Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. a ee Yarby a if iu A z. te, A BD } | He ica iw ia h U 4 ti Bn fu U.W. Brown & W.(. Hodge et ERS 18 Bt 7 NODMERT | Ua Nees Rocky Mountain nova Wie § Forcét © Range | canines Expcrimcnt @tation oS Missoula Montana Chas.L.Tebbe, Director Hee TA NS UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE i | Station paper N2 |3 June 1948 Prepared by the Division of Forest Economics M. B. Dickerman, Chief Paul D. Kemp was in charge of the compilation phase, prepared the ‘ volume tables, and determined the statistical accuracy of the re- source data. Clarence W. Brown supervised the photographic interpretation and field work. Assisting him were William Hodge, Thomas Finch, Melvin Metcalf, Elwyn Peffer, Willard Fallis, and Ronald Schulz. Office compilation of the data was done by the above men. FOREST RESOURCES OF NORTHERN MONTANA By C. W. Brown and W. C. Hodge June 1948 CONTENTS Theproresty survey aneMontana .o ses te. 6 es fe et eit el te ie Forest land. ° e e e e ° e e e e ° e e e e e e ° i e e e e TMhewriveribouvomunardwood forest sais c's 6) esos dle ells The semiarid ponderosa pine forest .......+.«+-e«e- Thenwestern mountain forest. soe See es eee eS Timbe r volume e e e e 6 e e e e ® e e e e e e e e ° ° e e e Statistical data by county Table Table al = Forest land area r) ) ° e ® ° eo 8 ry ® ° e ° e 2 = Timber volume, Oe Ore Oe; er Feccre ce LO) Or 162 211015 a8 © Standard statistical data for unit Table Table Table Table Table Table Table Sy— Wand) area by major use .)).3 29.) 2 « . 6 «| 4 - Forest land area by class. . . Rea eipre se cine 5 - Commercial forest land by forest type and Stand=sciZemclacs uci ise clne men tom oni teltenlnieiiiS - Board-foot volume on commercial forest land by species. ... Shillsh ok athe) i eiiketel elt edie Cubic-foot volume on Comme nedeal forest Jand! DVMRSPCCHCS ie) 5 eis: rol etatevetl oun . - Board-foot volume on commercial corest tana by stand-size and tree-—diameter classes .. 9 - Cubic-foot volume on commercial forest land by stand-size and tree-diameter classes .. ee} ~] Oo J Table 10 — Cubic-—foot volume on commercial forest land by species group, tree size, and class of mate rial e e e e e e e e e e e e e e e e e e Table 11 - Average volume per acre by stand-size class. De finitions e e e e e e e e e e e e e e e e e e e e e e e e POMEMG Geeieenye mlerdevorsl Gy eoig tol da or Gd 1 G61 6, doo On .aV0 ACCURACVROlaUMemGatayr.j. \miMelneniten to Tenweliai ce Weil culienl sli ell aletaMire Liston forest, survey reports for Montana. ~ 3.2 « « « et ‘0 © he i jee 9 . ie +e THE FOREST SURVEY IN MONTANA A survey of Montana's forests was begun in 1934 as a part of a Nation-wide inventory of the forest resources. Interrupted by the war, this survey was resumed in 1946 and is now about 80 percent complete. Present plans contemplate finishing the survey in 1949 to give Montana the first real measure of its forest wealth. Sta- tistics for four counties in Central Montana and for that portion of the state west of the Continental Divide have been published previously. This report presents basic inventory data on the extent of the forest land and the timber volume for 19 Northern Montana counties as indicated on the map below. These counties were covered by the forest survey between April 1947 and January 1948. A survey of Southern Montana is now under way. Upon completion of the survey, a comprehensive report, including data on forest growth and drain, is planned for all of the