CONTINENTAL SCALE VARIABILITY IN VEGETATION REFLECTANCE AND ITS RELATIONSHIP TO CANOPY MORPHOLOGY

We have measured the spectral canopy reflectance, biomass and projected leaf area index (LAI) of widely-dispersed plots of a North American coastal plant (salt marsh cord grass) in an attempt to identify potential impacts of continental-scale environmental variability on the assumptions underlying remote vegetation analysis. We found that important systematic changes in the canopy geometry and resultant near-infrared reflectance of this plant occurred within its 17 degree latitudinal range. Continental assessment of biomass using spectral indices would be severely affected by the observed differences. Use of spectral indices to assess more fundamental radiative transfer properties of the canopy, such as projected LAI, is not subject to the observed latitudinal changes, suggesting that large area studies can more reliably address canopy parameters such as adsorbed photosynthetically active radiation. The observed canopy changes also have potential functional consequences for the plant which would be of considerable ecological interest, particularly if similar trends are found for other plants and regions.