Nonnative plants are frequently associated with changes in soil biotic and abiotic characteristics, which lead to plant-soil interactions that influence the performance of other species grown in those soils. A large body of research has shown that these plant-soil interactions contribute to the dominance of singleton species in nonnative ranges because many nonnatives experience stronger positive feedbacks relative to co-occurring natives. However, there is growing evidence that nonnative plants may also alter soils that favor the growth of other nonnative species, which may be problematic for management programs seeking to reduce nonnative abundance within a site. There is increasing recognition that removing dominant invasives frequently leads to reinvasion by the same or other nonnatives This has been termed an “invasion treadmill,” and is a considerable obstacle to invasive species management programs.
One potential mechanism explaining invasion treadmills is invader-induced alteration of soils that promote invasive plants over native plants. Here, I review a case study of how PSF may promote invasive treadmills by synthesizing a series of PSF studies of native and invasive plants common to southeastern deciduous forest ecosystems, and then suggest testable hypotheses of how invasives may alter soils to favor other nonnatives.
Plant-soil feedback experiments provide a powerful tool for untangling whether invasive plants are more likely to create soils that favor other nonnatives, but few plant-soil feedback studies have intentionally focused on how nonnatives may condition soils to favor other nonnatives relative to native species. In a series of plant-soil feedback studies in southeastern deciduous forest ecosystems, invasive woody shrubs biomass is, on average, 1.5 times greater in soils conditioned by other nonnative shrubs relative to uninvaded soils. Comparatively, root mass of native herbaceous species are 1.5 times lower in soils conditioned by multiple nonnative invasive shrubs relative to soils conditioned by a single nonnative shrub or uninvaded soils. Taken together, this indicates that plant-soil feedbacks of these nonnative invasive shrubs may favor other nonnatives over native plants, and that management of these ecosystems may not lead to recovery of a native plant community. In the future, more plant-soil feedback studies should intentionally investigate how PSF may facilitate reinvasion of sites managed for invasives and could test more specifically how nonnatives are altering beneficial and pathogenic soil microbial communities that may favor other nonnative species over native species.