title: Nonlinear vegetation cover changes in the North Ethiopian Highlands: Evidence from the Lake Ashenge closed basin.
abstract: Vegetation cover changes in African drylands are often thought to result from population growth, social factors and aridification. Here we show that long-term vegetation proxy records can help disentangling these main driving factors. Taking the case of North Ethiopia, we performed an integrated investigation of land cover changes over the last four centuries around the endorheic Lake Ashenge, as derived from pollen analysis and repeat photography complemented with information from historical sources. Pollen and sediment analysis of radiocarbon-dated lake deposits shows a phase of environmental destabilization during the 18th century, after a more stable previous period. This is evidenced by decreases of tree pollen (Juniperus, Olea, Celtis, Podocarpus<5%), increases in Poaceae (>40%) and deposition of coarser silt lake sediments (>70%). Quantitative analysis of 30 repeated landscape photographs around the lake indicates a gradual decline of the vegetation cover since a relative maximum during the mid-19th Century. Vegetation cover declined sharply between the 1950s and the 1980s, but has since begun to recover. Overall, the data from around Lake Ashenge reveal a nonlinear pattern of deforestation and forest regrowth with several periods of vegetation cover change over the past four centuries. While there is forcing of regional drought and the regional land tenure system, the cyclic changes do not support a simplified focus on aridification or population growth.
authors.affiliation: Department of Geography, Ghent University, Krijgslaan 281 (S8), B-9000 Ghent, Belgium. Electronic address: sil.lanckriet@ugent.be.
authors.forename: Sil
authors.initials: S
authors.lastname: Lanckriet
authors.affiliation: National Museum of Kenya, Earth Science Department, Palynology Section, P.O. Box 40658 00100, Nairobi, Kenya.
authors.forename: Stephen
authors.initials: S
authors.lastname: Rucina
authors.affiliation: Department of Geography, Ghent University, Krijgslaan 281 (S8), B-9000 Ghent, Belgium.
authors.forename: Amaury
authors.initials: A
authors.lastname: Frankl
authors.affiliation: Centre for Development and Environment, University of Bern, Hallerstrasse 10, CH-3012 Bern, Switzerland.
authors.forename: Alfons
authors.initials: A
authors.lastname: Ritler
authors.affiliation: Department of Geology and Soil Science, Ghent University, Krijgslaan 281 (S8), B-9000 Ghent, Belgium.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Gelorini
authors.affiliation: Department of Geography, Ghent University, Krijgslaan 281 (S8), B-9000 Ghent, Belgium.
authors.forename: Jan
authors.initials: J
authors.lastname: Nyssen
mesh_terms: D057231:Climate Change; D003247:Conservation of Natural Resources; D004784:Environmental Monitoring; D005002:Ethiopia; D065948:Grassland; D060106:Lakes / Q000737:chemistry
keywords: Deforestation; Endorheic basin; Political ecology; Pollen; Repeat photography