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Oe. = ef . xy 8 0.0.02 ia nae “as Ele fica 5 > .LELELELEYT QBEESWALSEY LLSSE DSBs esis seus l ais 5 = Slo oD X- 5 w = Q - ] ca ics ° eet 3 - 4 P one =e =| es = /6Z2 E553 ie oe ° = C | ‘w] = WM Ne) 3) — oe s RELATION OF EROSION AND SOIL DEPLETION TO REVEGETATION. —— The establishment on eroded soils of a dense vegetative cover made up of desirable forage and other deep-rooted. soil-binding species, similar to the original type, is a most difficult task. In the first place, RANGE PRESERVATION AND EROSION CONTROL. 23 owing to the low moisture content due to exposure and lowered water-holding power, seed germinate poorly. Moreover, about nine- tenths of the plants which do come up die early in the spring while still in the seedling stage. The remainder usually dry up before the end of the season. Interesting contrasts have been recorded on the mountain ranges of the Manti National Forest as to the rate of revegetation and the character of species being established on overgrazed and subsequently eroded lands as compared with lands which have not been seriously overgrazed, and where the soil, therefore, is relatively productive. During observations extending over four years (1913-1916) it was most exceptional to find on the more seriously eroded soils an increase in the number or appearance of new deep-rooted perennial species of any kind. On the less seriously eroded soils, on the other hand, shallow-rooted perennial species, both seedlings and matured speci- mens have gradually increased in number each season; and on some- what overgrazed, but not eroded lands, deep-rooted perennials have increased relatively rapidly and steadily. -On analyzing the data recorded as to the rate and character of the revegetation it was found that by noting the seriousness to which the soil has been eroded, and hence its physical condition, including the relative amount of organic matter contained in it, it is possible to predict with much precision not only the rate at which the ground cover may be restored but the particular kind of plants that will occupy the soil for a temporary period prior to establishment of a permanent vegetation. As a general thing, many years must lapse before the more desirable forage species can reoccupy the site upon which’ they formerly predominated. The reestablishment of the deeper-rooted perennial species, if this type of vegetation is desired, and it usually is, can be accomplished: on these eroded soils under range conditions only by certain rather inconspicuous plants first gaining a foothold on the land and gradually reinstating the vege- table matter and plant foods which are invariably lacking. The. replacement of one set of plants by another through a series of successive invasions is known as plant succession. Where the fer- tility of the soil has been seriously impaired only rapidly growing and early maturing annual species first occupy the soil. Several species of this type of vegetation begin germination and growth promptly in the spring, and before the soil has dried out to a point where the vegetation wilts beyond recovery and further growth, the plants have developed fully and ripened an abundant seed crop of good germination strength. The ramifications of the roots of these inferior plants through the soil season after season, the aeration of the upper soil layer as a result of the innumerable penetrations res BULLETIN: 675, U: S. DEPARTMENT. OF AGRICULTURE. and subsequent decay of the roots; and the addition of humus to the soil by the decomposition of the portions of the plant developed both below and above ground, finally accomplish wonders in improving the physical and chemical condition of the soil, provided, of course, that serious erosion in the meantime has been checked. As the soil is improved and absorbs and retains more water than in the beginning, the annual plants develop more. luxuriantly. At this point, however, the space’ occupied by the annual species is gradually encroached upon by slightly deeper-rooted, more robust annual plants, usually accompanied by a few shallow-rooted bienniai and perennial plants. As the fertility of the soil is further improved, even the more robust annual species disappear and the more perma- nent perennial type of vegetation predominates as formerly: For many years after the latter type becomes conspicuous, however, less forage is produced, and of a poorer quality for stock generally, than before the soil became depleted. From the above facts, then, it is evident that soil depletion, as re- lated to forage production and revegetation, does not imply merely a temporary change in the character of the vegetation and. nutritious- ness of the forage; on the contrary, the time element enters as a highly important consideration. To reestablish completely the more desirable and permanent species, such as occupy the soil before it becomes depleted, often requires years of time coupled with