Lashley et al., 2011
RESEARCH BRIEF 7
Reducing forest canopy closure and adding prescribed fire leads to increased available deer forage and higher nutritional carrying capacity
If merchantable timber is present and a timber harvest is consistent with landowner goals, then a shelterwood harvest followed with prescribed fire can be an effective and economically sound plan to increase available forage for white-tailed deer
A fire return interval of 3 – 5 years may maintain forage availability, soft/hard mast production, and fawning cover
If both the deer population and forest are managed, then food plots may not be necessary for appropriate forage availability
Forest understory composition and structure greatly affect habitat quality for white-tailed used in pine systems, both with and without prescribed fire to reduce competition from hardwood species midstory trees; and greenbrier, lilies, poison ivy, Virginia creeper, wild grape, blackberry, blueberry, panic-grasses, and deer (Odocoileus virginianus, hereafter: deer). The closed-canopy conditions of many eastern United States oak forests, along with chronic over browsing by deer, frequently lead to reduced nutrition availability. Forest understories often do not rebound following deer density reduction without increased sunlight entering through the canopy to stimulate groundcover vegetation. Historic open forest conditions have been attributed to frequent low-intensity burning. In modern management, forest canopy closure can be reduced through silviculture treatments (e.g., shelterwood, retention cuts, and prescribed fire). Understory broadcast herbicide treatments are commonly used in pine systems, both with and without prescribed fire to reduce competition from hardwood species and increase herbaceous groundcover. The objectives of this study were to describe how prescribed fire and herbicide treatments affect forage availability for white-tailed deer following forest canopy disturbance in upland hardwoods.
This study took place at Chuck Swan State Forest and Wildlife Management Area (CSF) in northeastern Tennessee. Four upland hardwood stands were each divided into 12 two acre treatment units. A variety of oak and hickory species, as well as sugar maples, yellow-poplar, and American beech comprised the overstory. Sassafras, dogwood, pawpaw, and sourwood were common midstory trees; and greenbrier, lilies, poison ivy, Virginia creeper, wild grape, blackberry, blueberry, panic-grasses, and violets commonly populated the understory (scientific names omitted for brevity, see the full publication for these and more details). Pre-treatment basal area ranged from 87 to 105 ft2/acre. CSF deer densities were not considered excessive, reported as 25 -30 per square mile, with an average annual deer harvest of 8 – 10 per square mile.
The authors measured forage availability and calculated nutritional carrying capacity (NCC) following different silvicultural treatments. Experiment treatments included: shelterwood (S), shelterwood with fire (SF), retention cut with fire (RF), retention cut with herbicide application (RH), retention cut with herbicide and fire (RHF), fire only (F), and control (C). Shelterwood refers to the silvicultural method which involves multiple partial commercial harvests, leaving trees in the overstory (residuals) to provide shelter for developing regeneration. Shelterwood
treatments reduced basal area to approximately 56 ft2/acre, occurred in June/July, and were burned 4 years later. Trees retained in the overstory were not selected based on wildlife value. Retention cutting refers to non-commercial thinning of undesirable species. Soft and hard mast species (red/white oaks, blackgum, black cherry, American beech) were retained for wildlife value, and basal area was also reduced to 56 ft2/acre. Trees frequently removed included red/sugar maple, sourwood, and yellow poplar. Retention cuttings occurred in February and were burned three times over the following 6 years. Two retention cut units per stand were treated with a broadcast herbicide (triclopyr) 5 years post cut, one of which was burned one year after herbicide treatment, resulting in one RF and RHF treatment units. All fire treatments were low-intensity (6 – 18 inch flame lengths) and occurred during the early growing season (April).
Forage availability was measured and NCC estimates were calculated (deer-days per hectare) during two sampling periods, July – September 2007 and 2008 (6 and 7 years after cutting). NCC estimates following silviculture treatments were compared to those of warm-season forage food plots to evaluate their suitability in managed forests. All costs incurred by treatments (labor for different treatments, herbicide, seed, etc.) were tracked for comparison (cost per kilogram of forage production).
Canopy treatments with prescribed fire (RF and SF treatments) increased forage availability significantly (>3 X) over the control units; all treatments increased NCC compared to the control units seven years post-harvest. Understory broadcast herbicide treatment in retention cut units did not affect species composition or NCC, either 1 or 2 years post-treatment.
Although herbicide treatment killed woody stems in the understory, seedlings from surrounding trees colonized quickly and replaced those that were killed within 1 – 2 years. Shelterwood treatments provided monetary income, and RH and RHF were the least economical of all treatments. RF was similar in cost (per kilogram of forage) to warm-season forage plantings. Repeated burning can increase NCC, though its important to note that this study conducted repeated prescribed fires with a relatively short return interval (2 – 4 years). Other studies have shown
that one fire has short-lived effects (see Wood 1988 and Shaw et al. 2010 for more information about this). Repeated burning without reducing canopy closure did increase forage availability over control, but did not reduce woody composition, nor did it increase herbaceous composition. Food plots produced more available forage than all treatments, except for retention cut with fire (RF) 2 years post-treatment. The authors suggest forage food plots should be considered a tool to buffer deer browsing pressure while population reduction is implemented, not as a means to maintain artificially high deer populations.
Marcus A. Lashley, Craig A. Harper, Gary E. Bates, and Patrick D. Keyser. The Journal of Wildlife Management, 75(6):1467-1476; 2011
FOR FURTHER READING
Shaw, C.E., C.A. Harper, M.W. Black, and A.E. Houston. 2010. Initial effects of prescribed burning and understory fertilization on browse production in closed-canopy hardwood stands. Journal of Fish and Wildlife Management. 1(2):64-72.
The Oak Woodlands and Forests Fire Consortium seeks to provide fire science to resource managers, landowners, and the public about the use, application, and effects of fire in the region. www.oakfirescience.com
This research brief was funded by The Joint Fire Science Program. http://www.firescience.gov/