Effect of Frequent Clipping on Plant Production in Prairie and Pasture

Abstract

The degeneration of native bluestem prairies of eastern Nebraska occurs slowly under moderate grazing or slight overgrazing but within two to five years where overgrazing is pronounced. Although the changes in the plant populations are continuous until the soil is finally almost bare, for convenience of study they have been grouped into several more or less distinct stages (Weaver and Harmon, 1935). An intermediate stage in deterioration is indicated by a great increase in the abundance of bluegrass (Poa pratensis), blue grama grass (Bouteloua gracilis), or buffalo grass (Buchloe dactyloides), the latter especially on low ground. Under long continued grazing and trampling, the native bluestems and most other prairie grasses disappear. This stage is characteristic of the bluegrass or short-grass pastures or a mixture of these. The purposes of this investigation were to ascertain the decrease in yield accompanying close grazing of virgin prairie, and to determine the relative yields of various types of prairie and of native pastures which replace them. The clip quadrat method was employed, a total of 190 meter quadrats being used at six stations. Yield per unit area was determined at various intervals or at the end of the growing season. Height growth was used as a criterion of favorableness of environmental conditions, especially water content of soil and temperature, as well as an indicator of the effects of overgrazing. Dry weight of plants is one of the best quantitative characteristics of vegetation (Hanson, 1938), and increase in dry weight is the best measure of growth (West, Briggs, and Kidd, 1920). The clip quadrat has been widely used by numerous American investigators (Sarvis, 1923; Taylor and Loftfield, 1924; Aldous, 1930; Black, et al., 1937) and has been found to be the most suitable form of the percentage production method on the grassveld in South Africa (West, 1936). Although clipping studies serve as a valuable supplement to grazina experiments, they differ in several respects from actual grazing. The chief differences as observed by Culley, Campbell, and Canfield (1933) and others have been summarized by Weaver and Clements (1938) and the fact pointed out that clip quadrats are widely used. In the early spring of 1933, typical experimental plots were selected in the several types of prairie and pasture at Lincoln, Nebraska. Exclosures were established and groups of meter quadrats laid out before the grasses resumed growth. The position in which the quadrats were placed was given careful consideration. The areas selected after years of acquaintance with the vegeta-