Silvicultural Methods and Successful Oak Regeneration

The oak forest type in the Central Hardwoods Region (CHR) is the largest forest type in the United States. Mature forests (>80 yr) in the CHR are dominated by oaks (Quercus spp.) regardless of site, aspect or slope. However, without proper management, oaks on intermediate and mesic sites will be replaced by more mesophytic species, such as maples (Acer spp.) and tuliptree (Liriodendron tulipifera). In general, oaks will dominate xeric sites such as ridgetops because of their resistance to drought. The key to managing a sustainable oak forest is obtaining ample advanced oak regeneration: stems greater than 1.2 m (4 feet) in height. This is accomplished by managing light intensity. Currently, forests in the HR are 1.5-2 times as dense as the forests at the time of European settlement. In the past, fire was the ecosystem process that maintained the open woodland settings which provided the proper light conditions for oak forest sustainability. Oak species evolved adaptations that allow them to withstand repeated fires, such as root development and basal sprouts. However, successful fire suppression programs in the United States have essentially removed fire from these ecosystems for the past 70 to 80 years, allowing the development of advanced reproduction of mesophytic species. Partial harvesting techniques (e.g., shelterwood, two-aged cuts) can provide the proper light for advanced oak regeneration; however, these methods also release the competing mesophytic species. Reintroduction of high-frequency, low-intensity, prescribed fires may not be successful in restoring the proper forest structure for successful oak reproduction in the short term. Fires must be intense enough to kill a few overstory trees and injuring the remainder; causing a great loss in timber value. However, the combination of partial harvests and repeated prescribed fire can create the desired forest structure for oak regeneration quickly, and may control the advanced mesophytic species. Seedlings and saplings are more susceptible to root death if prescribed fires are executed after bud break, when the starches have been transferred above-ground. Maples leaf-out before oaks, providing a window to enhance selective mortality. Prescribed fires should not be conducted for three-five years after a bumper acorn crop to give the oak seedlings time to establish adequate roots. The use of herbicide is a silvicultural tool to eliminate undesirable non-oak tree species prior to harvest and prescribed burning. It should be noted that these management techniques may be ineffective if white-tailed deer (Odocoileus virginianus) browsing is intense.

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