Mount Psiloritis forms part of the backbone of Crete rising to 2,500 metres within 15 km. of the sea. Its semi-natural garrigue communities are of world significance for endemism and biodiversity. Its headwater streams feed the adjacent Messara rift valley which has seen intensive irrigation and farming since 1985. Hydrological studies have shown that ground water levels have dropped systematically and streams are drying out seasonally. Serious concern surrounds the impact on vegetation communities. Previous work by the applicants has enabled creation of a GIS containing ortho-corrected TM/ERS satellite imagery, land cover maps and a 10 metre, stereo-matched DEM. NDVI analysis has revealed a strong relationship between garrigue biomass and altitude over 1200 metres but this breaks down completely at lower altitudes. It is hypothesised that this is caused by disturbance. Despite extensive floristic and hydrological studies no detailed mapping of the vegetation structure is yet available. This study seeks to use high resolution LiDAR, CASI and ATM data to characterise the 3d structure and biomass of the vegetation at strategic locations on the mountain. It will use LiDAR derived measures of vegetation quantity and classified ATM data to calibrate the NDVI profiles. CASI will be used for examination of vegetation health. By comparison of survey sites it is hoped to explain the observed, macro patterns in NDVI and to further test the hypothesis that lowering of ground water levels is a threat to ecosystem sustainability.