Characterizing the microhabitats of exotic species in Illinois shale barrens

Like native species, exotics form part of the mosaic structure of plant communities. However, their role in these communities is unclear. Thus, we ask, are invading exotic species present in recognizable microhabitats within plant communities? We compared the microhabitat of exotic species and random locations to determine if exotic plants occupied a recognizable subset of habitats within three barren communities. Fourteen exotic species were identified. The factors that characterized their habitats varied between barrens and among species. Considered as a group, exotic microhabitats comprised a subset of available habitats within the barrens, specifically, edge habitats rather than the open conditions of the barrens interior. Soil properties such as low temperature or neutral pH, and high litter or woody species cover, were common factors associated with the occurrence of exotics. Individual exotic species occupied different habitats within those identified for exotics as a group, but the range of variation between the different species was not generally significant. Within each barren, exotics occupied a distinct subset of microhabitats. This distribution suggests that exotics are not widely dispersed within these areas. Site conditions may be restricting the establishment of exotics to specific microhabitats, and in addition, some exotics may be altering the microhabitats that they colonize. Therefore, management efforts toward maintaining open conditions in the barrens may also discourage further encroachment by exotics into these areas.