Sheep Grazing Effects on Tall Forb Vegetation.

Authors: KLEMENT, KEITH - NOBLE FOUNDATION; Moffet, Corey

Submitted to: Society of Range Management
Publication Type: Proceedings
Publication Acceptance Date: 9/5/2008
Publication Date: 3/1/2009
Citation: Klement, K.D., Moffet, C.A. 2009. Sheep Grazing Effects on Tall Forb Vegetation.. Society of Range Management. Paper No.2030-8.

Interpretive Summary: The perennial tall forb vegetation type is found on several high elevation ranges across portions of Idaho, Montana, Nevada, Utah, and Wyoming. The type is very productive, high quality grazingland, but little is known about the long term consequences of sheep grazing on these communities. Data from repeated samplings, from 1959 through 1994, of 25 different perennial tall forb locations in the centennial mountains of Montana, were analyzed to determine whether shifts in the vegetation were occurring as a result of sheep grazing. The data showed that although the vegetation differed among years the differences between years were similar regardless of whether grazed or protected from grazing. These results will help land managers to understand the effects of long term sheep grazing on perennial tall forb vegetation types and will inform their decisions on sheep grazing use in these communities.

Technical Abstract: Perennial tall forb (PTF) communities are productive, high elevation, grazinglands characterized by a short growing season (<90 d) and abundant 0.5- to 1.5-m tall perennial forbs. In a southwest Montana study area, domestic sheep have grazed these communities from July 1 to August 15 each year prior to 1989, and in just 2 of every 3 years since 1989. In 1994, 25 PTF locations, including 3 with grazing exclosures, were sampled. Surveys were also conducted in 1959, 1978, 1979, and 1980. We tested the hypotheses that site conditions such as biomass, taxonomic composition and richness, cover, bare ground, and gopher mounding were constant among years and between levels of grazing. In the grazed locations, sampled in 1959, 1978, and 1994, there was significant among year variation in several site condition elements, including total and within functional group biomass, taxonomic composition, plant cover, bare ground, gopher mounding, and species richness. In general, 1978, a relatively wet year, had greater biomass, species richness, and cover and less bare ground and gopher mounding. The relatively dry years of 1959 and 1994 had similar site conditions. Perennial forb biomass in 1994, however, was greater than in 1959 and similar to that in 1978. In the 3 exclosure locations, sampled in 1978, 1979, 1980, and 1994, differences in site conditions among years were significant, but grazing effects were not detected. Year, most likely due to differences in weather, had greater influence on the site conditions of these communities than did moderate to light grazing use.