Background/Question/Methods Nonindigenous invasive species (NIS) are considered a significant threat to rare and endangered species. Though experts debate the degree to which NIS are responsible for declines in populations of rare species, public and private land owners devote substantial resources toward the control of NIS. It is common to evaluate species based upon their likelihood of invading or potential ecological consequences, but little research is devoted to determining the degree to which specific NIS threaten specific threatened or endangered species. I used the relative risks model to explore these risks in both current and forecast scenarios for invasive and rare plants in Nebraska. I modeled the suitable habitats for 8 NIS, which I subsequently compared to documented occurrences of 10 rare and endangered plants in a Geographic Information System. This, in combination with an assessment of ecological impacts of each NIS, provided relative risk scores for NIS, rare and endangered plant species, and sub-regions of Nebraska. Finally, I used Monte Carlo simulation to determine how uncertainty of input variables influenced risk scores.
Results/Conclusions Results indicate that the Western High Plains and Nebraska Sand Hills are at greater risk than other sub-regions of the state, in both current and forecast scenarios. Risk scores for all rare species increase in the forecast scenario. Interestingly, while the invasive plants Alliaria petiolata and Lonicera maackii both have relatively low risk scores individually, together they contribute almost 40% of the total risk score for the rare species Panax quinquefolius, making it the highest risk rare species in the model. Risk scores increase for some invasive species and remain unchanged for others in the forecast scenario, suggesting that future risks may be averted by limiting the continued establishment of certain species. This risk assessment demonstrates how a regional risk assessment with the relative risks model can be adapted to consider risks from multiple invasive species to multiple rare species.