Classification of barrens and other natural xeric forest openings in Southern Illinois

HEIKENS, A. L. AND P. A. ROBERTSON (Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901-6509). Classification of barrens and other natural xeric forest openings in southern Illinois. Bull. Torrey Bot. Club 122:203-214. 1995-Twenty-two natural xeric forest openings in southern Illinois on a variety of substrates were sampled using a modified Daubenmire canopy coverage method in order to classify, describe and define these plant community types. Barrens, xeric forest, sandstone glade, loess hill prairie and limestone glade plant community types were identified from an agglomerative hierarchical clustering of sites using Percent Similarity as the resemblance function and an Unweighted Pair Group method of classification. Some vegetation types were strongly related to substrate (i.e., limestone glades, sandstone glades) while others reflect successional status (i.e., xeric forests and barrens). Discriminant Analysis identified soil pH, soil depth, soil texture, amount of exposed rock, slope angle, cation exchange capacity and soil nutrients as significant discriminators among the community types. Four of the twenty-two sites are barrens, an endangered plant community in the Midwest (Heikens and Robertson 1994). Barrens are characterized by open-grown trees, primarily Quercus stellata and Quercus marilandica, and a mixture of prairie and dry woodland herbaceous species, including Schizachyrium scoparium, Danthonia spicata, Helianthus spp. and Chasmanthium latifolium, with 1-5% exposed rock, and soil depth of 8-15 cm on sandstone, shale and chert substrates. In this region, barrens appear to be timetransgressive communities that are remnants of a once more widespread community type and, unless maintained by fire or other disturbance processes, will succeed to forest.