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www.biogeosciences-discuss.net/6/2285/2009/
doi:10.5194/bgd-6-2285-2009
© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
Improved understanding of drought controls on seasonal variation in Mediterranean forest canopy CO2 and water fluxes through combined in situ measurements and ecosystem modelling
1CREAF, Autonomous University of Barcelona (UAB), 08139, Bellaterra, Barcelona, Spain
2LSCE, Orme des Merisiers, Gif sur Yvette, Paris, France
3Department of Geography, University of Cambridge, Cambridge CB2 3EN, UK
4Department of Ecology, University of Barcelona (UB), Diagonal 645, 08028, Spain
Abstract. Water stress is a defining characteristic of Mediterranean ecosystems, and is likely to become more severe in the coming decades. However, our current understanding of how soil moisture controls ecosystem functioning is not sufficient to adequately constrain model parameterisations.
Canopy-scale flux data from four forest ecosystems with Mediterranean-type climates were analysed in order to determine the physiological controls on carbon and water flues through the year. Stomatal and non-stomatal limitations on photosynthesis were separated, and new parameterisations were derived and implemented in two independent modelling approaches.
The effectiveness of the two approaches to ecosystem process-based modelling, one a dynamic global vegetation model (ORCHIDEE), and the other a forest growth model (GOTILWA+), was assessed and modelled canopy responses to seasonal changes in soil moisture were analysed with respect to in situ flux measurements.
In contrast to commonly held assumptions, we find that stomatal control does not dominate photosynthesis under natural seasonally-developing soil moisture stress. However, applying a soil moisture dependency to photosynthetic capacity results in accurate prediction of both carbon and water fluxes under all soil moisture levels encountered in the field. The new parameterisation has important consequences for simulated responses of carbon and water fluxes to seasonal soil moisture stress, and will greatly improve our ability to anticipate future impacts of climate changes on the functioning of Mediterranean ecosystems.
Discussion Paper (PDF, 1899 KB) Interactive Discussion (Closed, 6 Comments) Final Revised Paper (BG)
Citation: Keenan, T., García, R., Friend, A. D., Zaehle, S., Gracia, C., and Sabate, S.: Improved understanding of drought controls on seasonal variation in Mediterranean forest canopy CO2 and water fluxes through combined in situ measurements and ecosystem modelling, Biogeosciences Discuss., 6, 2285-2329, doi:10.5194/bgd-6-2285-2009, 2009. Bibtex EndNote Reference Manager XML
