Vegetation Disturbance Regimes and Conifer Succession in Gunnison Sage Grouse (Centrocerus Minimus) Habitat

The major reason for Gunnison sage-grouse decline in southwestern Colorado is thought to be loss and fragmentation of its sagebrush habitat by pinyon and juniper encroachment. This encroachment could be driven by both anthropogenic disturbance and natural climate variation. This project determines these potential drivers of Rocky Mountain juniper and pinyon pine forest expansion into sagebrush area at low elevations in Gunnison County, Colorado. Fire, grazing, and other anthropogenic activities was assessed to explain juniper and pine forest invasion patterns on sagebrush steppe. I hypothesize that recent land use, climate variability, over-grazing, and fire will drive pinyon or juniper tree invasion of sagebrush. Field work done in late summer and early fall 2017 collected data on the establishment dates of trees invading sagebrush. Juniper and pine forest structure, density and lower treeline elevation, and fire history were analyzed using tree cores and forest inventory data. Climate, fire history and livestock data were extracted from published database and literature. We found that the tree establishment in the mid-and later- twentieth century (post 1970s) was caused by wet and cool growth season after the great drought period in the 1950s. The outcome of this project will help land managers to understand current lower treeline conifer condition, and decide whether current tree removal treatment is necessary to improve sage-grouse habitat