Seasonal variations in leaf area index, leaf chlorophyll, and water content; scaling-up to estimate fAPAR and carbon balance in a multilayer, multispecies temperate forest

Seasonal differences in phenology between coniferous and deciduous tree spe cies need to be considered when developing models to estimate CO2 exchange in temperate forest ecosystems. Because seasonal variations in CO2 flux in temperate forests are closely correlated with plant phenology, we quantifie d the phenology of forest species in a multilayered forest with patches of Scots pine (Pinus sylvestris L.) and oak (Quercus robur L.) in Brasschaat, Belgium. A scaling-up modeling approach was developed to simulate reflectan ce at the leaf and canopy scales over a one-year cycle. Chlorophyll concent ration, water content, specific leaf area and leaf area index of the forest species were measured throughout an entire year (1997). Scaling-up from th e leaf to canopy was achieved by linking the PROSPECT and SAIL models. The result is the annual progression of the fraction of absorbed photosynthetic ally active radiation (fAPAR) in a 1 km(2) forest area, which can be direct ly related to high-resolution, remotely sensed data.