To answer the question of how long-term changes in temperature and precipitation might affect vegetation, we monitored vegetation plots across 22 years in a wildland Great Basin site in Utah. The study was started in 1993 with the establishment of 100 randomly-distributed permanent plots at Camp W.G. Williams, an approx. 24,000-acre military training site in the Transverse Mountains situated between Salt Lake City and Provo. Point-intercept data were collected at 1-meter intervals along a 100 meter-long transect in each plot for species presence/absence and height. Following a standardized “Land Condition Trend Analysis” (LCTA) protocol established by the U.S. Army, we conducted an initial two-year biological inventory throughout the Camp, documenting a total of 420 species of vascular plants.
Results/Conclusions
One quarter (105) of the 420 species of vascular plants occur within the monitoring plots. Initial data showed a 2:1 ratio in abundance of native and non-native species. Using historical random forest models for longitudinal data, we explored potential effects of various plot-level environmental and climatic measures, including elevation, slope, and exposure along with annual average daytime and nighttime temperatures and annual precipitation. From 1993 to 2015, on average, there was a 43% increase in the abundance of non-native vegetation. The greatest species increase was in the abundance of highly flammable non-native Bulbous bluegrass (Poa bulbosa). Our results suggest that increased abundance of non-native species observed over the study period is associated with dramatically increasing nighttime temperatures and modestly decreasing annual precipitation.