1_ __ 51 8 4 1 0 0) 1 Based on entire plot. According to table 7, the tallest trees are in neither the densest nor the most heavily thinned stands, but in the intermediate thin- nings. Nevertheless, the unthinned plot contains as many distinct dominants as are needed to develop the desired irregular crown canopy. Height growth in all the plots has been greatly retarded by tip moths, which appear to be most active in the heavily thinned stands. An important factor in future development is the relation be- tween. density and ground cover. In the 10 x 10-foot spacing, blue grama grass in 1941 formed a broken turf; in the 40- to 48-inch spacing grasses had been largely replaced by needle litter; in the closer spacings replacement was complete and a uniform mat of needles covered the soil. From the standpoint of tree growth and water infiltration, needle litter is the more desirable cover. It is too early to draw final conclusions. During the next 10 years the dominants will be entering the pole stage and in 20 years the sapling stand will have been converted into a pole stand. Only then can final judgment be passed. The desirable type of pole stand is one in which the dominants have been crowded by sub- ordinates sufficiently to bring about natural pruning on the lower portion of the bole; but if the dominants should be numerous enough to compete severely with one another, additional thinnings will become necessary. Arbitrary stocking or spacing tables, whether applied to sap- lings, poles, or more advanced classes, are impractical in the many- aged and otherwise heterogeneous stands generally encountered in ponderosa pine. An ecological approach is more satisfactory. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST ao Saplings and poles should be dense enough to promote natural pruning without stagnation. The foremost objective in this stage is to build a growing stock. Above 8 inches d. b. h. the increment borer is a good guide. Up to a diameter of about 24 inches the goal should be a diameter growth of 1.5 to 2 inches per decade, and where it is less than the lower figure thinning is in order. As di- ameters advance beyond the 24-inch class a moderate decline in growth rate must be expected, but it should be kept as near to 1.5 inches per decade as possible and should not be allowed to fall below 1 inch per decade. FORM Form may be more important than volume in determining the value of a stand for saw timber. Of the form characteristics which tend to lower the value of stems those most common in the South- west are: rapid taper, coarse branching, forking, crook, and lean. In many instances two or more of these characteristics are asso- ciated. High Taper Taper acts directly in reducing board-foot volume, inasmuch as logs are scaled at the small end and the number of logs in a tree is determined by the merchantable length below the point where the diameter of the bole falls to 8 inches, or whatever is the mini- mum merchantable limit. Rapid taper is an effect of open spacing and long crowns. It is not uncommon to find open-grown trees 18 inches d. b. h. contain- ing but a single 16-foot log whose upper diameter is only 8 or 10 inches. An 18-inch, 1-log blackjack, according to the Southwestern Region ponderosa pine volume table, contains 100 board feet, but individuals of the wolf type may scale only half that much. An 18-inch blackjack grown in a fairly dense stand usually contains three logs and scales 200 board feet. The lesson taught by these comparisons is that d. b. h. measurements alone may give a mis- leading estimate of volume increment. Long-crowned trees usually are credited with a much higher rate of increment than they are entitled to on the basis of actual growth in merchantable volume. Added to the waste and loss of stumpage values in trees of high taper is the cost per M of transporting and handling logs a large part of whose contents goes into the slab. In hewn tie operations, the labor cost is materially increased by sharp taper. Stems of the dimensions usually cut for poles may likewise be rendered value- less by high taper. Abnormal Branching Coarse branching is commonly associated with high taper, both characteristics being the result of a common cause—open spacing in youth. The lower branches die eventually, even in open-grown trees, but not until they have grown too large for natural pruning 34 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 (fig. 9, A). It is not uncommon to find trees over 24 inches d. b. h. whose first two logs are studded with dead branches or stubs 3 to 4 inches in diameter. In sawn timber, these dead limbs result in large loose knots in the outer layer of wood deposited since the branches died. They also are the most common entrance point of heart rot (2, 3, 42). Although small pieces of clear wood may be sawed out between knots, the whole picture is one of inefficient production. When the branches are large in diameter they are also, aS a rule, numerous and close together. If the distance be- tween branch whorls is 2 feet or more, quality material can be sawed out between knots, but if the whorls are only 1 foot apart or even less, a common arrangement in wolf trees, resaw opera- tions are hopelessly handicapped. The only way to obtain high-grade sawlogs from open-grown trees in the Southwest is to prune to the height of one or more logs while the trees are relatively small, preferably below 9 inches d. b. h. Since open-grown trees commonly attain a diameter of 30 to 40 inches in 150 years, they offer an excellent opportunity for profitable pruning if the operation is performed in time. Mistletoe is a contributing cause of coarse branching. Asso- ciated with the large branches are pitch flow and distortion of the bole. If, however, the affected tree is in a dense stand, the abnor- mal branches usually die at an early age, although the mistletoe continues to be active in the bole. Forked Boles Forking is the cause of much waste and sometimes the loss of an entire tree. A fork within the first log length results in exces- sive if not total waste of what is usually the most valuable part of the stem (fig. 9, B). Forking above the first log length is less seri- ous, and in large trees it is sometimes possible to utilize all or the major portion of the members of a fork. The cause of forking may be either hereditary or accidental. Positive proof of hereditary forking is not available in ponderosa pine, although circumstantial evidence is not difficult to find. Strongly suggestive of this are trees which fork and refork, pre- senting a succession of forks in each of the main divisions of the trunk. Examples of forking due to injury are abundant and in many instances the chain of evidence is complete. The most familiar ex- ample is that of a crotch with a dead, pitchy spike in the middle remaining as mute evidence of how, some 50 years earlier, a por- cupine girdled the main stem and two or more side branches grew up around it. Essentially the same effect may be created when the slender terminal stem is cut off or peeled by the Abert squirrel or killed by the pine tip moth. In this case, however, the terminal stem is usually smaller and breaks off and disappears. The gen- eral effect of killing the leader is to stimulate the growth of side branches, and thus wolf trees may result from injury rather than heredity or early environment. 35 MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST UI 02F 8 0} 9 JO 9}SVA\ UT Sq[Nse uv [el10}VU oTQesn suUIOs Ysn VELTEV-006ZLF— RS I UO4FO SUTYLOF MOT OUFTV “punors ay} 0} Ysowye pus}xe sqnys ‘ qd snow LOUd ST 9 1 SVM oY} ‘ SjOUuy UseA\Joq Saoard pvep 10 seyoueiq ssiev0D ‘9[0q 94} JO 41Vd Jamo] oy} yno surmes £ ‘VY ‘sejoq [eur q peurezgo oq LOUGWY— 6 FUND 36 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 Crooked or Leaning Boles Crooked and otherwise deformed boles are the result of various forms of injury, including those which cause forking. One of the most common sources of crook is snow pressure. A slender stem is bent to an angle of perhaps 45 degrees from the vertical by a load of snow. When growth resumes, the young leader rises ver- tically, and although the old stem struggles to regain the upright position, it often remains out of plumb while the new top grows erect. Similar effects are brought about in many ways, notably by windfall or logging in which a large tree or log is thrown against a smaller one. Lean is in most instances purely a natural phenomenon. When several trees start in a group, those on the edges tend to lean out away from the middle of the group if there is an open space ad- joining (fig. 7). The base must remain fixed but the top is pushed outward, so to speak. If these forces act throughout the early life of the tree the stem may remain straight though inclining at an angle from the vertical. If leaning trunks are in a stand, neigh- boring trees exert a counter influence, but if they border on an opening the tops grow farther and farther apart. The branches on the inside are shaded out while those on the outside are unre- strained. Thus, the unequal distribution of weight exerts an addi- tional force which tends to pull the trunk away from an upright position. Leaning boles tend to develop a structural peculiarity on the lower side known as compression wood. Compression wood is brash and weak, warps badly, and in other ways is inferior to wood of normal structure. AGE GLASSES The oldest ponderosa pine on record in the Southwest bore 650 rings on the stump. Trees over 400 years old are found occasion- ally, but mature trees in general are not much over 300 years old and most of them are less than 300. Age in the Southwest is commonly determined by ring counts on the stump without correction for the number of years required to reach stump height. Although technically incorrect, this practice is regarded as legitimate as long as its limitations are understood. The time required to grow from the ground line to stump height is extremely variable because of agencies which retard early height growth. Except as a measure of these retarding influences, the time required to reach stump height is unimportant because in a selection forest, seedlings cannot be said to be occupying space or using water in competition with older trees. Physiologically, there is no apparent reason why ponderosa pine should not commonly live to an age of 500 years in the Southwest as it does in eastern Oregon and eastern California. Higher pre- cipitation and faster growth in Arizona and New Mexico should favor a longer, rather than a shorter life. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST Sil Why do relatively few trees in the Southwest attain really great age? One answer is lightning. As soon as a tree rears its head well above the general crown level, it becomes a lightning rod. Light- - ning is one of three most common causes of mortality in the South- west, but it is a minor factor in California and the Northwest. Lightning may not be the sole cause of the earlier death of south- western trees, but it is undoubtedly a major one. For purposes of management, trees are commonly divided into six broad age classes: three juvenile classes (seedlings, saplings, and poles) ; blackjack, under 150 years old; intermediate, 150 to 200 years; and yellow pine, 200 years or over. The three older age classes, readily recognized by the color of the bark and form of the crown, are the basis of important silvicultural distinctions in man- agement. Juvenile classes.—Below the 12-inch diameter are the seedlings, saplings, and poles, of ages commonly ranging from less than 20 up to 80 years, and occasionally higher. These classes are the source from which must come the replacements as merchantable sizes are cut or lost through mortality. Blackjack class ——Blackjacks are young trees which possess all the biological advantages of youth. They are characterized by a dark, almost black bark, a relatively short, rapidly tapering bole, a pointed or rounded top, and ascending upper branches. Although sometimes attaining large diameters, blackjacks are character- istically shorter and more tapering than are mature trees of the same diameter. Clear and select lumber grades form a smaller per- cent of the volume than in yellow pine; but blackjacks also contain less of the extremely low grades due to heart rot and large, loose knots. In blackjack lumber from trees well grown and harvested in the right stage, there may be knots, but these are mostly of the firm and relatively small type permitted in lumber grades No. 1 and No. 2 Common. Defect due to heart rot in blackjacks is gen- erally less than 5 percent of the gross volume. Intermediate age class.——Intermediate trees have practically all the biological advantages of blackjacks. They represent a tran- sition stage from blackjack to yellow pine. This applies to the color of the bark which may be described as turning from black to yel- low or brown. Intermediate trees are often dark on one side of the trunk and light on the other, and the upper portion of the bole is darker than the lower part. The tops are somewhat more rounded than those of blackjacks. The branches generally are more nearly horizontal but the upper ones are distinctly ascending. Boles of a ~ given diameter are longer and less tapering than are those of blackjack though less cylindrical than those of yellow pine. As in blackjack, the percent of heart rot is relatively low. Di- ameter growth is almost as vigorous as that of blackjack. Lumber grades, however, are likely to reflect the disadvantages of yellow pine without its advantages. After the lower branches die there is a period during which new wood is deposited around these dead branches or stubs, thus forming loose knots. Unless the bole has been pruned, this period falls predominantly in the advanced blackjack or the intermediate stage. Left to grow to full maturity 38 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 and to the large diameters common in the yellow pine stage, many of the branches are shed and overgrown by a layer of clear wood. If grown in dense stands or if the bole is pruned while the branch- es are still alive, intermediate trees will have a central core con- taining firm knots covered by a clear layer, thus combining rela- tively high percents of lumber grades from No. 2 Common up through the Select and Clear grades. Yellow pine class.—Yellow pines commonly range from 200 to 300 years old. As far as years are concerned, trees 300 years old may have all the potential vigor necessary for good growth and 400-year-old trees are often found to be growing vigorously. When vigor is declining the reasons for such decline are associated with but not necessarily a result of old age. Large size, which is a nor- mal product of age, exposes the tree to increased danger from physical agencies such as lightning and wind. If the stand is crowded the large tree encounters increasing difficulties in obtain- ing enough water. Parasites such as mistletoe and heart rot, hav- ing once gained a foothold, exert a cumulative effect with advanc- ing years. All things considered, old trees are a poorer risk than young ones, but age is not in itself a limiting factor. A 300-year- old tree which has escaped the many deteriorating agencies is not a poor risk except as large size may expose it to unusual hazards. Yellow pines are characterized by a reddish yellow or cinnamon brown bark on all sides of the bole, this color extending quite or almost to the tip, a flat or broadly rounded top, and horizontal or drooping branches. Trees which have grown in close formation have long cylindrical boles comparatively free of branches for one or more log lengths. Surface-clear logs, however, are rare and are confined mainly to trees of large diameter. Boles affected by heart rot suffer a large reduction of net volume and this loss, together with mortality, tends to offset increment in trees over 30 inches d. b. h. Sound, well-formed trees which have cleared their boles are, however, to be considered for their value increment. In nat- ural stands they are almost the sole source of clear lumber. In con- trast, yellow pine boles that are studded with dead limbs or stubs are a liability which should usually be eliminated from the grow- ing stock to make room for more valuable trees. Balanced Gradation of Age Classes In order to maintain a sustained yield under selective logging on short cutting cycles, it is important that at least five of the age classes—seedlings, saplings, poles, blackjacks, and intermediates —be well represented. What proportion of the total area or num- ber should be allotted to each class has not been determined. Con- siderable latitude is permissible. As for the yellow pine class, its presence is not essential in a forest fully stocked with younger classes. Actually, most stands under management after conversion - from the wild state will contain many gradations within the broad age classes listed. Assuming intervals of 20 years between classes, an extreme range of 200 years would provide ten age classes. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 39 Age-Diameter Relationships In practice it is not necessary to make fine distinctions in age. Within limits of about 100 years, actual age is less important than diameter. In order to regulate yield it is necessary to observe cer- tain relationships in distribution of diameter classes. Although these relations need not be ironclad, it is at least essential to have many more trees in the lower than in the upper diameters. Exam- ples of actual distribution of diameter classes on areas of 80 acres or more are given in the next chapter. On none of these areas are diameter classes under 18 inches d. b. h. adequately represented. In typical even-aged blackjack groups of about 140 years, di- ameters commonly range from below 12 inches to 26 inches or even higher. The 9- to 11-inch trees are usually subordinates in the intermediate crown class; except for greater height, smaller crowns, and cleaner boles, they are equivalent to poles 50 to 60 years old. The largest trees are dominants corresponding in di- ameter to yellow pines of the 200-year class. In between these ex- tremes are stems ranging mostly from 12 to 20 inches. The group as a whole, though actually even-aged (with a 20-year range), is for management purposes equivalent to a many-aged group with age classes ranging from 60 to 200 years. All trees, barring the suppressed or diseased, have the capacity for growth when given adequate space. Stems over 24 inches d. b. h. are for the most part ready to be cut now, having already passed the stage of most profitable increment. Some of the smaller stems have marked time for 100 years; they may continue in a subordinate role during an- other cutting cycle and then grow rapidly to merchantable size if released. The fact that such trees may be as much as 300 years old when harvested does not mean that under management they could not have attained merchantable size in a much shorter period. Average diameter-age tables are interesting and may be of prac- tical value if used with an understanding of their limitations. It must be borne in mind, however, that on the same site individual trees may depart 100 percent or more from the average because of peculiar environmental conditions. An example of the extreme variability is furnished by a summary of records obtained from the Wing Mountain area logged in 1939 (table 8). The ages were deter- mined by ring counts on stumps of trees felled in a second cutting. TABLE 8.