Indiana barrens are defined as terrestrial ecosystems where edaphic drought and infertility prevail. Causative factors for dryness include excessive drainage due to soil particle size (e.g., sand), southern or western aspect of site, excessive steepness of slope, presence of a hardpan or bedrock at or near surface, and fire. Soil chemistry is an important regulating factor of barrens vegetation, as most barrens are nutrient deficient. Barrens vegetation consists of a varied admixture of shrubs, small trees, grasses and forbs adapted to drought; such vegetation is commonly in the form of open scrub, but physiognomy alone does not define the community, because barrens may range from mostly graminoid to possessing a closed canopy (this dependent on substrate, and fire history or other environmental perturbations). A rather consistent suite of species characterize each type of Indiana barrens, depending on the type of substrate and the geographic location within the state. Chert, limestone, sandstone, siltstone, gravel, clay, and sand are types of barrens known to occur in Indiana.