PROTECTING WISCONSIN'S BIODIVERSITY

 
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Oak Barrens

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Photo by Armund Bartz

 

Counties with Mapped NHI Occurrences

Black oak (Quercus velutina) is often the dominant tree in this fire-adapted savanna community of xeric sites, but white oak (Quercus alba), bur oak (Quercus macrocarpa), northern pin oak (Quercus ellipsoidalis), and occasionally red oak (Quercus rubra), may also be present. Canopy is variable but is typically between 5% and 60% in good-quality sites.

The tall shrub layer is often dominated by oak saplings. American hazelnut (Corylus americana) and serviceberries (Amelanchier sp.) are also frequently present, while smooth sumac (Rhus glabra), gray dogwood (Cornus foemina), and prickly-ash (Zanthoxylum americanum) may be present in more degraded sites. The low shrub layer often contains members of the heath family such as huckleberry (Gaylussacia baccata), blueberries (Vaccinium angustifolium and V. myrtilloides), and bearberry (Arctostaphylos uva-ursi) along with species such as sweet-fern (Comptonia peregrina). Bracken fern (Pteridium aquilinum) may also be common at some sites.

The groundlayer is typically dominated by graminoids such as Pennsylvania sedge (Carex pensylvanica), savanna running sedge (Carex siccata), poverty grass (Danthonia spicata), June grass (Koeleria macrantha), little bluestem (Schizachyrium scoparium), and panic grasses (Dichanthelium spp.) along with sand-loving species such as three-awn grasses (Aristida spp.), fall witch grass (Digitaria cognata), and love grasses (Eragrostis capillaris and E. spectabilis). In sites with a lack of fire, Pennsylvania sedge may become so dense it forms a near monoculture and excludes other species. Indicator forbs in good quality sites include leadplant (Amorpha canescens), false toadflax (Comandra umbellata), western sunflower (Helianthus occidentalis), stiff sunflower (H. pauciflorus), round-headed bush-clover (Lespedeza capitata), rough blazing star (Liatris punctata), wild lupine (Lupinus perennis), dotted horsemint (Monarda punctata), goat's rue (Tephrosia virginiana) and spiderwort (Tradescantia ohioensis). Additional indicator species can be found in the Coarse-level Monitoring Protocol for Oak Barrens (O’Connor et al, 2019).

Distribution of this community is mostly in southwestern, central, and west central Wisconsin. Barrens communities occur on several landforms, especially outwash plains, lakeplains, and on the broad sandy terraces that flank some of the major rivers of southern Wisconsin. Soils are usually excessively well-drained sands, though thin-soiled, droughty sites over bedrock can also support this community.

 
 
 
Key Environmental Factors

Oak barrens are most similar to pine barrens, with the former being dominated by oaks and the latter dominated by pines. In general, prairie species are better represented in the more oak-dominated barrens to the south, and pines and some of their characteristic associates are more prominent in the north. However, there is some overlap between the two communities, especially in some sites along the Lower Wisconsin River (e.g., Gotham Jack Pine Barrens SNA), and in portions of central Wisconsin (e.g., Juneau County). Frequently burned "brush" barrens in northwest Wisconsin are intermediate between the two communities but are typically lumped with pine barrens due to their more northerly location and ground flora, despite often being dominated by repeatedly top-killed shrubby oak saplings, also known as oak grubs.

Oak barrens can be distinguished from sand prairies by their greater cover of oak trees. Oak barrens also share similarities to sand barrens. However, sand barrens are believed to have originated from human disturbance to areas previously dominated by a different community type, typically forests on sandy plains. After clearing and failed attempts at agriculture, these sites were abandoned and reverted to weedy barrens species. Disturbance from off-road vehicles can also lead to the development of sand barrens.

Bracken grasslands of northeast Wisconsin contain barrens elements like Pennsylvania sedge but are characterized by bracken fern, scattered shrubs, depauperate forbs, and are usually embedded in a matrix of aspen forests. Similar to sand barrens, bracken grasslands are believed to be largely the result of large-scale human disturbance following the cut-over and repeated post-logging fires on nutrient-poor sandy soils.

Oak barrens also share similarities with the drier side of oak openings, particularly where they occur along sandy river terraces and shallow sandy soil over sandstone bedrock. In these settings, tree species are the main differentiating factor, with oak barrens typically dominated by black or Hill's oak, sometimes with pines co-dominant. In contrast, oak openings tend to be dominated by bur oak or occasionally white oak, and rarely by swamp white oak in wet-mesic settings. In addition, while they share some prairie flora, oak barrens are typically dominated by species of dry sandy sites as described above, while oak openings support more classic prairie species.

Wildlife Action Plan

Species of Greatest Conservation Need (SGCN) are associated with habitats (or natural communities) and places on the landscape. Understanding relationships among SGCN, natural communities and ecological landscapes help us make decisions about issues affecting SGCN and their habitat and how to respond. Download the Wildlife Action Plan association score spreadsheet to explore rare species, natural communities and ecological landscape associations

Conservation actions respond to issues or threats, which adversely affect species of greatest conservation need (SGCN) or their habitats. Besides actions such as restoring wetlands or planting resilient tree species in northern communities, research, surveys and monitoring are also among conservation actions described in the Wisconsin Wildlife Action Plan because lack of information can threaten our ability to successfully preserve and care for natural resources.

For more information, contact

Ryan O'Connor
Conservation Biologist
tel:+1-608-354-2383