Ohio subset of Plant Communities of the Midwest ... - NatureServe

Savannas and Non-Rock Barrens: Midwestern Deep Soil Oak Savannas
Quercus macrocarpa - (Quercus alba, Quercus stellata) / Andropogon gerardii Wooded
Herbaceous Vegetation
Bur Oak - (White Oak, Post Oak) / Big Bluestem Wooded Herbaceous Vegetation
Central Bur Oak Openings
CEGL002159
DESCRIPTION: 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. 1998). 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. 1998).
In Missouri, this community was found on gentle to moderate lower- to mid-slopes of hills and ridges. Examples on
north- and east-facing slopes tended to be more mesic. In Illinois, these savannas occurred on the slopes or tops of
moraine ridges and (rarely) as islands in wetland vegetation. Soils are moderately well-drained to well-drained and
deep (40-100+ cm). The parent material is loess sometimes shallow, glacial till, gravel, or deeply weathered rock with
no appreciable rock residuum (Nelson 1985, McClain et al. 1998).
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 periods, 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 firetolerant
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.
COMMENTS: 3, MCS. This type represents the oak openings of the central tallgrass prairie ecoregion, but it is not
entirely clear how this type is different from the more northern bur oak openings type, Quercus macrocarpa -
(Quercus alba, Quercus velutina) / Andropogon gerardii Wooded Herbaceous Vegetation (CEGL002020). In eastcentral
Illinois, stands appear similar to the more northern oak openings, whereas in west-central Illinois, the
presence of species such as Quercus stellata become more common (B. McClain pers. comm. 2000). This
community has been so widely extirpated in eastern Nebraska and southern Iowa that it is considered extirpated in
those states. Most remnants are currently either called oak woodlands or small patches of tallgrass prairie. Inclusion
of Ohio stands in this type needs review.
CONSERVATION RANK: G1. This community type has virtually been eliminated. Most sites have been converted to
cropland or pasture. Other remnants are now so overgrown that the tree canopy structure is very closed, and the
ground layers are either very woody or dominated by exotics. Several remnant stands are described from east-central
Illinois, some of which are undergoing restoration (McClain et al. 1998, LaGesse et al. 1998), but high-quality ground
layers are very rare indeed.
PLANT COMMUNITIES OF THE MIDWEST – 2001. APPENDIX: ASSOCIATION DESCRIPTIONS
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