Plant succession in the Cross Timbers eco-region moves from grassland toward a closed canopy forest if left free from disturbances such as fire. Cross Timbers woodlands are usually comprised of oaks, Eastern red-cedar, elms, hackberry, greenbrier, poison ivy and several other woody plants. As consultants, we work with several managers who tell us that these closed canopy woodlands are left undisturbed because they are good habitat for wildlife, particularly white-tailed deer. In reality, these areas typically only fulfill a small portion of the habitat requirements of white-tailed deer.
Usually, very little herbaceous vegetation grows in mature Cross Timbers woodlands (Figure 1). About 44 percent of a white-tailed deer's annual diet is comprised of forbs, and, as you can see in Figure 1, very few forbs are available. About 41 percent of a white-tailed deer's annual diet is comprised of browse (woody plant parts), with acorns making up 8 percent of their annual diet. At first glance, it looks like ample woody vegetation exists for white-tailed deer to eat, but most of it is too high and, thus, unavailable for them to consume. These mature woodlands can produce a lot of acorns, which are very important to white-tailed deer. However, acorns are only available a few weeks out of the year.
One way to increase the available food for white-tailed deer is to introduce a little sunlight. A chainsaw, skid loader, bulldozer, herbicide or fire can reduce the amount of overhead cover and allow more sunlight to reach the ground to promote more herbaceous vegetation. The pictures in Figures 1 and 2 were taken at the same location and angle. Figure 1 was taken on Dec. 4, 2013, and Figure 2 was taken on Sept. 30, 2014. In between taking the two photos, the site was thinned with a chainsaw, leaving only a few oak trees. Stumps were not treated with herbicide to allow them to resprout so they can be browsed by deer. The site was also burned in March as part of a larger prescribed burn. There was no seed added to the soil because most sites have ample seed in the soil bank from when these sites were once prairie.
Usually, prescribed burning alone will not return such dramatic results, due to the low intensity of ground fires fueled only by tree leaves during typical prescribed burning conditions. Herbicides and mechanical treatments are usually needed to remove enough trees to get adequate results. Prescribed burns can then be used to maintain the openings. Mature Cross Timbers woodlands provide cover for white-tailed deer and are used by other animals such as woodpeckers and raccoons, so not all of the area should be thinned. Small openings can be created throughout a property to make more usable space for white-tailed deer and other animals. The openings can also be grazed by cattle since they are now grazeable acres, while the closed canopy woodlands were not.
Managers need to understand the habitat requirements of the animals that they want to promote and manage accordingly. Creating openings provides more edge and usable space for many animals.