Out of the weeds? Reduced plant invasion risk with climate change

Background/Question/Methods

Invasive alien plants can alter population dynamics, community composition, and ecosystem function in affected systems.  Resources for early detection and management programs are limited, yet are key to preventing or mitigating the effect of invasives.  Identifying areas with the high and low potential invasive plant richness may help in effective allocation of conservation resources.  We developed an occurrence database of 900 terrestrial invasive plant species listed as invasive or noxious at the federal or state level to determine the intensity of invasive plant risk across the contiguous United States.  We identified hotspots of current invasion debt (1 - observed/potential invasive species richness) based on an ensemble of individual species distribution models created using MaxEnt under current climate.  We projected future changes in invasion risk based on an ensemble of 13 future climate models.  The spatial extents and ecoregional context of invasion hotspots under current and future climate conditions can identify areas under constant threat over time, candidate areas in high need for early detection monitoring, and areas at low risk of invasion.

Results/Conclusions

Eastern temperate forests, which constitute about 20% of the contiguous US land area, were most at risk under current climate, with a projected 481 terrestrial invasive plant species capable of invading and an invasion debt of 0.84.  Mediterranean California and marine west coast forests, both small ecoregions, contained suitable areas for many species (374 and 414 species, respectively), but had the lowest invasion debts (0.39 and 0.49, respectively).  A striking pattern emerged for future projections, with lower projected invasive species richness (up to 250 species less in some areas) compared to current across a majority of the country.  Northern latitude and high elevation locations constituted the subset of places projected to have increased invasion risk. Uncertainty in future invasive richness projections ranged from 1-43 species and was highest in areas with uncertainty in the climate model ensemble.  Measures to prevent introduction of new invasive plants, particularly tropical and subtropical species, may allow us to capitalize on plant responses to climate change without direct management in a large portion of the country.  However, management to curb the spread of species projected to shift their ranges may still be beneficial to prevent movement of species into new areas and ecoregions.