An Analysis of US State Regulated Weed Lists: A Discordance between Biology and Policy

Abstract

Weedy and invasive plants threaten our food supply, native biodiversity, and the structure and function of ecosystems. The number and impact of these damaging plants are expected to continue to grow with ongoing global change. Some of the most common policy tools to help mitigate this threat are regulatory weed lists, which limit the importation and movement of listed plant species, but there has never been a comprehensive analysis of plants regulated in the United States. We analyzed US state regulatory lists (e.g., noxious, invasive, prohibited) to evaluate their composition, patterns of listing, congruities with weed distributions, and limitations. In total, 46 states maintain regulatory weed lists that include 3210 total listings of 1249 unique species; 48% of them are introduced, 40% are native, and 12% are not yet found in the United States. Overall, the listed species are not a good reflection of the weeds in each state, and listing appears largely reactive, regulating species after they become widespread. We highlight patterns and incongruities among lists and discuss their implications, especially the large number of regulated species native to the United States.

Plant regulatory lists in the United States are reactive and inconsistent

“…While there were several taxa regulated consistently across the United States, most taxa were regulated in only one or two states (Figures 1 and 4). Because political boundaries often do not coincide with ecological boundaries, it is unlikely that neighbouring states are at risk from vastly different sets of species (Lakoba et al, 2020;McCubbins et al, 2013). In a recent study, Lakoba et al (2020) found that regulated species occur in distinct geographic regions within the United States, but regulated lists do not reflect this spatial clustering (e.g.…”

“…states will appear to have longer lists if they list a diverse genus, e.g. Oklahoma; Lakoba et al, 2020) and to more easily compare regulated taxa across states, we considered a genus as one listed taxon.…”

“…Species distribution models were available for 48 of the 110 proactively listed taxa (65 of the 165 cases). Of the 62 taxa lacking models, 27 were considered native to the lower 48 states (Lakoba et al, 2020) or had no native status listed, 14 were aquatic and two were listed genera; these taxa were excluded by Allen and Bradley (2016). The remaining were excluded because they are recent additions to regulatory lists or had insufficient occurrence data to model.…”

“…These issues are exemplified in the United States, where both regulatory processes and regulated taxa vary among states (Beck et al, 2008;Lakoba et al, 2020;McCubbins et al, 2013;Quinn et al, 2013), resulting in a 'patchwork' of state regulations that fail to address problematic invasive plants at the regional scale (Beaury, Patrick et al, 2021;Buerger et al, 2016;Lakoba et al, 2020;Lodge et al, 2006). There is also little geographic clustering of regulated species and a tendency for species to be regulated after they are introduced to the United States (Lakoba et al, 2020), suggesting low consistency across state borders and reactive approaches to regulation.…”

“…To further characterize the extent to which current listing processes lead to consistent or proactive regulations, we quantified the consistency and proactivity of lists of regulated plants across the lower 48 United States. We expand on previous work (Lakoba et al, 2020) to quantify consistencies among regulated taxa of neighbouring states, classify taxa as proactively listed at the national, state and county level, and evaluate whether any species were climate change proactive (regulated, not present, but could establish by 2050). Quantifying current levels of consistency and proactivity in invasive plant regulations can inform actions needed to optimize cross-border invasive plant management, particularly in light of climate change.…”