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

Abstract

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 degrees 47' N, 30 degrees 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.

Climatic versus biotic constraints on carbon and water fluxes in seasonally drought‐affected ponderosa pine ecosystems

“…Some studies of forests suggest that R e varies more than GPP on an annual basis [ Valentini et al , 2000; Janssens et al , 2001; Valentini et al , 2003]. Other studies indicate that GPP varies more than R e [ Arain et al , 2002; Aubinet et al , 2002], while other studies show that the interannual variation of R e and GPP is roughly the same [ Barford et al , 2001; Suni et al , 2003; Wang et al , 2004]. Our results are important because they suggest that in forests with similar climate, the relative importance of R e and GPP may depend upon the development stage of the forest.…”

Fertilization effects on forest carbon storage and exchange, and net primary production: A new hybrid process model for stand management

“…Climate exerts a strong influence on the seasonal patterns in NEP (Wang et al, 2004). Simulated NEP for CW plots for 1996 and 1997 suggest that autumn and winter, with low temperatures but favorable incident shortwave radiation, may be important periods for C uptake as they influence the annual C budget (Fig.…”

“…Lai et al, 2002) has provided a means to validate short-term (days to years) model outputs (e.g. Wang et al, 2004). However, upscaling processes that occur at small-scales (leaves) to large spatial and temporal-scales (ecosystems) is subject to large errors due to functional non-linearity and heterogeneity in the distribution of processes (Jarvis, 1995).…”

Characteristics of soil CO2 efflux variability in an aseasonal tropical rainforest in Borneo Island

“…The efflux of CO 2 from soil surface (soil respiration) is one of the major components of ecosystem C cycling, contributing 50-95% of total ecosystem respiration (e.g., Law et al 1999;Janssens et al 2001;Wang et al 2004;Yuste et al 2005). The main sources of CO 2 are considered to be root and soil microbial respiration (Hanson et al 2000;Kuzyakov 2006).…”