© 2004 Heron Publishing—Victoria, Canada
Component carbon fluxes and their contribution to ecosystem carbon exchange in a pine forest: an assessment based on eddy
covariance measurements and an integrated model
K.-Y. Wang (1, 2, 3), S. Kellomäki (2), T. S. Zha (2) and H. Peltola (2)
1. Chengdu Institute of Biology, Chinese Academy of Sciences, P.O. Box 416, 610041 Chengdu, P.R. China / 2. Faculty of Forestry, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland / 3. Author to whom correspondence should be addressed (kaiyun@joensuu.fi) / Received March 14, 2003; accepted June 2, 2003; published online December 1, 2003
Summary
We used a combination of eddy flux, canopy, soil and environmental measurements with an integrated biophysical model to analyze
the seasonality of component carbon (C) fluxes and their contribution to ecosystem C exchange in a 50-year-old Scots pine
forest (Pinus sylvestris L.) in eastern Finland (62°47′ N, 30°58′ E) over three climatically contrasting years (2000–2002). Eddy flux measurements
showed that the growing Scots pine forest was a sink for CO2, with annual net C uptakes of 131, 210 and 258 g C m–2> year–1 in 2000, 2001 and 2002, respectively. The integrated process model reproduced the annual course of daily C flux above the
forest canopy as measured by the eddy covariance method once the site-specific component parameters were estimated. The model
explained 72, 66 and 68% of the variation in daily net C flux in 2000, 2001 and 2002, respectively. Modeled annual C loss
by respiration was 565, 629 and 640 g C m–2 year–1, accounting for 77, 77 and 65% of annual gross C uptake, respectively. Carbon fluxes from the forest floor were the dominant
contributors to forest ecosystem respiration, with the fractions of annual respiration from the forest floor, foliage and
wood being 46–62, 27–44 and 9–10%, respectively. The wide range in daily net C uptake during the growing season was largely
attributable to day-to-day fluctuations in incident quantum irradiance. During just a few days in early spring and late autumn,
ecosystem net C exchange varied between source and sink as a result of large daily changes in temperature. The forest showed
a greater reduction in gross C uptake by photosynthesis than in C loss by respiration during the dry summer of 2000, indicating
that interannual variability in ecosystem net C uptake at this site was modified mostly by summer rainfall and vapor pressure
deficit.
Keywords:
Finland, interannual variation, Pinus sylvestris, process modeling, Scots pine, sink, source.
