Karst sinkholes as foci of biodiversity in the Hoosier National Forest

Sinkholes are a well-known, but poorly studied, aspect of karst environments. In 2015, the Hoosier National Forest in southern Indiana, USA, commissioned a study of sinkhole habitats to assess their ecological role. The ecosystems of 26 sinkholes were evaluated to determine if sinkhole floor biological communities and species richness were a function of the surrounding plant community. Each sinkhole was sampled four times for five target groups of invertebrates at intervals of approximately three months, for a total of 104 visits. The sampling resulted in finding 140 taxa, including 31 land snails, 14 millipedes, 3 terrestrial isopods, 83 spiders and 9 pseudoscorpions. Of exceptional note were at least 12 new state records and a probable new species of pseudoscorpion. Several of these species appear to be endemic to sinkhole habitats. A link was confirmed between species richness and the surrounding plant community, specifically that the highest biodiversity was found in sinkholes surrounded by native deciduous forest, followed by native glades. Sinkholes in fields from which deciduous forest had been removed possessed markedly decreased species diversity, as did non-native plantings of pines. Sinkhole habitats had a significantly higher species richness than adjacent non-sinkhole control sites. Moreover, the arthropod communities that were found in each sinkhole within each plant community type were different from each other and the surrounding non-sinkhole areas. These data suggest that sinkholes are more than just depressions in epigean landscapes, but possess unique invertebrate communities linked to the surrounding plant community.