—Age in relation to diameter for three 30-year age classes on the Wing Mountain area of the Fort Valley Experi- mental Forest 30 years after first cutting 3 Age class Diameter at breast height Trees in class Mean Range Mean Minimum | Maximum Years Years Inches Inches Inches Number 11 |) Yes i eee aoe came 111-140 8 IVA ee ge ak pn ee 141-170 ZieS 10.9 39.8 1,055 ZAG Seen he, gene Lo: 231-260 SileZ 14.8 46.8 1 Data compiled by Wm. L. Chapel (15). AO U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 Rotation At present the rotation period is less important than the cutting cycle; but after the old-growth timber has been removed, the time required for trees to grow from stump height to a specified di- ameter will assume increasing importance. Under present utiliza- tion standards the diameter of the average tree felled in commer- cial logging in the Southwest is approximately 22 inches, and the average age is estimated at 250 years. According to table 8, trees in the 145-year age class averaged 21.8 inches d. b. h., ranging from 10.9 to 39.8 inches. At 130 years, the average tree was 20.8 and the extremes were 9.7 and 40.5. From what is known about the response of tree growth to increased spacing, it seems likely that with timely improvement cutting 22-inch trees could be grown on this area in 130 years or even less. SITE QUALITY The site classification developed by W. H. Meyer (44) for selec- tively cut ponderosa pine forests of the Pacific Northwest has been used in this monograph to rate the relative productive capacity of ponderosa pine forests in Arizona and New Mexico. This classifi- cation recognizes six site qualities varying from I (the most pro- ductive, where total height of mature dominants averages about 190 feet) to VI (the least productive, where mature dominants average about 63 feet in total height). On this basis, southwestern ponderosa pine forests vary in site quality from III to VI, but the large majority of stands fall in classes IV and V. It should be recognized that the use of a height-age relationship may underrate the relative productive capacity of southwestern ponderosa pine. The prevalence of lightning tends to reduce the average height of mature dominants since exceptionally tall trees are highly susceptible to damage from this source. TREE CLASSIFICATIONS IN RELATION TO GROWTH Classification of tree crowns with respect to size, shape, physi- cal character, and exposure to sunlight dates back to the earliest silvicultural practice. The basic concept is that capacity for growth is determined by the capacity of the food laboratory which is vested in the foliage. A circumstance often overlooked is that the output of the food laboratory is limited not only by its own size and mechanical efficiency but also by the raw material and energy available. The raw materials are mainly water, carbon dioxide, nitrogen, and certain mineral elements; the energy is sunlight or solar radiation. Deficiency in one or more of these essentials may become the limiting factor in growth. Several classifications em- ploy different criteria. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST Al Position in the Crown Canopy Dominance, or the relative position of individual tree crowns in a stand, was the basis of the oldest classification and is still a sound basis when used understandingly. Four classes, defined in standard textbooks, are: Dominant, codominant, intermediate, and overtopped or suppressed. A fifth class—open grown—has been used with ponderosa pine in the Southwest for isolated trees not competing for crown space. The limiting factor .is assumed to be exposure to sunlight. The great abundance of sunlight in the ponderosa pine type, together with the open character of the pine forests, has led many to assume that light is never deficient and therefore to discount the importance of dominance. This as- sumption overlooks the fact that a small tree may be almost wholly deprived of direct solar radiation through interception by one or more larger trees. It is of common observation that when ponderosa pine needles are continuously subjected to shade they become thin and pale and the twigs eventually die. In dense stands the death of twigs and branches proceeds from the ground up- ward until the only remaining green foliage may consist of small tufts at the extreme tips of tall, slender poles. In such stands, the individuals which chance to be a few feet taller than their neigh- bors have a great advantage. This relation was readily observed by early foresters, even though they may not have known much about photosynthesis and metabolism. Diameter growth in the four classes is generally in descending order from dominant to overtopped, although the relationship be- tween dominant and codominant classes is not strictly consistent. The reason for this lack of consistency is that the classification does not take ground space into account. Generally a dominant has more ground space than a codominant, but this is not always true. The dominant in a large group may be pressed by many smaller trees which, though unable to interfere seriously with its access to sunlight, may encroach upon its root zone and exert severe root competition. Dominants in such positions sooner or later decline in diameter growth and their crowns may suffer sharp reduction by loss of foliage through shading of lower branches. Codominants generally grow less rapidly than dominants because both crowns and roots, especially the latter, are subjected to more intense com- petition. With correct spacing, however, it is possible for codomi- nants to grow as rapidly as dominants. Trees in the intermediate and overtopped classes are always of slow growth because their position is the result of crowding. As will be shown later, the slow growth of trees under domination is no criterion of growth ca- pacity when released by management. Age-and-Vigor Classes Another system of classification is based on age of trees and the size and physical condition of their crowns. It integrates the rela- tion between the size of the tree and the area of active crown or leaf surface, assuming that in the final analysis area of leaf sur- 42 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 face is a measure of growth capacity. The idea was first intro- duced by Dunning (21) in California who separated the trees of cut-over ponderosa pine stands into seven classes. More recently, Keen (31, 32), working in the Northwest, elaborated a similar scheme which, though based on the same general concept, organ- ized the classes on a different plan. Keen used four age classes cor- responding roughly to the broad age classes of the Southwest: each class is further divided into four ‘“‘vigor” classes correspond- ing roughly to the standard dominance classes, but placing more stress upon size and density of the crown than upon its position in the canopy. A modified age-and-vigor classification was developed by Thom- son (84) for use with ponderosa pine in the Southwest. Thomson recognized four age classes and five vigor classes, which may be briefly described as follows: AGE CLASSES I. Young blackjacks (mainly below 12 inches d. b. h.). II. Blackjacks of saw-timber size (usually 12 inches d. b. h. or larger). III. Intermediates or young yellow pines (mature). IV. Old yellow pines (overmature). V1IGOR CLASSES AA. Extremely large crowns, length 70 percent or more of total tree height (wolf-type trees). . Full vigor, crown 55 to 70 percent of tree height. . Good to fair vigor, crown 35 to 55 percent of tree height. . Fair to poor vigor, crown 20 to 35 percent of tree height. . Very poor vigor, crown less than 20 percent of tree height. SAWP Thomson’s modified classification has been used for describing individual trees on several of the Fort Valley plots and is the basis for the “tree class” designations given in this and later chapters. Keen designed the age-and-vigor classification primarily for purposes of rating bark-beetle susceptibility, but timber managers have used it widely as a basis for silvicultural practice. The theory is that growth rate decreases with age and increases with size of active crown. That young trees grow more rapidly than old ones cannot be disputed; but under 200 years, age is no serious handi- cap in southwestern ponderosa pine. As for crown size, growth figures obtained by mass averaging support the theory; but on examination of individual trees, exceptions are so striking as to raise doubts as to the soundness of the principle. Analysis in the light of plant physiology points in the same direction. It is true that the average A tree grows faster than the average € tree, but many individual C trees grow as rapidly as the best A trees. There is a “law of the minimum” which says, in effect, that growth rate is governed by the essential element which is least available. In a region such as the Southwest, which is characterized by an overabundance of sunshine and a deficiency of precipitation, mois- ture rather than solar energy is most likely to be the critical fac- tor. And growth is dependent more upon a large root system than upon a large crown. It is possible that leaf surface beyond the re- MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 43 quirements of photosynthesis can become a hindrance by inducing excessive transpiration. The enormous volume of limb wood in Class A trees and wolf trees furthermore represents wasted energy, to say nothing of lumber quality. It follows that crown size, used as an index of growth, is sub- ject to the same limitations as crown dominance: neither a large crown nor free exposure to sunlight avails if the root system is unable to supply the needed water. Class A trees usually maintain a superior growth rate because, in addition to being dominant, they are also usually isolated. In less degree, the same is true of B trees, as compared with those of classes C or D. Not only is crown size associated with position but it is determined by position. A large crown is not the cause of rapid bole growth, but is itself an effect of the same factor that produces rapid bole growth, namely, abundant moisture made possible by a large root system in an area relatively free of competition by other vegetation. Growth tables based on the age-and-vigor classification have shown a marked decline in growth rate through the series of “vigor” classes from A to D. These tables, however, disregard the fact that class A and class B trees usually occupy much more ground space than do class C and class D trees of the same di- ameter. Briegleb’s (11) tables are based on growth in virgin stands where A and B trees are the dominants which have appropriated more than the average share of space. Hornibrook’s (30) and Thomson’s (84, 85) figures on growth in cut-over stands evidently have not taken into account the fact that only a small proportion of the C and D trees have been adequately released in past cutting, ~ whereas the A trees and, to a less extent, the B trees remaining after cutting are generally isolated. Another practice which places the C and D trees at a disad- vantage is that of throwing into these classes all trees suffering from any ailment which has reduced the leaf area. Thus a large A or B tree which is declining as a result of lightning, mistletoe, or squirrel injury, automatically falls into the C or D class. Position on the Ground Within well-stocked stands it is impossible, without extensive excavation, to outline the root pattern of individual trees and thus determine the degree to which one competes with another. From observations of windfalls, however, it is apparent that trees within groups have more restricted root systems than trees on the edge of the group or entirely outside. Occasionally an interior domi- nant, usually older than its associates, may send some roots clear beyond them into an open space, or a large tree outside of a group may send roots into the group. With the foregoing clues, the fol- lowing rough classification is used for rating the relative space - available to the individual tree or its position on the ground. The following symbols have been used to designate typical positions: X. Isolated—At least 30 feet (usually more) from other trees. O. Open.—Detached from a group but nearer than 30 feet. M. Marginal.—In the outside rank of a group or only slightly inside. I. Interior.—Distinctly within the group. 44 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO: 6 Growth rates of tagged trees have shown a fairly consistent corre- lation with position on the ground. Figure 10 illustrates the influence of ground space on diameter growth in three blackjacks, all in age class II and crown class B, but one interior, one marginal, and one open. Despite similarity in age and vigor, the open-grown tree is growing about three times as fast as the interior dominant. F-433035. FIGURE 10.—Three blackjacks, all with class B crowns but in different posi- tions in a large group. Diameter growth during decade 1929-39: tree at left, interior, dominant, growth 0.8 inch; right, marginal, codominant, growth 1.5 inches; rear center, open, dominant, growth 2.5 inches. A Comparison of Ground Space and Crown Vigor Growth records from tagged trees on the Wing Mountain ex- perimental area (S3) provide a basis for comparing position on the ground with crown vigor, as a basis for rating growth ¢a- MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST A5 pacity. In table 9, 10-year diameter growth of 348 trees classified by both systems is summarized. Trees were classified in 1939 and the diameter growth is for the third decade (1929-39) following the first cutting. All trees are immature (age classes II and III) and they include all stems in 21 selected blackjack groups. v TABLE 9.—Average 10-year diameter growth of 348 trees in 21 blackjack groups by Keen’s vigor class and by ground position class. Wing Mountain Sample Plot (S3), 1929-39 Ground position class All class X O M I classes trees (isolated) (open) (marginal) | (interior) Inches Inches Inches Inches Inches Number peepee air alee 2 74 ee OO sh ee rune en sdienes ileal 59 Irae sacar eee ini Pe 1.79 igey 0.84 1.36 84 Cee en Re 1.74 185) .98 1.29 140 [DY SV a Ail a oa aa cee .90 52 0.63 65 All vigor classes _ __ 2.39 16 129 6) NEA Sip aie eres he ai Number Number Number Number Basis, trees_ 15 60 alfeli RO 2ea Sires 348 1 All trees in age classes II or III. Crown length in percent of total height: A, 55 or more; B, 35-55; C, 20-35; D, under 20. Average diameter growth by crown-size classes, disregarding ground position, follows the conventional downward trend from A to D. Essentially the same relationship has been reported from all ponderosa pine regions and has been accepted as conclusive evidence that growth capacity is directly related to crown “vigor” as measured by size of active crown. When the vigor classes are further divided into ground position subclasses, however, the picture changes radically. Corresponding position classes show almost identical diameter growth through vigor classes A, B, and C. X (isolated) trees are represented in only one vigor class—A, whereas I (interior) trees are missing from class A. This mode of occurrence is characteristic and ex- plains the high average diameter growth usually found in class A trees. All the class D trees were in ground positions M or I; they were mostly of subnormal root and crown development be- cause of prolonged subordination. When a second cutting was made in 1939, about half of the trees in ground position M or I (table 9) were released and retained in the reserve stand. A record of their average 5-year diameter growth following cutting (table 10) shows that all vigor classes respond well to release. Response is ordinarily most pronounced in position classes M or I, because it is here that increased space is most needed. Average diameter growth following release was almost identical in vigor classes A, B, and C. On a percentage 46 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 basis, class D trees showed the greatest response to release, but actual diameter growth was considerably below that of the other vigor classes. TABLE 10.—Average 5-year diameter growth of released tr ees im ground positions I and M, by vigor classes, before and after cutting Average 5-year diameter growth Vigor class Trees Before cutting After cutting (1934-39) (1939-44) Number Inches Inches IRE aha as eee eng ee eee 0.66 | 1.00 1 ec Secu a Make od «Sea chy at 2 MN 33 .62 02 (GOS Ag SRO Te ED Ses 2 Re ie Unie. eel Cepek 63 61 96 1 © ee ee ers See ete rine ee ee 31 32 56 Of the two classifications ground space evidently provides the best clue to the growth capacity of the individual tree. Where harvest cutting operations are involved, however, it should be re- membered that the space after cutting, not before cutting, will exert the primary influence. Use and Limitations of Tree Classifications Young trees grow faster than old ones; but ponderosa pine re- mains physiologically young until at least 200 years old, and if other conditions are favorable good vigor persists to an age of 400 years or more. Injury, disease, competition, and sheer size, rather than age, are the limiting factors in old trees. Crown size becomes limiting only in extremes. Rapid growth is found in classes A, B, and C, but class D is below or near the limit of photosynthetic adequacy. There are indications that ex- tremely large crowns are a hindrance to bole growth, and this is certainly true as regards quality. Crown dominance is important to the extent that it expresses access to direct sunlight. Exposure of the upper portion of the crown equal to one-third the total height of the tree is sufficient. Ground space as an expression of access to soil moisture ranks with crown dominance. Utilization of soil space, however, is diffi- cult to measure or estimate because the roots are hidden. The terms isolated, outside, marginal, and interior are only rough ap- proximations of the soil actually utilized. Obviously, ground space does not avail if the root system is subnormal on account of dis- ease, injury, or restricted development. Tree classifications are useful mainly for purposes of descrip- tion. Collectively, the three classifications here discussed, when supplemented by an appraisal of bole form and general physiolog- ical condition, can serve as a guide to silvicultural cutting; but no one system is adequate when used alone. Cutting in Virgin Stands Silvicultural cutting aims at three broad objectives: (1) To harvest the crop of merchantable timber; (2) to leave a growing stock capable of producing satisfactory future crops at required intervals; and (3) to encourage natural regeneration where stock- ing is deficient. Ideas regarding the best ways of achieving these objects have been modified from time to time. They have found expression in ‘‘methods of cutting” applied in both extensive and experimental practice. METHODS TESTED AT FORT VALLEY Six methods of cutting have been tested in the Fort Valley Ex- perimental Forest: Group selection, light selection, scattered seed tree, favoring dominants, improvement selection, and salvage. The sample plots representing each method are listed in table 11, along with pertinent information concerning each plot. An undis- turbed virgin stand is included in the series for the purpose of comparison. An additional method of cutting, maturity selection, is not included in the Fort Valley series, but it has been widely employed and is discussed later in the chapter. Residual stands, broken down into 3-inch classes above 8 inches d. b.