Respiration as the main determinant of carbon balance in European forests

Abstract

Carbon exchange between the terrestrial biosphere and the atmosphere is one of the key processes that need to be assessed in the context of the Kyoto Protocol. Several studies suggest that the terrestrial biosphere is gaining carbon, but these estimates are obtained primarily by indirect methods, and the factors that control terrestrial carbon exchange, its magnitude and primary locations, are under debate. Here we present data of net ecosystem carbon exchange, collected between 1996 and 1998 from 15 European forests, which confirm that many European forest ecosystems act as carbon sinks. The annual carbon balances range from an uptake of 6.6 tonnes of carbon per hectare per year to a release of nearly 1 t C ha(-1) yr(-1), with a large variability between forests. The data show a significant increase of carbon uptake with decreasing latitude, whereas the gross primary production seems to be largely independent of latitude. Our observations indicate that, in general, ecosystem respiration determines net ecosystem carbon exchange. Also, for an accurate assessment of the carbon balance in a particular forest ecosystem, remote sensing of the normalized difference vegetation index or estimates based on forest inventories may not be sufficient.

Ozone deposition into a boreal forest over a decade of observations: evaluating deposition partitioning and driving variables

“…The carbon and water exchange of the ecosystems has been monitored and analysed across geographical locations and different ecosystem types over a long period with the use of micrometeorological stations (e.g., Goulden et al, 1996;Lindroth et al, 1998;Valentini et al, 2000). Similar results/reports on long-term measurement of ozone fluxes at the ecosystem level are rather limited (Zhang et al, 2002;Turnispeed et al, 2009;Fares et al, 2010).…”

Towards operational remote sensing of forest carbon balance across Northern Europe

“…Since NEE gives the net amount of carbon uptake or release, this is a more appropriate measure than NPP and GPP of carbon sink strength (Schulze et al, 2002). However, using the LUE approach, or remote sensing techniques in general, for NEE modeling is problematic due to the difficulties involved in obtaining information on the heterotrophic respiration from space (Valentini et al, 2000). The mechanisms behind decomposition of soil organic matter are not yet fully understood as decomposition depends not only temperature but on a range of different environmental constraints (Davidson and Janssens, 2006).…”

“…Accordingly, estimating soil decomposition is hard in general, and especially so using only data from satellite. Given the importance of ER in controlling the forest carbon balance, especially boreal forests at high latitudes (Valentini et al, 2000), there are strong arguments for including information on ER when studying carbon balance from space, despite the difficulties involved.…”

Partitioning sources of soil‐respired CO2 and their seasonal variation using a unique radiocarbon tracer

“…The portion of total ecosystem respiration that takes place below-ground, soil respiration, has been estimated in forests to be as much as 69% of the total ecosystem respiration (plant and soil) and 55% of the carbon assimilated through photosynthesis annually (Janssens et al, 2001). Besides representing a large loss of carbon, soil respiration is also a major contributor to interannual variability in the net ecosystem balance (Goulden et al, 1996;Valentini et al, 2000).…”