The effects of fuels treatments on soil carbon respiration in a Sierra Nevada pine plantation Leda N. Kobziar a, * , Scott L. Stephens b a School of Forest Resources and Conservation/School of Natural Resources and Environment, Institute of Food and Agricultural Sciences, University of Florida, P.O. Box 110410, Gainesville, FL 32611-0410, USA b Department of Environmental Science, Policy, and Managements, University of California, Berkeley, 137 Mulford Hall #3114, Berkeley, CA 94702-3114, USA Received 23 June 2006; received in revised form 4 September 2006; accepted 22 September 2006 Abstract Fire-prone forests in the American west are presently slated for extensive fuels reduction treatments, yet the effect on soil CO 2 efflux rates, or soil respiration, has received little attention. This study utilizes the homogeneity of a Sierra Nevada ponderosa (Pinus ponderosa Dougl. ex P. & C. Laws)–Jeffrey pine (Pinus jeffreyi, Grev. & Balf.) plantation to investigate changes in soil respiration following mechanical shredding of understory vegetation, or mastication, in 2004; mastication coupled with prescribed burning in 2005; and burning alone also in 2005 as measured over the growing seasons from 2003 to 2005. Soil respiration, soil temperature and soil moisture were measured in two masticated stands which were burned the following year, and in one burned stand; the three of which were compared with two controls stands. Soil respiration response to treatments was detectable even though spatial variability within sites was high (coefficients of variation of 39–66%). Mastication produced short-term reductions in respiration rates, reduced soil moisture by 20%, and mitigated a year-to-year reduction in soil temperature evidenced by controls. Prescribed fire in masticated stands lowered soil respiration from 3.42 to 2.68 mmol m 2 s 1 while fire in the untreated stand raised rates from 3.41 to 3.83 mmol m 2 s 1 , although seasonal increases in control sites were greater than those in the untreated stand. Masticated then burned site soil moisture increased by 52% while soil temperature decreased over the span of the growing season. Microclimate variables were not consistently effective in explaining spatial trends. Exponential models using soil temperature and/or moisture to predict temporal trends in respiration were only significant in treated stands, suggesting that treatment implementation increased sensitivity to environmental factors. These results imply that fuels reduction practices in water-stressed forests may have important consequences for ecosystem carbon dynamics. # 2006 Elsevier B.V. All rights reserved. Keywords: Fire; Soil temperature; Soil moisture; Gas exchange; CO 2 1. Introduction Forest soils contain more than 70% of the terrestrial world’s soil carbon pool (Post et al., 1982), and thereby play a major role in global carbon cycles and their influence on climate. Yet little is known about how management practices, especially prescribed fire, affect forest soil carbon emissions. Soil surface CO 2 efflux rates, which include respiration from both autotrophic (root) and heterotrophic (soil macro- and microorganisms) sources, have been shown to account for up to 67% of total mean ecosystem respiration in a young ponderosa pine plantation in California (Xu et al., 2001). As the importance of sequestering carbon www.elsevier.com/locate/agrformet Agricultural and Forest Meteorology 141 (2006) 161–178 * Corresponding author. Tel.: +1 352 846 0901. E-mail address: lkobziar@ufl.edu (L.N. Kobziar). 0168-1923/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.agrformet.2006.09.008