Oak savanna restoration: Oak response to fire and thinning through 28 years

Abstract

We used a small plot study on Pushmataha Wildlife Management Area in southeast Oklahoma to determine the efficacy of fire frequency and thinning as management tools for restoration of oak savanna, oak woodlands, pine-bluestem woodlands, and pine savanna for application on a landscape scale. On selected experimental units, we initially reduced stand density to favor either oak canopy dominance or pine dominance to near presettlement stand density. Thinned stands were then subjected to 0-, 4-, 3-, 2-, and 1-year late dormant season (late February - early April) fire frequency regimes for 26 years. For comparison, we withheld control units from treatment and also included unthinned but with 4-year burn regime treatment units. We included two additional thinning treatments, the oak-savanna and pine-bluestem treatments, both with annual burn regimes; the oak-savanna had all pine removed (approximately 50 percent of the basal area) and the pine-bluestem had half of the hardwood thinned (approximately 25 percent of the pre-treatment basal area). We compared mortality rate, acorn production, and growth response of selected post oaks and blackjack oaks. We also assessed nutrient content of post oak acorns to determine prescribed fires potential influence on nutrient status. We found a differential response by species to presence or absence of fire; but all selected trees responded favorably in diameter growth to thinning. Blackjack oak mortality was highest on unthinned and unburned sites versus any of the fire treatments because of hypoxylon cancer, an indirect result of high stand density (competition) and drought stress. Mortality of post-oaks was related to initial burns, and to some extent, cumulative effects of fire frequency interacting with fuel loads. Although thinning efforts on a landscape level were applied on the Wildlife Management Area beginning in 1978, fire frequency was >4-year intervals, inadequate for maintenance of savanna and woodland structure. Based on small plot study results we begin landscape application of frequent fire on a 1-3 year cycle in 1997 and increased thinning in 1999-2001. Restoration thinning and a more focused burn regime was applied in a site specific manner on the landscape in 2008 through present. Woodland-grassland and forest-shrub obligate songbirds, white-tailed deer, and Rocky Mountain elk have responded favorably.

Parent Publication

• Proceedings of the 4th fire in eastern oak forests conference

Citation

Masters, Ronald E.; Waymire, Jack R. 2012. Oak savanna restoration: Oak response to fire and thinning through 28 years. In: Dey, Daniel C.; Stambaugh, Michael C.; Clark, Stacy L.; Schweitzer, Callie J., eds. Proceedings of the 4th fire in eastern oak forests conference; 2011 May 17-19; Springfield, MO. Gen. Tech. Rep. NRS-P-102. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 69-91.