units. FOREST SURVEY UNITS ARE | ag i 4 —t ‘ \ ROSEBUD | a | —-+-— eee L. Wain ae N } ation uf LLWATER | [ H ——" 7 | | CARTER | zis pee B10 HORN | eis Sh J | CARBON [eee a \ |) AREA COVERED IN THIS RECLORT MX 4664 COVERED IN PREVIOUS REPORTS 2 Li J £35 wer’ es ee LG i a ol anesiccn irredgoee 3A rer artate FOREST LAND Northern Montana has nearly one million acres of forest land and lies largely in the Northern Great Plains region. Only 3 percent of the 31.7 million acres of land in the 19 Northern Montana counties is forested. Though not extensive, the forests of Northern Montana have had an important place in the development of the plains country and are a significant factor in protecting part of the upper Missouri River watershed. In the frontier days, the cottonwood forests along the Missouri were the principal source of fuelwood for the river steamers coming to Fort Benton. Then later, hand-hewn ties from the North- ern Montana forests were used by the transcontinental railroads as they pushed westward. More recently, though, the recreational and water- shed values of these forests have in- creased appreciably. The western portion of Northern Montana, including part of Glacier National Park and the Sun River Primi- tive Area, is rugged and massive with a number of snow-capped peaks. From these the prairie country extends eastward to North Dakota. Three iso- lated mountain ranges stand as forested islands in the prairie. They are the Bear Paw Mountains, the Little Rockies, and the Sweetgrass Hills. The major streams in the northern counties which originate within forested drainages are the Milk, Marias, and Teton — all tributaries of the Missouri River. All of the 19 northern counties have some forest land. Glacier County, with 400,000 acres of forest land, has the largest forest area. Teton is second with 236,000 acres. In contrast are McCone and Roosevelt Counties, each with less than 1,000 acres. Table 1 gives the forest area by counties. The forests of Northern Montana can be divided into three broad groups: a 37. OF THE TOTAL AREA | IS FOREST LAND NONF ORE ST FOREST 24's OF THE FOREST LAND IS CLASSED AS COMMERCIAL NON= COMMERCIAL SOFTWOODS COVER 75/. OF THE FOREST AREA, HARDWOODS 25/. SOFT WOODS HARDWOODS tS oy ps re MS : ag ‘ Lad girchg bedi | | = ol 7 be THE RIVER BOTTOM HARDWOOD FOREST The hardwood type occurs in narrow strips or stringers along the Missouri, Marias, Milk, Teton, and Sun Rivers and their tributaries. Cottonwood is the principal species. Many of the river bottom cottonwood trees average about 24 inches in diameter at breast height and run two logs in height. To date utilization of the hardwoods has been limited to local uses: fuelwood, and ranch con- struction lumber, There are, however, some commercial possibili- ties for producing lumber, crating material, excelsior, and veneer. >< oe a hi oh ; it ad ni THE SEMIARID PONDEROSA PINE FOREST Scattered stands of ponderosa pine occur along the breaks of the Missouri River in Blaine, Phillips, Petroleum, and Garfield Counties and also on the outslopes of the Bear Paw Mountains in Hill County. Most of this pine grows under semiarid conditions and extremes of climate. As a consequence, the timber is short, scrubby, and of low commercial value. It is used locally for fuel, posts, and lumber. nal , ‘pha wounet ame Af aes ah gy 8 te * THE WESTERN MOUNTAIN FOREST This forest, typical of the Northern Rocky Mountains, consists mainly of lodgepole pine, spruce, Douglas-fir, and alpine fir. Most of the