Upper Midwest forest–savanna transition
The Upper Midwest forest–savanna transition is a terrestrial ecoregion that is defined by the World Wildlife Fund. An oak savanna plant community located in the Upper Midwest region of the United States, it is an ecotone (a transitional area) between the tallgrass prairies to the west and the temperate deciduous forests to the east. A part of the Upper Mississippi River basin, it is considered endangered with less than 5% of the original ecosystem remaining intact, due mostly to overgrazing and conversion to agriculture. 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