Predicting future trajectories of plant invasion with climate change in the western United States

Non-native plant invasions in the western United States have become a major problem, reducing the health of native ecosystems and costing millions of dollars per year in control costs and lost revenue.  Plant invasions change ecosystem function, including fire frequency, hydrology, nutrient cycling, and biodiversity.  One factor affecting the extents of plant invasion in the west is climate; current geography suggests that several species are tightly coupled to narrow climate envelopes.  However, the aerial extent and location of suitable climate conditions will shift with climate change.  Here, I present climate envelope models for three invasive species in the western United States: yellow starthistle (Centaurea solstitialis), cheatgrass (Bromus tectorum), and spotted knapweed (Centaurea biebersteinii).  An analysis of present climate conditions shows that considerable land area falls within suitable climate envelopes and may currently be at risk of invasion.  An analysis of future climate conditions using several global climate models (GCMs) shows that suitable extents may expand or contract depending on the GCM used.  Change in suitable extents for these three species is affected primarily by change in summer precipitation.  Wetter conditions in the west lead to a reduction in suitable land area, while drier conditions lead to an expansion in suitable land area.  Although there is uncertainty in the GCM predictions of future climate, these results constrain potential expansion or contraction of invasive plants in the western United States.  Using the modeled invasion-climate relationships, I identify land at risk and land with potential for restoration under future climate change scenarios.