United States forests are increasingly invaded by problematic non-native plants

Abstract

Non-native invasive plants cause significant ecological impacts to forests while requiring costly management interventions. We used data from Nationwide Forest Inventory plots to assess the extent and recent patterns of invasion by problematic non-native plants across United States forests at multiple scales (county, regional, and national). We estimated the proportion of forests that have been invaded and calculated the mean plot-level richness of invasive plant species during two recent inventory periods (ca. 2010 and 2018). We found that ∼99.5 million ha of forest have been invaded by understory non-native plants nationally (37.9 % of the inventoried area) with a greater degree of invasion in the East than in the West. Nationally, the percent of invaded plots and the mean plot invasive richness at the county scale both significantly increased over time while mean plot invasive plant cover decreased. We evaluated potential drivers of invasion using an ensemble learning approach and applying simultaneous autoregressive spatial error models. Recent invasion and change in invasion metrics were associated with anthropogenic fragmentation (a measure of disturbance), change in agricultural land cover (an indirect indicator of propagule pressure), and tree richness and change in tree biomass (measures of forest invasibility). We also found consistent evidence of invasion debt, the temporal lag of invasion outcomes, especially in eastern U.S. forests. These results are important for the long-term monitoring of forest effects associated with invasive plant species and offer a glimpse into ongoing national, regional, and local invasion of United States forests.

Citation

Potter, Kevin M.; Riitters, Kurt H.; Iannone Basil V.; Pandit, Karun; Guo, Qinfeng; Oswalt, Christopher M. 2025. United States forests are increasingly invaded by problematic non-native plants. Forest Ecology and Management. 599: 123281. https://doi.org/10.1016/j.foreco.2025.123281.