timber lies on the east slope of the Rockies in Glacier, Pondera, and Teton Counties. There are also small patches in the Bear Paw Mountains, the Little Rockies, and the Sweetgrass Hills. Most of the timber cutting in Northern Montana has been in this forest type, supplying fuelwood, posts, poles, mine timbers, and other products for local use. These forests were the site of early day tie-cutting operations. “6a A es 0 vee rp ea i fy) Ve Aen oe Oh ty. TIMBER VOLUME the coniferous Torests so typical of Montana decrease as they extend east- ward. In the Northern Montana unit hardwoods in stringer type make up a major part of the forest area and vol- ume. 1x hardwood species occur: cottonwood, aspen, elm, willow, green ash, and boxelder. Cottonwood is by far the most common, both from the standpoint of distribution and volume. Aspen occurs throughout the unit but the largest concentration is in Cilacrvers bilaine,. and Hill (Counties. Only small volumes of the other species are found. Nine species of conifers grow here: ponderosa pine, spruce, lodgepole pine, Douglas-fir, white bark pine, limber= pine, alpine fir juniper, and alpine larch. However, only the first four listed above are important from a volume standpoint. Altogether there are nearly 600 million board feet of saw timber on commercial forest land in Northern Montana. Forty-two percent of the volume is cottonwood, 18 percent spruce, 18 percent Douglas-fir, 9 percent lodgepole pine, and 13 per- cent miscellaneous species. About one third of the saw-timber board- foot volume is in trees 20 inches and larger, whereas on a cubic-foot basis such trees make up only about 14 per- cent of the total volume. Because of the poor growing conditions — short season and low rainfall — the board- foot volume per acre of forest land is comparatively low throughout the unit. However, because of the general scarcity of all timber in these counties, utilization of existing timber supplies is good except in re- mote mountainous areas. Approximate timber volumes by counties are shown in table 2. AG) SOFTWOOD SPECIES MAKE UP 57/. OF THE Bd.Ft. Vol. BOARD FEET SOFT WOODS . HARDWOODS ~~ > %'s OF THE Cu. F+.Vol. 1S SOFTWOOD CUBIC FEET SOFT WOODS / HARDWOODS \ COTTONWOOD |S THE PRINCIPAL SAWTIMBER SPECIES A cottenwers > : “ fawor Ba vm pue[T ySoeloy Tetosow0) eoue puelT 4Sedog *T eTQeL eIngpTnotasy Fo snsuap °S * SH6T Val €°Ge : LL 3 0°OOT 3 ws 3 0°00T sTeyo} FO JUSdIEg 606° LST : 129 ‘99% 2 925729 : VTE *€86 : O9S°7TA°TE = Te VOL 987 Ose 2 9c" e ore Os Se age xneqTM oS SOT 3 o9L‘€ 2 oo€ SVT : oo€ “VT : ost *ese°€ : AOTTEA enh S47 2 6€5‘8 3 eee. el : eee ‘ET 3 0096 LS52¢°T : aTOO], L50°2 : 898°L8T 3 626‘ 68T : 928 “S€z : o9T ‘897° T : u0zel, 8€5°T : = 3 BES *T : BES ‘T : 000‘ 880‘ T : uepT toys 692. 3 = : 692, 3 692 - : 007 £925 T : 4TOAeS OOY 688° : = 3 6889'S : 688° : OC ASST : pueTyuoTy OLT Sz : =, 2 Oui 3 Ouitne. : ose‘ Sotst : oTAT eld G€0SOT 3 6647 60S 3 47°09 $ 790° TL 3 025° TSO‘ T : eaopuod O€TSeT : 6247647 3 66592 : 860 ‘62 3 096‘ 89€6€ : sdt{ttud BEE : O€¢ ‘ez : 899‘2ez : 899 ‘zz : 096‘790°T : uMeTOr4ed G€9 3 = 3 G€9 : G€9 : oze £889 ‘T : ouogoy eel : 9202 : 608 6Z 3 ELS°S : 092° €€6 : Aq19QTT 67954 : oge‘€ : 62652, : 62652, : o9t‘7898°T : TItH ost ‘gg : 6€0‘ 2% : 61S ‘OTT : 628 66E : o9€ * €06ST : TeToeT) 00% - : TLz*69 : T19°69 : T19° 69 : 026 ‘L906 € : preryaey LL9°" : GLe°T 3 2565S 3 Cine ; OzT‘ 60S ST : uosMe(] EC6L“E 3 = 3 C6L‘€ : Cb6L°E : 026 °€z6 : sTetued L6E 3 GL7°O8 : 718 ‘08 : oor ‘28 : 08s ‘oel6z : ouTe