Carbon and water exchanges of regenerating forests in central Siberia

Abstract

Direct measurements of CO 2 and water vapour of regenerating forests after fire events (secondary succession stages) are needed to determine the role of such disturbances in the biome carbon and water cycles functioning. An estimation of the extension of burnt areas is also required in order to quantify NBP (net biome productivity), a variable that includes large-scale carbon losses (such as fire) bypassing heterotrophic respiration. Hence, eddy covariance measurements of CO 2 and water vapour were carried out in a natural regenerating forest after a fire event. Measurements were collected continuously over a Betula spp. stand in central Siberia during summer 1999. Minimum carbon exchange rate (NEE, net ecosystem exchange) exceeded −30 μmol m −2 s −1 (net flux negative indicating CO 2 uptake by vegetation) and the partitioning of the available energy was mostly dominated by latent heat flux. Structure, age and composition of the forest were analysed to understand the secondary succession stages. The results were compared with previous studies on coniferous forests where biospheric exchanges of energy were dominated by sensible heat fluxes and small carbon uptake rates, thus indicating rather limiting growing conditions. A classification of a Landsat-4 Thematic Mapper scene has been carried out to determine the magnitude of burnt areas and the extension of broadleaf regenerating forests. Analysis of burnt areas spatial frequency and carbon exchanges of the regenerating forest stress the importance of considering large area disturbances for full carbon accounting.