Date of this Version
The origin of native midwestern pastures from virgin prairie and the degeneration of the prairie under long-continued grazing have been outlined in some detail in a previous bulletin (Weaver & Hansen 1941). During the last four years much study has been given to the converse phenomenon of the regeneration of native midwestern pastures when grazing animals were excluded. This universal phenomenon of the return of vegetation to something of its former natural condition is summed up in the term plant succession (Clements 1928). In connection with pastures derived from true prairie, it is of great practical as well as scientific importance, since no pasture at any stage in the degeneration of true prairie produces continuously so great an amount of highly nutritious forage as do the native bluestem grasses. Recognition of this fact has led to such practices as deferring grazing in bluestem pastures until late spring or early summer, but few or no studies have been made in the true-prairie area to determine the rate of regeneration of the better grasses in pastures already dominated by species of lower forage value. Much work has been done in the more arid ranges in the western United States (Sampson 1919; Campbell 1931, 1940; Whyte 1939).
This study falls naturally into two phases or parts. The first, begun as materials for the junior author's doctoral thesis in 1937, deals with changes in the plant population. The original plans have been considerably extended and continued through a period of four years. The second part, executed in 1939 and 1940, has to do with relative production of forage in pastures protected from grazing during a first, second, and fourth year, and of native prairie. The results reveal not only the profound changes in the numbers and kinds of grasses and forbs, as well as their total yield under different lengths of periods of protection, but also the degree of their utilization.