Clayey Upland Savannas

Description

The reference state is a mesic to wet-mesic savanna community on clayey soils that exhibits a diversity of native grasses and forbs along with scattered oak species. Plant community structure and composition within are variable and dependent upon the impacts of drought, grazing, and fire events. Fire was historically present on these sites but to a lesser degree than the prairie ecological sites. This reduced occurrence of fire resulted in a plant community that included woody shrubs and scattered trees. A secondary trigger for maintenance or conversion of this ecological site is grazing. Intensive grazing can reduce the extent of highly palatable species thereby allowing the growth of less desirable plants to increase.

Fire frequency, periods of drought, and grazing will create variability in the plant community. A high fire frequency will create a shrubby prairie with a reduction in woody species. A longer fire free interval will allow trees to increase and the community will exhibit a bur oak-northern red oak savanna structure. An absence of natural fire will transition the site closer to a mixed oak woodland. Characteristic vegetation in the reference savanna state includes bur oak, northern pin oak, American hazelnut, leadplant, and big bluestem. Other prairie grasses and native forbs will also be present within the reference plant community. High-quality, untilled areas of the Clayey Upland Savannas ecological site are uncommon in MLRA 103 as most sites have been transitioned to agricultural production.

Submodel

Description

Soil tillage is the primary mechanism to transition a site to the Tillage State. In this state, dynamic soil properties such as bulk density, structure, organic carbon content, and saturated hydraulic conductivity are altered by agricultural practices. Certain practices can mitigate the impacts of traditional agricultural practices on soil health. Conservation tillage minimizes soil disturbance and can improve soil structure and overall soil health. Corn or soybean plantings and a cover crop rotation can build soil structure, improve infiltration rates, reduce runoff and erosion, and protect water quality.

Some areas in this ecological site are not appropriate for intensive crop production due to slope. Where the gradient exceeds 20 percent row crop production is not feasible due to limitations on farm machinery.

A few areas have been seeded back to warm-season or cool-season grasses. Under conservation programs such as the NRCS Conservation Reserve Program (CRP), previously tilled areas have been converted to warm-season grasslands. Native forbs are commonly included in seed mixes to benefit wildlife and pollinators. Although highly beneficial to wildlife, these sites generally lack the diversity of native plant species that occurs in the Reference State. Cool-season grasses are also feasible. Species selection will depend on the landowner’s objectives and site specifics.

Most areas in this state will remain in use for crop production in the foreseeable future – primarily in an intensive corn and soybean rotation.

Submodel

Description

The Degraded Oak Woodland is characterized by a disturbed woodland condition. Characteristics of this site include the dominance of trees (no longer a true savanna community) and the presence of invasive plant species. Bur oak and other hardwood species have increased. Invasives, such as Kentucky bluegrass and common buckthorn, are often dominant the understory. As the tree and shrub density increases, the ground layer plant diversity transitions to more shade-tolerant forest species.

Submodel