Holocene palaeovegetation of the Tigray Plateau in northern Ethiopia from charcoal and stable organic carbon isotopic analyses of gully sediments Tsige Gebru a , Zewdu Eshetu b , Yongsong Huang c , Taddese Woldemariam d , Nikki Strong e , Mohammed Umer f , Michael DiBlasi g , Valery J. Terwilliger e, ⁎ a Department of Environmental Sciences, P.O. Box 1176, University of Addis Ababa, Addis Ababa, Ethiopia b Ethiopian Institute of Agricultural Research (EIAR), Forestry Research Centre, P.O. Box 30708, Addis Ababa, Ethiopia c Department of Geological Sciences, Brown University, Providence, RI 02912, United States d Ethiopian Coffee Forest Forum, Addis Ababa, Ethiopia e Department of Geography, University of Kansas, Lawrence, KS 66045, United States f Department of Earth Sciences, P.O. Box 1176, Addis Ababa University, Addis Ababa, Ethiopia g Program for the Study of the African Environment, African Studies Center, Boston University, Boston, MA 02215, United States abstract article info Article history: Received 8 February 2009 Received in revised form 7 August 2009 Accepted 25 August 2009 Available online xxxx Keywords: Palaeovegetation Charcoal analysis Soil organic matter Stable isotopes Human impact Holocene Ethiopia A long history of supporting sophisticated but unsustainable kingdoms makes the Tigray Plateau of the northern Ethiopian highlands a promising region for the study of relationships between palaeoenvironmental change and the trajectories of human civilizations. The natural vegetation above 2200 m elevation is thought to be forests dominated by Juniperus procera. Nonetheless, this hypothesis is not supported in the vegetation cover now and is scarcely studied in the palaeorecord. To examine changes in vegetation, climate, and land use, we identified buried charcoalized wood and estimated the percentage of organic carbon from C 4 plants (% C 4 carbon) from δ 13 C values of bulk organic matter in the soils of gully walls in the boundaries of the ancient Aksumite Empire. Charcoal ranged in age from ca. 13,700 to 110 cal yr BP. Juniperus procera occurred in even the youngest samples, although at lower percentages of the total charcoal than in older samples. Nevertheless, rapidly regenerating angiosperms usually dominated or co-dominated charcoal even in some of the oldest strata. A shift towards higher % C 4 carbon and % total organic carbon (%TOC) in soils younger than 3300 cal yr BP began during a period when agricultural uses of land may have increased in order to support the needs of growing societies. A shift towards higher % C 4 carbon but lower %TOC began at ca. 6000 cal yr BP, however, during a period when no charcoal was found and no changes in human societal complexity are known. These results indicate that juniper forest types have long been present at >2200 m in the Tigray Plateau but that they have rarely been the dominant natural vegetation. Furthermore, lack of repeatable correspondence between factors suggests that the causes of similar shifts in vegetation composition were not always the same. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Studies of relationships between changes in palaeoenvironments (climate and land use) and the rise and fall of complex societies are becoming increasingly important for assessing the consequences of anthropogenic activities today (Turchin, 2003; Diamond, 2005; Dearing, 2007; Broecker and Kunzig, 2008). The highland region of northern Ethiopia is an important location for examining possible relationships between palaeoenvironments and the trajectories of civilizations. Known best for its present extreme poverty, degraded lands, and cycles of drought and famine (Africa Watch, 1991), the region once had a probable center of origin of agriculture and a long succession of civilizations (Butzer, 1981; Phillipson, 1998; Bard et al., 2000). Its palaeoenvironmental changes have received very little study, however. The Tigray Plateau has the longest history as a region of support for northern Ethiopia's past civilizations. Vegetation history, one of the most fundamental proxies for past environment, is almost unstudied there (Wilson, 1977; DiBlasi, 1997; Nyssen et al., 2004). In addition to crops and exotic plantation forest species, the dominant vegetation is now heavily-grazed grassland with sparsely distributed trees consisting mostly of Acacia abyssinica. The natural vegetation above 2200 m elevation on the Tigray Plateau is thought to be predominantly juniper (Juniperus procera) forest types (Geography Division, 1988; Friis, 1992; Bard et al., 2000). Acacia spp. woodlands and savannas may also naturally occur at elevations under 2600 m (Wilson 1977). Inferences about natural vegetation do not come from the region itself but from voucher specimens that G. W. Schimper collected elsewhere in northern Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2009) xxx–xxx ⁎ Corresponding author. Tel.: +1 785 864 5143; fax: +1 785 864 5378. E-mail addresses: gebts@yahoo.com (T. Gebru), zewdu61@yahoo.com (Z. Eshetu), Yongsong_Huang@brown.edu (Y. Huang), abiyotmulu@gmail.com (T. Woldemariam), stro0068@umn.edu (N. Strong), moha_umero@yahoo.com (M. Umer), mdib@bu.edu (M. DiBlasi), terwilli@ku.edu (V.J. Terwilliger). PALAEO-05099; No of Pages 14 0031-0182/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2009.08.011 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo ARTICLE IN PRESS Please cite this article as: Gebru, T., et al., Holocene palaeovegetation of the Tigray Plateau in northern Ethiopia from charcoal and stable organic carbon isotopic analyses of ..., Palaeogeography, Palaeoclimatology, Palaeoecology (2009), doi:10.1016/j.palaeo.2009.08.011