Soil Management on Ranges

C. H. Wasser, Lincoln Ellison, and R. E. Wagner.

Three-fourths of the area west of the 100th meridian about 40 percent of the total land area of the United States is spoken of as "range" in reference to its use by livestock.

On this vast area there are estimated to be about 9 million range cattle, 9.5 million sheep, and (in the 11 Western States) some 4 million big-game animals deer, elk, antelope, bighorn sheep, and mountain goats.

Nearly 200 million acres of forested range in the Southeastern States are grazed by livestock. Here some 7 million cattle forage for at least part of the year, in addition to some sheep, innumerable hogs, and large numbers of game animals.

The value of this range-forage resource certainly amounts to many millions of dollars annually. Such sums result from the vastness of the range, not from high values per acre. An index to the low economic value of rangeland in general is the fact of public ownership. Some 54 percent of the 11 States is federally owned.

The grazing resource cannot be evaluated by itself. Western grazing lands occupy a considerable part of the drainage basins of major western rivers. The grazing management that is employed on them has much to do with the maintenance of stable stream-flow and freedom from silt.

Inasmuch as practically all forested lands are grazed by livestock or wildlife, intimate relationships exist among grazing and forest management, wildlife habitat, and recreational uses. The value of these associated uses may be such that grazing can have an economic impact far beyond the value of the livestock products themselves.

RANGELANDS ARE of many kinds and uses. They vary from extensive grasslands of the plains to high alpine slopes and meadows, from the deserts of the Great Basin and Southwest to the open forests of western mountains and piney woods of the South.

Some ranges are used for yearlong grazing, like the desert grasslands of the Southwest. Some, like the sub-alpine herblands of the West, are grazed only in midsummer after the snow melts. Others, like certain desert-shrub types, are grazed primarily in winter when livestock water is available. Ranges at intermediate elevations, dominated by sagebrush, pinyon-juniper, or mountain brush, are grazed by livestock in spring and fall, and by big-game animals in winter.

CONSIDERABLE OVERLAP exists between soil management for range and soil management for pasture partly because the effects of cropping vegetation and compacting soil by grazing animals are likely to be similar on ranges and on pastures, but even more because no sharp line separates grazing lands that are classified as pasture from those that are classified as range.

Pasture management strives to increase production through such measures as periodic seeding, fertilization, and irrigation. The approach of the pasture manager is agronomic whenever the productivity of his pasture drops, he plows it up and plants it over, or he applies fertilizer or water. His pastures are usually composed of tame plants, seldom of species native to the site. Utilization is relatively heavy. The maintenance of the vegetation indefinitely is not the pasture manager's criterion of success: High production is his primary criterion.

Range management, on the other hand, strives to improve the forage resource mainly by manipulating the grazing animal and by the infrequent use of such natural agencies as fire. The approach of the range manager is ecological, and he tries to achieve relatively long-time objectives. His ranges are mostly dominated by forage plants native to the site. His chief criteria of success are the maintenance of an adequate cover of living plants and litter to protect the soil and the perpetuation and increase of desirable forage species. Range utilization, as compared with pasture utilization, is light.

One other distinction might be drawn. The pasture manager avoids erosion, of course, but because of more luxuriant plant cover or gentler terrain, erosion is less commonly a serious problem on pastures than on ranges. Ordinarily he is more concerned with improving soil fertility. In contrast, the range manager may have as a primary objective protection of the soil against accelerated erosion in order to keep the normal productivity of the site.

THE SITE is the fundamental ecological unit of range management.

The site or range complex, or ecosystem is made up of many different but closely interrelated parts that involve elements of topography, climate, vegetation, animals, and soil.

Animals may change the composition of vegetation by selective grazing and by trampling. By disseminating seed, they may introduce new species--sometimes desirable, sometimes undesirable. The effects of grazing are not necessarily damaging, either to vegetation or soil. Grazing has a stimulating effect on growth under certain conditions and, as a general rule, if the grazed plants are given an opportunity to make regrowth, foliage removal is not injurious.

Animals may accelerate erosion by removing the plant cover, by compacting the soil, or by actual displacement of very loose or very wet soil. On certain big-game ranges in early spring as the snow is leaving, for example, the soil may be so churned by the hoofs of animals that far more damage is done than by the amount of forage the animals eat. Contribution to soil fertility through animal waste is probably not of too great importance on rangelands; it is offset by the loss in plant nutrients through removal of the animals.

