A reconstruction of the Afro-alpine Erica arborea L. treeline in the Northern Ethiopian highlands since the 1930s

North Ethiopian high altitude forests play an important role in the hydrology of the surrounding valleys and are critical in terms of biodiversity. Their composition and extension is potentially responsive to the risen average temperatures of the past century. We reconstructed the extent of the upper Erica Arborea L. tree limit since the 1930s in 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 record by high resolution Google Earth satellite imagery and field data (February, 2012). Historical treelines were studied from aerial photographs (1930s- 1965-1982) and historical terrestrial photography (1907-1916). Automatic classification of the forest cover from orthorectified aerial photographs (1965 and 1982) and Google Earth images (GeoEye, 2010) enabled a raster based change trajectory of the forest cover since 1965. Italian aerial photographs from the 1930s and historical terrestrial photography (1907-1916) are qualitatively analyzed to detect changes from the early 19th century. Preliminary results indicate a severe decrease of the forest cover extent from early 1900 up to 1982 as a resulted of increased human impact, followed by a recent increase of the forest density in isolated patches between 1982 and present. The elevation of the Erica Arborea L. treeline increased slightly, which has to be understood against important land use changes on the mountains and potentially by regional temperature rise.