Human-Environment Interactions in the Bale Mountains
Human-Environment Interactions in the Bale Mountains during the Late Pleistocene and Holocene Epochs: Anthracological Study
By Tefera Tarekegn
Tefera Tarekegn is a lecturer at the Department of Archaeology, Wolayta Sodo University. He has been laureate of the CFEE 2021 Field Grant and has defended his MA thesis in Archaeology at Addis Abeba University, Department of Archaeology and Heritage Management under the supervision of Dr. Alemseged Beldados (AAU) and Dr. Götz Ossendorf (UOC), in September 2021. His MA research – summarized here – is devoted to the anthracological analysis of the outstanding corpus of the Bale Mountains project of which he is an active member. Tefera has been recently awarded a Ph.D. grant from the French government to continue this fruitful research in collaboration with the CEPAM laboratory (Nice, France).
An ongoing archaeological investigation under the “Mountain Exile Hypothesis” (MEH) project at the Bale Mountains in South-Eastern Ethiopia is shedding new light on the human adaptation to high-altitude environments in Africa (Ossendorf et al., 2019). In the Bale Mountains, several sites including Fincha Habera, Mararo, Fish Shelter, and Simbiro with an altitude of 3469, 3779, 3423, and 3519 meters above sea level respectively, have been the focus of archaeological investigations (Fig. 1). A range of archaeological remains such as lithic stone tools, pottery, faunal and floral was uncovered. They suggest that the African high-altitude ecozones were occupied by hunter-gatherers during the Late Pleistocene due to their environmental stability at times of environmental uncertainties in lowlands (Ossendorf et al., 2019).
The occupation chronology of the sites varied from year to year as the excavation went deeper down to the older strata and from site to site as well. According to radiocarbon dates published in 2019 concerning Fincha Habera site, the oldest levels suggest that the occupation began during the Late Pleistocene, between 47,000 and 31,000 years ago (Ossendorf et al., 2019; Zimmer, 2019). According to Ossendorf et al. (2019), hunter-gatherers occupied most sites in the Bale Mountains in times when resources were depleted in the lowland either as a result of rapid population increases or ecological changes.
Anthracological data are among the paramount collected findings which make the settlement sites promising in achieving research objectives. Anthracology is an emerging archaeobotanical approach used for tackling archaeological problems related to human-environment interaction. It is a multi-disciplinary science encompassing archaeology, palaeoecology, botany, forestry, and geology, among others. It deals with the study of interactions between humans and their environment in the past through the identification of wood anatomy. Therefore, anthracology has importance for understanding the ancient landscape, dwelling space, site catchment area, fuel economy, and use of wood in domestic and ritual contexts, among others (Asouti, 2001; Kabukcu, 2018; Scheel-Ybert et al., 2018).
A bulk of anthracological assemblages have been collected from various sites in the Bale Mountains. Their analysis, consisting of wood taxa category identification, allows a better understanding of the dynamics of vegetation history and helps us to capture information about the vegetation pattern and the relationships that men had. Understanding past human adaptation to a certain type of environment is also a key and significant precondition for conceptualizing patterns, processes, and natural selection pressures that may affect the course of human biological and cultural evolution (Ambrose, 1984). Therefore, in studying the interactions between past humans and their environment in African high-altitude ecozones anthracology approach has been used to strengthen and further elucidate the ‘Mountain Exile Hypothesis’.
Previous studies have recorded a total of 331 rock shelters in the Bale Mountains (Reber et al., 2018). Among these, ten sites Fincha Habera, Mararo, Simbiro, Fish shelter, Gata I, Gata II, Umburi, Garba Guracha, Wela, and Dimtu were selected for this study based on certain criteria such as traces of human presence, altitude, and concentration of charcoals.
Sorting is the first step of the methodology used in this study. The selected anthracological samples at this stage were checked for mixed occurrences of artifacts such as ceramic sherds, lithics, and bones. Here the charcoals have to be separated from sediment by sieving. In this stage, samples were also weighed using a digital weighing machine called ‘Voltcraft’ (Fig. 2).
Documentation of anatomical features is the second step of our analysis. That takes place after the fresh sections of the charcoals were exposed by fracturing either by using hand pressures or a steel razor blade based on the size and nature of the sample. This produces a fresh section of the charcoals in all three anatomical planes (cross-section, radial, and tangential). This was followed by taking microscopic images through cross-sectional, radial, and tangential views. To do this, a KEYENCE electron microscope with magnification levels of 100X, 150X, and 200X was used to see the anatomical differences in 3D views and to capture microscope images of the samples.
One way to identify archaeological charcoal is based on a comparison with modern wood anatomy. This comparison allows for identifying the family, genus, and species levels of the archaeological samples. In this way, a total of seven different taxa were identified from all ten sites. The structure of the fossilized charcoal and its anatomic characteristics were carefully compared with modern ones retrieved from the inside wood database and Alemseged Beldados teaching references to find similar structures and descriptions. Some of the identified taxa through close correlation of charcoal samples from the BM and modern anatomy from inside wood data set are shown in (Fig. 3 and 4).
