Upper Midwest forest–savanna transition
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Through Agriculture, Hectare and Biodiversity
Fire and disturbance
Historically, wildfire has been the primary driver and determinant of the forest dynamics in the plant community. Due to this the resulting canopy structure has been relatively sparse (the basal area ranges approximately from 4 to 29 meters hectare−1). Presence and biodiversity of plant species is largely controlled by the frequency of fire. Typical tallgrass prairie vegetation such as grasses, forbs, shrubs, and sedges, increase with an increase in the amount of fire, whereas tree density and basal area decrease.
After European American settlement and the abandonment of fire as a land management regime, most savannas have been converted into closed canopy woodlands, with shade tolerant and fire-intolerant species dominating rather than the historic primary and secondary succession species dependent on fire.
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Species distribution
Trees:
- Quercus macrocarpa (Bur oak)
- Tilia americana (American basswood)
- Acer saccharum (Sugar maple)
- Quercus rubra (Red oak)
Intact habitat
A survey in 1985 concluded that only 26 square kilometres (10 sq mi) of oak savanna remain, roughly 0.02% of what is estimated to have existed at the time of European settlement. Highly dispersed and fragmented, none of the present habitat falls under the designation of National Forests but comes under the administration of the states' Department of Natural Resources organizations or federal entities such as the Fish and Wildlife Service. Remaining intact habitat areas include:
- Devil's Lake State Park, on the Baraboo Range in south-central Wisconsin
- Savanna Army Depot in extreme northwestern Illinois
- Parts of the Upper Mississippi River National Wildlife and Fish Refuge in eastern Minnesota and western Wisconsin
- Richard J. Dorer Memorial Hardwood State Forest in the Driftless Area of southeastern Minnesota
- Whitewater State Park, also in the Driftless Area
- Necedah National Wildlife Refuge in central Wisconsin
- Horicon Marsh in southeastern Wisconsin
- Kettle Moraine State Forest in southeastern Wisconsin