expert management. Too much care can not be exercised by the stockman and farmer in preserving the dark surface layer of soil, for that portion is the very life of any land. Preserving the surface soil in the first place is much cheaper than replacing it, and this is not a difficult matter if proper precautions are taken when incipient erosion becomes apparent. INFLUENCE OF GRAZING ON EROSION AND STREAM FLOW. While it is evident that the extent of run-off and erosion are roughly proportionate to the effectiveness of the ground cover in binding the soil, other factors being equal, the question as to whether run-off and erosion are augmented or retarded by grazing is one upon which opinions vary widely. Some stockmen contend that if a soil is cut up more or less by the trampling of stock, or the surface pretty thoroughly pulverized, more water will be held and subsequently absorbed by the soil than if the surface is undisturbed. Others are of the opposite opinion, contending that the packing of the soil, which unavoidably results from grazing, especially if the soil is fairly moist when stock travel over it, prevents the rain from being absorbed in maximum amounts. In carying out the details of the experiment on RANGE PRESERVATION AND EROSION CONTROL. 25 the selected areas, strikingly significant results as to the effects of grazing and nongrazing were obtained.! On July 21, 1915, when both areas had been protected from graz- ing since August, 1914, a heavy rainstorm occurred in which area B received approximately twice as much precipitation as area A; but only about one-twelfth as much run-off and one-ninth as much erosion was recorded from area B as from area A. On August 5, 1916, area B was grazed closely by sheep, area’ A being at that time ungrazed. Late in the day of August 5, a rainstorm occurred in which both of the selected areas received an average of 0.25 of an inch of rain. Practically the same amount of run-off was recorded PRECIPITATION ZS Inc Hi AREA-A< STREAM FLow AAANS ito} Sa a EROSION nei 5 PRECIPITATION era 5 "? AREA-B< STREAM FLOW UNGRAZED EROSION [ES] PRECIPITATION 2 AREA-A STREAM FLOW UNGRAZED " EROSION [Eee] - S & PRECIPITATION _& AREA-B ¢ STREAM FLOW GRAZED EROSION 0 Fic. 6.—Relation of grazing and nongrazing to erosion and run-off. from the two areas, and the erosion from area B was one-half that from area A, as shown in figure 6. It will be noted, then, that the ratios of precipitation, run-off, and erosion on area B as compared with area 4 were changed from 2/1, 1/12, 1/8, respectively, to 1/1, 1/1, 1/2, respectively, as a result of grazing area B and not area A. Since grazing was the only factor changed as compared with all previous records, it appears safe to 1 The grazing of the areas was carried out as follows: Both pastures were grazed mod- erately close by sheep at practically the same time in the season in 1914-1916, inclusive. The prescribed time for cropping the areas is when the forage is sufficiently developed to afford good grazing, a time which corresponds fairly closely to the grazing of the unprotected adjacent range. In case the ground is sufficiently wet to injure the vegeta- tion seriously by trampling, or to cause harmful packing of the soil, grazing is deferred until a later date when soil conditions are normal. sheep raisers who have abandoned the use of the regular bed ground would never think of going back to the practice, for the reason that ihe feed is infinitely better than formerly and because appreciably larger gains are made by the sheep. When no regular bed ground is used and the sheep are given all the freedom possible consistent with the grazing of suitable range, the band is more content and easier to handle and there are less losses from poisonous plants. At the same time the all-important ground cover is not destroyed, pro- — vided the “leaders” and “lavgers” of the band are not excessively dogged and roughly handled. Often as much vegetation is de- stroyed through the excessive use of dogs as from overgrazing and subsequent run-off. On lands where the sum of conditions favoring floods and erosion—such as deficient vegetative cover, steep slopes, and the presence of numerous gullies of the mncipiens and advanced type exist—it is the safest plan to undergraze rather than utilize the herbage so closely as possibly to injure the existing vegetation. In general, greater injury is done on such lands by trampling than by actual grazing; consequently, unless the range is excessively rough and irregular, it is often a distinct advantage to graze the lands by cattle rather than by sheep. RANGE PRESERVATION AND EROSION CONTROL. Sil REMEDIAL MEASURES WHERE THOROUGH REVEGETATION BY ORDINARY MEANS ° IS IMPOSSIBLE. TOTAL EXCLUSION OF STOCK, On the more important fan-shaped basins at high elevations, where the original vegetative cover, including the seed plants, has for the most part disappeared, ana where the fertility of the soil has been seriously depleted