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This paper analyses the evolution of the Normalized Difference Vegetation Index (NDVI) in the central Spanish Pyrenees. For this purpose, Landsat-TM and ETM+ were used. The selected images correspond to August of 1984, 1991 and 2001. The difference in days between the images was not very important to diminish the effects of phenology. The images were geometrically and atmospherically corrected by means of a mixed method based on physical and statistical procedures. Using the NDVI images we calculated coefficients of variation within a radius of 150 meters by means of a moving window procedure. This approach allows to analyse the spatial variability of the vegetation cover. The results show that the NDVI changes have not been important in the analysed period. Nevertheless, there are noticeable modifications in the spatial structure and variability of the NDVI, resulted in homogenization/heterogenisation processes. The forests located at high altitudes have suffered the most important homogenisation processes. On the contrary at low elevated areas the spatial diversity of the vegetation activity increases. Nevertheless, in these areas some spatial differences are found: the heterogenisation of the vegetation cover is less important in the forests than in areas dominated by sclerophyllous vegetation and those characterised by the transition from shrubs to forests. These areas show less mature successional phases after the land abandonment and they are characterised by an increase of the spatial heterogeneity of the NDVI.

pirineos

Diversidad espacial de la actividad vegetal en campos abandonados del Pirineo Central español: análisis de los procesos de sucesión mediante imágenes Landsat (1984-2001)