A century of vegetation instability and resilience on the Colorado Plateau

Abstract:

Vegetation in dryland ecosystems is highly sensitive to changes in precipitation amount and timing. Globally, forecasted increases in climate aridity and variability in these regions are likely to alter vegetation dramatically. The Colorado Plateau (CP) is an important dryland ecoregion in the southwest United States for which drier and more variable conditions are forecast. The CP is characterized by moderate to high elevations, cold winters, and shallow soils. Vegetation across much of the CP has already undergone significant changes during the past century, that have been largely attributed to grazing intensity and multidecadal shifts in precipitation regime. Long-lived native tree and shrub species (Populus fremontii and Salix exigua) as well as non-natives (Tamarix chinensis and Eleaegnus angustifolia) have filled previously barren streambeds, shifted plant functional type dominance, and remote areas have been colonized by invasive annual plant species. These large shifts in plant functional type have changed leaf area, phenology, and net primary productivity in many habitats, consequently altering the magnitude and timing of evapotranspiration and soil drying. We combine 100 years of historic repeat photography with remote sensing and field observations from across southeastern Utah, USA, to build a model of local water balance with respect to state changes in vegetation, climate, and land use. This model will aid in understanding how vegetation changes influence water cycling, and how climatic and edaphic factors limit the scope of vegetation change.