Vegetation Change after 65 Years of Grazing and Grazing Exclusion

The Nevada Plots exclosure system was constructed in 1937 following passage of the Taylor Grazing Act to assess long -term effects of livestock grazing on Nevada rangelands.A comparison of vegetation characteristics inside and outside exclosures was conducted during 2001 and 2002 at 16 sites.Data analysis was performed with a paired t test.Out of 238 cover and density comparisons between inside and outside exclosures at each site, 34 (14% of total) were different (P < 0.05).Generally, where differences occurred, basal and canopy cover were greater inside exclosures and density was greater outside.Shrubs were taller inside exclosures at 3 sites grazed by sheep (Ovis aries).Perennial grasses showed no vertical height difference.Aboveground plant biomass production was different at only 1 site.Plant community diversity inside and outside exclosures were equal at 11 of 16 sites.Species richness was similar at all sites and never varied > 4 species at any site.Few changes in species composition, cover, density, and production inside and outside exclosures have occurred in 65 years, indicating that recovery rates since pre Taylor Grazing Act conditions were similar under moderate grazing and grazing exclusion on these exclosure sites.Resumen