as a result of erosion, the best plan is to discontinue grazing entirely. The small amount of forage pro- duced, consisting, as it usually does, of annual weeds and many poisonous species, by no means compensates for the further skim- ming off of the already deficient organic matter and tearing down into the gullies of the loose soil. Im most instances stock will not have to be excluded longer than during the period required to re- establish the fertility of the soil and the incoming of the deep-rooted, permanent type of perennial vegetation, provided, of course, that hght grazing and proper handling of the stock are at all times resorted to. On the other hand, where the soil fails to regain its former productivity within a reasonable length of time, as indicated by the character and density of the vegetative cover following the exclusion of stock, grazing should be permanently discontinued. To graze such lands after a few years of rest, even though they pro- duced a little feed, would be to undo in a season all that nature has accomplished in building up the soil during the seasons that stock was excluded. TERRACING AND PLANTING. There are local areas, mostly of small size, where the proper regu- lation of grazing and, indeed, the total exclusion of stock from seri- ously eroded lands is delayed until the vegetative cover can not be effectively reestablished and the erosion thus eliminated. The estab- hshment of a dense cover of vegetation should not be hoped for on the bottom and along the sides of deep, vertically cut gullies where the water rushes by after each rainstorm of appreciable size. The force of the water does not permit many seeds to lodge, and in the beginning the soil is too thin and dry to favor growth. Depressions of the more prominent. gullies which have been revegetated, how- ever, would still serve as drainage channels following heavy rain- storms, but the resistance afforded by the vegetation would tend to hold the water back; and since the soil would be held firmly by the roots, the channels would tend to flatten out rather than become more prominent. Where it is no longer possible for the vegetation to hold the soil intact, some means of artificial control is necessary. The gully 82 BULLETIN 675, U. S. DEPARTMENT OF AGRICULTURE. systems can usually be effectively broken up by the eonemuenen of terraces laid out approximately at right angles to “the gullies but so placed as to allow water to be carried through their channels. Hf reinforced by small rock fills built into the washes at sufficiently frequent intervals to check the run-off before the cumulative effect of the water’s force becomes uncontrollable, the terraces appear to be effective. Sumwait 40,000 Gee ~~ Nx & & Pe Ye VIP», ~ bee ==! Ve eee 2a i ie < my JE SSP CEE a t ere Beal AruCus { | ——— = s — o. ate aGob Lo. eaestae’ acatect) Pl eae TMUEGREREKG eee ee ei = pO lee Terrac a Fock butt ——-— Dry ris — > Continues —~< Plays our Fic. 7.—Tree and shrub planting to check erosion. The place of successful attack of an evil like the one in question is at the origin of its source. In order thoroughly to test the value of terraces located near the heads of the gullies and planted to soil- binding species, a badly gullied area was selected on a southwest slope at an elevation of approximately 10,000 feet. This study is still in an experimental stage.. As shown in figure 7, the distances between the terraces which were established vary considerably, being determined by the number of gullies and other topographic features. In establishing a terrace, strips are plowed about 4 feet wide, or even wider on the steeper slopes, fellowing which the loosened soil ee RANGE PRESERVATION AND EROSION CONTROL. 83 is smcothed out by means cf a homemade terrace drag (fig. 8). The drag is constructed in a V-shape and can be made any width provided the proportions are followed as given in the sketch. In order that the drag may work effectively one or two men usually stand on the crosspiece supporting the side beams. As soon as the terrace is well smoothed it is ready for planting. Planting early in the spring before growth has started has given the best results; and since the soil can not be worked satisfactorily at that time terraces can best be established in the autumn. At the intersection of the more prominent gullies and the terraces, the former are built up with rock butts and overlaid with soil. In order to hold the terrace soil as effectively as possible, the terraces are planted to such soil-binding species as wild gooseberry (Grossularia), mountain elder (Sambucus), yellow brush (Chrysothamnus), sweet sage (Artemisia), yarrow (Achillea), and several species of sub- ie 3 109s flattened on Upper surface Ra 5" Fic. 8.