Monitoring vegetation dynamics in semi-arid African rangelands - Use and limitations of Earth observation data to characterize vegetation structure

lVegetation community structure is a key indicator of long-term vegetation change in semi-arid ecosystems, This study uses ground-based spectral measurements and a canopy reflectance model to investigate the potential of Earth observation data to characterize variations in vegetation structure along a grazing gradient in the eastern Kalahari, Botswana, Despite differences in the bidirectional reflectances of soil, plant litter, bush and grass canopies towards the end of a dry season, it is unlikely that Earth observation data can be used to estimate vegetation structure at this time. This is due to an ambiguity in the relationship between spectral reflectance and vegetation structure caused primarily by the limited dimensionality of reflectance data. Variations in canopy architecture cause differences in the level of inter-canopy shadowing but the net effect-lower reflectance with an increase in hush cover-parallels the darkening effects of any vegetation cover on relatively bright sandy soils in semi-arid environments, These results highlight the continued need for long-term ground-based ecological monitoring in conjunction with satellite-based monitoring of changes in vegetation cover. (C) 1998 Elsevier Science Ltd. All rights reserved.