POSSIBILITIES OF SHELTERBELT PLANTING IN THE PLAINS REGION

CONTENTS

Emergency employment
Effect an field craps
Gardens and orchards
Protection of farmsteads
Protection of livestock
Checking soil blowing
Block planting on sand hills
Planting on breaks and gullies
Wood products
Disadvantages cited

The Plains shelterbelt project represents a national effort applied to the amelioration of regional conditions. The interest attaching to the undertaking from the national point of view is not solely whether annoying dust storms can be kept out of the East but rather what returns in farm and range economy, in property and tax values, and in improved living conditions may be expected from the general readjustment of land use, of which shelterbelt planting is an early and striking phase. In evaluating the effects of shelterbelts, then, no narrow or sectional basis of appraisal can be taken into account; the necessary assumption is that benefits accruing to an interstate region that contributes vitally to the national economy accrue in like measure to the welfare of the Nation collectively.

EMERGENCY EMPLOYMENT

To begin with a matter of common necessity, it must be remembered that the Plains shelterbelt project received public support largely as a measure for the immediate relief of drought-stricken farmers in the prairie-plains region. The preparation of the planting sites, the fencing of the areas, the actual planting of the trees, and the future care and maintenance of the shelterbelts will require a large amount of local labor and can provide a considerable proportion of the cash income of many farm families in the shelterbelt zone for years to come. Much of the necessary work can be done in off seasons. The renting of farmers' machinery and, especially, the purchase and leasing of more than a million acres of land will provide a further flow of much-needed and productive income into this hard-pressed region.

Such benefits would, of course, flow from any other land-engineering project of similar scope, and the specific use value of the shelterbelt project must be judged by more objective standards.

EFFECT ON FIELD CROPS

Evidence of that value is not lacking. Thousands of examples have been reported from our Plains region in which crops have been benefited by plantations of trees. Similarly, there have been many reports to the effect that crops adjacent to shelterbelts have received no apparent benefit or may even have produced lower yields than those unprotected. On the basis of experience both in our own country and in Europe. we can generalize upon certain effects with reasonable accuracy.

The effect of shelterbelts on field crops varies with the relative dryness of the season. In wet years any beneficial effect is at a minimum; the crops do not need such protection. In moderately dry years, such effects are at a maximum, and the effect of the shelterbelt may provide the margin between a partial crop in the protected zone and complete crop failure in the open plains.

The question of increased or decreased yields of grain straw and hay crops as affected by tree wind breaks needs further investigation, it is true; hearsay is not sufficient. Russian studies, mentioned in another section have given some quantitative basis for expected effects of protective strips of trees. A study conducted in several of the Prairie and Plains States in 1908,⁴ in which crops both protected and unprotected by shelterbelts were harvested and measured, showed increased yields for the protected crops in most cases. The fact, however, that the study was completed in a single season and dealt with various crops on many soils and with windbreaks of variable composition and condition disqualifies it as a final answer to the crop question.

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⁴BATES, C. G. WINDBREAKS: THEIR INFLUENCE AND VALUE. U. S. Dept. Agr., Forest Serv. Bull. 86, 100 pp., illus. 1911.

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What is now urgently needed is a wide-scale comparison of protected and unprotected fields with respect to their production of similar crops under otherwise similar conditions. The data can be collected, under all necessary scientific control, from existing farms throughout the shelterbelt zone. Analysis of the data would answer many practical questions of shelterbelt density, orientation, and the like, and would be of immense value in checking experience of the past and further adapting planting plans already in effect. In the meantime, valuable leads will be obtained by measuring physical factors and perhaps even the yields on small plots as affected by artificial windbreaks whose heights, densities, and orientation can be controlled.

On the basis of present knowledge, gained both in this country and abroad, of effects on wind velocity, evaporation, humidity of the air, and the like, it is possible to determine the proper spacing of shelterbelts to protect the whole territory between them. The present program of one shelterbelt per square mile, on the average, is merely the framework on which further developments may be based. Considering that the height of shelterbelts will be about 40 feet on the average, Forest Service studies have indicated that a single belt will extend some degree of protection to a distance of one-fifth mile. European data, based not on occasional windbreaks but on a succession of them at regular intervals, indicate that cumulative protection can be obtained if the belts are established at every one-third mile. Since the unit of land in the Plains region is the 40-acre tract, it will be convenient in the final development to make the interval between belts one-quarter mile, thereby insuring a high degree of protection for the entire area.