—Terrace drag. alpine grasses. Since seed of native grasses, which soon become firmly established on the terraces, can not be purchased from com- mercial seed houses it has been necessary to collect seed wherever a good crop developed naturally. However, following the establish- ment of the terrace a great deal of seed of native species is caught ‘during the natural seed dissemination period in the autumn, and in two seasons or so the terraces become fairly well vegetated. As the soil is enriched through the accumulation of decayed vegetable matter, conditions for growth are gradually made more favorable and the vegetation develops luxuriantly. The area experimented with, prior to the establishment of the ter- races and fill work, had been subject each season to serious erosion. Since the establishment of the terraces and supplemental work, no erosion whatsoever has occurred and the lands are generally becoming 34 BULLETIN 675, U. S. DEPARTMENT OF AGRICULTURE. revegetated. The establishment of terraces and subsequent planting to suitable native species, therefore, offers considerable promise on lands that have eroded to such a point that revegetation is extremely slow and the subterranean parts of the vegetation uneffective in binding the soil and in preventing erratic run-off. The cost of the establishment of terraces will vary greatly according to the depth and number of gullies and the amount of fill work necessary. Where a moderate stand of native vegetation occurs within the vicinity of the terraces it will not be necessary to plant directly, provided a satis- factory seed crop is produced. 3 3 CONSTRUCTION OF DAMS. In various parts of Europe, notably in the Swiss Alps, and to a less extent in this country, elaborate earth, stone, and concrete dams have been constructed where the less expensive contour terraces are inadequate in preventing continued destructiveness from erosion in critical localities. Obviously, the construction of elaborate dams is expensive and their use is limited to situations where the destruction to personal and other property is of much more than average seri- ousness. Problems of this character properly fall under the scope of engineering. — SUMMARY OF PREVENTIVE AND REMEDIAL MEASURES. The maintenance of an effective vegetative cover may be accom- plished by the following means: ; 1. Avoidance of overgrazing. 2. Avoidance of too early grazing. 3. Deferred and rotation grazing. 4. Artificial reseeding (in choice sites only). 5. Proper control and distribution of stock. Where the depletion of the soil and the formation of long estab- lished gullies make thorough revegetation impossible, destructive floods and erosion may be controlled in the following ways: 1. Total exclusion of stock. 2. Terracing and planting. 3. Construction of dams. CONCLUSIONS. 1. Erratic run-off and erosion have been responsible for a great deal of damage on western ranges where the vegetative cover had pre-_ viously been materially decreased or practically eliminated. 2. Though the damage from erosion usually is measured merely by the injury caused to farm land and works of construction, the damage to the forest range lands upon which erosion occurs is often RANGE PRESERVATION AND EROSION CON’BROL. 35 greater and shows itself in decrease in carrying capacity of the lands. 3. While topography, climate, and soil are the primary factors in determining erosion, the combination of these factors on the lands under consideration is such that erosion is slight where the native ground cover has not been greatly disturbed. The seriousness of the erosion, therefore, is largely determined by the extent to which the ground cover is maintained. 4, Serious erosion on western range lands is due chiefly to the destruction of the vegetation as a result of overgrazing and mis- management of live stock. 5. The sum of conditions favoring destructive run-off and erosion is most pronounced in the fan-shaped drainage basins of the spruce- fir type (on the Manti National Forest between 9,000 and 10,500 feet), where the ground cover is naturally rather sparse, where there is a characteristic sparseness of tree growth. and where the most desirable summer sheep ranges are located. 6. To maintain an effective vegetative cover, overgrazing and too early cropping of the herbage must be avoided, deferred and ro- tation grazing should be applied, and stock should be properly con- trolled and distributed at all times in the season. 7. In the case of incipient erosion, only slight changes in the use of the lands are generally necessary, and these changes do not neces- sarily imply even a temporary financial loss. 8. Where erosion has had full play for a number of years, the reestablishment of the ground cover, even though grazing is dis- . continued, does not always afford adequate protection. In such in- stances, which fortunately are relatively rare in this country, a combination of terracing and planting or, in exceptional cases, the construction of dams is justified. ADDITIONAL COPIES OF THIS PUBLICATION MAY BE PROCURED FROM THE SUPERINTENDENT OF DOCUMENTS GOVERNMENT PRINTING OFFICE WASHINGTON, D. C. AT 10 CENTS PER COPY V PF in THERE eae. a Ae a 2 YIN