Many scientists assume that climate change will cause invasive plants to expand their ranges, thereby increasing risk to native ecosystems.  Many factors associated with global change, such as increased disturbance and higher resource availability through N and CO₂ fertilization, are thought to favor invasive plants.  However, climate change could also reduce invasion risk if future climate conditions are unsuitable for invasive species.  Identifying areas where climate change may help or hinder plant invasion will require species-specific projections of change.  Here, we project the impacts of climate change on three widespread invasive plants in the western United States: cheatgrass (Bromus tectorum), spotted knapweed (Centaurea biebersteinii), and leafy spurge (Euphorbia esula).  We use bioclimatic envelope modeling to assess current invasion risk and project future invasion risk based on an ensemble of 12 Atmosphere-Ocean General Circulation Models (AOGCMs).

Results/Conclusions

Bioclimatic envelope modeling results suggest that each of these species will shift in range, expanding in some areas, but retreating in others.  By 2100, B. tectorum is likely to expand across Montana and Wyoming, but retreat in parts of southern Nevada and Utah.  Ecosystem vulnerability to C. biebersteinii expands across Rocky Mountain states, but retreats from parts of eastern Montana and Wyoming.  E. esula shows substantially reduced risk in Minnesota, Nebraska, and Colorado, but may expand into parts of Canada not included in the model.  Envelope model results can inform management planning aimed at preventing new invasions associated with climate change, and can identify opportunities for restoration.  However, altered climate conditions may prevent the native species that once occupied restoration target areas from recolonizing them.  Identifying restoration opportunities and determining appropriate species to establish in them will pose a tremendous challenge for ecologists and land managers.  This challenge must be anticipated and addressed without delay if we are to seize any restoration opportunities created by climate change before those opportunities are eliminated by a new wave of invaders.