The point should be clearly made here that most of the advantages that accrue to the surroundings from the presence of a row or grove of trees can be traced either to the trees' checking of run-off or to their wind-stilling effect. Romantic expectations such as raising the water table or increasing the rainfall should not be entertained. The entire section, Shelterbelt Experience in Other Lands (pp. 59 to 76), forms an interesting commentary on the actualities of the case. The most remarkable effect, perhaps, is seen in the lowering of the evaporation rate in a sheltered area at one of the Russian experiment stations. Humidification of the air does apparently occur to a slight extent, but evaporation is checked in much more pronounced fashion, and the inference is strong that a lowering of wind velocity is the cause. The increased expectation of a fair crop yield in a dry year under shelterbelt influence, may find part of its explanation on this same basis.

GARDENS AND ORCHARDS

Farmers in the Plains region are able to point out very distinct benefit to flower and vegetable gardens and somewhat less benefit to orchards, as a result of tree-belt protection. Gardens are often planted between two or inside of four rows of trees, which act as a snow-trap in winter and release the accumulated moisture rather gradually in spring. The response of garden plants is marked, since they are heavy users of water—much more so than the cereals, which, as a group, represent one of nature's highest adaptations to wind and drying.

A high demand for water does not wholly characterize orchard trees, of which apricots and some varieties of apples can be set down as decidedly drought-resistant. Yet fruit trees in general show favorable reactions to shielding from dry winds. Protection against late spring frosts is also a large factor in fruit bearing. It may be said that benefit to orchards is to be expected if there is a cold storm, or a sudden cold snap accompanied by wind, such as is very common in the Plains region even after spring is well advanced. Planting too near the windbreak may result in root competition and loss of vigor of fruit trees.

PROTECTION OF FARMSTEADS

The value, both materially and personally, of tree planting about the home is attested by the high expenditure of time and money that has gone into the establishment of farmstead windbreaks throughout the Great Plains region. Except for the South, the settler's first wish is for shelter of his house, and next his barn, from the "cold", by which is meant the driving cold of a penetrating wind. On this account a good windbreak can take an actual financial rating, for its protection can be translated into a substantial saving of fuel.

Far beyond this consideration is the invaluable benefit of an enjoyable home surrounding, not expressed in Federal appropriation acts but deeply implied in all their provisions that have made tree-planting stock cheaply available to farmers. The shelterbelt planting program does not specifically contemplate farmstead planting until some of the major lines have been established. But there is no doubt that living conditions will be enhanced in many neighborhoods through the general improvement of the countryside. Figure 6 illustrates the striking contrast between a neglected schoolhouse and a tree-sheltered farmstead, one slightly to the east and the other slightly to the west of the shelterbelt zone.

FIGURE 6.—A, An unprotected schoolhouse on the open plains in South Dakota (F298776); B, A farm home protected by trees in the plains of Kansas (F296033). (See text, p. 35).

Enthusiastic farmers frequently state that they would not take a thousand dollars (or other considerable sum) for their groves. That such statements are something more than figments of the imagination is reflected by the fact that practical real-estate men add several hundred dollars to the value of a farm upon which thrifty groves of reasonable extent occur.

PROTECTION OF LIVESTOCK

A great benefit to the farmers' livestock will ensue upon establishment of the shelterbelts, Under many conditions the animals get along very comfortably with only the protection of a good windbreak. In connection with feed lots, the value of such shelter in terms of feed saving has been fully recognized by livestock feeders in Iowa, one of whom stated that his windbreak enabled him to save from $5 to $10 on the cost of feeding each steer.⁵ Horses and cattle, particularly, are very sensitive to wind, and unless driven by hunger will rarely remain in an open pasture on a windy day when they can find any degree of protection. Protection from driving rain is equally welcome to stock, and in hot weather the shade of trees is eagerly sought.

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⁵SHERLOCK, C. C. THE ECONOMY OF WINDBREAKS: THE DOLLARS AND CENTS VALUE OF THE PROTECTION THEY AFFORD. Successful Farming 19 (2): 53, 153, illus. 1920.

