Assessment of Forest Management Influences on Total Live Aboveground Tree Biomass in William B. Bankhead National Forest, Alabama

Forests contain a large amount of carbon (C) stored as tree biomass (above and below ground), detritus, and soil organic material. The aboveground tree biomass is the most rapid change component in this forest C pool. Thus, management of forest resources can influence the net C exchange with the atmosphere by changing the amount of C stored, particularly in landscapes dominated by forests, such as in the southeastern United States. Our work focuses on the influence of prescribed burning and thinning on total live aboveground tree (TLAT) biomass in the William B. Bankhead National Forest, Alabama. We implemented a large-scale study that involved a factorial arrangement of three levels of thinning (heavy thin to 11 m ha basal area; light thin to 15 m ha basal area; and no thin) and three prescribed fire intervals (no fire, 3-year return, 9-year return). Biomass was assessed among treatments using allometric equations related to tree species and diameter. Pre-treatment stands ranged from 117 to 137 Mg ha TLAT biomass. Overall burning showed no significant influence on TLAT biomass. All but one treatment (light thin, no burn) had a higher rate of TLAT biomass gain post-treatment than the control. Control had an average yearly TLAT biomass gain of 4 percent per year, with the thinned treatments having averages ranging from 5 percent to 7 percent per year. Our results provided a first step for reliable and accurate measurement of biomass potential, which is increasingly important, particularly for sustainable forest management, monitoring global climate change, and forest productivity. INTRODUCTION Over the last 30 years, carbon dioxide (CO2) emissions from the use of fossil fuels has grown at an average rate of 1.9 percent per year (Nabuurs and others 2007). Mitigation of atmospheric CO2 requires an approach that combines CO2 emission reductions with increased CO2 storage (Birdsey and others 2006, D’Amato and others 2011, Malmsheimer and others 2008). Forests contain a large amount of carbon (C) stored as tree biomass (above and below ground), detritus, and soil organic material (Fahey and others 2010) and as such have the potential to play a crucial role in the mitigation of atmospheric CO2 through increased C storage (D’Amato and others 2011, Nabuurs and others 2007). Areas of deforestation, such as tropical rainforests, can be large sources of C (Canadell and Raupach 2008), and areas of growing forest can be large C sinks. It has been estimated that forest ecosystems contain approximately half of the total terrestrial C pool (Dixon and others 1994) and, at a global scale, forests sequester 1.3 to 4.2 GtCO2-equivalents (1.3 to 4.3 billion tonnes) per year (Nabuurs and others 2007). Currently in the United States, forests sequester enough C each year to offset 10 percent of annual emissions from fossil fuels (Birdsey and others 2006). In the southeastern United States, forests make up over 60 percent of the land area (Wear and Greis 2012). The most rapid component of forest change in this C pool is the aboveground tree biomass (Fahey and others 2010). Thus, management of forest resources can influence net C exchange with the atmosphere by changing the amount of C stored (Canadell and Raupach 2008, Malmsheimer and others 2008). It has been suggested that net C sequestration can theoretically be maximized by maintaining the landscape at a maximal stage of net ecosystem productivity (Fahey and others 2010), and that forest management targets both mitigation (using the forest to sequester C) and adaptation (increasing forest health and resiliency) (Malmsheimer and others 2008). Changing species composition, rotation length, fire, harvest management practices, and other