Topography induced spatial variations in diurnal cycles of assimilation and latent heat of Mediterranean forest

C. van Der Tol (1) , A. J. Dolman (1) , M. J. Waterloo (1) , K. Raspor (2)

1 Dept. of Hydrology and Geo-Environmental Sciences
2 Dept. of Civil and Geodetic Engineering

The aim of this study is to explain topography induced spatial variations in the diurnal cycles of assimilation and latent heat of Mediterranean forest. Spatial variations of the fluxes are caused by variations in weather conditions and variations in the vegetation characteristics. Weather conditions reflect short-term effects of climate, whereas vegetation characteristics, through adaptation and acclimation, long-term effects of climate. In this study measurements of plant physiology and weather conditions are used to explain observed differences in the fluxes. A model is used to study which part of the differences in the fluxes is caused by weather conditions and which part by vegetation characteristics. Data were collected at four experimental sub-Mediterranean deciduous forest plots in a heterogeneous terrain with contrasting slopes and aspect, soil water availability, humidity and temperature. We used a two leaf layer model to scale fluxes from leaf to canopy, and calculated the canopy energy balance. Parameter values were derived from measurements of light interception, leaf chamber photosynthesis, leaf nitrogen content and ¹³C isotope discrimination in leaf material. Leaf nitrogen content is a measure of photosynthetic capacity, and ¹³C isotope discrimination of water use efficiency. For validation, sap-flux based measurements of transpiration were used. The model accurately predicted diurnal cycles of transpiration and stomatal conductance, both their magnitudes and differences in afternoon stomatal closure between slopes of different aspect. The diurnal cycles were more strongly affected by spatial variations in vegetation parameters than by meteorological variables. This indicates that topography induced variations in vegetation parameters are of at least equal importance to the fluxes as topography induced variations in radiation, humidity and temperature. Weather conditions mainly affect the shape of the diurnal cycles, and vegetation parameters the magnitude of the fluxes.

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]; Interfaces continentales, environnement; Océan, Atmosphère; Sciences de la Terre

C. van Der Tol, A. J. Dolman, M. J. Waterloo, K. Raspor. Topography induced spatial variations in diurnal cycles of assimilation and latent heat of Mediterranean forest. Biogeosciences Discussions, 2006, 3 (5), pp.1631-1677. ⟨hal-00297851⟩