Tq SS SS i SER IN te IG Eo A EC poomp.e H 3 PpOOMyjOS 3 Teq0L 3 puet 3 [1 $ : somos TeqvoOL, =: eore TeYO] 8 Ayun09 yee UNUTUTWM YoUT-Q° © 04 Setoeds poom ut =ne x . piey LOJ poomqutT fo oum ure oe cee eee ae oy a é I JOA punos 9y. Sutpn uTu ut 4 dumys Worgz seety T[No Fo euMTOA punos syy pue Sseery punos 56 ee SE canes “au / t A SUL /C eee ee ‘oTna wY/T Teuotzeusequy A 0°O0T egy ode ee pue seyouy o°TT seeay /T $ 3 e z 3 2°95 amas SIGE OMA S OSs eteflee +: €Sc'Oh + 6sotutz + 966'865 : oe — : 3 : : eiz‘ose 406) 76L,° SHE : Ten 5 Si : = : : } 5 oo ee ae gee =. xneqt : LCS 3 638 € : 678 S17 ° £92677 $ 985‘T : fo QTM > To%‘T : er Me ae ee ge = ee : stood TITS : : 3 : : 86 : : ae pe poe Sell oS u0zel, =. 36 : = : : : : LSE 3 ¥ i 49 ; S L9 : al f LTL9 : TAs Jee eae, = ic0 i set 1'79°% ° 19%zZ $ = 2 878 62 8 gg‘ 6c s ce : Hee tel T68°€7 3 815 S7T ° ‘ : 6€6-TT 3 666°TL 3 = 3 Tyoty 3 | ; ETE 62 : €7652TT $ CTLSLS > ofz'ss : ee ee Swit 8 Gale ae : ; = LL ide = B6L"€ 5 eG : Wee Me OY ; sdtTttud 64enT : LL ® -. : 167° © 6H EC Z 106 G ° mmeTo17eg Bel <€ : ao : 6€0°T > 0S5°€ 2 OGGAG : . ; SuognoW : ; €09 -T : Mio > T6L*2 2 oie an Be0 oe : gie‘st + Gott iG eS. a 69€*€ eo SG Se =e ee sores €€% : oo é ; Be FIO) 2 260°9 5 eo Ce : pletszey 2 c 3 = 9 $ = : OLS “9% acer a 60c.9¢ a ‘ ee: = : stored eee 8 2 3 c9S TT ss ELe* 6S ° ouTe TA Ss as oe qeey preoq W- - - ----- —TeyoL __F__poompaey = poomayos” /T tequry mes _Te30L, TT poGMpIEH = poong gos /é t9quE4 TTY ° Aqun09 oumToA Jequrty, ‘*¢ elqelL age STANDARD STATISTICAL DATA FOR UNIT NORTHERN MONTANA Table 3. Land area by major use Major use : Acres ; Percent Forest land 983,314 Siiodk Nonforest land BOMB 26 96.9 Total SN (BUhAcO 100.0 Table 4. Forest land area by class Forest land class : Acres : Percent Commercial forest land 624,526 63.5 Noncommercial forest land Withdrawn i/ 95,269 Other 2, 263,519 358,788 36.5 Total 983,314 100.0 1/ Commercially valuable forest land actually withdrawn from com- mercial use for parks, reserves, wilderness areas, etc. 2/ Remote and inaccessible alpine areas, and other land which owing to very low productivity, excessively poor quality timber, or extreme inaccessibility appears to be permanently out of the com- mercial timber producing class. =O = i lag i! ; i, a a Table 5. Commercial forest land by forest type and stand-size class Forest type : and stand-size class : meee Rep iectihs Softwood : : Saw timber : 67,035 : 10.7 Pole : Oy ANS} : 18.8 Seedling-sapling : 32,650 : oe Poorly stocked and denuded :;: 249 ,723 : 40.0 Total : 466,621 : 7h.7 Hardwood : : Saw timber : 595) O.0}/ : 8.5 Pole : 92,697 : 14.8 Seedling—sapling . 10,182 : IL Gf/ Poorly stocked and denuded :; 2,019 : 65) Total : OD ° 25 63} Total : : Saw timber : 120,042 : 19.2 Pole : 209 ,910 : 33.6 Seedling-sapling : 42,832 : 6.9 Poorly stocked and denuded :; 251,742 : 40.3 Total : 624,526 : 100.0 Nile Table 6. Board-foot volume on commercial forest land by species Species . Volume M board feet Percent Softwood Ponderosa pine 48,243 8.1 Douglas-fir 105 , 833 iL AT/ Alpine fir 21,756 3.6 Spruce 106 ,934 76 Lodgepole pine 51 brs bys 8.6 White bark and limber pine 14,436 2.4 Subtotal 348,754 58.2 Hardwood Green ash 24D 0.1 Aspen 491 nat Cottonwood 249 5239 41.6 Boxelder 157 a Willow 75 i Elm 5 1/ Subtotal 250,242 MLE Total 598 996 100.0 1/ Less than 0.1 percent. 