Effects of Grazing on Vegetation and Soils in Southeastern South Dakota

Abstract

The effects of grazing on vegetation and soils in Union Co., South Dakota, were studied in 1965-67. Sites chosen for intensive study were confined to Knox silt loam and Lamoure silt loam, both upland soils developed from loessal parent material. Plant communities occupying Knox silt loam are dominated by Andropogon scoparius, Koeleria cristata, Stipa spartea, Amorpha canescens, and Ceanothus ovatus. Where the habitat is more mesic, as on Lamoure silt loam, Sorghastrum nutans, Andropogon gerardi, and Artemisia ludoviciana are added important species. This grassland is productive and can be grazed for 5-6 months each year at the rate of one animal unit/3-4 acres without seriously damaging the quality of the pastures. However, overgrazing is common and results in decreased productivity as well as a decrease in palatable species, including those listed above. Species which are favored and increase with grazing include Bouteloua curtipendula, B. gracilis, B. hirsuta, Poa pratensis, Buchloe dactyloides, Panicum scribnerianum, Antennaria campestris, Aster multiflorus, and others. Species that invade heavily overgrazed pastures include Panicum capillare, Bromus spp., Hordeum spp., Cirsium spp., Ambrosia spp., Euphorbia spp., Chenopodium album, Verbena stricta, and others. Soil changes resulting from overgrazing include decreased organic matter, nitrogen, and moisture in the upper layers. Knox silt loam also erodes under heavy grazing practices. INTRODUCTION The natural vegetation of South Dakota has not been studied extensively (Hoffman and Rogers, 1966). Weaver et al. have studied the grasslands of eastern Nebraska quite extensively including the effects of grazing (Weaver and Fitzpatrick, 1934; Weaver and Hansen, 1941a, 1941b; Weaver and Tomanek, 1951; Voigt and Weaver, 1951). Much o,f what is known about the effects of grazing in eastern South Dakota is inferred from studies done elsewhere. The grassland vegetation of southeastern South Dakota is part of what has been called prairie (Weaver and Fitzpatrick, 1934). It is generally characterized by vast expanses of herbaceous and low-growing woody species with taller shrubs and trees confined to low areas in the landscape. Very little of this natural vegetation remains in southeastern South Dakota; there are a few scattered patches remaining which have never been plowed but have been grazed or mowed. The present studies concern the effects of grazing on the grassland and soils in southeastern South Dakota. The sites chosen for intensive study are located in Union Co. in the southeastern corner of the state (Fig. 1). All the sites are upland and the soils are derived from loess. Climatologic data were obtained from Vermillion, S. D., located 24 km west of the study sites. Mean precipitation for April through September is 47 cm and for October through March is 11.3 cm (U. S. Dept. Commerce, 1960). 1 Present address: Dept. of Botany, Univ. of Chicago 60601.