Vegetation Changes following Fire in the Pinyon-Juniper Type of West-Central Utah

Abstract

Highlight: The stages of succession following fire began with weedy annuals that reached a peak within 3 to 4 years. Juniper woodlands were well developed 8.5 to 90 years following fire. Intermediate stages of succession varied, but followed a general pattern of perennial grasses, perennial grasses-shrubs, and perennial grasses-shrubs-trees. The percentage of dead sagebrush was positively correlated with density of junipers. Thirtythree years was the average minimum age at which Utah juniper produced seed. Juniper and pinyon trees in the Intermountain region have expanded their range greatly since settlement, primarily in the last 100 years. Existing speculation suggests that a major cause of this expansion, either directly or indirectly, was the reduction in fires following settlement. Some authors consider the juniper-pinyon expansion to be several times that of the original cover (Cottam and Stewart, 1940; Woodbury, 1947). In 195 1 it was estimated that this type covered about 30% of the State of Utah (Reuss and Blanch, 1951). The expansion has been primarily into the sagebrush-grass community on the lower edges of original pinyon-juniper. If unchecked, trees become dominant and eventually crowd out most herbaceous and shrub species that provide forage for livestock and big game. The purpose of this study was to examine the vegetation on burns of various ages and determine the successional patterns following fire. The study was conducted primarily on the lower slopes and foothills of the Sheeprock Mountains in Utah and surrounding areas in the vicinity of the Benmore Experimental Range; however, one area was located in the Valley Mountains west of Fayette, Utah. Fire scars of various ages are generally evident in these areas. Tree species in the areas studied were Utah juniper (Juniperus osteosperma) and singleleaf pinyon (Pinus monophylla).