-h., are shown for each area in table 12. Cutting practice under each method and special conditions encountered on each area are described in the following pages. Group Selection Understanding the philosophy of group selection requires that the governing conditions be taken into account. Large operations before about 1930 usually employed railroad logging. Liquidation of fixed charges required a minimum cut of 4,000 to 6,000 board feet per acre, depending upon location and total volume available to amortize the cost of railroads. Such growth figures as were to be had indicated that from 60 to 100 years must elapse before in- crement could provide enough volume to justify a second cut. In ‘such a program large yellow pines left for seed were regarded as a liability chargeable against regeneration. Consequently, where advance reproduction was present heavy cutting in the yellow pine class was common. Contracts generally called for reserving one- third of the merchantable volume; but in many instances, par- ticularly where few seed trees were thought necessary, the re- serve was considerably lower. Residual volumes varied from 4,000 board feet per acre to as low as 1,500 board feet. In general, black- jack groups were left intact while yellow pine groups were heavily Cub. The effect was dense groups of blackjack separated by spaces 100 to 300 feet in diameter occupied only by occasional large seed trees. Such a cutting is illustrated in figure 11. The map was made 47 48 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 ‘AJUO sjo[d VAISUO}XO UO paseq ‘poeyYst[qeyso o10M syo[d oY} oUtty oY} ye “Y “q ‘p SOYOUT G'T[ 19AO SdaL], ¢ ‘OVGT 0} to11d poyst[qeyse syzo[d Loy pozyeurjsy z 4SOMYILON IGlOVT VY} LOF UOTZVOYISSeL]D S,.LoAVJ, UO poseg 1 “UNI pet “qy sr] “UM Tpe TL “UINTPE TAL “KABOTY *KAGOTT “KAGOTT OP OLE Cai St GCP 620 8 6°81 ZEG LL8 ‘8 1°91 GVva G8e‘é 8° ST 628 01g‘ eS. 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Ab 66 §& 66 °% ERS GG i Gecesisate |S ocho ane sania cane IT-6 Ors 6S LS €-GS GSS T-S$ vS €S q9s syueu uot} 901} 9S (soyout) IBBA[CS © oy 400 (0) 0) -da]esS pees UIBILA ssvjo “4 “gq ‘q UOIQDe[eS JUSWIOAOICWIT SULIOAR qyUsvT pd1999899 UOTJOITIS Ano 1 7SOL0 4 [Opuaunwad xy hajjv A 710.4 ‘spoyjauM payroads fiq 4na s}0)d au pun ynaun fa] j0)d ads uo ‘ssM9 sajawmnrp fig ‘papsovas 78iyf UayN awap sad saaiy fo waqunn— oL ATEaV.L 50 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 directly after cutting; trees which died during the next 20 years were designated later. Three areas now included in the Fort Val- ley Experimental Forest (S83, $4, and S5-1) were cut under group selection from 1909 to 1918. They are briefly described in the fol- lowing paragraphs. Wing Mountain plot S3.—This is the largest and one of the two earliest sample plots. Lying 6 miles west of the Fort Valley head- 66 33 ° 66 FT. CD) YELLow PINE CO srackyack @ YELLOW PINE STUMP @ BLACKJACK STUMP @ YELLOW PINE, DEAD @ BLACKJACK, DEAD FIGURE 11.—Distribution of trees after group selection cutting. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST ol quarters, its altitude, temperature, and precipitation are similar to those at the headquarters (table 2). Site quality is a high V. The soil is a fairly deep, stony clay loam of volcanic origin, slightly acid in reaction. The original stand consisted mainly of three broad age classes ranging from 100 to 300 years old and from 12 to 40 inches d. b. h. An even-aged group arrangement was very pronounced. Cutting, in 1909, was strongly influenced by the ab- sence of advance reproduction and the presence of mistletoe. Many large yellow pines were left as seed trees. Blackjack groups were generally left intact, but in some places trees with heavy mistle- toe infection were cut as a saivage measure. The original gross volume on this plot was about 12 M board feet per acre. Of a residual stand of 3,520 board feet per acre, 58 percent was in the blackjack or intermediate age classes. Table 12 reveals a great deficiency of diameter classes below 18 inches, and other records show that the deficiency becomes even more outstanding on approaching the 4-inch class. The area occupied by trees just after the cutting is estimated at only one-third of the total. Spots a hundred yards or more in diameter were left un- stocked except for occasional seed trees. These open areas became almost completely restocked with seedlings in 1919. Cinder plot S4.—This area was logged and records begun in the same year as the Wing Mountain plot. In many respects the two plots present strong contrasts. The cinder area hes 13 miles east of Fort Valley at an altitude of 6,700 feet, near the lower bor- der of the ponderosa pine type. The site quality is low V, deter- mined by lower precipitation (about 20 inches) and higher evapo- ration than on the Wing Mountain plot. As the name implies, the soil is covered with volcanic cinders, black or red, to depths vary- ing from an inch to several feet. Water penetrates the cinders readily, but the upper layers dry out quickly. Age classes and di- ameter classes were about the same as on the Wing Mountain plot, including absence of advance reproduction. Although marking here followed the same principles as on the Wing Mountain area, a lighter and more open original stand re- sulted in leaving a thousand board feet per acre less. The trees are generally shorter and limbier. Unlike Wing Mountain, this area is entirely free of mistletoe. Young seedlings have come in spar- ingly, with the result that 35 years after cutting, large openings still remain sparsely stocked. Coulter Ranch plot S5-1.—This group selection cutting belongs in a series of three, logged and established in 1913 for the purpose of comparing group selection with light selection (S5-3), and scattered-seed-tree (S5-2) cuttings (fig. 12). The site quality is V-, determined mainly by a shallow soil. Altitude and precipitat’on are almost identical with Fort Valley and Wing Mountain. The original stand was considerably lighter than on the Wing Moun- tain area, and cutting removed about 60 percent, leaving 2,846 board feet per acre. Diameter classes show the characteristic de- ficiency of stems below 15 inches, although poles and saplings were more abundant than on the Wing Mountain area. Scattered ad- vance reproduction supplemented by partial restocking in 1919 52 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 a eX 7 F-16974A, 17020A FIGURE 12.—Three methods of cutting in the Coulter Ranch series of plots logged and photographed in 1913. A, Scattered-seed-tree method (plot S5-2). Trees left, primarily for seed supply, numbered 3.9 per acre, mainly over 18 inches d. b. h. Blackjack groups were cut severely. The hardwocds are Gambel oak of no commercial value. B, Group selection. Blackjack group intact, characteristic of both group selection and light selection. Under the scattered-seed-tree method nearly all the blackjacks 12 inches and over would have been cut. Under light selection several of the yellow pines represented by stumps in foreground would have been left. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 53 Biiieiecs.. ; 3 F-17067A FIGURE 12 continued.—C, Light selection. Under group selection most of the large trees would have been cut, though leaving a few for seed. Large natural openings as seen in the foreground are common to all methods of cutting. has given rise to a fair pole class. Mistletoe has infected a large proportion of trees in all age classes. Of the three Coulter-Ranch plots, S5-1 is the poorest site (table 11)—characterized by shallow, very stony, clayey soil and short timber. Light Selection The general principles observed in this method were the same as those of group selection, but cutting practice was modified in the hope that more seed trees and a denser crown canopy might favor regeneration, which at that time (1913) was a very serious prob- lem over much of the Coconino Plateau. Groups were treated the same as in group selection, except that in yellow pine groups more trees were left. On the whole, more large seed trees were left in the openings between blackjack groups than after group selection cutting. The thought of leaving a large volume for an early second cut was entirely subordinate to reproduction. Railroad logging de- manded relatively heavy cuts at long intervals; in fact, the first cutting in this instance was considered too light to be economic from the operator’s viewpoint. The first cut, which removed a net volume of about 3,000 board feet per acre, was not much out of line with present national-forest practice, except for leaving too many old trees over 30 inches d. b. h. Coulter Ranch plot S5-3.—This light selection cutting left nu- merous large yellow pines, which account for the relatively heavy residual volume of 4,500 board feet. Wind, lightning, and mistle- 54 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 toe have taken an enormous toll from these large trees; but for the most part they served their purpose in providing an ample seed supply before they were lost. Most of that portion of the area which received protection against grazing restocked well in 1919. Mistletoe is at its worst on this area, having infected all age classes, including large pole groups which but for this pest would contribute much to the future growing stock. This area is the only early example of light cutting under experimental record, and it has provided useful guides in the light-cutting practice developed in recent years. Scattered Seed Tree Cutting As the name implies, this method undertook to leave only as much merchantable timber as was considered necessary to pro- vide an adequate seed supply. In the absence of pole stands a second cutting under this practice could not be expected in much less than the full rotation period. Since only full-crowned trees could qualify as seed trees, groups of both blackjack and yellow pine were almost clear cut, the seed trees left being of the open- grown type. As viewed in 1913, advantages of the method were (1) a profitable cut for the operator and (2) assuming reproduc- tion, a young stand free from domination by an older generation. Disadvantages were (1) the uncertainty of regeneration and (2) a long wait for the second cut. From an experimental point of view, the method promised to bring out contrasts with the more conservative group selection and light selection practices. Coulter Ranch plot S5-2.—This plot has a general northerly as- pect whereas the other two Coulter Ranch plots face the south; in no case, however, are the slopes steep. Although accurate re- cords are not available, this stand is thought to have been some- what heavier than the other two. As shown by table 11, the re- served stand contained only 3.9 trees per acre 12 inches and over d. b. h., less than one-third the number on the companion plots S5-1 and §5-3. A few poles and clumps of Gambel oak helped to relieve the general barren effect following cutting. Advance re- production below the pole stage was deficient here as on the other two areas, but reproduction after cutting has exceeded all expec- tations, considering the few seed trees. With respect to reserved volume, this area compares favorably with some group selection cuttings; the difference is that in heavy group selection cuttings the volume is mainly in many small blackjacks, whereas here it is mainly in few relatively large yellow pines. Favoring Dominants One of the main tenets of ponderosa pine silviculture has been the belief that large-crowned dominants constitute the best grow- ing stock. During the many years when restocking was a major problem in the Southwest, seed production was a further and in fact the primary incentive to leaving this type of tree. The speci- fications for seed trees called for healthy, full-crowned, preferably MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 55 isolated trees at least 20 inches d. b. h. (54). Studies also indicated the need of at least four such trees per acre; and since the black- jack class seldom afforded enough seed trees in the right places the yellow pine class was called upon to make up the deficit. Investigations (37) had shown that well-released yellow pine seed trees were capable of a high growth rate, even in diameter classes above 380 inches. It was therefore reasoned that a more liberal quota of large yellow pines would add substantially to the increment, provided that too many were not lost before the second F-423672 FIGURE 13.—A blackjack group opened by cutting under the methed favor- ing dominants. Small-crowned trees large enough to make a log were generally cut. cut. Furthermore, it was recognized that the principle of acceler- ated growth after release cutting applied also to blackjacks. All this reasoning was influenced by the thought that the best re- sponse would be obtained from trees of relatively large, well- formed, and well-exposed crowns. Fort Valley plot‘\S7.—The area selected for this type of cutting consists of 160 acres located within one-fourth mile of the Fort Valley headquarters. It was logged in the fall of 1924 and the sam- ple plot was established in 1925. (Adjoining is the virgin stand, sample plot S6, also comprising 160 acres.) The original stand is estimated to have contained slightly under 12,000 board feet per acre. Cutting left 3,423 board feet. The remaining volume was almost identical with that of the Wing Mountain group selection plot S3. In the yellow pine class, volume and distribution on the 56 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 two plots were quite similar, and for this reason S7 has been re- ferred to as group selection cutting. But treatment of the black- jack groups was very dissimilar: on 83 they were left almost in- tact whereas they were opened up on S87. It is in the blackjack and pole groups that cutting to favor dominants found major ex- pression. Subordinate blackjacks were cut where large enough to make logs, in order to give more space to the favored dominants. Figure 13 illustrates a blackjack group after the cutting, and fig- ure 14 shows two common types in the intermediate and yellow pine classes. The rough dominant in figure 14, A is not only of poor quality but is also a mistletoe bearer. By contrast, the large, clean-boled yellow pine in figure 14, B will contribute value incre- ment as long as it can be kept growing. Seek F-423676-427990 FIGURE 14.—Two types of large trees left in cutting under the favoring- dominants method. Cut in 1924, photographed in 1940. A, 29-inch blackjack of poor form dominating good poles on all sides. Diameter growth by 5-year periods 1925-45: 0.9, 0.7, 0.8, 0.6 inch. B, 34-inch yellow pine of good bole in a group of 12 stumps representing trees down to 12 inches d. b. h. Although this is a fine tree it is a high risk, and when gone it will leave a vacant space of about % acre. Diameter growth by 5-year periods 1925-45: 1.5, 1.0, 0.7, 0.4 inches. Salvage Cutting The salvage method removes only distinctly declining trees, with the object of salvaging usable material which would be lost if left until a regular commercial cutting is made 10 to 20 years later. An advantage of the practice is that the relatively light cut makes it possible to cover large areas in a short period. Since only small mills are usually interested in this type of operation, however, the aggregate area covered is likely to remain small. Many small op- MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST o7 erations sprang into existence under the stimulus of boom prices during and immediately after World War II. It is reasonable to expect a decrease in this class of activity if the demand for lum- ber declines toward prewar levels. Since the volume removed in salvage cutting is relatively small, the existence of adequate roads, or a terrain which requires little or no road building, is a pre- requisite. Fort Valley plot S6B.—This salvage cutting area is the east half of a 160-acre virgin stand which had been carried as a sample plot (S6) since 1624. Thus, the cut-over area has individual tree records which began 15 years before the 1940 cutting. Cutting in 1940 removed 4,000 board feet gross from a stand containing 12,000 board feet per acre. Cull and defect amounted to 48 per- cent. Since a second cut in 10 years was planned, only distinctly declining trees were removed. This left a considerable number that had been struck by lightning but gave promise of persistence. Many trees in early stages of decline were left because appearance indicated that they would live 10 years more. Maturity Selection Maturity selection was developed in the Pacific Northwest un- der conditions in which operators found it unprofitable to handle any trees but those of relatively high quality. The method is an at- tempt to harmonize silviculture and economics under adverse eco- nomic conditions. It makes use of classified growth tables designed to show the net percent of volume increment in each class; it also employs tables showing the marginal value, after deducting cost of logging and manufacture, of trees of different diameter and log grades (10, 12, 47, 48). Assuming that gross earning capacity is proport_onal to net volume increment, net earnings are ex- pressed by increment percent minus a fixed interest on the invest- ment. If the interest rate is as high as 3 percent the net earning capacity of the larger trees is nearly always a minus quantity and is called a carrying charge or the cost to the owner of holding the tree in question. If the marginal value of the tree is low, the carry- ing charge becomes correspondingly. low, and if the marginal value is negative the carrying charge becomes zero. Only young and fast-growing trees of relatively low diameter are capable of positive earnings—that is, a net annual volume increment exceed- ing 3 percent. Selection by Age-and-Vigor Classes Maturity selection growth tables give the growth in diameter or increment in percent by Keen’s age-and-vigor classes.° Invariably the growth rate is higher for relatively young trees than for old trees and higher for large-crowned trees than for small-crowned trees. A combination of age and vigor in merchantable diameter > Age-and-vigor classes are defined on p. 41. 58 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 classes gives the highest growth rate for II-A trees and the lowest for IV-D trees, with intermediate rates for intermediate grades. On the basis of carrying charges as indicated by growth capacity and log grades, Bruce (12) has developed a marking schedule for the Northwest, and a slight modification of the same table has been used by Munger and Briegleb (48). Key points in the specifi- cations are: (1) The older age classes are marked to a lower di- ameter than are young age classes, (2) small-crowned trees are marked to lower diameters than are large-crowned trees, and (3) trees of a high log-grade composition are marked to a smaller di- ameter than are those of a low log-grade composition. In classes IV-C and IV-D, trees of high value are marked to the lowest mer- chantable diameter, but those of the lower grades are not cut un- less the diameter is at least 34 inches. No trees in age class II are cut, and of course this rule applies also to class I, which includes mainly those trees below 12 inches d. b. h. Modified Practice in the Southwest For several years prior to 1946 maturity selection was employed in modified form in the Southwestern Region of the Forest Serv- ice. Log-grade composition and carrying charges were disre- garded; but the Keen tree classification was used as an index of growth capacity. Application of the method has been discussed by Thomson (84, 85). Maturity selection was not included among the more recent Fort Valley cutting experiments because its major tenets are not in accord with findings on management areas where individual tree records have been carried 20 years or more (70, 72). Following are some of the more important discrepancies: 1. Fort Valley tree records indicate that diameter growth is related more closely to ground space available following cutting than to age and vigor prior to cutting (tables 9 and 10). 