Plant regulatory lists in the United States are reactive and inconsistent

Abstract

1. 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.2. 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.3. 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).4. 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.

Breaking down barriers to consistent, climate‐smart regulation of invasive plants: A case study of US Northeast states

“…As a result, northeast states should agree about which plants are high risk, ideally leading to similar regulatory lists. Unfortunately, inconsistent regulatory lists are common internationally (Courchamp et al, 2017;Early et al, 2016) and across US states (Beaury, Fusco, et al, 2021;Lakoba et al, 2020). For example, Buerger et al (2016) evaluated regulated species in six Midwestern states and found only 14 species F I G U R E 4 Risk assessment scores for 52 terrestrial invasive plants evaluated by both New Hampshire (NH) and New York (NY) showed a weak positive correlation (R 2 = 0.179).…”

“…We also excluded five species ( Sagittaria japonica , Typha gracilis , Typha laxmannii , and Typha minima listed in NH, and the hybrid Myriophyllum heterophyllum × Myriophyllum laxum listed in NY) whose scientific names were not listed in the USDA PLANTS database (USDA PLANTS, 2021). Following Beaury, Fusco, et al (2021), we measured consistency between states by aggregating all regulated species into a single “regional list” and we calculated the percentage of this regional list that was regulated within each state. Also following Beaury, Fusco, et al (2021), we calculated the proportion of counties within the state where each regulated species was present as a metric of proactivity.…”

“…In other words, these states evaluated species considered existing threats to the state (Figure 1c), with a high likelihood of being assessed as invasive, and proceeded to regulate them. Given that there are 128 regulated invasive plants in the Northeast and over 500 regulated plant taxa across all US states (Beaury, Fusco, et al, 2021), it should not come as a surprise that there are plenty of potentially invasive plants to choose from. While differences in the process between risk assessment and regulation could add more inconsistency (e.g., weight given to economic profits, length of public comment period, and the regulatory body), our evidence suggests that inconsistent and reactive regulations in the Northeast are predominantly the result of a failure to evaluate similar sets of species (Figure 2).…”

“…Although plant regulatory aims are broadly similar (preventing the spread of harmful invasive plants or noxious weeds), a recent analysis showed that across the United States, regulated plant lists for neighboring states had only a 17% species overlap (Beaury, Fusco, et al, 2021). There are several factors that could lead to this low level of consistency.…”

“…First, states could select different sets of species to evaluate for potential regulation. Across the United States, there are hundreds of unique species regulated as noxious or invasive by one or more states (Beaury, Fusco, et al, 2021; Lakoba et al, 2020). Conducting a risk assessment for a single invasive species could take as many as 40 h, depending on the complexity of the protocol and availability of information about the species (Verbrugge et al, 2010).…”