Wyoming Big Sagebrush and Herbaceous Cover Relationships

Abstract

We measured 328 sites in northern, central, and southern Montana and northern Wyoming during 2003 to test the competitive relationship of herbaceous cover in the interspaces to Wyoming big sagebrush (Artemisia tridentata wyomingensis) cover. Long term annual precipitation at all sites was approximately 31 cm. Sagebrush and total herbaceous cover varied from 5 to 45 percent and 3.5 to 55 percent, respectively. Simple linear regression was the best fit model for predicting herbaceous cover from sagebrush cover using the highest R_a² values as the model selection criteria. In northern Montana, herbaceous vegetation was predicted by sagebrush cover with the following model:  Y = 37.4 – 0.61X (R_a²  = 0.16, P < 0.001, n = 87). In central Montana, the model was Y = 14.0 – 0.00X (R_a²  = 0.00, P = 1.0, n = 155). In southern Montana, the model was Y = 35.9 – 0.39X (R_a²  = 0.14, P < 0.001, n = 86). When all sites were combined, the best fit model was Y = 23.7 – 0.15X (R_a²  = 0.01, P < 0.061, n = 328). This analysis determined that only 1 percent of the variation in herbaceous vegetation cover was associated with Wyoming big sagebrush cover. Management suggestions to reduce Wyoming big sagebrush in order to increase long-term herbaceous production for greater sage-grouse (Centrocercus urophasianus) would not be recommended.