2. In a region characterized by drought and low-quality timber, release of desirable trees from root competition by cutting less de- sirable stems is the key to effective silviculture. 3. Large-crowned trees are often the limby dominants or wolf trees which have grown more or less in the open; small-crowned trees are the codominants or intermediates in crowded stands. Small-crowned trees usually display the clear, cylindrical boles that should be retained to promote value increment. 4. Ponderosa pine stands are characteristically deficient in erowing stock of young age (or small diameter) classes. Building up this part of the growing stock by favoring the better type of poles, blackjacks, and small yellow pines is considered a primary object of silviculture in the Southwest. The nearest approach to maturity selection in the Fort Valley Experimental Forest is the cutting to favor dominants on sample plot S7, logged in 1924. Marking in the mature class followed es- sentially the pattern of maturity selection, though without use of an age-and-vigor classification. In immature classes it went a step beyond maturity selection by cutting subordinates, if merchant- able, where they were competing with the favored dominants. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 59 Improvement Selection Improvement selection was developed in the Fort Valley Ex- perimental Forest because it was realized that other methods had proved silviculturally deficient. As the name implies, improvement selection is planned and directed toward improvement of the stand (70, 72). | Improvement selection recognizes and undertakes to correct, as far as possible, the common deficiencies of ponderosa pine stands: (1) General understocking accompanied by local over- stocking, (2) a preponderance of mature classes at the expense of immature classes, (3). poor spacing and inefficient use of soil mois- ture, (4) prevalence of low quality due to inadequate natural prun- ing and dominance of inferior types, and (5) high mortality rate and low productive efficiency of large trees. These factors are closely interrelated; individually or collectively they account in large measure for the low yield of unmanaged ponderosa pine. Silviculturally and economically the primary aim of improve- ment selection is to build up an effective growing stock. This takes precedence over immediate timber sale receipts and yield of the near future. Initial increment may be low but it is expected to rise with development of the growing stock, and quality is expected to rise more than volume increment. But ponderosa pine stands are usually so irregular that development of a satisfactory grow- ing stock is a slow process. An adequate growing stock must first of all contain enough well-distributed trees to make reasonably full use of the soil; and the gradation of size classes must provide for a succession of cuts at relatively short intervals. The first step, in conjunction with harvesting the crop, is to liberate trees which have a silvicultural and economic future. Trees of good bole and potential growth capacity will be found in mature as well as immature classes. In yellow pine groups they are the smaller stems, codominants or intermediates, of short crown and relatively clear bole. In addition to removal of declin- ing and low-quality trees, the stand must be opened up enough to enable remaining trees to grow and bear seed. No rules can be given as to what volume should be left, but generally there should be enough relatively large trees to provide several cuts within the next 50 years. Blackjack groups offer the greatest opportunity for salvage of potential growing stock. Removal of a single limby dominant usu- ally liberates several smaller trees of good form. The increment borer is a better guide than spacing rules. Diameter growth of less than 1.5 inches per decade generally calls for thinning; but it should be borne in mind that moderate growth on many stems is preferable to maximum growth on a few. If spaces between yellow pine or blackjack groups have been occupied by poles, saplings, and seedlings, the future of sustained yield is secure. Wolf trees and other undesirable types should be cut if merchantable. A market for stems below sawlog size would open new vistas in silviculture, but at this point commercial cut- ting merges into stand improvement, which is discussed in a later section. 60 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 Better Use of Soil Moisture It is axiomatic that wherever moisture is the limiting factor in survival and growth, silviculture calls for development of a strong root system, in proportion to the size of the tree. The demand for root space invariably exceeds the demand for crown space. Fastest growing trees may be in vigor class A, B, or C, but they are nearly always in position class X (isolated), O (open), or M (marginal), meaning that the roots can extend freely in at least one direction. Slow growers may be in any vigor class but are invariably in posi- tion class I (interior). Partial cutting, in addition to harvesting the mature crop, ef- fects a redistribution of soil moisture among the remaining trees. Ideally, a harvest cutting under any selection system should leave the soil almost fully occupied. In overmature stands this result is not always attainable but it should still be held up as an objective. In typical blackjack groups, as will be shown later, 30 to 40 per- cent of the volume can be removed without lowering the volume increment during the ensuing 20 years, and if the trees have been well selected, value increment will increase greatly. If the stand is stocked to the limit of the moisture supply, in- crease in size of individual trees must be accompanied by decline in diameter growth unless some of the trees are removed. Under a stocking that makes most efficient use of the soil, stems above the 20-inch class seldom grow in diameter at a rate exceeding 1.5 inches per decade, and as they approach 30 inches the growth will decline to 1 inch or less per decade. Wider spacing can increase these figures, but it should be remembered that the ultimate cri- terion is not diameter growth of individual trees but volume and quality increment of the stand as a whole. Placing Increment on the Best Boles Improvement selection endeavors to place the increment on the best boles in the stand. If a desirable clean-boled tree is crowded, additional space is provided by cutting less desirable neighbors of the rough-boled type; these are usually present in abundance. Occasionally several excellent stems occur in a clump; other things being equal, the largest is cut because two or three small trees have a higher potential earning capacity than a single large one. Stems below 24 inches d. b. h. are preferable as growing stock; but high-quality larger ones up to 26 inches, and even larger, may be left if they are provided with space in proportion to their size. Limby dominants usually represent the lowest quality and the least efficient soil utilization in a stand. They grow rapidly for a time at the expense of subordinates, but eventually they too must yield to competition. Not only do they suffer from root competition but side shade from surrounding trees causes the lower branches to die. This last process would be desirable but for the fact that it usually begins too late to bring about natural pruning. Figure 15 illustrates a large tree of this class. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 61 In pole stands most of the trees should be crowded into vigor class C and held in that class until about 50 feet tall. As soon as a commercial cutting can be made, groups should then be opened by removing first the limby dominants and others of poor form, then further cutting to improve spacing and finally supplementing with stand improvement. Limby class A trees should not be left unless they are in isolated positions and then they should be pruned while below 12 inches d. b. h. Figure 16 illustrates a Laue pole group treated in about this manner. F—-421060 FIGURE 15.—A 22-inch class C tree (extreme left) whose rough bole shows that it was formerly in class A but that the crown was reduced by intense side shade. It will grow as a result of release, but the bole will remain rough until it reaches at least 30 inches d. b. h. Well-released class C trees will tend to build up their crowns, approaching the B class, but under light or moderate release they will remain in class C. Decline of some trees to class D is not seri- ous but overtopping should be avoided. Early crowding forms a good bole and encourages natural pruning while the branches are small; cutting beyond the pole stage checks extreme competition and sustains diameter growth. Boles are of two broad classes: (1) Those which have been cleared of branches early in life, at least to the extent of forming a surface-clear butt log while below 20 inches d. b. h., and (2) those which still bear coarse limbs either living or dead after reaching the 20-inch diameter class (fig. 15). Only the first class 62 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 has high potential value. Although mill-seale studies show that the value of rough boles increases with size, it should be under- stood that substantial improvement in this class of tree comes only as the diameter exceeds 30 inches. Green limbs are preferable to dead ones in large boles. F-427513 FIGURE 16.—A pole group after improvement selection cutting and stand improvement in 1941. Several stems were cut for sawlogs; those marked with white cards at breast height were poisoned; all remaining have been pruned to one log length, Several trees will be large enough for sawlogs in 1951. Application of Improvement Selection Improvement selection, in contrast to group selection and ma- turity selection, removes fewer trees from yellow pine groups and more from blackjack groups. It leaves a larger total volume than does group selection, and about the same volume as maturity selection. Improvement selection leaves fewer large yellow pines but more in the m‘ddle and lower diameter classes, of a size and type that may be expected to become valuable in 20 to 40 years (fig. 17). In contrast to salvage and maturity selection, it opens up blackjack groups by taking out the largest and limbiest trees (fig. 18). In both yellow pine and blackjack groups it aims to leave the best available stems with respect to potential value increment, so spaced as to encourage growth. On an average, from 40 to 50 percent of the gross volume 12 inches and over d. b. h. is left and MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 63 F—427510 FiguRE 17.—-A desirable type of yellow pine stand after the first cutting by improvement selection. The three largest trees, between 24 and 28 inches d. b. h., will furnish volume for a second cut. The remaining five, between 18 and 24 inches d. b. h., can be held over two or three cutting cycles of 20 years each. this is distributed as uniformly as circumstances permit. The pro- portion cut or left is subordinated to silvicultural objectives. Advantages of extending the first cut to blackjack groups in- stead of confining it to the older age classes are that it makes possible: 1. Relief from stagnation in relatively young groups. 2. Liberation of potentially valuable subordinates while they are still capable of response. 3. In substance, a transfer of the growth which can be sustained by a fixed moisture supply from the poorest to the best stems in the stand. 4, Arresting extreme crown reduction which leaves coarse dead limbs on the upper portion of the bole. 5. Stimulation of root development sufficient to maintain growth and build up resistance to wind and bark beetles before the trees approach maturity. Analysis of cutting on two areas.—Improvement selection is represented in the Fort Valley Experimental Forest by two areas (S9 and 810) logged in 1941 and 1942. Both plots are site quality Vt, but 89, with an original volume of almost 17,000 board feet per acre, had by far the heavier stand. Plot S10, with an original volume of about 13,000 board feet, is more typical of stands as found on the Coconino Plateau. The two areas are compared as to number of trees and volume cut and left in table 13. 64 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 A second cutting on both of these areas in 10 years and a third 20 years later is contemplated. Removal of about 3,000 board feet per acre on S9 after a 10-year interval, assuming a net annua! increment of 100 board feet in the meantime, will leave a reserve of approximately 6,000 board feet per acre. A cut of 2,000 board feet on 810 will leave about 4,000 board feet per acre. In both in- stances the second cut would remove: (1) Practically all yellow pines over 30 inches d. b. h.; (2) most yellow pines over 25 inches d. b. h.; (8) diseased, injured, or otherwise inferior trees of all age classes; and (4) additional stems as needed to improve spac- ing and especially to liberate trees of good form. In stands whose original volume is appreciably less than 9,000 board feet it may be advisable to defer the second cut 20 years. 3 Advantages of a light second cut in 10 years over taking an equivalent additional volume in the first cut are: 1. Less violent disturbance of yellow pine groups. 2. Increased opportunity for salvage as compared with a second cut de- ferred 20 years. 3. Additional opportunity for refinement in spacing, release, and selection of a superior growing stock. 4. Less damage to reproduction because nearly all trees in the second cut can be felled either within open tree groups or into spaces where trees were dropped in the first cutting. F—427512 FIGURE 18.—A blackjack group after the first cutting by improvement selection. The trees are 10 to 18 inches d. b. h. and about 100 years old. Those under 16 inches d. b. h. have been pruned to a héight of 17 feet. A few will be removed in 20 years in order to maintain vigorous growth, 65 | MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST VG 86 vt OLS PZ 62 Oe ey ee ee 6S 1210,L aurd IDCYODI_ mona X 24nd suIN[OA Fo yusdi1ed ul “[[No pue yoojod “yueorted gq ‘OTS ‘yusoI1ed ZG “GS JNd oUIN[OA SsOIs Jo JUddI0g ; "yooF plvog 9Z8‘ZT ‘OTS ‘Joe; pLVog ZG68‘9T “GS SWINIOA SSO1s [VUISIIO 1 916 °S 6208 SLL T LLZ'9 G6 I OL 6 869 oGh 1 aE NES eee i ee [e301 L00‘T 8h 189 oT Lg" 8a" OLE | 62 62 C0 Oe er eee Le PLY & 669‘ 9G0‘T 280° eat Lg'9 SIPS LTO GI? 1G | era 08-12 G68 LY T 16 Tvl LE 0 G0'§ V08 ° 901 T 61 9 COPS as es Se ees 0G-61 CAAT OSh*L €98°8 egg '¢ 910°9 GeV 92-9 G6¢ ‘T LI8'S ESSc SL Gee = s/s [e701 61 ¥ 88L'é 68 & 18a '& 20% LT 008. POS, Co. fee ene eee ee P18 976 G L6OV V Gob I LOG @ Aa) 88°36 vc0 I 066 I 89 1 OS SG ee eee ee 0&-Te GLE 8Lg vor G66 98 0 oie ILG 6GE iS) LOE SS a ee 0c-GI aINSDAU alNSDIUW aANSDIW alNspaul LaQuUun N laqun N alnspaw alNSDauUl LaQuUn NT laquen N pl00g j2a4q | p4vog Jaayq | p1v0g Jaayq | p4vog ja0q plvog aay | pLvog 120 4q Ors 6S OTS 6S 01s 6S 01s 6S 01s 6S ouNj[oO A. SOdL J, ouInjo A. SOoL J, (Seyout) SOSse[D 988 |[[e dnois Joj0Wieid ‘ouIn[O A auld MO][OX dVIPSUlojUl pue yoelsoe[g_ 2 LMO 1 01S pun 68 si0)d ajduns UO poyzow worgoajas quamaaoidur fig 1f2] puv 7nd a.ion sad aWNjoa SSOLB PUD Saat} fO LaQUuNnN— ST AAV], Growth After Partial Cutting Timber yields are determined by three elements: Growth, mor- tality, and replacement. Growth is directly manifested in the di- ameter and height accretion of individual trees, which is first translated into volume increment of trees and ultimately into vol- ume increment of stands. Mortality works in the contrary direc- . tion by eliminating individual trees and thus lowering the aggre- gate increment. Replacement through regeneration and advance into the merchantable classes tend to counteract mortality. In virgin stands, growth and mortality are often assumed to be in equilibrium. This is true only under certain conditions. In a fully stocked mature stand mortality is likely to exceed increment but only temporarily, because eventually replacement comes into play. In understocked stands containing a fair representation of immature age classes, increment exceeds mortality until such time as increased stocking and maturity bring about an equilibrium. The majority of virgin ponderosa stands in the Southwest are in the understocked class and they may therefore be expected, under protection, to increase their volume per acre substantially. Harvest cuttings on a selection basis anticipate mortality, and if frequent enough they convert practically all growth into yield. Well-ordered selection cutting permits neither prolonged decline nor prolonged understocking. DIAMETER GROWTH Diameter growth is less closely related to diameter of bole than might be expected. Obviously, a given diameter growth represents a much greater volume increase in a large tree than in a small one. Nevertheless, it is not uncommon in cut-over stands to find that trees up to 24 inches d. b. h. are growing practically as fast in diameter as are 12-inch trees. Assuming a more or less con- stant relation between volume increment and growing space, the unexpected phenomenon of constant diameter growth through ascending diameter classes can only be explained by a decrease in the number of active stems per unit of area. In dense young stands the larger stems are the faster growing ones in diameter as well as in volume. They are the dominants, which have been able to appropriate more and more space at the expense of their smaller neighbors. The subordinate stems are at the same time continually losing ground, thus lowering the average growth for their diameter class. Diameter Growth Affected by Cutting Comparison of Virgin and Cut-Over Stands - The effect of cutting on diameter growth can best be analyzed by considering also the rate of growth in virgin stands. A direct 66 *~ MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 67 comparison is furnished in the Fort Valley Experimental Forest by two adjacent areas of 160 acres each, one a virgin stand (S6) and the other a cut-over area (S7) logged in 1924 (tables 11 and 12). Although the cut-over area appears to have had a better representation of younger age classes, even before cutting, the stands and sites were generally similar. Apart from the expected deficiency in number of large trees on the cut-over area, numbers on both areas are sufficient to give a fair representation of the various diameter classes. Table 14 shows the number of trees and growth rate by diameter classes on the two areas during the 10-year period, 1925-35. Be- low the 12-inch class, diameter growth in the virgin stand com- pares favorably with that in the cut-over stand. Beyond the 11- inch class diameter growth forges ahead in the cut-over stand and — this lead is retained throughout the series. In the 18-inch class and upward the effect of cutting is shown in the decreased number of trees as well as the increased average diameter growth. TABLE 14.—Diameter growth of ponderosa pine in a virgin stand and in a cut-over stand (sample plots S6 and S7, Fort Valley Haeperimental Forest) Trees in class, 1925 Diameter growth !1925—1935 Deb hs class (inches) Virgin Cut-over Virgin Cut-over Number Number Inches Inches A eae Steps ee Mane hy 605 2,396 g9il 74 (Cte) RESO ROBE SEDC MGT: Tab alee 635 2,109 1.69 1.78 Qe [ilar theese tion Oe ed BN: 367 996 1.66 1S ANS Aveta ke Steshie hate yO 376 681 i On 1.58 SLES ae Bk Shee als AK ad 447 599 .99 58 TCE "(9Q) 8uIQ3No OU ‘UISILA Sos (@-GS) UOTZDeTES JYSTT ~(Z-GS) 901} pases paleq}VIg ~->>(J-GQ) uorqoeyes dnoiy ee (PS) Uoroepes dnospH ea (ES) WoIoe[es dnosy 8ul}{No Jo poy] SPUDIS UL PUD PUD{S MHMA YD Us hzYDILOW jonuun IUpOIIG—91L ATIAV IL, U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 72 99 Ov 8'T an G3 3) o 8°F 8682 BUSTA RS ma DP we Ee a Na ie [F401 66 I v6 I 39 GL LG G LS LST 996 GG? soos PA eae Me eee BOT oie gS ae hs 69 vg ive! 8% & §& Vas 8 PV ISIS] Sy VOUGS Ate | oad Wheaties arn tet a aney a O&-126 86 0 o& 0 90 Gas eae 8 0 L 0 016 MOG ihe olf oie Rae Noto OS eg Coe 06-GL T-GS LOTd “ONILLOO NOLLOWTAS dNOWD 66 GG GG 0 we Ul 6 6G VG 108 °S« | Ace ale OR Sagn a ar ne [®39\L 0g” 0G Seay ) 0) 6 8 6 6G LVE OG eS oe es ree cot Rees sue LE 68 1§ Lt 0) 6 1 bas G & ICL T OS SGr, chlo date sald 60 ade A Baie naa 0&-12 9T 0 LT 0 6 1 0) ee V0 gaol &E8 ACS: aa had ame ame eins Saree a) oc 06-61 VS LOTd “ONILLNO NOLLOWIOS dnowo 09° GV 8 es) oe GY ee CG's 00 Gl Lay eet poe [830.1 cv I | 68 T e) eee Gu 8 VI 6 VI 18P creas flare Rees See es ectele Gg GV iS tol, Le 0 v SEY 696 | OL §& P5 hee eae 0&-12 8&0 8&0 |! G9 8 0 (0) |! 