The study falls within the national project Dryade (“The vulnerability of forests to climate change: tree to climate areas”). It concerns the decline of silver fir (Abies alba Miller.) in the Mediterranean hinterland. This contribution aims to find the causes of this decline in the Mont Ventoux, on a transect in contour line (plots at same elevation, 1100 m asl, but different soil characteristics). Two axes were studied. First, the health characterization of fir was made on the basis of the DSF protocol adapted by URFM, INRA Avignon. Secondly, a soil characterization (soil depth and coarse elements rate) with estimate of moisture content by measuring the electrical resistivity of the soil through tomography (EMMAH, INRA Avignon) was made and was supplemented by description of the stand structure and competition between trees. The results of the correlations analysis show that the most predominant factor explaining defoliation and mortality of trees is the stand structure. Contrary to our expectation, defoliation is lower when the first soil meter has a high resistivity (lot of coarse elements, low water content): the low vulnerability of the trees located there is probably due to an acclimatization to these soils; also, the dominant individuals are probably able to catch deep water (low resistivity between 5 and 20 m). A functional study at tree-level should be carried out to better understand this fir decline. According to our results, foresters should manage the stand at moderate density levels in order to reduce the risk of drought damages, especially for mid-size trees