12 OG I NR tem Sm 8 I NN OS Cr " sport avg, yopelee. eae aaaae Cras WER, OE ae Ale Ae ANE ays SA Table 7. Cubic-foot volume on commercial forest land by species Species : : Volume M cubic feet Percent Softwood Ponderosa pine 36,610 ID Douglas-fir 77,019 26.8 Alpine fir 19,722 6.9 Spruce 29 ,188 HOSE Lodgepole pine 45,446 15) of White bark and limber pine 9 336 3.2 Juniper 338 oe Subtotal 217,659 75.6 Hardwood Green ash 2,619 0.9 Aspen 6,928 2.4 Cottonwood 60 , 366 21.0 Boxelder 304 ol Willow 31 i) Elm 5 ay Subtotal 70,253 Phalh Total 287,912 100.0 1/ Less than 0.1 percent. ee Fin dh cal hia weil OF GEIR, Table 8. Board-foot volume on commercial forest land by stand-size and tree-—diameter classes : Volume by tree-diameter class Stand-size class : 1292 Se Oluimches in: Total : inches sand wlangends -------- M board feet- - - - - - - Saw timber S225 8ise ce) V2O5RCOK Psa S26./ Al Pole : 41,890; LOSi ene oe Seedling-sapling : 5,664 : - : 5,664 Poorly stocked and denuded : 22 290 : BO2N Ts 22,592 Total 3) 392.6550. a 206,3hInl 598996 Table 9. Cubic-foot volume on commercial forest land by stand-size and tree-diameter classes : Volume by tree-—diameter class Stand-size class : 12 - 18 : 20 inches 3 Total : inches :_and larger : Saw timber Q dleyhaaliey) 0 8 BeinslOh Gon JLBi,03/8 Pole : 2 SORS I e TY macnn tt .2) AP2EYS Seedling-sapling : ZS - : 2,482 Poorly stocked and denuded : BROS SimmE: 630 suesoeOl: Total = 218/768 2 39,1ky e weszon2 mes piel — dasol a Soe ay BS a en ee aml cs HSE SS Add, fet € Zh saat? Pie 3 Mu A bap a= ee js ae - rt 4 56 &s Se 6% * F 1. “ Wr ts took f, ; ; / mad Ant Sok atv rea Ge a ‘ A rants T 14 : i ae ae ir : 4 : Any ita») | a \ ) . a 1 , ’ fe ‘ i i 4 Dee! pi a “1 ‘ ih D a] 7 “ay se rail <.9 cw ’ fae it ar LA} if Sia PoaAS mi yo ee ser : Mary hl wes Table 10. Cubic-foot volume on commercial forest land by species group, tree size, and class of material Volume soln Softwood * Hardwood * Total =------+--- M cubic feet- - - - - - - Saw-timber trees Sawlog portion 1/ : @iLa/hals) 9 BS,090 a LOO MOS Other 2/ oT LAS OO ee) oreo OOO ue me OniOls Subtotal ; 74,582 52,288 126,870 Pole trees 3/ 143 ,077 17,965 161,042 Total 217,659 HOWZDS 287,912 1/ Sound trees only. 2/ Upper stems of sound trees, usable volume of cull trees, and limb- wood of hardwood species. 3/ Sound and cull trees. Table 11. Average volume per acre by stand-size class Average volume per acre Stand-size class ee 88 e@ Board feet ‘* Cubic feet Saw timber : 4,402 : 1,442 Pole : 202 : Bits Seedling-sapling : 132 : 58 Poorly stocked and denuded : 90 : ibs ial All stands : 959 : 461 Lutes Pe es yh as A 5 wr ae ae ae : S208 Teas cant; To seer” EASLG Sain hie patentee oe Pabd skit” oF ee k ] we ; i ¢" oa ¥ ¥, ‘ s] ‘ = t ey uh 7 a o| Kye + + i j ‘ ji , Teas AY i 25 xa std - Cee oe) oe eT DEFINITIONS Following are definitions of terms used in this report: Area Classes Forest land is land bearing forest growth or land from which the forest has been removed but which shows evidence of past forest occupancy and which is not now in other use. Commercial forest land is forest land bearing or capable of bearing timber of commercial character and economically avail- able now or prospectively for commercial use and not withdrawn from such use. Noncommercial forest land is (1) commercially valuable forest land actually withdrawn from commercial use for parks, re- serves, wilderness areas, etc., and (2) remote and inacces- sible alpine areas, and other land which owing to very low productivity, excessively poor quality timber or extreme in- accessibility appears to be permanently out of the commercial timber-producing class. Softwood forest consists of stands with 25 percent