Vegetative Responses of Some Great Basin Shrub Communities Protected against Jackrabbits or Domestic Stock

Abstract

We surveyed the vegetation at 19 locations inside and outside 12 exclosures built at various times in Curlew Valley, northern Utah. The exclosures were in semidesert shrub vegetation and included several communities definable by a dominant perennial shrub distribution having sharp boundaries. At the level of the individual quadrat, there was no correlation between the density of any of the abundant annuals and the percentage of the soil surface that was bare, or covered by rock, dead plant matter, or cryptogam crust. The communities as defined by dominants arranged themselves in the order winterfat, shadscale, shadscale and perennial grasses, sagebrush, black sage. These communities are known to be found on progressively less xeric sites. The changes which resulted from protecting samples of these communities from grazers were fairly consistent within each community, but differed among communities; and moreover these changes were not correlated with a trend from more to less xeric sites. Protection against sheep, with or without protection against jackrabbits, did not have very many effects even over 15 years: halogeton generally decreased; peppergrass increased where present; winterfat increased in vigor but not in density where it was dominant. Other dominant shrubs and perennial grasses, did not respond to protection. Protection against jackrabbits had no consistent extra effect on the parameters studied. The classical concept of range succession is that recovery from overgrazing moves a community through secondary succession parallel to a gradient towards relatively more mesic conditions. On the whole, this concept has not been useful in interpreting the results of excluding grazers from these semiarid shrublands.