8 I GOL 1 HO? a Sug ONtsigae = ar ines beter eae 06-61 JUWardad JUIIL0 JUWaIla ]Wada 1uaadaq [UII 1UWaIda adNsS Daub OQuenN panog 100 yf auIN[o A Soa. J, eae 90}0])SIJ ee SULUYY SUT pum auNnyoO A S90. J, a Eile RAT oe ae ee Sees Es es dnois 10j9wWeid pues [BUIBLLIO JO JUdd.10d —fq potted IvaA-(g poystqeyso yo[d UI SSO] [VeNuUe [240 J, UL Po[L], PWNIOA poAdasat JO JUAILEg udyM atoR tad pueqs dajawunup pun asnno fiq payisspja ‘Burqna sazfo , suvah _ Saad_ fO Anous 6S LOITd ‘ONILDLOO NOLLOWTAS dnNoOwo & Buunp aud vsoiapuod fo fyyv,J4oW— LT AIA L, 73 MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST ‘Yyeop JO ull, 4% Saar} poeT[D] JO sUN[OA 9Y} PUB P.10I01 BY} JO SUTUULSeq oY} Je AnoOIs yey} UL OUIN[OA jOOj-plv0q ey} UO paseq SI JUISB SUIT[IY Yove 04 poe nqi4s47e SsoT Jo adsejusd1ed oy} ‘sdnois JojyewWeIp ve1y} 94} JO Yyove UT z "SP-ST6L Saved ‘sqo[d 194}O LOZ *GE-G06T Savek TaAoo FY pue Sg szo[d 1OF spxovay ‘peutquiod sjo;d aAIsUajJUT pUB VAISU9}xXO TOF oe Bie Tt eee By Oe 9 & L& 9 L'6 ooh V CP Pilon ee ee ee [210 ,L, oa I 01 Lt 0G 88 € ST 6°81 TP0‘T GO0 1a esa ae eee seo" seer ee ee +1¢ 69 a 8" 9° 8 8°Z 67 0°6 666° OU Ve a ea oe ae eee ee 08-16 88 0 VE 0 80 6 7 oS 80 LEG aie VODG. 3 aa ee ee eee 02-21 | Ue sae pale eae 8 0& 0g 6 GI L6 co6 I RONG sie oi eaten pa ace ee nee [210], ae eat 8 99 L'8 9° &Z % ST 9¢9 Op te & Aes eso see sar ee ae +e LL 69 ea Veh L§ VL 0 6 9G0 ‘TI QS ees ae Sat ee ee 08-12 o& 0 &V 0 6 3G 6 & 0 Gali GEG OZ GO a uses a 2 ae ee SOs eee 02-21 74 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 5-year periods are considered. This may be partly due to tempo- rary disturbances such as wind or insect epidemics, but even in the absence of such disturbances there is a tendency for casualties to come in surges. A period of exceptionally high losses is often fol- lowed by one of comparative quiescence, suggesting that for the time being the most susceptible trees have been eliminated. Some agencies, such as windfall, tend to be most violent during the first few years after cutting; others, such as mistletoe, tend to increase in virulence. On the whole, however, there is a progressive weakening which may not manifest itself so much in outright death as in decline. Some areas logged 20 years ago now present a skyline of spiketops and stagheads suggestive of the uncut forest. In addition to dead trees there are many which are only partially dead from the effects of lightning or parasitic attack. Many of these trees linger for years, and undergo a process of deteriora- tion which for practical purposes writes them off the forest inven- tory long before death removes them from the tally sheet. Of the five 30-year records in table 16, all but one show a higher volume of loss during the last 15 years than during the first 15, and a higher loss during the entire 30 years than during the first 20. The one exception is the scattered-seed-tree plot (S5-2) where high loss from windfall and lightning occurred during the first 5 years after cutting. Causes of Mortality The four main causes of mortality in the Southwest are wind, lightning, mistletoe, and bark beetles, as shown by tables 17 and 18. Their relative magnitude varies with locality and other factors (65). Wind and lightning are the most universal killers; mistletoe | and bark beetles may cause as much loss as the other agents, but they are more variable. The high mortality on the Wing Mountain area (S83) and the light selection area (S5-3) in the last decade was due to increasing virulence of mistletoe. In con- trast, no mistletoe loss is reported on the cinder area (S4) be- cause mistletoe does not occur here. Bark beetles are generally a minor cause of mortality in cut-over stands, but in the virgin stand (S6) it ranked as a major factor. In tables 17 and 18 mortality which could not be definitely attributed to any one agent is grouped under the general heading ‘‘unclassified.”’ Recent information indicates that much of this loss is due to root rot, of which there are two kinds, and a stem rust Cronartium fila- mentosum (Peck) Hedge. Both of these agents are more fully discussed later under “Control of Damaging Agents.” Fire is another factor that exacts a sizable toll each year; it is not listed as a cause of mortality in tables 17 or 18, however, because no destructive fires have occurred on the experimental areas during the period of record. A 10-year summary for the southern Rocky Mountain region (90) indicates, however, that timber killed by fire and not salvaged, averages only 1 to 2 board feet per acre annually. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 15 The agencies causing mortality are generally the same in uncut stands as in those which have been logged, but their relative rank as measured by loss inflicted may change appreciably as a result of cutting. As previously stated, bark-beetle losses, nor- mally low in cut-over stands, were almost as high as lightning and higher than windfall in the virgin stand. During 15 years of simultaneous records bark beetles accounted for only 11.5 percent of the total volume lost in the cut-over stand as compared with 27.3 percent of the total volume killed in the virgin stand (table 18). During this period bark beetles killed 16.5 board feet per acre annually in the virgin stand, as compared with 1.3 board feet in the cut-over stand. During the same period lightning killed an average of 25.9 board feet per acre annually in the virgin stand and 5.8 board feet in the cut-over. An important side light in this record is that in both stands only one-third of the lightning- struck trees died during the 15-year period. TABLE 18.—Percent of trees and of board-foot volume killed by different agents in a virgin and a cut-over stand, 1925-40 Percent of 1925 stand killed, Percent in diameter group (inches)— of total 5-year Kind of stand talit and killing 12-20 21-80 |81 and overll2 and over) © agent Vol- Vol- Vol- Vol- Vol- Trees) ume | Trees| ume | Trees} ume | Trees) ume | Trees | ume Virgin (S6): lightiningees| 0.4 Oe4e teatime Oo Grsnle GL Anil beiko son) 30s 6 42.8 Wanidir eco ot 50) Gules Meo ibe slag dO AK = 20) 4 182 Bark beetles__| .8 MOial ese Ovals Ol ln isle icine lel Ono eo Ze Qs Mistletoe® 222|- 23 33 sil aul nA. 53 3 22, (all 2.6 Unclassified__| .5 6 73 a ee 8} 55 Mel tOwe 9.1 Allkagentses|asom natal onon lpe ele Oniten4y oe ete OOeO! > 10080 Cut-over (S7): Lightning ____ 5 te ee Ge Ae) 0 io e2 6a) 4448 50.0 WGRe nea aa 2 A OBS a CON Ba Molen Orel ee letaee Qane Bark beetles__ il w2 6 BO 0 0 38) AB WO Idk 59 Mistletoe ____ 4 PASE) 0 0 0 nS 22 LORe 3) to) Unclassified __ 5 A 6 .8 | 0 0 ais) Gr Pulitae Lhe Allagents__| 1.7 2.0 CAGE inne I OsOulaceon omc. LOOLOF le 10050 Notwithstanding one severe blow-down in the virgin stand (negligible in the cut-over stand) windfall ranked below bark- beetle losses in this stand. Wind accounted for a loss of 11 board feet per acre annually in the virgin stand and 2.7 board feet in the cut-over stand. Mistletoe was relatively inactive on both of these areas: it is charged with only 2.6 percent of the volume loss in the virgin stand, and 3.8 percent in the cut-over stand. During 30 years mistletoe loss accounted for 37.6 percent of the total volume lost on the Wing Mountain area (S3) 6 miles distant. 76 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 Mortality in Relation to Size and Age Closely associated with causes of mortality is the size of trees, which in turn is broadly related to age. Mortality is much greater in large than in small trees, and this is true whether the per- centage is based on number or volume. Most killing agents take a relatively small toll from the 12- to 20-inch diameter class, but mistletoe is an exception. Not only are large trees more susceptible to certain killing agencies, but because of their large size they contribute more to the volume loss. According to figure 20, mor- tality, based on number of trees on the Wing Mountain sample 60 oO (eo) NUMBER OF TREES LOST (PERCENT) ~ Ow fe) (eo) ro) 8 2 16 20 24 28 32 36 40 1909 DIAMETER BREAST HIGH (INCHES) FIGURE 20.—Mortality by diameter classes, sample plot S3 (456 acres), 1909-39. plot (S38), decreases from the 12-inch class to the 20-inch class, then rises, slowly at first, but rapidly beyond about 26 inches. The main factor in the lower diameter classes is mistletoe and in the higher classes there are two major agents—wind and lightning. Large yellow pines struck by lightning usually die at once or within a few years, whereas blackjacks usually recover. The following tabulation shows mortality separately for the two broad age classes, blackjack and yellow pine, in a virgin stand and a cut-over stand. The data cover the period 1925-40, percents being based on the stands as measured in 1925. Proportion of trees lost POD er eet of hsaeeags as Kind of Stand and Age Class: aA ees Virgin stand (S6): Blaekiaeks | 2:26 ok. aoe 1.41 1.33 Mellow, “pines eet sects was 7.96 9.40 Cut-over stand (S7): Blackjaekse oo. feb 2 woes Oe 2.04 2.68 Yellow pines) cicol2cowiee es: 9.74 LETT MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST TEA Losses in the yellow pine class were much greater than in the blackjack class. During the 15-year record the total loss per acre in the virgin stand was: blackjack 33 board feet; yellow pine 874 board feet. In the cut-over stand corresponding figures are: blackjack 66 board feet; yellow pine 109 board feet. Mortality in Relation to Method of Cutting Method of cutting affects mortality mainly through size, num- ber, and character of trees left. The only cut-over areas on which results are really comparable are the Coulter Ranch series, S5-1, 55-2, and S5-38 (tables 16 and 17), all of which are on nearly the same site and whose records cover the same years. The light selection plot, with its large reserve volume, suffered the greatest loss per acre, but on a percentage basis the loss was lower than in the scattered-seed-tree plot, which had a far smaller reserve volume. Lowest in both quantitative loss and percentual loss was the group selection area. The main reason for the high loss on the scattered-seed-tree -area is that the stand was made up of relatively few but large trees. The scattered-seed-tree area had a reserve of only 1,922 board feet per acre made up of 3.9 trees averaging 493 board feet, whereas the group selection area had a reserve of 2,893 board feet per acre made up of 12.2 trees averaging only 237 board feet (table 17). On all three areas the higher losses occurred in the larger trees. The two latest methods of cutting—salvage and improvement selection—are too recent to yield authentic records of mortality. Plots representing these two methods lie almost side by side, being separated by the uncut plot S6A. Annual losses per acre during the first 5 years were: Virgin (S6A) 63 board feet, salvage (S6B) 11 board feet, improvement selection (S9) 13 board feet. It is evident that both cuttings largely eliminated the mortality which would have been experienced if no cutting had taken place. Lightning accounts for nearly all the mortality on the salvage and improvement selection cuttings; trees struck but not killed far outnumber the fatalities. REPLACEMENT Advance Reproduction Prompt replacement of the trees which die or are cut calls for reproduction in advance of logging. Few trees are literally replaced in the sense that a young tree grows beside the stump of the dead one. But in a well-managed selection forest, saplings, poles, or larger trees should always be near enough to send their roots into any space that may be vacated. When poles reach the 12-inch class, they are credited with a board-foot volume and classified as “new” trees or “ingrowth,” 78 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 In mature forests lacking advance reproduction, mortality and cutting usually leave large spaces unoccupied by trees. This is a common condition on sizable areas of cut-over land. Even if nat- ural reproduction promptly follows cutting, decades must elapse ee the young generation begins to contribute to the board-foot volume. The Wing Mountain plot (S3) is typical of the condition just described. Only about half of the land was occupied by trees before the first cutting, which reduced the occupied area to less than one-third. In 1939, 30 years after cutting, there were only about 10 poles per acre between 6 and 12 inches d. b. h., and few of them were in the spaces formerly occupied by the trees which were cut in 1909. Abundant reproduction which started mainly in 1919 reached the sapling stage about 1939 and in 30 more years many will be entering the 12-inch class. The young generation will more than replace the original stand, but 50 years will have elapsed in the process. If the forest had been placed under adequate protection 40 years before the first cutting, scores of poles on nearly every acre would have stood ready to step into the ranks when logging removed 8,000 board feet gross per acre in 1909 and 3,000 more in 1939. Now that most of the old- growth forests contain a large representation of saplings and poles in what were formerly treeless spaces, these advancing young classes bid fair to become an important source of board- foot increment after logging. In predicting yields over long periods, allowance must be made for space occupied by young trees below the stage in which their growth is measurable in board feet. In other words, if a stand is fully stocked with trees 12 inches and over d. b. h., then the younger age classes are not adequately represented. These classes require both sunlight and root space. Seedlings less than 3 feet tall may not make great demands upon the soil, but beyond that stage their demands increase rapidly. Generally, sufficient open- ings will come about automatically through logging and brush burning, but the fact remains that a ponderosa pine stand can- not remain 100. percent stocked with trees in saw-timber sizes while at the same time building up the desired younger age classes. Redistribution of Diameter Classes Through Growth Diameter growth over a period of years results in a progressive upward movement of individual trees toward higher diameter classes, which may or may not be compensated by the entrance of new trees into the lower classes. This upward movement is of interest in relation to the availability of merchantable sizes for future cutting. Figures 21 and 22 (38) illustrate the progressive advance of diameter classes and the replacement of dead trees on two group- selection cuttings (S38 and S5-1). In figure 21 replacement from diameter classes below 12 inches has been inadequate because advance reproduction was practically absent at the time of cut- MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 79 TREES PER ACRE (NUMBER) 4 8 12 16 20 24 28 32 36 DIAMETER CLASS (INCHES) FIGURE 21.—Number of trees of different diameters per acre in 1909 and 934 on group-selection plot S38. ting. Figure 22 illustrates a more satisfactory condition in which poles from 8 to 11 inches d. b. h. are advancing toward the 12-inch class, and the number of trees per acre in all diameter classes has increased. VOLUME INCREMENT OF STANDS For purposes of analysis, distinction is made between net increment, gross-increment, and ingrowth. As used in this monograph, the term ‘“‘net increment” is the total change in board-foot volume of the living trees (11.6 inches d. b. h. or larger) in a stand when the same stand is measured at different times. Net increment is based on the full volume-table values and no deductions have been made for decay or other defect. Net increment includes both the volume increase of the original trees that lived through the remeasurement period and the total volume of the trees that grew into the minimum mer- chantable size (11.6 inches d. b. h.) during the period. In some of the analyses that follow, net increment has been broken into 80 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 TREES PER ACRE (NUMBER) 4 8 12 16 20 24 28 32 DIAMETER CLASS (INCHES) FiguRE 22.—Number of trees of different diameters per acre in 1913 and 1933 on group-selection plot S5-1. these two components—‘‘original” tree increment and “new” tree increment or ingrowth. Gross increment is a theoretical value designed to express potential growth if mortality were eliminated. It is obtained by adding to the net increment the volume of the trees that died during the remeasurement period. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 81 Increment in Relation to Volume and Character of Growing Stock Table 19 by Lexen (39) correlates volume growth with average diameter and residual volume on the Coulter Ranch plots 85-1, -2, and -3. Since the table takes into account neither mortality nor ingrowth, it represents the gross increment of original trees only and is chiefly valuable as an indication of growth capacity. The high growth values in the two lower lines of the first three columns suggest possibilities of well-stocked stands made up of young age classes. Average diameter is used as a rough index of diameter distribution; in specific areas it may be fairly uniform or may range from 12 to 40 inches. Extensive stands in which the average diameter is as low as 16 inches are practically non- existent in partially cut forests; but after 50 years of manage- ment such stands should become the rule rather than the excep- tion. The values are probably conservative because the site quality at Coulter Ranch is slightly below average for the region and growth is handicapped by mistletoe. TABLE 19.