Article

Wildland Fire in Oak Woodlands and Savannas of the Midwestern United States

Oak trees with a grassy understory.
Oak woodlands lack a woody midstory and have a rich understory of forbs, grasses, and sedges. La Cygne State Wildlife Area, KS.

M SHORT, Used with permission.

Distribution and General Characteristics

Oak woodlands were prominent across the landscape in the central United States. Historically, they occurred in all Midwestern states; the Central Great Plains served as the border on the west, and the Eastern Deciduous Forest to the east. Savannas and forests often intermix with oak woodlands. These woodlands are quite variable in tree density. For example, an oak woodland can cover anywhere from 30% to 100% of the canopy. Overstory trees are less dense in oak woodlands than oak forests. Oak woodlands do not have much woody midstory, and have a patchy, sparse woody understory. The open tree canopy of woodlands results in dense ground plants rich in forbs, grasses, and sedges.

Tall oak trees grow above milkweeds and other herbaceous plants.
Milkweeds and other herbaceous plants grow in the understory of a recently burned oak woodland. Marais des Cygnes State Wildlife Area, KS.

M SHORT, Used with permission

Historic Role of Fire

Oak woodlands depend on disturbances like fire to survive. Frequent fire created and maintained the open structure and make-up of the woodlands. Before European settlement, fires would burn every 3 to 20 years. Most often, they were low-intensity surface fires. In the central United States, humans were the main source of fire on the landscape before and after European settlement.

Oaks have adaptations that make them very successful at surviving fire. Oaks can resprout after fire because of their large root systems and their root collar buds below the ground. Oaks also have thick bark, which helps to protect the trees from fire. Frequent fire also benefits forbs, grasses, and sedges in the understory. On the opposite side, fire kills the above ground stems of vines, shrubs, and other woody vegetation.

Medium sized flames consume vegetation near oak trees.
Frequent fire is necessary to maintain the structure and composition of oak woodlands. La Cygne State Wildlife Area, KS.

M SHORT, used with permission

Current State and Management Actions

Today, there are fewer oak woodlands across the central United States. Oak woodlands are converting into forests due to a lack of fire. Without fire, trees that cannot survive fire, and other woody plants, begin growing in and invading woodlands. Trees become denser and the canopy begins to close. Fewer forbs, grasses, and sedges grow because less light reaches the ground. In addition, oak trees do not regrow well under a closed canopy. Oak woodlands need frequent fire to survive. Prescribed fire has many benefits for the oak woodlands – fewer trees, less woody plants, and more forbs, grasses, and sedges under the trees. The combination of tree thinning and prescribed fire can help to restore and maintain oak woodlands.

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