Physiognomy and Structure: No Data Available

Floristics: The vegetation is dominated by scattered trees with spreading canopies and a continuous herbaceous layer. This community has an average tree canopy between 10 and 60%, typically strongly dominated by Quercus macrocarpa. One study reports that densities of trees >25 cm dbh may have ranged from 40-75 stems/ha (McClain et al. 1998b). Quercus alba is a common secondary species, whereas Carya ovata, Quercus imbricaria, and Quercus stellata may be present in low abundance. There may be shrubby areas within the community, but these were, at least historically, relatively sparse. Common species may include Corylus americana and Prunus serotina. The herbaceous vegetation is thought to be similar to that of mesic prairie, but few extant stands remain. Dominant grasses could include Andropogon gerardii, Schizachyrium scoparium, and Sorghastrum nutans (Nelson 1985, McClain et al. 1998b).

Dynamics:  Fire and grazing are the two important natural disturbances that shaped this community. Fire appears to be the most important of these two, since woody growth release was not commonly noted until fire suppression began in the early European-settlement period, well after the period of massive reduction of bison and elk herds (Pruka 1994).

Fire eliminates intolerant tree species. Fires in areas of oak opening were infrequent enough to allow certain species (Quercus alba, Quercus macrocarpa, Quercus velutina, and occasionally Carya spp.) to reach a fire-resistant size. Oak openings may have been most typical on morainal ridges that were, at least in part, surrounded by wetlands that would only burn during dry years, thereby allowing tree establishment and persistence. Quercus alba, being less fire-tolerant than Quercus macrocarpa, is often limited to areas that supported less grass fuel (and hence less intense/frequent fires), and it is usually found on hillier topographies or mesic bottoms that are slightly less prone to fire. In flat, upland, mesic areas, with their higher fuel loads, only Quercus macrocarpa was able to persist, if at all.

Before European settlement, fires were frequently and intentionally set by Native Americans to create conditions favorable for travel and for supporting large game. This may have led to larger expanses of savanna than would have occurred without human presence. It also probably encouraged savanna formation farther into the humid east than would have occurred without human-set fire (Pyne 1982). Fires in the central tallgrass prairie region could easily spread across an entire county, and some in east-central Illinois were severe enough to convert savannas to prairie (B. McClain pers. comm. 2000), perhaps forming what farther north in Wisconsin has been called ''brush prairie'' (Curtis 1959). Several authors have suggested that Native American fires were most often set in the fall (Swink and Wilhelm 1994, Chapman 1984, Schwegman and McClain 1985). Grimm (1984) noted that several early European settlers recorded summer burns ignited by lightning.