Plant Regulatory Lists In The United States Are Reactive And Inconsistent

Global invasive species introductions are rising, necessitating coordinated regulatory strategies within and across national borders. Although states and nations address their unique priorities using plant regulations, these regulations are most likely to reduce invasive plant introduction and spread if they are consistently enacted across political borders and proactively restrict spread early in the invasion process. Further, a unified regulatory landscape is particularly important given the imminent range infilling and large-scale climate-driven range shifts of invasive species. In the United States, federal and state regulations restrict the introduction and spread of several hundred invasive and noxious plant taxa in an effort to reduce their negative impacts. Using plant regulations for the lower 48 United States, we assessed consistency among regulated taxa based on similarities in adjacent states' regulatory lists. We assessed proactivity by comparing regulatory lists to plants' current and potential distributions given occurrence records and species distribution models under climate change. States regulate from 0 to 162 plant taxa, with an average of only 16.8% overlap of regulated taxa between adjacent states. Up to 137 plants may be present but unregulated in a state, and only 110 of 553 listed taxa were regulated in one or more states where they were not yet present. However, 36 states listed at least one taxon proactively (regulated but not present in the state). Of the 48 proactively listed taxa with species distribution models, we identified 41 cases (38 species in 21 states) where listing was 'climate proactive' (regulated, not present and where climate could be suitable for establishment by mid-century). Policy implications. US plant regulatory lists were inconsistent across borders and reactive to climate change. However, most states regulate at least one plant taxa prior to its introduction, suggesting that a more proactive approach is possible under existing regulations. Coordination across borders is imperative given gaps in regional defences against invasion and projected invasive plant range shifts under climate change. We suggest that subnational, national and international governing bodies evaluate their plant regulatory lists for consistency and proactivity, as it is paramount for preventing the next wave of plant invasions.