Prescribed fire effects on the herbaceous layer of mixed-oak forests

In 1994, a multidisciplinary project was established to study the effects of prescribed fire on oak forests in southern Ohio. Here we describe the herbaceous layer response to fires over a 5-year period. In four study sites, treatments imposed were unburned, periodic (1996 and 1999), and annual (1996–1999) fires. Sample plots (n = 108) were stratified by an integrated moisture index. Species' frequencies were recorded annually, and a total of 452 species (97% native) were documented. Though species composition was significantly affected by fire, the effects were shown by ordination to be small in magnitude relative to overall compositional variation. Burned areas developed greater small-scale species richness as grasses, summer forbs, and seed-banking species increased in frequency; however, these changes were also not large in magnitude. Though a few species increased substantially via germination after fire, most common species exhibited frequency increases or decreases of <10% on burned units. Fire effects on vegetation were largely similar between annual and periodic burns and also among integrated moisture index classes. Direct fire effects on vegetation were limited by the dormant-season timing of burns and the resprouting of woody plants. Indirect effects were limited, as fires caused relatively minor changes in forest structure and resource availability in these long-unburned forests.