Radiation, temperature, and leaf area explain ecosystem carbon fluxes in boreal and temperate European forests

Abstract

[1] We analyzed measurements of net ecosystem exchange of CO 2 (NEE) over 15 European forests (the EuroFlux data set) to investigate which climate and forest characteristics explain temporal and intersite variations in NEE and its components, gross primary production (GPP) and respiration (R). Informed stepwise regression was used to derive a parameter-efficient, empirical model that was consistent with process knowledge. The resulting model required seven site-specific parameters to describe flux behavior at different temporal scales as a function of radiation, temperature, and air humidity. The interpretation appeared robust despite method and data uncertainties, although the data set was probably biased toward well-watered boreal and temperate European forests. Radiation, temperature, and leaf area (through forest assimilation capacity) appear to be the main drivers of the observed temporal and intersite variation in gross primary production, ecosystem respiration, and net ecosystem exchange.

Summertime influences of tidal energy advection on the surface energy balance in a mangrove forest

“…The lack of energy budget closure was 20 % for various terrestrial ecosystems (Wilson et al, 2002) but was ∼ 50 % in tidal marsh (Moffett et al, 2010) where advection and sea breezes likely contributed to lack of closure. In other wetlands, such as rice paddy fields, only 5 % to 9 % of the energy budget remained unaccounted (Tsai et al, 2007;Gao et al, 2003). In this study, lack of energy budget closure was 25 %, 14 %, and 17 % based on the 30-min and daily sum regressions and 10-day cumulative sum methods, respectively.…”

“…Sources of water other than tidal flows have been shown to serve as heat capacitors in flooded and coastal ecosystems. Heat stored in the water column during the daytime in a rice paddy in Taiwan (Tsai et al, 2007) represented 7 % of available energy, on average, during a 10-day period in April. Determined from energy budget measurements over a coral reef flat in Australia (McGowan et al, 2010), shallow waters served as a significant sink of energy during the spring as the atmosphere warmed, but waters shifted to a net source of energy to the atmosphere during the winter.…”

“…These estimates of energy balance closure were consistent with those obtained from the slope of the regression (0.798 and 0.857, respectively) of daily sums of energy. Processes that contribute to enthalpy change in the water column (i.e., H tot ) should not be ignored for their contribution to the surface energy budget in flooded ecosystems such as rice paddy fields (Gao et al, 2003;Tsai et al, 2007) and ecosystems flooded by high tides such as mangrove forests. Fig.…”

“…This study did not include the necessary measurements for estimating S, and was therefore not included in the analysis. The H includes both the sensible heat flux (H EC ) determined from the EC system at a height (h EC ) of 27 m and heating of the air mass from the surface to 27 m (Tsai et al, 2007) and is given by…”

“…These unique energy exchange processes have not been previously explored in coastal systems. It is necessary to understand these energy flows because their temporal variability has implications for fluctuations in soil and air temperature, which influence net ecosys- tem carbon exchange (NEE) over daily and annual timescales (Barr et al, 2012;Ito et al, 2005;van Dijk et al, 2005).…”