Effects of Denudation on the Productivity of Grassland

Denudation (close mowing and removal of mulch) of ungrazed prairie and ungrazed cropland plots near Norman, Oklahoma, did not result in significant change in composition, but increased the biomass in both the priarie and cropland during the growing season. Total biomass in all plots was low in February—March, increased to a maximum in late July, and declined rapidly thereafter. Although 115 species were sampled, only the following six species contributed significantly to the total biomass: Andropogon gerardi, Panicum virgatum, Sorghastrum nutans, Andropogon scoparius, Leptoloma cognatum, and Panicum scribnerianum. Average daily productivity was very low in February—March, moderate in April, relatively high and approximately equal in May, June, and July, and negative in August and September. The cumulative productivity was moderate for April, approximately equal but relatively high during May, June, and July, but declined rapidly thereafter. The terminal standing crop of living material (early September) was considerably lower than the maximum biomass in late July. In the denuded plots, the much increased steadily in weight throughout the period of the study. The amount of mulch attained a relatively steady state in the denuded prairie by the end of the third year, and in the denuded cropland by the end of the fourth year.