ASSESSMENT OF A METHOD FOR MAPPING WOODY PLANT-DENSITY IN A GRASSLANDMATRIX

Determining patterns of land degradation, and by inference the ecologi cal processes at play, is critical to designing and implementing strat egies and tactics to halt degrading practices and restore already degr aded areas. In this paper we describe the application of a new image a nalysis technique to determine the presence and density of shrubs in a grassland matrix and evaluate its use for assessing rates and pattern s of shrub increase, a common form of land degradation in rangelands t hroughout the world. By analysing a series of images derived from aeri al photography to identify and separate objects (shrubs) in progressiv e steps, we were able to detect accurately individual shrubs with cano pies greater than 9 m(2) (about 85% of the sample population). The met hod also was moderately successful in predicting canopy area of indivi dual trees. This approach offers land managers and policy-makers a too l for defining both temporal patterns and rates of shrub increase as w ell as for defining the current extent of an invasion as a basis for t argeting control technologies. (C) 1998 Academic Press Limited.