Livestock Defoliation Patterns on Native Range Under Season-Long and Spring-Deferred Grazing

A study was conducted to examine, under similar stocking rates, the effect of season-long and spring-deferred grazing on the frequency and intensity of defoliation of western wheatgrass (Agropyron smithii, Rydb.), blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Steud) and buffalograss (Buchloe dactyloides [Nutt.] Engelm.). The study was conducted in 1990 and 1991 at the Cottonwood Range and Livestock Research Station, located in western South Dakota. Data were collected on three replicate pairs of pastures, for each of two range condition classes. One pasture of each replicate was grazed season-long and the other was deferred from use in the spring and then grazed to the same calendar date as the season-long treatment. Under the conditions of this study, western wheatgrass appears to contribute the most to the forage resource. Use on individual blue grama or buffalograss tillers is not common, especially in HI pastures. Repeated grazings of a tiller were very uncommon under both season-long and spring-deferred grazing. Spring-deferment appeared to improve the likelihood western wheatgrass will not be subjected to repeated use early in the growing season. Occurrences of defoliation on mixed grass prairie pastures that are in low and high range condition were not found to be as frequent nor as severe as those used in published clipping studies. This study provided information on these two components of defoliation that should permit the development of clipping studies that more accurately reflect those that happen under livestock grazing