Analysis of upper timberline elevation in the European Alps using MODIS data

Natural timberlines are remarkable indicators of climate conditions. Maps of natural timberline elevation in the European Alps, however, are rare and not concordant. In this paper, a large-scale approach for the approximation of natural timberline with remote sensing methods is presented. The potential of two vegetation indices, which were calculated from MODIS surface reflectance data, to give indications on natural timberline position was analyzed. The normalized difference vegetation index (NDVI) proved more suitable for our purpose than the soil-adjusted vegetation index (SAVI), as in our data the latter is clearly influenced by aspect. Thus, our approach to describe the large-scale spatial variability of timberline elevation uses an NDVI threshold and filtering techniques. Although numerous sources of error and uncertainty have to be considered, encouraging results have been obtained.