—Average annual growth’ per acre in board feet and cubic feet during 20 years after cutting, sample plot S5 Growth when average stand diameter is— Reserved : volume per acre ih, 16 20 24 28 32 inches inches inches inches inches inches Board feet | Board feet | Board feet | Board feet | Board feet | Board feet | Board feet O00 74 47 33 25 Zep) ees DAW 2 2 a8 120 76 53 40 31 26 OOO. 2s 159 101 (a 53 42 34 AN) Oia see 194 1S} 86 65 51 4] SAO ee 2277 144 101 76 59 48 G.000 2.2" 257 163 114 86 67 54 Cubic feet | Cubic feet | Cubic feet | Cubic feet | Cubic feet | Cubic feet | Cubic feet OAV) se sel 9.8 Ue 5.6 4.6 AN Qi MOU tins ATURE Ea A) Oe wet an ts eae | 8.8 aod 6.2 pd 60022 2— 19.6 14.4 i 9.4 8.0 6.9 SO OZ) ea ks: 23.4 ea2 13.6 2 9.6 3) 18) 100 Opes 27.0 19.8 15.6 18) tO 9.6 2002 eae 30.2 Ze 17.6 4b 6 12e3 10.7 1Gross increment of original trees only. No allowance for ingrowth or mortality. - Reasons for a higher rate of increment in stands made up of small rather than large trees are almost self-evident. Other things being equal, a given volume of growing stock divided among several small trees is more effective than if concentrated in a single large tree on the same plot of land. The several small trees, if well distributed, have better access to soil moisture and their roots are able to permeate the soil of a given area more completely than those radiating from a single large tree. 82 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 The foregoing relationships between large and small trees are further illustrated by figure 23. In this instance, gross increment and mortality are coordinated, so that the difference between the two graphs represents net increment. Since values are expressed in percent of the original volume in each diameter class, they indi- cate the earning capacity of the wood capital, or interest on the investment. The average 16-inch tree earns about 5 percent an- nually as compared with less than 1 percent for the average 28-inch tree. The data plotted in figure 23 were compiled from the three sample plots of the S5 series, representing group selection, scat- tered seed tree, and light selection cutting. Separate graphs for the three areas (66) show the same general trend of both growth and mortality as in this case where all three are combined. Since the point for each diameter class represents an average value, the graph cannot be expected to fit every type of tree. Growth values are too high for crowded, overtopped, or mistletoe-infected trees and too low for normal, open-grown trees. The growth rate of. blackjack is generally higher and the mortality lower than that of yellow pine of equal diameter. The graph is not intended for rating the growth capacity of individual trees but rather to show general trends. Its greatest value lies in pointing out the low efficiency of large, mature trees, beginning approximately with the 28-inch class. Here the question of spacing and general vigor does not enter because large yellow pines reserved from cutting have always been well isolated and in at least fair physical condition. What happens to such trees under the impact of lightning, wind, and bark beetles is clearly told by the mortality graph. Increment on Large Cut-Over Areas Table 20 gives average increment together with other pertinent data on the large plots in the Fort Valley Experimental Forest. Net increment in table 20 is considerably below the highest values given in table 19. One reason for this is that table 19 does not take mortality into account. In stands of good advance reproduc- tion mortality might be more than offset by new trees, but new trees have thus far been a small item on all but a few of these plots. Another factor is the low volume of growing stock on the old plots in table 20 as compared with the highest in table 19. Of greater importance than volume is the size and number of trees in the growing stock. The “average diameter” class of 12 to 16 inches in table 19 signifies a general absence of large and old trees; that is, the stand is made up of blackjack groups almost entirely. Average diameters in the cut-over plots in table 20 are mostly between 18 and 20 inches; it is known that yellow pines over 30 inches d. b. h. contribute in large measure to this high average diameter. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 83 Gross increment — —— Mortality © 130 Original number of trees + 20 No. trees dying in 20 years ANNUAL GROSS INCREMENT OR MORTALITY IN PERCENT OF ORIGINAL VOLUME DIAMETER CLASS (INCHES) FIGURE 23.—Annual increment and mortality during 20 years after cutting in percent of reserve board-foot volume in each diameter class. Coulter Ranch plots (S5). U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 84 ‘poysl[qeyso o10M SOTA oy} oul} oy} 7e “Y “q “p SoOYoUT G'T[ 19A0 soot} A[UO Sapnyouy , GL G te OL €§ 66 ol SOT G8E's Tesi Siecil O9T OG ee (LS) SjuRUIWOp SULIOAR YF 61° T 8). Le Z 18 Ge 9TT OIg'b | 8 6I Iss oI 082 ae Nearer (€-GS) UOIPeTes JY SIT Gowl LO 1 OV ZG GG 0G cv E18 ‘T L 66 6 € ASA O€ ~~~ (Z-GS) 921} paas pasie}}BIg 90 oe Gaon OL 61 68 9782 ¢ 81 aGit 6&1 O€ ~""""""(T-GS) worpejes dno 69 G 68° ORG 1) 6 OL BSE °s 0 61 v6 VOE Soe atk et see ees (PS) UOoTeTes dnoir 08 G ) 66 G 18 CG SOT 029 ‘8 9 61 L It 9SP (Of Sarena) reer ccer (GS) Worajes dno.) Iv 0 vg 0 G6 0 SV v9 oll Ba lliliealedae G ¢ 61 O9T Cig ns veces tage wee ae oe ~(9S) 6uryqnod ON 1UaI0dd I 1UWaIda J Madad | °UWqiW “Ww Q1a “Wa | Suwa iy | sayouy ‘ON Salo na X ON AYLL4L0 J SSOI) JON AyyewWoyy | ssoiy | otov sed | *y “q ‘p | odov tod dUINTO A ISBIOAV Sood [, Xo} (6! plovod UOTJVUSBISEp yo|d - , oe 5 face ; JO jo pue 3uiqynd Jo poyeyy quaoied Ul aloe Jed veaN PoE JUOWIOIOUL JENUUB ISBIOAY JUIULAIOUL [VNUUB ISBBIDAY ; pueqs [enpisey IsalOy ozouaMiuaduny hayoA JOY YZ Ut plodas Huo) fo sjo)d aj)dwns Abin] UO JUEWALOUT— 0% ATAVL MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 85 Increment on Small, Well-Stocked Plots Table 21 substantiates in a general way the high yields indi- cated for heavy stands of low diameter in table 19. It should be noted, however, that wherever heavy mistletoe infection is preva- lent, it cuts down the increment, partly through mortality but also by retarding the growth of living trees. TABLE 21.—IJncrement on small plots of ponderosa pine in black- jack and intermediate age classes. Wing Mountain sample plot (S3) ; Average annual increment Subplot Residual stand, 1909 1 per acre 1909-34 Area Mistletoe No. Trees | Average | Volume per acre | d. b. h. | per acre| Gross | Mortality) Net A. No. In. Eee | Eton. Bt.beams. | Nt.0.m: i abr 0.8 16 21.9 6 , 062 156 0 156 | Light DEPT Ki ake lee, 29 Salt 5,918 158 8 150 | Moderate Gites 6 nb 17.0 4,347 178 0 178 | Light bila sres ane 6 32 16.7 4,900 232 0 232 | Light Hye wale 1.2 Die, 16.6 3,298 153 15 188 | Moderate (SP ead 2.0 19 18.8 4,404 154 9 145 | Moderate (as. le 37 18.0 7,482 236 5 231 | Moderate Sitbk eee 2.0 31 Spel 6,337 144 40 104 | Heavy Qieciea cats. EAD 26 WTS A509 135 BW 108 | Heavy IL) reeset 4.0 25 18.9 5,907 165 2 163 | Moderate 1 Includes only trees over 11.5 inches d. b. h. at time plots were established. These plots constitute large groups or an aggregation of small groups in the blackjack or intermediate age classes. Because of uneven distribution of the trees, few if any plots can be regarded as properly stocked, some portions being overstocked and others understocked. In order to allow for root spread, the boundary lines were drawn 20 to 30 feet outside of the crown projection of living trees, including also stumps of large trees felled in 1909 and groups of reproduction. The 4-acre subplot No. 10 is regarded as an example well within the possibility of attainment under systematic management on large areas. It is by no means an example of a model forest, but contains enough area stocked with saplings and poles to maintain a succession of diameter classes. A salvage cutting in 1939 was too long delayed and did not remove enough of the large dominants in dense groups. In order to maintain a high rate of increment in any stand, cutting must be frequent enough to salvage declin- ing trees and to relieve congestion in dense groups. Increment in Relation to Time Since Cutting Table 22 indicates general trends of increment after cutting. All methods of cutting except favoring dominants (S7) show a sharp rise of both gross and net increment in the second 5-year period, followed by a more or less rapid decline, which in the old 86 U.S. DEPARTMENT OF AGRICULTURE’ MONOGRAPH NO. 6 plots continues through the 30th year. The trends on the group selection cutting (S3) are shown graphically in figure 24, which also includes mortality. . The second-period rise reflects the effect of increased growing space which apparently was not fully appropriated during the first 5 years. That the rise in the second period is not due to climatic effects is suggested by the fact that the second period in the Coulter Ranch series (S5) occurs 4 years later than in 140 Pe XN ye > ~ 120 y < ~ R F —~ = TENT ly V4 fe ty 100 : & . ~ & oe “I INCRENy SS Ss 80 ci — ly & S . : FEET ROUEEGU oe ssoeee Ce PER ACRE, |N HUNDREDS OF BOA RO FEI S TOTAL VOLUME PES oncnet > 40b------ | oe __MORTALITY | - 20 - —_—-" es , : | 5 10 = - 1 | YEARS AFTER CUTTING FIGURE 24.—Periodic annual increment and mortality in board feet per acre, 1909-39. Sample plot S8. group selection cuttings (S38 and S4). In other words, increment reached its peak in one series after it had started to decline in the other. Plot S7 (favoring dominants) has a different growth pattern, probably because the blackjack groups were opened up in cutting. Net increment was relatively high during the first period and remained almost constant for three periods, then fell sharply in the fourth. Mortality remained relatively low through all four periods; this was due in part to a low incidence of mistletoe. If it were possible to maintain increment at the high level reached in the second period on such plots as S3 (group selection) and $5-3 (light selection), management of ponderosa pine would be revolutionized. But on both of these cuttings the current net annual increment at the end of 30 years was only about half that attained in the 10th year. Where will it be at the end of 40 or 50 years? 87 MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST ‘EP-EEGT ‘S1veA OT sjuseseidat g-Gg pue °Z-Gg ‘T-gg UL poled YIXIS 1 spoiled 1evah-¢g Aq yoo} pivoq Ul JUSEUAIOUL JON OTT 601 vIT ae cv G9 66 VIT GL v6 OTT vél SOT IIl 6 G spotted 1eak-G Aq 400] pivo0q UL JUSWaIOUL SsOI4 80T 80T 60 v8 19 96 Tél I Gc6l S161 S161 S161 6061 6061 Sc6l unseq pilodey (1S) syueuIWOp SuLI0ARy Se (€-GS) UOTPeTES WYSTT ~-------------- (Z-GS) 901} poss patez}BI¢G ~ = -------------- 7 (T-Gg) uooe[es dnoiry See ee ae (7S) UOTQeTes dno1y -- == ---------------- (gS) worqoeTes dnory ee ee (9S) 8ur}zgnd ON UOT}VUSISEp yo|d pue suiz3no Jo poy] spor.sad iah-gG fq sioj}d ajdwuns 7Yfhia UO a1on Lad JUaWMaLIUL JORNUUY IYpOLLad JaU PUN SSOLN—GZ ATAVL 88 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 There are strong indications that cut-over stands with a large residual volume tend, after about 20 years, to assume the char- acteristics of a virgin stand (S6). A large portion of the stand has ceased to be growing stock; it is capable of some growth, but the increment of the old stock is outweighed by mortality. What little net increment accrues is attributable largely to the younger age classes which constitute a small part of the total volume. Reasons for Decline of Increment In seeking an explanation of the downward trend of increment, following the initial rise, attention at once falls upon the rising mortality; but gross increment, which excludes the influence of mortality, follows the same general trend. Associated with mor- tality and contributing directly to it, however, is a growing army of slowly dying trees suffering from old lightning strikes, chronic mistletoe infection, or stagnation resulting from prolonged com- petition in dense groups. The skyline of a light selection cutting, as viewed 30 years after logging, resembles that of a virgin stand (fig. 25). In addition to the dead trees are still larger numbers which are slowly dying. Figure 26 illustrates a tree which was struck by lightning 20 years ago. It was still classed as living in 1943 but it had ceased to grow and the bole was deteriorating. Trees in advanced stages of mistletoe infection fall in the same class. ; F427521 | FIGURE 25.—A stand 30 years after cutting by light selection (S5-3). In addition to dead trees, many are in a dying condition. Note mistletoe- infected branches on tree at right. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 89 F—427987 FIGURE 26.—A 28-inch yellow pine struck by lightning between 1923 and 1928 (plot S5-3). Diameter measurements at 5-year intervals beginning 1913 and ending 1943 are: 26.4, 26.9, 27.6, 27.9, 28.0, 28.0, 28.0. The cumulative effect of mistletoe infection is illustrated by a 30-year record of diameter growth in a group of 10 blackjacks. All 10 trees are mistletoe-infected. Diameter growth averaged 1.2 inches the first decade, 0.8 inch the second, and only 0.5 inch the third decade after cutting. Influences other than mistletoe are at work in this group, some favoring and others retarding growth, but mistletoe is credited with the consistent decline of all trees in the group, irrespective of ground position. 90 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 Competition is less conspicuous but may be as effective as lightning and mistletoe in retarding growth. Figure 27 illustrates two blackjack groups, both practically free of mistletoe and both on the best site found on the light selection cutting. The group in figure 27, A was little affected by the 19138 cutting; the trees re- mained closely spaced. A few of the trees made fair growth dur- ing the first decade after logging, but in the third decade only two grew as much as an inch and the majority were far below that mark. Group B which was opened up grew vigorously from the start, and although the rate had declined by the end of the third period, 7 of the 17 trees were still exceeding 1.5 inches. Table 23 gives the average diameter growth in the two groups during the 30 years since logging. TABLE 23.—Average diameter growth in a densely stocked black- jack group and in one opened by cutting (plot S5-3) Mean periodic diameter growth Condition Trees | | | Ist decade | 2d decade 3d decade | Number Inches | Inches | Inches Densely stocked (not released by | | fOnesccutting ous wen een eee | 23 | 0.9 0.7 0.5 Open (border trees removed in | | {O13 scutting) 22 Se eee | ily | 2.0 | 1.6 1.4 | Original Trees and New Trees Table 24 throws further light on what is taking place in the cut-over stands. It separates the net increment into that contrib- uted by “original” trees or those in and above the 12-inch class at the beginning of the record, and “‘new” trees or those which have entered the 12-inch class since the record began 20 or 30 years ago.° The latter were small poles or saplings released by the cutting ; some were less than 4 inches d. b. h. when the plots were established, and the largest are now 18 inches d. b. h. In the light selection plot (S5-3) the new trees contributed 35 board feet annually to the net increment during the last decade as against 28 board feet for the original trees. It is obvious that without advance reproduction, which was fairly abundant on these areas at the time of cutting, net increment would in another decade approach the vanishing point. Moreover, the growth of small trees, including large numbers of 1919 origin and still below the 12-inch class, is largely dependent upon removal of dominat- ing members of the old stand. Present indications are that the 6 This distinction cannot be made on the earliest group selection cutting's, S3 and S4, because the trees were not numbered individually until 15 years after the plots were established. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 91 F—427524-427525 FIGURE 27.—Two blackjack groups 30 years after logging. A, Dense stand; not a tree has grown more than 1 inch in third decade after cutting. B, Stand opened up; 12 trees have grown over 1 inch and 6 more than 1.5 inches during third decade. (See table 23.) 92 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 yield of original trees will decline even more rapidly henceforth than in the past. New trees, on the other hand, promise to con- tribute at a rising rate, both through the growth of those now in or above the 12-inch class and through the addition of new mem- bers as they advance into the 12-inch class. TABLE 24.—Periodic net annual increment, per acre, of original trees, new trees,’ and all trees on four method-of-cutting plots Annual increment per acre Item _ in board feet, by 5-year periods— Leia oa) 4b yandiGs Net increment, all trees: | Group’ selection (S5-1)_2-____2_____| 58 | 97 83 80 53 Scattered-seed-tree (S5-2)__________ | 7 =| GA6 28 te 12 Light selection, (S5-3)2 5 tes = eee (eget wal Nis 78 84 | 63 Favoring dominants (S7)___________ 98 96 96 yam) Mase SA oS 8 Net increment, original trees: | | Group selections) 22-2 wanes eae DOT UC Se ho bos eee 25 Scattered-seed-tree________________ 13 Al Zot SOM -14 Lightsselectiont) 3s hk sea ee 72 108 [Osh eee Geu 28 Favoring dominants_______________ SiisiE Oban, wane iy tigate Net increment, new trees: Group: selection. {3222 es ees | 8 9 8 8 | 28 Scattered -secd-tree == aan aan | 4 | 5 5 | 7 26 hight selection, 9-20) Usin sane [eee Gol Oip eaas 8 | 35 Favorme dommants2o.5 seein ote base Petes a Eas Me se 24D Nts jc | al | | | 1 All trees 12 inches d. b. h. or larger at beginning of record. 2 All trees reaching 12-inch diameter class after plot was established. 310-year period, 1933-43. Decline of the original stand and the mitigating influence of ingrowth is still more strongly demonstrated on the ‘“‘Favoring Dominants” plot (S7). Net increment of the stand as a whole held a high and even course through the first three periods, then dropped sharply in the fourth, but decline of the “original” stand began in the second period (table 24). Although net annual in- crement of the entire stand was 96 board feet per acre in the second period, that of original trees, excluding ‘“‘ingrowth,”’ was only 81. In the fourth period, original tree increment fell to 55. The saving element was ingrowth, which increased steadily dur- ing the four periods. Ingrowth, indispensable as it is to future production, should not be allowed to blind the manager to the true condition of his forest. Few of the stems that appear as ingrowth during the first 20 years will figure in the log cut within four decades. In all of the cut-over stands listed in table 24, the class of timber that will make up the second and third cuts began declining in growth rate after the tenth year. Although total mortality on the favoring-dominants cutting has been low, lightning has accounted for half of it and has resulted in damage to twice as many trees as were killed. But in addition MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 93 to visible deterioration, there has been a slowing of growth dis- closed only by successive measurements of individual trees. Open- ing up the blackjack groups resulted in excellent diameter growth during the first decade, but a noticeable slow-down is evident in the last 5-year period. The greatest decline in growth and physio- logical condition has occurred in the large, more or less isolated trees of yellow pine age class. In many instances the cause is ap- parent in lightning damage, squirrel damage, mistletoe, or rust (Cronartium), but in other instances there is no sign of injury or parasitism; in the latter case indications point to root compe- tition either from neighboring trees or from groups of poles and saplings (fig. 28). F-423673-442719 FIGURE 28.—Large trees are declining in growth 15 years after the 1924 cutting favoring dominants. A, A 26-inch tree (class III-B), sole remnant of a large group; top injured in 1940, apparently by lightning; saplings encroaching on root area; growth by 5-year periods: 1.8, 1.2, 1.2, 0.4 inch. B, A 30-inch tree (class III-AA), open grown, no apparent injury but surrounded by dense sapling stand; growth by 5-year periods: 0.4, 0.6, 0.4, 0.2 inch. 94 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 Increment of Large Trees A tabulation of growth records in the 24-inch and larger diam- eter classes on the plot cut to favor dominants (S7) discloses a noticeably higher diameter growth during the first decade than during the second, and a very pronounced decline during the last 5 years. Of the 248 trees 24 inches and over in 1925, 28 or 11.5 F—427988 FIGURE 29.—A nearly worthless blackjack 28 inches d. b. h. which is dominat- ing groups of poles. The dominant itself is declining in growth as a result of root competition. