Abstract

Critical mule deer (Odocoileus hemionus) winter ranges in southeastern Utah dominated by Wyoming big sagebrush (Artemisia tridentata var. wyomingensis [Beetle and A. Young] Welsh) have developed dense cheatgrass (Bromus tectorum L.) understories. These communities are currently characterized by predominately mature to decadent stands of sagebrush with few perennial grasses and forbs. Sagebrush seedlings and perennial grasses compete for limited resources with annual grasses and forbs. To determine the affects of cheatgrass control on sagebrush growth and reproductive characteristics, imazapic (PLATEAU®, AC 263,222) herbicide was sprayed at 438.5 ml/ha with water and methylated seed oil during active fall growth of cheatgrass in 2002. Sagebrush growth and reproductive variables were measured on browsed and unbrowsed (caged) plants on sprayed and non-sprayed paired plots on 6 sites. Cheatgrass and other annual forb pretreatment cover was reduced from 23% to less than 3% the first year after the herbicide treatement and only increased to 4% the second year. Soil moisture on the treated plots was available at 15, 30, and 60 cm for several days to several weeks longer than on the control plots depending on the depth in the soil and year. Annual leader growth and flowering seedstalk length were similar on unbrowsed and browsed shrubs, but the number of seedstalks per plant was decreased by browsing. The number of sagebrush flowering seedstalks was significantly reduced by the herbicide the first year after the treatment, but recovered by the second year. The decrease in flowering seedstalks per sagebrush reduced the number of sagebrush seedlings observed the second year after the treatment (control = 81,800 seedlings/ha and treated = 16,700 seedlings/ha). Both seedstalk length (treated = 13.4 cm and control = 11.2 cm) and annual leader growth (treated = 6.2 cm and control = 5.3 cm) were greater on treated plots than control plots. Overall, imazapic can provide a window of cheatgrass and annual forb control to allow big sagebrush seedlings and perennial grasses and forbs to establish.

Degree

College and Department

Life Sciences; Plant and Wildlife Sciences

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