Monitoring temporal changes in the spatial patterns of a mediterranean shrubland using Landsat(TM) images

Abstract

The overall goat of this study is to understand the structure and function of a Mediterranean shrubland at landscape scale by means of satellite images and GIS. Specifically, to assess the sensitivity of several spatial statistics to characterise landscape pattern, measure fragmentation and quantify the change through time. We study the landscape structure of a Mediterranean shrubland located in the east part of Spain (Valencia) and the change in spatial patterns of different shrubs types from 1984 to 1994. To accomplish these objectives, we used 10 Landsat(TM) images from 1984 to 1994 (except 1988) to which a geometric correction and an atmospheric normalization was applied. In addition, a Digital Terrain Model (DTM) of 10 x 10 m resolution, which was resampled to 30 x 30 m to make possible the comparison with the satellite images, was used to extract the topographic information. Firstly, the landscape was divided into a set of units based on their different spatial patterns of shrub-type distribution on topography. The elaboration of 'landscape units' involved a quantitative description of each topographic gradient derived from a DTM as a function of their vegetation composition. The results obtained differentiated clearly among areas showing different vegetation developments under diverse environmental conditions in which differences in solar radiation (aspect), availability of soil nutrients (slope) and humidity (elevation) were very important. These environmental constraints exert a strong and persistent effect on vegetation composition and strengthen the association between current vegetation and site variables. Finally, we analysed the multitemporal behaviour of those landscape units in which the species and communities were adapted to biotic and abiotic environmental changes (rainfalls and phenological dates).