The biggest threat to habitat quality in southern Wisconsin is buckthorn. Buckthorn is an aggressive European species that invades woodlands. Along with exotic honeysuckle, it is the first to leaf out in spring and the last to drop leaves in the fall. As a result it initially shades out ground covers like sedges and wildflowers. As it takes over, native shrubs and young trees will be affected. Eventually, regeneration of oaks and hickories will be greatly disrupted. As the mature oaks die, there will be no young oaks to succeed them and eventually the woodland will revert to a brushy wasteland dominated by buckthorn, honeysuckle and a few straggling elms, box elder, and cherry.
Deer typically do not use a buckthorn woods for cover because of the lack of ground covers. While a buckthorn thicket may look dense to us, to a coyote, it looks like an umbrella. Under the canopy is bare soil. Deer make very little use of buckthorn for food as it is generally unpalatable (Loos, 2013).
Deer thrive in a diverse landscape surrounding a forest matrix. In southern Wisconsin, the criteria are as follows:
Open oak woods with healthy ground covers and multiple age classes of trees and native shrubs
Adjacent meadows or openings with legumes and wildflowers
Brushy thickets of native shrubs and young trees and away from roads and along the edges between forest and meadow
Areas of tall grasses.
Therefore, a well-managed property will ensure that these structural elements exist in some form. On a given property, it may be possible to identify areas that provide different needs which already exist. It is equally likely that developing good habitat will require an active approach of planting trees and shrubs, eliminating invasive species, and introducing prescribed fire.
The oaks are the cornerstone species in southern Wisconsin. While the ancient giant white and burr oaks that are found throughout the region are beautiful to behold, the landowner should look more carefully. Are there young oaks present? Or, do you see buckthorn, box elder, cherry and elm growing in the understory? If young oaks are not present, your forest is on a negative long term trajectory. It is possible to bring an oak forest back to a healthy state, but it requires time and attention and the skills of a talented professional.
In a healthy oak woodland, deer find shelter and food. The oaks create the matrix around which a property owner can establish openings, meadows, prairies and food plots. An unhealthy woodland will provide poor cover and little food. Meadows, prairies, and food plots will not be attractive to deer without the woodland matrix.