Vegetal Change in the Absence of Livestock Grazing, Mountain Brush Zone, Utah

Abstract

Canopy cover of vegetrtion dominated by Cambel oak was determined in 1983 in adjacent canyons characterized by different grazing histories. Results were compared with data collected in 1935, and the methods replicated those used in the earlier study. Vegetal changes since 1935 in Red Butte Canyon where livestock grazing had been excluded since 1905 were small compared with those of Emigration Canyon where heavy graxing contfnued into the 1930’s, but was gradually phased out and discontinued in 1957. Large differences in vegetal cover between the 2 canyons reported in 1935 were mostly eiimhrated by 1983. Selective foraging by livestock is an important factor determining the composition of plant communities, and directly affects associated animal communities. Livestock select palatable forage and thereby give a growth advantage to less palatable, ungrazed plants. On many mule deer winter ranges in the Intermountain Region livestock grazing shifted presettlement, grassdominated communities to shrublands (Stewart 1941, Reynolds 1960, Christensen and Johnson 1964, Hull and Hull 1974, Harniss and Wright 1982). Mule deer herds responded to the increase in available winter forage and numbers significantly increased (Hancock 198 I). Authors are wildlife biologist, associate professor, and research assistant, Department of Range Science, UMC 52, Utah State University, Logan 84322. This oaoer is a contribution of Utah State Division of Wildlife Resources. Federal Aid Project W-105-R. Manuscript accepted 9 June 1986. However, due to erosion problems often associated with excessive livestock grazing and increased emphasis on watershed and recreation values, livestock grazing on many Intermountain winter ranges has been decreased or eliminated (Stewart 1936, Stoddart and Smith 1955). On those ranges where previously heavy livestock grazing was eliminated, secondary succession, accelerated by deer use in winter, would be expected to slowly alter plant communities toward more grasses and forbs and fewer desirable shrubs (Rogers 1982). Consequently reductions in numbers of mule deer may be predicted. The mountain brush zone found throughout the Intermountain Area commonly occurs as transition range between sagebrush foothills and coniferous forest. Open stands of deciduous trees, with abundant grass and forb understory having high nutritive value, make the zone valuable and attractive for grazing. Consequently many areas were highly impacted by livestock before grazing was curtailed. However, little is known about post-grazing succession. This study reports changes in vegetal composition from 2 areas previously grazed by livestock, but receiving no livestock use in several decades.