Estimating Light use Efficiency of a Mediterranean Pine Forest from Leaf to Ecosystem Scale using Spectral Indices
Stagakis, S.¹; Markos, N.¹; Vanikiotis, T.¹; Tzotsos, A.²; Sykioti, O.³; Kyparissis, A.^1
1University of Ioannina, GREECE; ²National Technical University of Athens, GREECE; ³National Observatory of Athens, GREECE

The prospect of accurately tracking photosynthetic processes using satellite observations is very important for understanding and monitoring global carbon cycle and climate change. The present study investigates the efficiency of simple vegetation indices derived from reflectance spectra in detecting light use efficiency (å) in different spatial scales. The main focus concerns versions of the Photochemical Reflectance Index (PRI) and spatial scales refer to leaf, canopy and ecosystem levels. To that purpose, field measurements of needle and canopy reflectance are performed in a dense and homogenous forest dominated by the evergreen coniferous Pinus nigra (Epirus, Greece, 1000 m. a.s.l.) throughout a growing period. For the ecosystem level, satellite images from hyperspectral (Compact High Resolution Imaging Spectrometer, CHRIS) and superspectral (Moderate Resolution Imaging Spectroradiometer, MODIS) sensors are used. As a reference for the evaluation of vegetation indices against å, either direct photosynthesis measurements (leaf level) or a Canopy Photosynthesis Model (canopy and ecosystem levels) are used. Accordingly, field and laboratory measurements of canopy structure (Leaf Area Index - LAI, needle and shoot structure characteristics), needle pigment concentrations, needle photosynthesis and shoot water potential are performed throughout the growth period. These measurements are used for the parameterization of the Canopy Photosynthesis Model, but also for an accurate description of Pinus nigra ecophysiological performance. The results are expected to give significant information about the attributes, potentialities and limitations of various light use efficiency spectral indices when scaling up from leaf to the entire ecosystem.