Spectral assessment of indicators of range degradation in the Botswana hardveld environment

Abstract The literature suggests that two different approaches have been applied to problems of rangeland monitoring using MSS data. These are referred to as the near infrared over red ratio which has been successfully applied to areas of relatively dense vegetation in the humid zone, and the darkening effect which is applicable in the sparsely vegetated semiarid zone. Data from Botswana suggests that neither of these is singularly appropriate in the savanna woodland zone of southern Africa. In the Botswana hardveld the measured vegetation cover consists of green vegetation which generally occupies less than 60% of the cover in a given area. The soil component is dominant. This, in addition to other vegetation components which produce a darkening effect, results in high reflectance values in the red and infrared parts of the spectrum for areas with a low vegetation cover and low reflectance values in both wavebands for areas with a high vegetation cover. In savanna woodland environments which contains elements of both the near infrared to red ratio and the darkening approach, the most suitable indicators of range condition and degrees of desertification can be obtained by directly applying spectral ranges from the red band. The range of values used is heavily ecosystem, therefore soil-type-dependent, and is referred to as the savanna woodland model.

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