or more of ponderosa pine or 50 percent or more of other coniferous species. (Based on cubic-foot volume.) Hardwood forest consists of stands with less than 25 percent of ponderosa pine and 50 percent or more hardwood species. (Based on cubic-foot volume. ) Stand-size Classes Saw-timber stands include stocked areas with a plurality of the total net cubic volume in trees 11.0 inches and larger in diameter and generally with 2,000 board feet per acre or more in saw-timber trees. ihe Pole stands include stocked areas in which a plurality of the total cubic-foot volume is in trees from 5.0 inches in diameter to saw-timber size. Seedling-sapling stands include stocked areas in which the plurality of the total cubic-foot volume is in trees less than 5.0 inches in diameter, Poorly stocked and denuded stands include areas with less than: a) 2,000 board feet per acre, (b) 10 percent stocking of pole trees, and (c) 40 percent stocking of seedling-sapling trees. =6= FOREST SURVEY METHOD A. The forest resource statistics in this report are based on a field survey made during 1947. Briefly the method used in making this survey was as follows: 1. The forest area was determined by an area sampling system . which involved measuring and classifying systematically distributed sample segments. 2. The timber volume was determined by measuring the trees found on randomly selected one-fifth acre plote located within the sample segments. B. The basic data from which the area and volume were determined con- sisted of the following field samples: 5 Area : Volume Gilacs :Number of: Area per : : Area per : sample :sample segment:Number of:sample plot ents : acres : plots : (acres I BH 2,560 li1 1/5 LOE CSG ae 96 640 192 5) C. Distribution of the area sample segments and volume plots was con- trolled by the following method: 1. The entire area was divided on l-inch-to-the-mile base maps into three primary classes: Class I Areas predominantly forest for which aerial photographs were available. Class II Areas predominantly nonforest for which aerial photographs were available at moderate cost. Class III Areas predominantly nonforest for which aerial photographs cost more than $2 per print, or for which there were no aerial photographs. 2. Each of the three primary classes were further subdivided in- to units in the following manner: Beginning with a random selection, Land Office section corners were marked on a base map at 4-mile intervals for areas in Class I, 7-mile intervals may t ’ ‘ 4 fu sere * for areas in Class II, and 10-mile intervals for areas in Class III. Thus, the three classes were subdivided into units containing approximately 16, 49, and 100 square miles respectively, each unit centered on one of the section corner control points. 3. The control points were transferred to aerial photo index maps from which photographs were selected to give photo coverage for a segment of each unit containing forest land. For Class-I units the sample segments consisted of four Land Office sections (2,560 acres) centered on the control point, for Class-II and -III units the sample seg- ments consisted of one section (640 acres) lying northeast of the control point. 4, All sample segments containing commercial forest land, in- cluding those with doubtful forest cover by photo in- terpretation and all sample segments without aerial photo- graphs, were examined and mapped in the field. For each sample segment the forest cover was stratified by com- mercial character, forest type, stand-size, stocking, age, and site classes. The area of these stratifications was determined from the mapped sample segments and as re- fined by line transects was multiplied by a sample factor (the area of a class divided by the area as computed for the sample segments) to get the total area by forest con- dition classes. 