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 95 percent died by 1945. During the 20 years the diameter growth rates of the 215 trees still living in 1945 were as follows: First decade pecotd decade Growth per decade: lice, Pa hae DeINeChes and wove. wees ees Fad 0 PH eCOne QeINCheShre he a ae se ae 53 18 (eminchwand Oversea oa eae 164 80 ONO Rsinichisoniwless aera. aoe ee! 51 135 Extremely slow growth, 0.3 inch or less in 5 years, was recorded for 20 trees during the first 5 years, and for 103 trees in the last 5 years of the two decades. Of no less consequence than the slow growth of large trees on the favoring-dominants cutting (S7), is the fact that many of the still vigorous survivors of the upper diameter classes are of the wolf type. During the 20 years since cutting, crowns have in- creased their spread and limbs have attained enormous size. Since the subordinates cut were necessarily of merchantable size, the stimulation of remaining dominants was considerable, but the boles in many cases are so rough that value increment has been negligible (fig. 29). In the light of recent findings, a reversal of the favoring-dominants practice—cutting the rough dominants and thus liberating healthy subordinates of good form—would have improved the stand. Increment on Small Cutting Plots in New Mexico A series of 11 small plots in New Mexico gives results which stress even more than do the Arizona plots the importance of mor- tality and new trees (74). Pertinent data appear in table 25 and figure 30. In general, the New Mexico stands are made up of smaller trees and more trees per acre than are found in Arizona stands. A much larger pole class in the New Mexico plots adds to the role of new trees. The New Mexico plots are too small to give the regular periodic trends obtained from larger numbers of trees in the Arizona plots. Individually, they tend to exaggerate particular features. The group as a whole, however, points to consistent trends in agree- ment with those of the Arizona plots. Figure 30 brings out emphatically: (1) The high potential yield capacity as reflected in net increments as high as 149 board feet in the first decade; (2) high mortality and declining growth of orig- inal trees; and (8) high net increment of new trees. To Keep the Forest Growing The foregoing tables show clearly that yield or rate of increment in the heterogeneous, many-aged, and usually understocked stands of ponderosa pine is not a stable quantity which can be determined once and for all by some formula. All the large sample plots and nearly all of the small ones show that when ingrowth is eliminated the current rate of increment undergoes a progressive decline U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 96 ‘ssedsa.} UL Jno Joos "SUBOA Ge ‘sIeok OL - GT sopnyouy ; ae 1g 66 9¢ TL 6 VI 6 6 SES 3G 2) GG C161 ee VGS sia oa SIL él 66 oe cvI 6G I 9°06 G VG 686% v Vi O€ O161 ~ Ves GV 61 Gl Tg Lb L 9T G 66 L180. % %) O€ O161 See ecis al Giles 66 — 09 69 i) w)]! 8 OI v6 I 9 O€ O161 7 hey Lola ee BIO) Lee | 6 vL 66 « (Soe amma rent (Cd 0 6 oL0 § Vv 0G C161 ; BB9U9I/) le aaa 681 GL “LST ; § 8I L IL 208 ‘I 6G 0G VI6I | gjowy |; — uosley) LG ol Gg 66 6L LE LS L OT 062'9 9 O€ LT61 hea Aas go 6V 66 vit LL 0) 9V G 61 616 9 O€ L161 Ee Allis) S000 L6 96 66 vél IST 8 86 8 €1 GLY 9 O€ IT61 Be VéS gg 89 8G ST L9 8 SI 8 6 168 & 9 O€ [EG iaem | se eee Vos VG GG ee 96 Gol 6 && ¢ Lt E28 9 O€ IT61 ee AGS :‘ZoWof | oO BIUBS WO | WO | wea | wg | waa | ON ‘ON | "mq | Sauoy | Supa x G 7 g Z I +,21 | ,TI-8 | ewnjo, Sool], S901], plodat | Buryyno 4Sa10J ROLY jo jo 101d [euolyeN polled IvdK —spotied ivak-¢ Aq o1oe Jod YUAUWAJOUL JenuUR JON aloe Jad pueys poaAsesoy MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 97 160 ] GROSS ieeenee | ; NET INCREMENT NET INCREMENT ALL TREES ALL TREES NEW TREES GROSS INCREMENT MORTALITY NET INCREMENT AO ORIGINAL TREES | ORIGINAL TREES ORIGINAL TREES INCREMENT OR MORTALITY PER ACRE (BOARO FEET) ANNUAL 1 10 20 30 YEARS AFTER CUTTING Jemez S3-A =----- Pecos SI-A — — — Cibola S2-A — --— Carson Amole FiGuRE 30.—Increment and mortality by 10-year periods during 30 years after a group selection cutting on four ponderosa pine sample plots in New Mexico. which begins about the tenth year and continues at an accelerating rate. In stands left to take the natural course, this trend can be reversed only through build up of young age classes. The problem of silviculture is to stop the decline in trees of mer- chantable size by combating the agencies responsible for death, stagnation, and deterioration, As an emergency measure, decadent 98 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 and injured trees can be cut before they die; parasitism can be curbed by cutting infected trees, and stagnating stands can be re- vived by release cutting. In the long look ahead, silviculture must aim to checkmate destroying or retarding agencies by developing stands which are resistant or little affected. For the time being, we shall consider only emergency measures in which depressing agencies already at work are met in the most direct way—by cutting. Salvaging diseased, injured, and dying trees at least staves off a loss equivalent to mortality. But it ac- complishes more by incidental liberation of dominated trees and reproduction. A full measure of liberation, however, requires more than salvage; it requires systematic removal of low-grade or sur- plus stems in order to improve spacing. Salvage cutting, to be fully effective, should cover the forest annually, but for economic reasons such a program is seldom practical in the ponderosa pine region. The answer, for the present at least, seems to le in fre- quent periodic cuttings (64, 73). A 10-year interval, with provi- sion for supplementary operations in the event of heavy storm damage or bark-beetle infestations, would salvage most of the lightning-struck trees and windfalls, and practically all of the trees which decline slowly under the infiuence of mistletoe, rust (Cro- nartium), and squirrel damage. A 10-year cutting cycle, or even one of 20 years, is a far ery from the 60-year cycle formerly used under railroad logging. The old rule that a minimum cut of about 5,000 to 6,000 board feet per acre is necessary for economic justification of logging operations no longer blocks effective sustained yield. Many investigators have shown that with truck and tractor logging it is not low vol- ume per acre so much as small and low-quality trees that increase logging costs. Investigations by Hasel (25) dealing with ponderosa pine in Blacks Mountain Experimental Forest, Calif., and by Reynolds, Bond, and Kirkland (78) dealing with second-growth shortleaf pine at Crossett, Ark., reached almost identical conclu- sions. In the last-named study, the time required to cut, skid, and load a thousand board feet of logs remained virtually unchanged in cuts ranging from 500 to 5,000 board feet per acre. In the Fort Valley Experimental Forest several second cuttings before, dur- ing, and immediately after the war removed only 1,500 to 2,500 board feet per acre, and though no time studies were made, the sales encountered no objections from contractors on grounds of low volume per acre. Volume of cut per acre affects transportation costs only insofar as road building must be financed by the timber operation. In the case of public lands the cost is variable since most roads are built for a variety of purposes, of which timber transportation may be only one. On the other hand, a private operator who must finance essential roads entirely out of the proceeds of a timber project may find the cost of road construction a formidable item. In this case, the volume per acre, which determines the total number of thousand board feet to pass over the road, may determine the fea- sibility of the entire project. This explains why some large areas of timberland, even in the virgin state, are regarded as economi- cally inaccessible. Once a road has been built and the initial cut MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 99 completed, however, only the cost of maintenance is a legitimate charge against future cuttings. A common obstacle to the short cutting cycle is a heavy initial cut. If the first cut is relatively light, a part of the reserve may be used to bolster up subsequent cuts, and at the same time a fairly high rate of increment may be maintained; but if the first cut takes nearly all the merchantable timber, future cuts are de- pendent almost entirely upon current growth. If, for example, the first cut leaves only 2,000 board feet per acre, and the net annual increment is only 60 board feet, a second cut in 10 years is prob- ably out of the question, and even at 20 years a logging operation on such land may be a doubtful financial venture. But if the first cut leaves 5,000 board feet per acre, there is a good chance that increment in merchantable sizes will contribute 1,000 board feet in 10 years, which with 1,000 board feet of the reserve would provide a cut of 2,000 board feet without impairing the growing stock. Absence of advance reproduction is another handicap. Some stands, because of overmaturity, mistletoe, or for other reasons, do not contain as much as 3,000 board feet which is fit to leave for 20 years. Twenty years may still see deficient restocking and then the manager must choose between two evils: leave declining trees for seed in the hope that reproduction will finally occur through a break in the climatic complex; or salvage all that are below par, thus further impairing the chances of regeneration. With good advance reproduction a second cut at the end of 10 or 20 years might take nearly all of the merchantable volume and still leave a growing stock which, though deficient in immediate board-foot increment, would eventually develop into a productive stand. A review of all the old sample plots in the Fort Valley Experi- mental Forest—those logged prior to 1930—reveals that at the outset not one of them possessed the characteristics required to maintain continuous high increment. The group selection cuttings removed too much of the smaller yellow pine class and failed to open up dense blackjack groups; the blackjack class was deficient ; advance reproduction was almost totally absent; and mistletoe was serious in two of the three plots. The light selection cutting left a fair volume, but poorly distributed, and there were too many large yellow pines; the younger age classes from seedlings to blackjacks were inadequate; mistletoe was a scourge which has persisted and increased since cutting. A second cut at the end of 20 years should have been made to improve this stand. The scattered-seed-tree cutting removed even more of the growing stock than did group selection cutting; defi- cient growing stock, deficient advance reproduction, and mistletoe put this plot out of the running at the very outset; reproduction after cutting has, however, preserved the forest stand. The cut- ting to favor dominants was blessed with good advance reproduc- tion; but too many of the smaller stems were sacrificed in favor of a few relatively large ones which after 10 years began to de- cline at a rapid rate. 100 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 A New Silvicultural Program Rarely are natural ponderosa pine forests found in such condi- tion that cutting can at once put the stand into a high state of production. A common handicap is predominance of old trees and a corresponding deficiency of young and intermediate age classes. Advance reproduction is of great help but cannot bridge a gap of 100 years in age classes. Mistletoe foreshadows an in- crement rate 10 to 50 percent below site capacity. Nevertheless, the first cutting can determine whether postponement of full production is a matter of 20 or 100 years. Enemies such as fire, bark beetles, wind, lightning, plant parasites, and rodents present hazards which must be anticipated and met by scientific counter- attack. Poor form can be overcome by correct spacing, selection, and training through the juvenile period. Timber growing is not merely correct harvest cutting, or restocking, or protection, but all of these and much more coordinated in a long-range program. With these thoughts in mind, a new series of plots was begun in 1940. Three areas of approximately 80 acres each were selected almost side-by-side in a fairly uniform stand. The usual disad- vantage of too much old timber was partially offset by excellent advance reproduction mostly in the sapling stage but also a fair representation of seedlings and poles. A salvage cutting (S6B) and an adjoining control plot in a virgin stand (S6A) were estab- lished in 1940, and an improvement selection plot (S9) in 1941. The board-feet volumes in 1940-41 were, in round numbers, virgin stand 13,000, salvage 9,000, and improvement selection (S9) 8,000. Further details regarding residual stands are given in tables 11, 12, and 18. Methods of cutting have been described earlier under “Cutting in Virgin Stands.” The first 5-year record is Summarized in table 26. TABLE 26.—Annual increment and mortality, in board feet per acre, during 5 years after salvage cutting and improvement se- lection, compared with nearby virgin stand Virgin stand, Salvage, ! Improvement selec- 80 acres (S6A) 72 acres (S6B) | tion, 85 acres (S9) Item | 1930-40 | 1940-45 | 1930-40 | 1940—45 1941-46 Volume at beginning | | Ol ECOG syeeienge ce ait 12630) Loe 22s eA OG eS soil 8,029 Gross annual incre- ment, original trees__ 106 101 101 98 116 Mortality, annual, Oniginalitrees ==. 67 55 82 11 13 Net annual increment, Originalitrees= 22.84 2 39 46 19 87 103 Net annual increment, NEW bTCeS ee es ere 9 11 {( 4 5 Net annual increment, allctreestet ince tec 8 | 48 57 26 91 108 11930-40 before cutting; 1940-45 after cutting. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 101 A second improvement selection cutting (S10) is, for reasons explained later, not comparable with the above series. Salvage Cutting Salvage cutting as applied at Fort Valley is regarded as a pre- liminary measure preparatory to a silvicultural cutting to come later. The program calls for a second cutting by improvement selection in 10 years. The merits of a salvage cutting have been questioned on the grounds that it neglects silvicultural oppor- tunities in the younger age classes while placing all the stress on - saving declining trees which, in this instance, were 48 percent defective (fig. 31). Nevertheless, it is of interest to consider the effect of the salvage cutting on the remaining stand. In this ap- praisal, the companion plot in the virgin stand may be used as a yardstick on one side, and the improvement selection plot (S9) on the other. The virgin stand is more directly comparable since records on the two plots cover identical periods; the improvement selection plot records began a year later. Another check on the performance of the salvage plot is furnished by records in this same stand covering the 10-year period before cutting (table 26). According to the 1940-45 mortality records in virgin and sal- vage stands (table 26) the salvage cutting accomplished a saving of 44 board feet per acre annually which would otherwise have been lost. Gross annual increment of original trees in 1940-45 was 3 board feet per acre less on the salvage area than on the uncut area; but net annual increment of original trees during the same period was 41 board feet higher on the salvage area. The last figure (disregarding ingrowth) may be assumed to express ap- proximately the net effect of the salvage cutting. Unfortunately, a large portion of this apparent gain is only on paper. It has been pointed out that much of the volume saved through reduction of mortality was defective. More disturbing is the fact that a large part of the net increment is on inferior boles. Salvage, as usually practiced, makes no conscious effort to re- move trees of this type unless they appear to be dying; on the contrary, they are favored because they are usually the limby dominants or open-grown individuals which may be expected to live indefinitely. Often they are dominating smaller trees of better | form which would grow if liberated. Salvage cutting automatically opens up the stand and provides release in many tree groups. However, far too many crowded groups, especially in the blackjack age class, are denied the bene- fits of release under this method. A gradual decline takes place in dense groups of both blackjack and yellow pine when they are ignored in the salvage operation. This is illustrated by the follow- ing record of average 5-year diameter growth in two typical nonreleased groups. Average 5-year diameter growth (inch) Trees in pce SRE AB AAAI GELLAR IAAL SE ELSES ZAIRE Age class: group Before cutting, 1935-40 After cutting, 1940-45 Yellow pine .... 11 0.40 0.24 Blackjack .:.... 21 42 .04 102 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 F—427986 FicurE 31.—Declining trees in a virgin stand. in salvage cutting only the three dying trees, already in advanced stages of deterioration, would be cut. More would be accomplished by cutting the nearer less decrepit tree, which is still worth salvaging. In both groups, the diameter growth rate was considerably lower after cutting than before, indicating that stagnation had not been relieved. The yellow pine group (fig. 32, A) is relatively young and of better-than-average quality; several of the subordinates have two almost clear logs. The group as a whole would benefit greatly from the removal of two or three of the largest stems before they begin to deteriorate and before their crowding of good subordinates proceeds further. In the blackjack group at least seven rough boles MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 103 Vitis i F—433049-432121 FIGURE 32.—Crowded tree groups left in a salvage cutting, 1940. A, Yellow pine group. Three large trees (marked x) have passed the stage of profitable growth and should be harvested. The space they occupy could be used to better advantage by smaller and better stems under their domination. Small stumps resulted from a cutting for poles or house logs about 50 years ago. Turpentine faces date back to 1910. B, Blackjack group. Proposed removal in the next cutting of seven trees (three marked x illustrate the type) would stimulate growth to the extent that volume increment would exceed that of the entire group before cutting. 104 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 should be taken out. Those marked x in figure 32, B illustrate the type. In handling trees of this class the important question is not how much they will grow but how much they will damage better trees if allowed to stand. Their removal would leave the group stocked to the full capacity of the soil and would result in a sub- stantial increase in volume increment in the group as a whole, all placed on boles classed as fair to good. If salvage is followed within 10 years by a silvicultural cutting, the delay in improvement of the stand may not prove serious; if, on the other hand, cutting is postponed as much as 20 years, the loss from decline or death of good subordinates will more than offset the apparent gain through salvage of defective and low- quality trees. Improvement Selection Improvement selection undertakes to accomplish in the first cutting what the salvage method would do in two cuttings, assum- ing that the second cut gives adequate attention to improvement of the stand. As in the salvage method, improvement selection contemplates a second cut in 10 years; but instead of a light first cut and a heavier second cut, improvement selection would reverse the order. Theoretically, it might be possible in improvement selection to make the first cut heavy enough to give all the release necessary for a 20-year period. Actually, however, this would result in leav- ing too much soil unused during the first half of the period. The most urgent reason for a short interval between the first two cuts is that it affords an opportunity to salvage large trees which usually begin to decline soon after the first cutting. In the event of heavy windfall, a salvage operation should be made without delay. In order to justify such salvage from the operator’s stand- point, it may in some instances be necessary to take a portion of the reserve which may in turn necessitate postponing the sched- uled 10-year cut. With a reserve of as much as 5,000 board feet per acre, however, it is not likely that the cutting program need be disrupted. Originally it was contemplated that both of the improvement selection areas in the Fort Valley Experimental Forest would be put on a 20-year cycle after the second cutting. But the trend throughout the ponderosa pine region is continually toward lighter and more frequent cuts. Silviculturally, a 10-year cycle, or even a shorter one, is highly desirable as a general program. Such a program would accomplish far more than mere salvage. It would make possible the frequent reduction of competition which is necessary to keep stands growing. Wherever advance reproduc- tion is abundant and provision is made for future regeneration, it is only a question of time until short cutting cycles must become the rule. With the disappearance of old trees, salvage will recede farther and farther into the background, and increasing emphasis will be placed on quick growth of many young, clean-boled trees to diameters of 18 to 22 inches. