© 2005 Heron Publishing—Victoria, Canada
Forest thinning and soil respiration in a ponderosa pine plantation in the Sierra Nevada
Jianwu Tang (1, 2, 3), Ye Qi (4), Ming Xu (5), Laurent Misson (1) and Allen H. Goldstein (1)
1. Department of Environmental Science, Policy and Management, University of California at Berkeley, Berkeley, CA 94720, USA / 2. Department of Forest Resources, University of Minnesota, 1530 Cleveland Ave N, St Paul, MN 55108, USA / 3. Corresponding author (jtang@umn.edu) / 4. School of the Environment, Beijing Normal University, Beijing 100875, China / 5. Department of Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ 08901, USA / Received April 19, 2004; accepted July 31, 2004; published online November 1, 2004
Summary
Soil respiration is controlled by soil temperature, soil water, fine roots, microbial activity, and soil physical and chemical
properties. Forest thinning changes soil temperature, soil water content, and root density and activity, and thus changes
soil respiration. We measured soil respiration monthly and soil temperature and volumetric soil water continuously in a young
ponderosa pine (Pinus ponderosa Dougl. ex P. Laws. & C. Laws.) plantation in the Sierra Nevada Mountains in California from June 1998 to May 2000 (before
a thinning that removed 30% of the biomass), and from May to December 2001 (after thinning). Thinning increased the spatial
homogeneity of soil temperature and respiration. We conducted a multivariate analysis with two independent variables of soil
temperature and water and a categorical variable representing the thinning event to simulate soil respiration and assess the
effect of thinning. Thinning did not change the sensitivity of soil respiration to temperature or to water, but decreased
total soil respiration by 13% at a given temperature and water content. This decrease in soil respiration was likely associated
with the decrease in root density after thinning. With a model driven by continuous soil temperature and water time series,
we estimated that total soil respiration was 948, 949 and 831 g C m–2 year–1 in the years 1999, 2000 and 2001, respectively. Although thinning reduced soil respiration at a given temperature and water
content, because of natural climate variability and the thinning effect on soil temperature and water, actual cumulative soil
respiration showed no clear trend following thinning. We conclude that the effect of forest thinning on soil respiration is
the combined result of a decrease in root respiration, an increase in soil organic matter, and changes in soil temperature
and water due to both thinning and interannual climate variability.
Keywords:
carbon cycle, CO2 efflux, modeling, multivariate analysis.