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These benefits are by no means inconsiderable items in the economy as well as the comfort of the farm, and they have long been appreciated in regions of less severe climate than the dry plains. The field shelterbelts cannot be opened to use by stock, but such use is not imperative to supply a necessary minimum of protection. Wherever one adjoins a pasture or a stock lot, a very slight addition to the main shelterbelt can be made where the farmer is willing to fence off a few square rods of his own land. Even here stock should be kept out of the actual planting, as stock damage has been shown to be a chief factor in killing out planted groves. (See A Survey of Past Plantings, pp. 39 to 47.)

CHECKING SOIL BLOWING

There is no doubt as to the adequacy of almost any type of windbreak to prevent soil blowing within the area in which its effects on wind movement is appreciable. Figure 7 is a striking illustration both of the efficacy of a windbreak in this respect and the condition with which it has to cope.

FIGURE 7—Outbuldings and trees partly covered by wind-blown soil in Tripp County, S. Dak., May 1934. (F300747)

Even dead groves catch large quantities of blowing soil. The reasons for this are, (1) that it requires a wind of considerable velocity to effect any serious soil movement, and (2) that blowing soil almost certainly gathers intensity with travel, the movement of coarser particles at one point tending to abrade and loosen soil farther on; and the dead trees form sufficient obstacle to slow or halt such soil movement.

It is therefore of first importance to protect the points of weakness where soil blowing is most likely to start, if these be known. The importance of the shelterbelt lies in the fact that both the degree of reduction that is accomplished by an obstruction and the width of the area in which some reduction is felt are greater with a strong wind than with a moderate one. Since, also, the winds which cause soil blowing in a given locality are rather commonly from one direction, it follows that the zone of influence of a properly oriented shelterbelt is both more certain and more extensive as a preventive of soil blowing than as a factor to conserve moisture through all the variable conditions of a year or growing season.

It is not to be inferred, however, that shelterbelts will prevent dust storms, since many of them originate in the drier region to the west of the shelterbelt zone. However, the restoration of grass cover in the more westerly areas, along with strip cropping and shelterbelt planting in the present zone and eastward, will markedly reduce the possibility of frequent widespread dust storms.

BLOCK PLANTING ON SAND HILLS

The planting of solid blocks of trees on sand-hill areas has not been stressed nearly as much as the planting of shelterbelts around fields and farmsteads, yet it is a very important part of the contemplated program. Most sand-hill regions act as water reservoirs and feed many small streams. Although a good grass cover can afford real watershed protection, trees are capable of providing a more stable protective cover. In addition to preventing wind erosion of the area, it is possible that block planting over large areas may have some of the climatic effects attributed to forests. The deep-rooting trees are able to tap the subsoil moisture supply and make some of it available locally to the atmosphere through transpiration. This might conceivably have an effect in cooling adjacent regions and inducing more precipitation locally.

The conversion of sand hills covered with a sparse growth of grass to green forests has a very realistic value in relation to recreation. As has already been proved by the Nebraska sand-hill planting, Plains dwellers gather from near and far to enjoy these oases of trees. Various species of game birds and animals are provided shelter and protective cover, and their numbers increase, adding further to the recreational interest. The protection given to game and insectivorous birds by tree planting in the Plains region, whether as block plantings or as shelterbelts, is an ameliorative feature that has long been recognized.

Figures 8 and 9 indicate how the appearance of the Nebraska sand hills has been changed by tree planting.

FIGURE 8.—Block plantations near Lookout Ranger Station, Nebraska National Forest, 1929. Such plantations, now extending over several thousand acres, demonstrate that under favorable local conditions forest planting can be a success even in a region occasionally beset by great droughts. (F235223)

FIGURE 9.—Part of a jack pine plantation about 25 years old in the Nebraska National Forest (sand-hill region), 1931. Forest conditions are evidenced by the good litter cover on the ground, the tall narrow crowns, and the dense shade. (F262478)

PLANTING ON "BREAKS" AND GULLIES

The "breaks", which represent high escarpments along the valleys of streams which cut through the high plains, are primarily areas of very active erosion, and are usually almost devoid of vegetation, except for occasional red cedars. These can be planted successfully only in connection with fairly comprehensive developments for controlling run-off which will, instead of passing from the high plain to the lowland, carrying great masses of soil in each rain, be so far as possible impounded above the breaks and allowed to seep away in such a manner as to subirrigate the slopes below.