Vegetation is intimately involved in the management of soil. Living plants and the litter they produce alter the climate near the soil surface by casting shade and obstructing wind. The lowered light intensity, more equable temperature, higher atmospheric humidity, and reduced evaporational loss from the soil (as compared with open spaces free of vegetation) favor a more luxuriant population of animals and plants than could endure if the protecting vegetation were not there. Not only is vegetation an essential agent in the building of soil; it provides a protective cover of living crowns and dead parts litter or mulch essential to soil preservation. Because vegetation depends on soil for its existence and because of the formation and protection of soil by vegetation, the two are closely and obviously interdependent.

Soil provides a place for plants to grow and supplies them with water and nutrients. Soil nutrients on western ranges are usually sufficient, although there are some exceptions. In southeastern ranges, as on eastern pasturelands, nutrient deficiencies are more common. Most western range soils have an important role as a storage reservoir for water, making possible develop of all higher vegetation and prolonging the discharge of water into streams. Soil moisture is the critical element on most western ranges: It has been said that the most important fertilizer in the West is the oxide of hydrogen.

A significant characteristic of most rangelands with a normal plant cover is that the surface of the soil is highly Permeable to water. Because of this fact, large volumes of snowmelt and sudden, dashing rains are readily absorbed. When the cover becomes greatly reduced or when the soil is compacted by trampling, the surface becomes relatively impermeable, and water from torrential rains runs over it, eating away the soil and, in extreme cases, causing destructive floods.

Emphasis on site is significant from the standpoint of soil management. Experience has shown that emphasis on plants alone particularly upon a single species can be disastrous. Much damage has been done to the soil by basing standards of range use solely on plant indicators, so that certain sites have deteriorated beyond repair.

SINCE ON ANY RANGE SITE these components are normally in adjustment to one another, any very great pressure on one is bound to affect the rest, and in time the character of the whole complex undergoes change.

If mixed herbaceous vegetation is grazed heavily for many years by cattle, for example, the grasses diminish and the broad-leaved plants increase because cattle tend to graze the grasses more severely. If the same range were heavily grazed by sheep year after year, an opposite trend toward loss of broad-leaved plants and dominance by grasses may occur. Still more severe grazing may eliminate all perennials, so that the site can support only those opportunists of the plant world, annual weeds. If grazing pressure is lightened, the disturbed area is recolonized by successive invasions of perennials. Over the years, if no further disturbance occurs, one community succeeds another until the original native cover returns. Such trends are referred to as secondary succession or disturbance succession, in contradistinction to the changes involved in the slow development of soil and vegetation over the ages, or primary succession.

While these changes in the vegetation are going on, changes are also taking place in the soil. The most marked are the building up of the mulch and increase in soil structure and in amount of pore space. With those changes, more effective absorption of water and more luxuriant plant growth occur. An increased organic content and improved structure encourage more activity on the part of soil micro-organisms, so that the normal process of soil development goes forward.

An important distinction needs to be made between successional trend and trends involving accelerated soil erosion. The latter are referred to as destructive change. The former may alter the soil the latter destroys it. The former is orderly and is reversible the latter is chaotic and irreversible.

Restoration of the original cover in the course of secondary succession on the range usually can be reckoned in terms of decades. When any material amount of soil is lost from the site, however, to all intents and purposes it is gone for good. It cannot be replaced in our lifetime or in many lifetimes to come. Repair of destructive change therefore is a much more serious matter than range improvement through secondary succession.

THE RANGE MANAGER'S first concern is with the adequacy of the vegetation living plants and organic mulch to protect the soil. If soil is being lost at an accelerated rate, he modifies his grazing management to encourage a more vigorous growth of herbaceous plants and allow a greater accumulation of organic materials for a protective mulch on the soil surface. He lessens trampling or utilization, or both, in order to accomplish this.

If he is assured that soil is not being lost at an accelerated rate, the stage is set for improvement of both soil and vegetation by constructive successional trends. Through manner, time, and intensity of grazing, he strives to set in motion trends that will result in a desired species composition, all the while maintaining the integrity of the site with plant cover adequate in amount and dispersion to protect the soil.