RESPONSE OF HIGH-MOUNTAIN LANDSCAPE TO TOPOGRAPHIC VARIABLES - CENTRAL PYRENEES

An objective method for inductively modelling the distribution of moun tain land units using GIS managed topographic variables is presented. The landscape of a small high mountain catchment in the Spanish Pyrene es, covered with grassland, was classified in tan land units by hierar chical agglomerative clustering, using a sample of 194 random plots, i n which classes of vegetation, soils and landforms were defined. Addit ionally, seven layers of topographic variables (altitude, slope angle, aspect, solar radiation, topographic wetness index, specific catchmen t area, and regolith thickness) were created from a Digital Elevation Model. The affinity of each land unit to the topographic variables was calculated using Binary Discriminant Analysis (BDA), after dichotomis ing the latter around their mean values. Then, the distribution of eac h land unit was predicted by boolean operations combining step by step distributions for the seven topographic variables ordered, for each u nit, after the absolute values of the Haberman's residuals in BDA. The predicted distributions were tested (chi(2)) against that of the obse rved sampling plots. From the original ten land units, the distributio ns of eight of them were successfully predicted (four are related to t he slept sequence, two reflect the water accumulation in the soil, and two respond to geomorphic processes) while the remaining two had to b e rejected. Part of the catchment (39%) was not assigned to any land u nit, probably because more distributed variables accounting for snow d istribution are necessary.