The average gully, ravine, or draw is usually of an entirely different character from the raw, eroding breaks contiguous to the larger and deeper valleys. These smaller drains are characteristic of relatively fat country. They are usually moderately well sodded and eroding only in a normal degree except when overgrazed. They frequently contain scattered trees of such hardy species as elm, ash, hackberry, and box-elder. It is, therefore, but a step beyond natural processes to establish solid bodies of trees wherever such depressions occur and where the trees will receive some run-off. The primary purpose of such planting is to impound and conserve, in the soil, water which would run off to the adjacent streams during the more severe rains. The influence of this conservation will be felt in periods when rainfall is lacking. Moreover, the rural communities of the region need and will greatly appreciate groves of trees in such protected situations for local picnic grounds and park purposes.

WOOD PRODUCTS

Since the tree plantations in the Nebraska sand hills have reached sufficient size to require thinning, the trees removed have been sought eagerly as posts and fuel by local farmers and ranchers. A local supply of such material meets a very real demand, and the people account it a measurable benefit. With the increased block planting that is planned, such benefits will be available to a much larger number.

Although the main purpose of shelterbelt planting is protection from wind and storm, the value of the wood products which become available from thinnings and from removals as the groves mature cannot be overlooked. Indications are that acre for acre shelterbelts will produce as great a volume of wood as natural forest stands of similar age up to about 30 years, after which their production falls off.

The older windbreak plantings have provided many farmers with a considerable proportion of their needed fence-post material, and during the depression they have yielded a heavy toll of fuel as well. With the expansion of shelterbelt planting contemplated by the Plains shelterbelt project and the additional State and private activity which this is likely to stimulate, a much greater and more permanent supply of wood products will be available to the Plains farmer.

DISADVANTAGES CITED

The positive disadvantages of shelterbelts are so few and insignificant in their total effect as to call for only brief mention. It is obvious that in most cases the detriments arise from poorly planned use of trees, usually as to position.

In the present state of farm management, the greatest disadvantage of shelterbelts will be considered by many farmers to result from the breaking up of large fields into tracts in which large machines can not be used economically or conveniently. This may be a serious item on a good many farms which have been highly mechanized.

A dense shelterbelt causes considerable stagnation of air on its leeward side, resulting in both higher temperatures during the day and lower temperatures at night. Although the effect is generally stimulating to growth, it may, during warm and dry periods, tend to accentuate conditions which are detrimental, despite the fact that the evaporation rate is somewhat decreased through the reduction in wind movement.

"Still" frosts are slightly encouraged, and while these are perhaps not as often injurious as freezing storms, especially those of late spring, it is generally found advisable for the protection of orchards and the more sensitive garden plants not to have a shelterbelt which too fully cuts off air movement near the ground.

When shelterbelts are placed too close, either to buildings or roads, the snow which drifts on the leeward side is often in a place where it causes a maximum of inconvenience. A shelterbelt which lets the snow through should be set farther back.

All tree rows, belts, or groves sap moisture to some extent from adjacent ground. The distance to which this sapping will be felt in the field, however, is usually not much greater than the spread of the branches of the outside trees. But in some cases, as with cottonwood on sandy soil, and Osage-orange on fine soils, the spread may be considerably greater. It is best to plow or at least disk the ground fairly close to the stems of the trees in the outside row, unless the shade density is such that weeds will be kept down. But it is also far better for the trees to permit them to use the soil and soil moisture for a certain distance, instead of seeding this strip to annual crops which will barely survive.

The disadvantages of block and erosion-control planting are even fewer. Such planting will not occupy any area which should be in cultivated crops, but rather, areas of low to medium value for grazing. Grazing has been permitted on the Nebraska plantations after they have reached 10 years in age. However, they are coniferous plantings, and other areas planted to hardwoods would probably have to remain closed to grazing longer. Even if the land must be given over entirely to tree growth, a greater public benefit will no doubt result from such use, considering the need for their establishment, at least to a certain moderate extent.