Mapping a century of forest cover change and treeline dynamics in the north Ethiopian Highlands: the Lib Amba case

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: Lib 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 satellite imagery and field data (February, 2012). Historical treelines were studied from aerial photographs (1965-1982) and historical terrestrial photography (1907-1916). Automatic classification of the forest cover from orthorectified aerial photographs (1965 and 1982) and Bing Map images (Global Data, 2013) enabled a raster based change trajectory of the forest cover since 1965. Historical terrestrial photography (1917) is qualitatively analyzed to detect changes from the early twentieth century. Preliminary results indicate a severe decrease of the forest cover extent from 1917 to 1965, caused by recent land occupation and agricultural expansion of mountain regions. Subsequently between 1965 and present the forest density increased in small isolated patches and strongly degraded outside of these managed forest patches. We found evidence that the elevation of the Erica Arborea L. treeline increased slightly, which has to be understood against the important land use changes on the mountains and potentially by regional temperature rise.