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Track: Natural Resources and Conservation
Andrew Hudak
University of Colorado
Campus Box 216
Boulder, CO 80309-0216
Telephone: 303-492-5130
Fax: 303-492-5070
E-mail: hudak@hypatia.colorado.edu
Carol Wessman
Textural Analysis of Aerial Photography To Characterize Large Scale Land Cover Change
Cattle overgrazing in the semiarid savannahs of South Africa has led to widespread range degradation over the past several decades. Grass forage has gradually been replaced by unpalatable woody trees and shrubs in a process locally known as "bush encroachment." We studied two large areas (each of approximately 100,000 ha) where bush encroachment has been especially severe. By analyzing digitized historical aerial photography and land use maps in ARC GRID, we developed a technique for characterizing landscape patterns in bush encroachment. Textural filters were employed to generate multitemporal grids of bush densities. Land use zones defined by roads and fencelines were convolved with these grids to classify and map farms by varying degrees of bush encroachment. These maps proved useful for identifying the most optimal sites in which to (1) locate field transects for gathering other relevant ecological data and (2) recommend to land use managers which farms to include in a bush eradication program. We
feel that this technique could be applicable to characterizing other extensive, yet slow, changes to land cover wherever or whenever high spatial resolution satellite imagery is unavailable.
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