Browsing and Plant Age Relationships to Winter Protein and Fiber of Big Sagebrush Subspecies

Abstract

Plants of 3 big sagebrush subspecies, mountain big sagebrush (Artemisia tridentata ssp. vaseyana [Rydb.] Beetle), Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle and Young), and basin big sagebrush (Artemisia tridentata Nutt. ssp. tridentata) were sampled for crude protein and acid detergent fiber (ADF) content. The ADF was determined as an indication of energy content and digestibility. Crude protein and ADF levels were compared among the 3 taxa and between lightly and heavily browsed plants and young and mature plants within each subspecies. Current year growth collected in mid-January was sampled to coincide with the season of greatest ungulate browsing on big sagebrush. Crude protein for mountain big sagebrush (8.34%) was less (P ≤ 0.05) than for Wyoming big sagebrush (11.25%) and basin big sagebrush (11.29%). All are well above the maintenance requirements of deer at 7.5% crude protein. The ADF levels between age and browse-use classes were not different (P ≤ 0.05) within any subspecies, although mountain big sagebrush generally had a lower ADF level than the other 2 subspecies. Wyoming big sagebrush was the only taxon with a crude protein difference (1.2%) (P ≤ 0.05) between age classes, although the difference is not biologically significant. Crude protein was not different between browse-use classes within any of the 3 taxa. Crude protein and digestibility do not indicate ungulate preference for these big sagebrush subspecies.