Can treeline dynamics in the afro-alpine north Ethiopian highlands be used as proxy to study climate change?

Worldwide average temperatures have risen during the past century, a change that is most prominent and rapid at high altitudes and latitudes. The composition and extension of the temperature sensitive treelines within these zones are potentially responsive to climate warming. In contrast to dynamics at higher northern latitudes, treeline dynamics in the tropics are scarcely investigated. The purpose of this paper is to reconstruct the extent of the upper Erica Arborea limit since the 1960s in the semi-arid to subhumid mountain climate zone of the north Ethiopian highlands: Leb Amba of the Abune Yosef Mt. range (12°04’N, 39°22’E, 3952 m a.s.l.) and the Ferrah Amba Mt. (12°52’N, 39°30’E, 3939 m a.s.l.). The present upper and physiognomic treeline limits were recorded in the field (February, 2012) and compared to previous treeline elevations studied from aerial photographs (1970s-1990s) and Landsat images (1980s-present). Photogrammetric restitution of the aerial photographs resulted in DEM models and orthophotographs that enable comparison between historical and present treelines. For the Landsat imagery, an NDVI ratio based on ground truthed Landsat images is used to detect treeline dynamics as well as changes in forest density. To detect these NDVI values of treeline forests are compared to a stable reference forest. Preliminary results indicate that the elevation of the Erica treeline increased, which has to be understood against important land use changes on the mountains and regional temperature rise