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 105 According to table 26, the improvement selection area, not- withstanding a lower volume of growing stock, produced annually during the first 5 years after logging 17 board feet per acre (net increment) more than the salvage area. The important difference 'is in quality rather than volume of increment. Before the salvage ‘area can yield the quality of new wood produced under improve- ment selection it will be necessary to remove about 3,000 board feet per acre of wolf trees, imby dominants, and deformed or defective specimens, regardless of growth rate, which are using water needed by the remaining 6,000 board feet of relatively normal trees. The photographs in figures 32 and 33 illustrate better than words the difference between salvage and improvement selection cutting. Improvement selection has opened up both yellow pine and blackjack groups, not enough to obtain rapid growth but enough to arrest decline and start an upward trend. Measure- ments before cutting are not available for the improvement selec- tion area, but records during 5 years after cutting show that in yellow.pine groups 29 percent of the trees grew 0.5 inch or more in diameter, while in the salvage cutting only 9 percent of the yellow pines attained this mark. In a similar comparison of black- jack groups improvement selection scored 61 percent against 29 percent for salvage. Not until after the second cut, however, will pronounced acceleration come into play. And it is worth re- -emphasis that improvement selection stimulates growth of the -» best boles by removing the poorest. As previously stated, the improvement selection cutting of 1942 (S810, tables 11, 12, and 13) is not directly comparable with the series of plots in table 26. Because of great irregularities in stock- | : ing, however, it is valuable for analysis. The area lies on the east side of a large open area or “‘park’”’ which is being invaded by pine from all sides. A strip of nearly 20 acres within the cutting area, next to the park, bears a sparse stand of sawlog size but is densely stocked with saplings and poles which originated in 1914 and 1919. Residual volume, number of trees per acre, and average diameter have been computed by 2-acre or 2.5-acre subdivisions. Average volume of the whole 76 acres after cutting was 5,376 board feet per acre; but there are 8 acres on which the volume ranged from 0 to 1,050, and 9.5 additional acres which bore 2,800 to 3,700 board feet per acre. Thus, 17.5 acres or 23 percent of the area had a residual volume of less than 4,000 board feet per acre. The remaining 58.5 acres ran from 4,100 to 9,600 board feet per acre, with only 5 acres above 9,000. A freak storm sweeping in from the park cut a swath 4 to 6 chains wide diagonally across one end in 19438, blowing down enough timber to account for an average annual loss of 25 board feet per acre on the whole area during the first 5-year period of record. For this reason, only gross increment is considered in computing growth for this period. Average annual gross increment per acre on the area was 88 board feet. Subplots bearing 4,000 to 9,600 board feet per acre show an increment range. from 25 to 147 board feet, and the 106 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 F—410387-410384 h are still ic a second cut- h 1941 w in The program calls for . 1on k. ement select jac black ? B rov rowth, imp gs ? Yr good pine stocked for A, Yellow —Groups cut unde yY il i ] 19 in too heavy ting FIGURE 33. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 107 correlation between increment and volume is by no means con- sistent. Highest increment is not on the two highest-volume plots but on one of 6,100 feet. Of the seven 2.5-acre plots which pro- duced 130 board feet per acre or more, two were in the 5 thousand class, two in the 6 thousand class, three in the 8 thousand class, and none in the 9 or 10 thousand class. Evidently a large residual volume is not alone sufficient to insure a high rate of increment: the volume must be made up of many relatively small trees so distributed as to make good use of the soil. On the improvement selection cutting (S10), as in table 19, average diameter is fully as important as volume. With a given volume per acre, a low average diameter means smaller trees and more of them, usually occupying a greater proportion of the soil. Average diameter does not necessarily express the true situation because a few large trees may raise the average in a stand of prevailingly small trees; but it is the best single figure available. Average diameter on the $10 subplots ranges from 18 to 26 inches; the top ranking subplot, whose annual net increment was 147 board feet per acre, bears 19.6 trees per acre averaging only 18.6 inches d. b. h. In a stand as a whole each succeeding cut will continue to stress improvement of growing stock. The second cut will remove most yellow pines over 26 inches d. b. h., as well as inferior stems of smaller size in both yellow pine and blackjack classes. The third cut if made as much as 20 years later will leave very few yellow pines over 24 inches d. b. h. Thenceforth, the yellow pine class will be represented mainly by trees which rated as subordinates in the virgin stand—trees which in other methods would have been cut because of a small or unsymmetrical crown (fig. 34). Beyond the fourth cut, the original yellow pines will cease to figure prominently in the growing stock; their wide spacing will provide room for regeneration; the present blackjacks and _ in- termediates, along with an important class recruited from ranks now below 12 inches d. b. h., will then constitute the merchantable stand. Groups approaching maturity will have been opened up to such a degree that remaining trees will have room for develop- ment; they will also be relatively wind-firm by virtue of a strong root system. Present pole and sapling stands will then be the blackjacks (fig. 32, B). Stand improvement begun after the first cut will have eliminated undesirable types and provided space for unhampered development of the best. In about 50 years the new forest visualized in the first marking will have become a reality. Prediction of Yield Normal yield tables, granting that they represent stands which scarcely exist, nevertheless create standards which are useful in setting up goals to strive for. Meyer’s yield tables for even-aged, fully stocked ponderosa pine in the Northwest (45) give an indi- cation of the yields attainable if stocking and age classes on large areas could be made to conform to the standards on small plots. Lexen’s empirical growth table for the Southwest (39) provides 108 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 F—422701 FIGURE 34.—Subordinate trees of vigor class C released by improvement selection cutting in 1941. Diameter growth during 5 years after cutting, left 0.7 inch; right, 1.1 inches. Trees of this class usually have the making of an excellent butt log; they would be cut under group selection or maturity selection. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 109 a reasonably satisfactory basis for predicting gross increment on large, partially cut areas. Additional adjustments for mortality and ingrowth are called for, however, unless the forest technician is willing to assume that mortality is balanced by ingrowth. Lexen’s table also serves to bring out a significant contrast be- tween well-stocked young stands and the understocked and over- aged stands usually encountered. For large areas of national-forest cutting in sites IV and V in the Southwest, a mean annual increment of 60 board feet per acre on cutting cycles of 30 years is about as good an average growth estimate as can be offered. Large residual volumes, un- evenly distributed, will lower rather than raise the net increment unless the cutting cycle is short. Abundant ingrowth may increase this figure; deficient ingrowth will reduce it. The presence of good advance reproduction should raise the increment, looking ahead 50 years or more; but until cutting practice recognizes development of growing stock as the major objective, yields must ‘remain low in both volume and quality. On the whole, yield predictions in the present stage of man- agement are of only passing interest. It matters little whether the estimate of 60 board feet is 5 percent or 30 percent in error. What does matter is that lands now yielding only 60 board feet per acre annually can be made to double or triple their yield. For the next 50 years the problem is not so much the exact measure- ment of current increment as it is the need for aggressive steps toward raising the increment to a level commensurate with the productive capacity of the land. Regeneration—Natural and Artificial That a forest cannot be maintained without regeneration is axlomatic. The generally understocked character of virgin pon- derosa pine stands in the interior region is due either to faulty regeneration or to the destruction of young trees which normally would fill the gaps caused by mortality. In order to maintain a suitable gradation of age classes in many-aged stands, regenera- tion must go on more or less continuously. It is not uncommon to find gaps of as much as 100 years between age classes. Al- though this usually means that intervening classes have been de- stroyed, probably by fire, it is known that long intervals may elapse between years in which appreciable numbers of seedlings become established. Studies of increment have shown the advan- tages of an abundant inflow of new trees as expressed by “‘in- growth,” and by contrast the decline of increment where ingrowth is lacking. Restocking may be accomplished by either natural or artificial means. As explained later, artificial reforestation on the dry sites usually occupied by ponderosa pine is too difficult and expensive for general application, and for this reason reliance must be placed mainly on the natural process by which seedlings origi- nate from seed scattered by trees on the area. NATURAL REGENERATION Prior to the great seedling year of 1919, the Southwest was noted for its poor reproduction. This was not true of the whole region; in fact, a survey might have shown that less than half of Arizona and New Mexico was troubled in this way. But the sore spots were vital because they occurred almost invariably in localities of heavy timber use. Large areas of old cutting both within and outside the national forests had failed to restock. In some instances the reasons were obvious—heavy cutting or fire, often both. But national-forest cuttings were not restocking de- spite fire protection and safeguards for seed trees. Years of detailed study in the Fort Valley Experimental Forest and adjacent country have brought to light much information which has been presented in several publications (54, 56, 59, 61, 69, 71). Although the 1919 class of seedlings furnished the first opportunity for a comprehensive study, remnants of earlier classes occurred under conditions which indicated that with adequate protection, natural regeneration could be expected, though at long and irregular intervals. In the light of what has been learned from correlation of conditions surrounding all of these age classes, the factors which call for special consideration are: Seed supply, seedbed, climate, cutting practice, and protection. 110 MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 111 Seed Supply Nature is wasteful in the use of seed. Germination tests of ponderosa pine give from 5 to 97 percent viability, averaging around 59 percent. Under nursery conditions in the Southwest, practically complete germination takes place in 15 to 20 days, but in the forest it continues over a much longer period. The quantity required for adequate regeneration has been variously estimated at from 4 to 10 pounds per acre. Although large trees may occasionally yield 10 pounds of seed in a single crop, they average 2 pounds per tree in “good” years and 3 or 4 pounds per tree in “bumper” years. Good cone crops occur once in 8 or 4 years with lighter crops intervening; cones are practically absent about 1 year out of 4. At irregular intervals, evidently dependent on a number of chance variables, there is an exceptional seed crop such as was recorded on the Coconino and Kaibab National Forests in 1913, 1918, 1927, 1986, 1942, and 1945. Important factors in decreasing seed yields are the cone beetle (Conopthorus scopulorum Hopk.) which destroys the seeds within the growing cone, and the Abert squirrel which cuts off enormous numbers of cone-bearing twigs in winter and feeds on green cones from July until the seeds are shed in October or November. After the seed fall and until July of the next year, seeds on the ground are an important source of food for mice, chipmunks, and man- tled ground squirrels. If these rodents are numerous they may consume practically the entire seed crop. The minimum seed-tree requirement was formerly placed at four trees, 20 inches d. b. h. and over, per acre (54). In “good” seed years, these four trees average 2 pounds each or a total of 8 pounds. Contributions by smaller trees on the same acre might bring the total quantity to 12 pounds. Assuming an average of 10,000 seeds per pound and estimating that under moderately favorable field conditions only 1 seed in 100 produces a seedling that will survive, 10 pounds would yield only 1,000 seedlings. Really effective regeneration on cut-over lands in a single season requires at least 2,000 seedlings per acre, thus calling for 20 pounds of seed. When allowance is made for the numerous agents of destruc- tion and waste, together with the fact that about 10 percent of the seed trees will die over a period of 20 years, the minimum of four seed trees is barely sufficient unless the area has con- siderable advance reproduction. Since more than four suitable trees as large as 20 inches d. b. h. are seldom available, it seems necessary to lower the specified minimum diameter to 18 inches. The minimum seed-tree requirement for the Southwest may then be restated as six well-distributed trees 18 inches d. b. h. or larger. Obviously, the trees which make up this quota should be in or adjacent to areas in need of restocking, and the crowns should be freely exposed. Isolated individuals, or trees released by cutting in groups, meet the essential requirements. The old requi- site of large crowns may be modified by placing less stress on size and more on vigor of the top, because it is the upper part of the crown that bears most of the cones. 112 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 Seedbed It has been demonstrated repeatedly that pine germination is quicker and surer if the seeds are lightly covered with soil than if lying on the surface of the ground. Seeds which lie over winter tend to become covered by checking and heaving of the soil, but artificial covering is more effective. Unfortunately, artificial seed covering is seldom practical. Experience in the Southwest has borne out the old observation that germination is better when the seeds are in contact with mineral soil than in deep needle litter. In years of unusually heavy summer rainfall, however, germination in the litter under trees is abundant, but the seedlings invariably die in these situations if the litter is deep and if the ground is shaded more than half of the day. Effect of Herbaceous Vegetation Partial shade by grass and weeds favors germination, but later effects are on the whole detrimental to pine seedlings. Survival and growth during the first few years are greatly favored by elimination of all competing vegetation, especially the bunchgrass Arizona fescue. Generally the most adverse effect of herbaceous vegetation is root competition. Tests during drought periods have consistently shown more moisture in the soil at depths of 4 to 9 inches where vegetation has been removed than where it is pres- ent. Shade may become equally injurious if herbaceous vegetation is tall and dense, as in the case of Arizona fescue and lupine. Figure 35 shows an ungrazed stand opening that bears a dense F—43843A FIGURE 35,—A dense cover of herbaceous plants hinders ponderosa pine regeneration. A typical ungrazed bunchgrass area in which no pine segues have survived since 1909, although it borders an established stand, MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 1135 cover of arizona fescue. The area has remained unstocked with pine from 1909 to the present. Numerous seedlings started in 1919 but died within a year. The adverse influence of dense herbaceous cover on pine re- generation is shown not only by extensive observation but by experiments carried on from 1928 to 1944 (60, 71). Part of the area illustrated in figure 35, bearing undisturbed stands of Ari- a F—-354195-412919 FIGURE 36.—Plots seeded with ponderosa pine and completely protected against rodents. A, Portion of plots seeded in 1929, photographed in 1937. Wall of seedlings in background is on plot denuded of grass and weeded. An unclipped control plot and plots with grass clipped to 6-inch and 2-inch heights are in foreground; they contain 5, 4, and 11 seedlings, respectively. B, Plot seeded in 1987. Denuded-weeded area in foreground had 35 seedlings when photographed in 1941. Undisturbed grass area in background had 1 seedling, which has since died. 114 U.S. DEPARTMENT OF AGRICULTURE MONOGRAPH NO. 6 zona fescue, was enclosed with a rodent-proof fence in 1928 for seeding tests. One plot was denuded, one burned, and others were clipped twice annually to heights of 2, 6, and 10 inches; on two control plots the bunchgrass cover was left in natural condition. The denuded plot was kept free of vegetation other than pines. Equal quantities of pine seed were sown and excellent germina- tion resulted on all plots in 1929. By far the best survival and growth occurred where the grass and other vegetation were re- moved and kept out by weeding; distinctly less survival and slower growth where the grass was clipped (survival increased : | | 4-T0 6- INCH DEPTH | 6- TO 9- INCH DEPTH 30 + Denuded SO/L MOISTURE (PERCENT OF DRY WE/GHT) PRECIPITATION (INCHES) 1) 0 MAY JUNE JULY AUG. SEPiE OCT. FIGURE 37.—Soil moisture and precipitation in natural grass and on denuded plots, 1934. MANAGEMENT OF PONDEROSA PINE IN THE SOUTHWEST 115 96 sayouy 861 Ul peuing "yove Spoes § 10 J JO S|[IY UL SVM SuUIpess LEET - 0& sayouy Tr rj 0010 10 =) So CO rH 1OQUUN NT sayouy LOQUNN 0G sayouy MHOnnr fo) f=) ST LaQUnn 9€ sayouy 00 0010 N \ 300 00 2 100 SCALE - FEET Dd POO A po < ee <>