Short-Term Effects of Experimental Burning and Thinning on Soil Respiration in an Old-Growth, Mixed-Conifer Forest

To understand the roles of forest management practices in meeting the goals of forest sustainability and CO2 sequestration, we evaluated the effects of burning and thinning treatments on soil respiration and soil environments in an old-growth, mixed-conifer forest in California’s southern Sierra Nevada. Six experimental treatments with two levels of burning and three levels of thinning were implemented across three dominant patch types: closed canopy (CC), Ceanothus shrub (CECO), and open canopy (OC). We measured soil respiration rate (SRR), soil temperature (T10), moisture (Ms), and litter depth (LD), in the summers of 2000 and 2002. Soil total C and total N were measured in 2002. SRR was significantly different among the three patch types. In 2000, SRR was 0.75, 0.86, and 0.26 g CO2 m -2 hr in CC, CECO, and OC, respectively. In 2002, SRR was 0.79, 0.97, and 0.44 g CO2 m hr in CC, CECO, and OC, respectively. The analysis of variance indicated that burning and thinning significantly affected soil respiration and soil environments. In particular, SRR significantly decreased in burned CECO patches but increased in unburned and thinned CECO. SRR in CC and OC did not significantly change. T10 and Ms increased, whereas LD and soil C decreased in treated patches. We also developed preand posttreatment exponential models to predict SRR using soil environmental variables. The effects of burning and thinning on soil CO2 efflux and soil environments imply that forest carbon pools would be reorganized with widespread application of these forest management practices. Soil respiration, including autotrophic and heterotrophic respiration, plays an important role in global carbon cycling (Schlesinger and Andrews 2000). While it is well known that soil CO2 efflux is sensitive to soil environmental variables, such as soil temperature and moisture, texture, pH, total C, and total N (Singh and Gupta 1977, Orchard and Cook 1983, Raich and Schlesinger 1992), forest management activities, such as burning and thinning, can also change soil environments and significantly affect soil CO2 efflux (Raich and Schlesinger 1992, McGuire and others 1995, Schlesinger and Andrews 2000). Subsequently, sound scientific evidence is necessary to understand the impacts of forest management activities on soil respiration and soil environments (Wildung and others 1975, Parker and others 1983, Raich and Schlesinger 1992, McGuire and others 1995, Klopatek and others 1998). In the Sierra Nevada Mountains, prescribed burning and thinning are applied often to restore historical forest structure and composition (North and others 2002). Prescribed burning impacts soil environments by consuming accumulated litter and soil organic matter, whereas mechanical thinning compacts soil, causing a decrease in soil aeration and restricting root growth and microbial activities (Poff 1996). These forest management activities could significantly alter soil CO2 efflux. However, the effects of burning and thinning on soil CO2 efflux is not well known in this area. Our study was designed to understand the effects of prescribed burning and thinning on soil respiration and soil environments based on two-year field measure