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Autumn warming and carbon balance of a boreal Scots pine forest in Southern Finland
1Department of Physics, P.O. Box 48, 00140 University of Helsinki, Finland
2Department of Forest Ecology, P.O. Box 27, 00014 University of Helsinki, Finland
3Department of Computer Science and Helsinki Institute for Information Technology HIIT, P.O. Box 68, 00014 University of Helsinki, Finland
4Helsinki Institute for Information Technology HIIT, P.O. Box 68, 00014 University of Helsinki, Finland
5LSCE, UMR CEA-CNRS, Bat. 709, CE, L'Orme des Merisiers, 91191 Gif-sur-Yvette, France
6Department of Ecology, Peking University, Beijing 100871, China
Abstract. We analyzed the dynamics of carbon balance components: gross primary production (GPP) and total ecosystem respiration (TER), of a boreal Scots pine forest in Southern Finland. Our aim was to study how these dynamics are related to different environmental conditions and how they affect the inter-annual variation in the carbon balance in autumn (September–December). We used standard micrometeorological data and CO2 exchange measurements collected by the eddy covariance (EC) technique over 11 years. The intra-annual relationships between the carbon balance components and the environmental factors were studied by the correlation analysis. Two models, a stand photosynthesis model and a generic dynamic vegetation model (ORCHIDEE), were also applied in the analysis. EC data revealed that increasing autumn temperature significantly enhances TER: the temperature sensitivity was 9.5 gC m−2 °C−1 for the period September–October (early autumn when high radiation levels still occur) and 3.8 gC m−2 °C−1 for November–December (late autumn with suppressed radiation level). The cumulative GPP was practically independent of the temperature in early autumn. In late autumn, air temperature could explain part of the variation in GPP but the temperature sensitivity was very weak, less than 1 g C m−2 °C−1. The stand photosynthesis model predicted that under a predescribed 3–6°C temperature increase, the temperature sensitivity of 4–5 gC m−2 °C−1 in GPP may appear in early autumn. The TER and GPP sensitivities, produced by the ORCHIDEE model, were similar to observed ones when the site level ½ h time step was applied, but the results calculated by using daily meteorological forcing, interpolated to ½ h time step, were biased stemming from the nonlinear relationship between the processes and the environmental factors.
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Citation: Vesala, T., Launiainen, S., Kolari, P., Pumpanen, J., Sevanto, S., Hari, P., Nikinmaa, E., Kaski, P., Mannila, H., Ukkonen, E., Piao, S., and Ciais, P.: Autumn warming and carbon balance of a boreal Scots pine forest in Southern Finland, Biogeosciences Discuss., 6, 7053-7081, 2009. Bibtex EndNote Reference Manager
