GRAZING Too Early in Season Is Harmful to Livestock and Range
After a long winter, during which all the trees and shrubs have been bare and dormant and the herbaceous vegetation has been covered with snow, the appearance of bare ground and of growing plants is a welcome sight. Small stems and leaves are seen pushing upward from the ground, daily growing larger and longer. Some of these are biennial and perennial plants that are growing from the old bases of plants of the past year. Others are plants freshly germinated from seeds that have lain dormant, during the winter. Catkins and leaves appear upon the trees and shrubs, and by close observation one can see that the twigs and stems are beginning to grow.
The food necessary for this initial spring growth is stored in the seeds of annual plants and in the roots of perennials. Nature has provided this reserve of prepared food in order that early spring growth may be carried on until new leaves have developed enough to manufacture food. Nature, however, did not provide protection against heavy grazing by hungry livestock during this critical period.
What happens when a cow or sheep nips off the plant, or a large portion of it, in the early spring? Much of the stored food has already been used to make the growth the sheep or cow consumes. Not many, sometimes none, of the leaves are left to make more food. Even if some leaves remain on the plant, these can not always make appreciable amounts of food because the temperature is not high enough. The plant is greatly handicapped and does not recover its normal vigor during the entire summer. At the Great Basin Range Experiment Station in the mountains east of Ephraim, Utah, very careful studies were made to determine the effect of such early grazing upon plants. It was found that the plants grazed too early produce 25 per cent less growth over the season than do plants that are not grazed until they have a good start. Moreover, in the early spring it is necessary for livestock to consume a much greater number of small and very succulent plants, containing as much as 85 per cent water, than is necessary to secure the same nourishment if the plants are allowed to reach maturity. It is not uncommon for range animals to starve after plant growth has started just enough to lure them away from old dry feed in an eager search over a wide area for new, luscious, but inadequate forage.
That plants are injured by trampling when the ground is wet is self-evident. It is not so evident that they are injured indirectly because the ground is packed. The roots need air. The air enters the soil through the air spaces between the soil particles. When the soil is packed these air spaces are more limited and air is more or less excluded. Water evaporates more rapidly from packed soil because, for one reason, in packed soil there is a continuous passageway from soil particle to soil particle so the soil water can travel to the surface where evaporation is going on. In unpacked soils the air spaces between particles check the current to the surface and the soil moisture is held more as thin films around the soil particles. As water is one of the main factors affecting forage production, any condition that lessens the amount of it in the soil should be avoided if possible. For these reasons ranges should not be grazed in the spring while the soils are wet from the melting snow.
Several poisonous plants, especially larkspur and death camas, are among the very earliest plants on the ranges. They make a luxuriant growth, where they appear, before many of the other plants are well started. When stock are on the ranges too early, they eat many of these poisonous plants and die as the result.
In order to insure conservative and economical use of the forage, due consideration must be given the growth requirements of plants and their food value at different stages of development. In handling grazing on the national forests it is necessary to regulate the period of use so that livestock will not enter the ranges until the forage has developed far enough to permit grazing with safety. Much observation and considerable experimentation have been carried on to determine when plants have reached this stage, and the information gained has been pretty well confirmed in actual range practice. On the basis of this information, the following standards have been set up by the Forest Service as general guides in deciding when ranges are ready for grazing: The important browse plants, such as chokecherry, service berry, rose, birchleaf mahogany, snowberry, and bitter brush, should be in full leaf or nearly so.
The grasses should be from 6 to 10 inches high, and many of the earliest ones in boot.
The important herbs (other than grasses) should be well leafed out and well started in growth.
Generally ranges are ready for grazing about three or four weeks after active plant growth has begun.
The development of forage on the ranges is far from uniform. Often the grasses develop faster and are ready for grazing earlier than the other herbs and browse. Naturally the plants on the more southerly exposures develop earlier than those on the more northerly exposures. Generally every 1,000-foot rise in elevation makes a difference of from 10 days to two weeks in the development of the vegetation, other conditions being the same, and consequently plants may be on a south exposure but still be late developing if they are at a high altitude. There is much variation in the development of plants in different years. The plants may develop as much as three weeks earlier during an early spring than during a late spring.