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Efforts to prevent the introduction and spread of new invasive plants are most effective when regulated species are consistent across jurisdictional boundaries and proactively prohibit species before they arrive or in the earliest stages of invasion. Consistent and proactive regulation is particularly important in the northeast U.S. which is susceptible to many new invasive plants due to climate change. Unfortunately, recent analyses of state regulated plant lists show that regulated species are neither consistent nor proactive. To understand why, we focus on two steps leading to invasive plant regulation across six northeast states (Connecticut, Maine, Massachusetts, New Hampshire, New York, and Vermont): which sets of species are evaluated and how risk is assessed. Our analysis confirms previous findings that invasive plant regulations are inconsistent and reactive. Of the 128 plants regulated by one or more states, 54 were regulated by a single state and only 16 were regulated by all six states; regulated species tended to be widespread across the region (not proactive). These outcomes are largely driven by different sets of evaluated species. For example, neighboring states Vermont and New Hampshire evaluated 92 species in total, but only 26 overlapped. In addition, states rarely evaluated species that were absent from the state. Risk assessment protocols varied considerably across states, but consistently included criteria related to ecological impact, potential to establish, dispersal mechanisms, and life history traits. While none of the assessments explicitly consider climate change, they also did not contain language that would preclude regulating species that have not yet arrived in the state. To increase consistency and proactivity, states would benefit from 1) evaluating species identified as high risk by neighboring states as well as high risk, range-shifting invasives, both of which we compiled here and 2) explicitly considering climate change when assessing ‘potential distribution’ or ‘potential impact’ of target species. Additionally, a mechanism for sharing knowledge and risk assessments regionally would benefit states with fewer resources to address invasive species threats. Presenting a unified defense against current and future threats is critical for reducing impacts from invasive species and is achievable with better state-to-state coordination.


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