Current maps of global vegetation have been produced by the Normalized Difference Vegetation Index (NDVI) from the AVHRR satellite sensor. These maps have been related to absorbed solar radiation or surface leaf area index, but the NDVI has only been related theoretically to evapotranspiration and photosynthesis processes for vegetation and then only under optimal conditions of water and temperature, constraints that severely limit real world applications. The project will utilize a simple evapotranspiration and photosynthesis model for forests driven entirely by AVHRR data that is sensitive to sub-optimal water and temperature conditions. The investigators will (1) relate the seasonal trend of weekly composite NDVI to vegetation phenology and temperature limits, (2) test a satellite-derived surface resistance factor which is related to canopy diffusion resistance and (3) define physiologically based energy to mass conversion factors for carbon and water. These NDVI driven models will then be evaluated against a more complex ecosystem process model. The resulting simple, satellite-driven forest canopy models should allow a vastly improve computation of surface water and carbon exchange rates by global forests and improve accuracy of global carbon and hydrologic budgets. Output from the project should be useful in understanding the regional-to-global dynamics of water, CO2 and climate with regard to the "greenhouse effect" as well as possibly providing better, more rapid means of estimating forest production on large scales. The investigators are quite well qualified. Institutional accommodations and support for both collaborators is excellent. The Ecosystem Studies Program recommends support for this three- year collaborative effort.
