Effects of climate variability and functional changes on the interannual variation of the carbon balance in a temperate deciduous forest

摘要

The net ecosystem exchange of CO₂ (NEE) between the atmosphere and atemperate beech forest showed a significant interannual variation (IAV) anda decadal trend of increasing carbon uptake (Pilegaard et al., 2011). The objectives of this study were to evaluate to what extentand at which temporal scale, direct climatic variability and changes inecosystem functional properties regulated the IAV of the carbon balance atthis site. Correlation analysis showed that the sensitivity of carbon fluxesto climatic variability was significantly higher at shorter than at longertime scales and changed seasonally. Ecosystem response anomalies impliedthat changes in the distribution of climate anomalies during the vegetationperiod will have stronger impacts on future ecosystem carbon balances thanchanges in average climate.We improved a published modelling approach which distinguishes the directclimatic effects from changes in ecosystem functioning (Richardson et al.,2007) by employing the semi empirical model published byLasslop et al. (2010b). Fitting the model in short movingwindows enabled large flexibility to adjust the parameters to the seasonalcourse of the ecosystem functional state. At the annual time scale as muchas 80% of the IAV in NEE was attributed to the variation inphotosynthesis and respiration related model parameters. Our results suggestthat the observed decadal NEE trend at the investigated site was dominatedby changes in ecosystem functioning. In general this study showed theimportance of understanding the mechanisms of ecosystem functional change.Incorporating ecosystem functional change into process based models willreduce the uncertainties in long-term predictions of ecosystem carbonbalances in global climate change projections.