Causes of Juniper Invasion in Southwestern Idaho

摘要: Invasion of western juniper into vegetation dominated by mountain big sage- brush and perennial bunchgrass on the Owyhee Plateau southwest Idaho appears to be directly related cessation periodic fires. Evidence from adjacent climax stands indicates that fires were frequent for at least several hundred years preceding white settlement. Fires have been much less during past century due active fire control, develop- ment roads other barriers, reduced fuel because heavy grazing a shift towards decreased precipitation. Physical biotic factors affecting establishment juniper, seed dispersal mechanisms, history study area investigated. Results indicated range condition as such had negligible effect establishment. Juniper seedlings became established most readily areas supporting well-developed herba- ceous shrubby vegetation. Seed was primarily localized, accomplished gravity disturbance animal trampling. Abundant evidence in form charred stumps scars living trees found throughout area. Old are confined rocky ridges where understory is sparse intense. apparently kept out denser deeper soils more intense Most herbaceous species survived this treatment greater tolerance fire, or rapid reproduction seed.