Seedstalk production of mountain big sagebrush enhanced through short-term protection from heavy browsing

Abstract

Mountain big sagebrush (Artemisia tridentata ssp. vaseyana Nutt.) is an important browse species on many key mule deer winter ranges in the western United States. Big sagebrush on many of those ranges is declining due to the lack of recruitment. Plants subjected to heavy 0 8% use) browsing produce 50 to 93% fewer seedstalks than those not subject to such use. The objectives of this study were to determine: (1) whether protection from browsing for 1 winter would increase the number of seedstalks the following fall; (2) if protection increased length of seedstalk; (3) if there is a relationship between seedstalk length and number of seeds per seedstalk; and (4) if increasing seed production increased seedling establishment. Fifty-eight plots containing 344 plants at 4 sites in north-central Utah were established. At each plot, plants were randomly assigned to be either protected or browsed. The protected plants produced significantly (P<0.05) more seedstalks than those browsed during the previous winter. Length of seedstalks on a given plant and among plants showed considerable variation, and the data indicated no clear differences between average seedstalk length on browsed and protected plants. Seed per unit length of seedstalk was also highly variable. No seedlings were found during 7 years of observations of the original plot or in 4 years for the 57 plots established in 1986, regardless of the numbers of seedstalks on a plant. Seed production does not appear to be a limiting factor in seedling establishment for the study populations.