Estimating Vegetation Function from Satellite Data
in Seasonal Tropical Environments
Kazue Fujiwara
Yokohama National university
Institute for Environmental Science and Technology Hodogaya-ku,
Tokiwadai 156, Yokohama 240, Japan
Elgene 0. Box
Tokyo University, Institute of Industrial Science
Minato-ku, Roppongi 7-22-1, Tokyo 106, Japan 1
(permanently: University of Georgia,
Geography Department, I ~ Athens, Georgia 30602-2502, USA)
Abstract
Highly seasonal tropical environments have provided convenient situations for demonstrating the capabilities of satellite sensors to detect changes in the landscape, based on clear seasonal changes in the foliation status of the vegetation .Foliation status does not always vary so obviously, however, and
even when it does, such changes do not necessarily translate directly into high or low levels of functional activity, such as , net primary production or net carbon flux (net ecosystem .production) .Southeast Asia is an especially good place to study : this problem, due to its full range of deciduous to largely .evergreen vegetation, all in a highly seasonal monsoon climate. Production, water budget, and overall net carbon flux of : different vegetation types are simulated using a climate-based model of vegetation and detrital metabolism. Parallel monthly results are shown for vegetation phenology, satellite data (NDVI) ; and simulated carbon balance. Such models of vegetation function .can and should be used for better calibration of satellite data .in various parts of the world.
Introduction
When rainfall falls to near zero for several months each year and 5 defoliation is relatively complete, satellite data can infer r changes in ecosystem function quite effectively (e.g. Tucker et al. 1985) .The main processes of interest include primary r production (photosynthesis plus assimilation of its products into new biomass) , autotrophic respiration (energy use for maintenance .and growth) , detrital decomposition, and the resulting net biosphere-atmosphere C02 flux. This overall net metabolic balance of the landscape (vegetation-detritus system) and sometimes even of the living vegetation (net production) normally J becomes negative during defoliation (dry season) .It can also J become negative, however, in green landscapes, during their growing season, if respiration is higher than photosynthetic r gains (Box et al. 1989) .As a result, in using satellite data to estimate biotic function, it seems wise to, look at, parallel estimates of vegetation metabolism, as are provided by simulation models based on field-measured metabolism and climatic data. Southeast Asia is a good place to study this problem, due to its full range of deciduous to evergreen but seasonal vegetation