5, Timber volume was tallied on three 1/5-acre sample plots in each sample segment of Class I, and two 1/5-acre plots in the sample segments of Classes II and III. The plots were randomly located within the sample segments. Plot volumes when averaged for a given forest condition were multiplied by the area to determine the total timber volume. ACCURACY OF THE DATA In determining the extent of various cover types and stand-condition classes, there are two possible sources of error: (1) errors in classifying the cover of the field samples and in compiling the field data, and (2) sampling errors. The former result from mistakes of judgment or technic and the complexity of the cover which not in- frequently grades from one class into another with no clearly defined boundaries. These errors were minimized by the exercise of care and skill, but it is seldom possible to evaluate them. An effort was made to maintain a high order of accuracy and uniformity of standards in the classification, collection, and compilation of sample data, by field checks, by a continuing program of training, and by cross checks in the office. ae + ee : > aa rey 4 Sampling errors (standard errors of estimate) on the other hand do not involve human errors but rather are theoretical measures of the reliability of estimates based on the variability exhibited by sample measurements, They generally vary inversely with the square root of the number of samples and directly with the square root of the un- sampled proportion of the total population. Hence, they can be con- trolled by altering either the number of samples, the size of individual samples, or both. Analysis of sample variations in the unit indicate that the standard errors of estimate for the unit are ¢ 1.0 percent for total forest land area and * 3.1 percent for commercial forest land area. Accordingly, the probabilities are 2 out of 3 that the actual forest jand area and commercial forest land area are, respectively, within - 2 10) OOO acres and = 19,000 acres of the estimated areas if measure- ments and computing errors introduced no bias. In determining timber volumes, the possible sources of error in- clude in addition to those cited above (3) inaccurate measurement of sample plots, tree diameters, tree heights, and cull, and (4) bias resulting from improper construction, selection, and use of tree-—volume tables. All reasonable effort was made to eliminate errors from these sources. The standard error of the board-foot volume estimate for the block as a whole is = 16.2 percent and of the cubic-foot volume estimate, = 8.6 percent. Accordingly, the probabilities are 2 out of 3 that the actual volumes are within £ 97,037 M board feet and = 24,760 M cubic feet of the given estimates. The reliability of one statistic as compared with another presented in the same or a related table can be judged roughly by its rela- tive magnitude. In general, the larger quantities warrant greater confidence; the smaller quantities indicate only relative magnitude. This fact should be borne in mind in considering the small quantities associated with many of the counties covered in this report. 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