Globally, species that have decreased in number and contracted in range tend to be specialists, slow dispersers, and have lower fecundity. Like many other biotic communities worldwide, upland forest plant communities in Wisconsin have experienced species loss, homogenization, and invasion by weedy exotics over the last 50 years. We explore the relationship of the conspicuous regional trends observed in Wisconsin to the spatial distribution and association of individual species at high resolution, local scales. We expect that species with smaller patch or cluster size may be prone to decline and species with larger cluster sizes or spatially random patterns to be those that are able to spread geographically and increase in numbers. Using highly detailed baseline spatial data from 1953, we explore the changes in distribution of several spring ephemeral species in a southern Wisconsin maple-basswood forest. We sampled point pattern data of spring ephemerals and early summer species in three 15x15 m squares and estimated cluster size using Ripley’s K equation.
Results/Conclusions
Of the 14 species recorded in 2008, all were significantly clustered up to 7 meters, and all species increased in cluster size. Cluster radii ranged from 0.8m to 6.4m. As predicted, many species showing smaller cluster sizes (1.75-3.5m) were among those in decline in abundance across southern Wisconsin. Two species had small cluster sizes but increased in abundance and spread. Species showing large cluster size (~6m; Laportea canadensis and Impatiens pallida) have increased significantly in abundance through southern Wisconsin in the last 50 years. These patterns may reflect either dispersal properties of the species or habitat preferences for certain microenvironments. Laportea canadensis and Impatiens pallida are associated with areas of higher light, while other species were more prevalent in areas of lower light. We also present results on the relationship between patch size and functional traits and environmental variables to address these issues.