Results and Discussion
A total of 565 charcoal fragments collected from 10 different sites in the Bale Mountains were examined in this study. Of the total samples, 65% were identified in their respective taxa, whereas the remaining (35%) remain unidentified due to poor preservation, the absence of a sufficient number of comparative collections, and small sizes of the pieces less than the actual standard.
From the total identified seven different plant species were documented (Fig. 5). Based on charcoal evidence retrieved from the above discussed 10 sites, attempts were made to reconstruct the environmental condition of BM from terminal Pleistocene to Holocene (Fig. 6). The following diagram summarizes the percentiles of identified charcoal pieces from each occupational phase of Bale Mountains.
This study presents the results of the analysis of the anthracological remains retrieved from ten archaeological sites located in the Bale Mountains from the time span of 15,000 (terminal Pleistocene) to recent (late-Holocene periods). The results have shed new light on the poorly understood environmental conditions during human occupation phases in the Bale Mountains. By documenting and identifying the anatomical features of several hundreds of charcoal macro-remains from various excavated sites, the study also played a significant role to understand interactions between past humans and their environment in African high-altitude ecozones. In the findings of this study, various important issues such as firewood collection, vegetation cover, palaeoenvironment, prehistoric human settlement, ecological preferences, and adaptation strategies in the afro-alpine region of BM were also well-addressed.
Based on results obtained from anthracological analysis the characteristics of firewood collection in Bale Mountains during terminal Pleistocene to mid-Holocene suggested being either “naturalistic” or “embedded procurement”. Vegetation covers of the study area (characterized by low-density of vegetation cover) and the nature of occupiers (characterized by a group of mobile hunter-gatherers) are the two basic reasons that provided solid evidence to draw the nature of firewood collection in the region to be “naturalistic” during this period. It is also concluded that the nature of firewood collection in the region at the same time tends to be “embedded procurement”, so during hunting expeditions, or when returning, they collected firewood. Most resources (obsidian, chert, giant mole-rats, other prey, water, etc.) were available within a day’s walking distance, so there was no need for “direct procurement” or search for firewood only.
The finding of this study also indicates a change in firewood collection afterward the mid-Holocene either caused by increased awareness toward burning properties of specific taxa, environmental change, or change in the dietary system. This change was inferred from the co-occurrences of potential firewood with poor burning wood (A. afra and S. gigantum) with good burning properties (H. abyssinica, J. procera, and H. revoltanuem).
The results of this study also demonstrate the presence of varied vegetation cover and so a variation in environmental conditions between the plateau and the northern escarpments in the Bale Mountains during the terminal Pleistocene. Accordingly, the plateau areas were dominantly covered by Ericaceae vegetation indicating warmer and moisture climates, whereas in the northern escarpment Myrsinaceae and Ericaceae vegetation co-dominated together indicating increased drier climatic conditions. The early Holocene period was also characterized by the dominance of Myrsinaceae and Ericaceae plant families indicating the continued warmer climatic condition of the terminal Pleistocene. The Mid-Holocene occupation phase yielded the smallest number of charcoal samples indicating a dramatic decline in charcoal concentration caused by the shift of evergreen vegetation of terminal Pleistocene and early-Holocene to grassland during this period. The late Holocene anthracological analysis results were classified into the last LSA and pastoral occupation phases due to their difference in taxa compositions. The last LSA occupation phases of the late-Holocene period were characterized by the decline of the Ericaceae plant in the northern escarpment indicating the drier climatic conditions during this period. Sites located along the plateaus are characterized by the dominance of Ericaceae vegetation cover indicating humid and moist climatic conditions. The anthracological remains in the Bale Mountains after 2,000 years have shown increased selection toward specific taxa indicating the early arrival of pastorals in the region. This period was characterized by co-dominance of arboreal trees with Ericaceae vegetation signifying the occurrences of the dry and humid period.
Regarding ecological adaptation and preferences, the anthracology study results demonstrate that prehistoric hunter-gatherers used different ecological zones very variably, with different tasks at different sites. This was also proven by geographical, environmental, subsistence, and technological differences that were recorded between sites located in the northern escarpment and high-plateau settlement sites.
I would like to acknowledge Dr. Alemseged Beldados and Dr. Götz Ossendorf who supervised the work presented in this thesis. My heartfelt gratitude also goes to the “Mountains Exile Hypothesis research project”, for allowing me to join their research group and conduct my MA thesis research as part of their research project. I am extremely grateful to all staff members of ARCCH, especially Yared Asefa and Sahleselassie Melaku for letting me use their laboratories with all the organized equipment and computers. Financial support for this research has been provided by the French Center for Ethiopian Studies (CFEE) and the School of Graduate Studies of Addis Ababa University.
Ambrose, S. H. (1984). Holocene Environment and Human Adaptation in the Central Rift Valley, Kenya. [Doctoral Dissertations, University of Californian, Barkley].
Asouti, E. (2001). Charcoal Analysis From Çatalhoyuk and Pinarbasi, Two Neolithic Sites in The Konya Plain, South-Central Anatolia, Turkey. [Doctoral Dissertations, Institute of Archaeology University College London].
Ossendorf, G., Groos, A. R., Bromm, T., Girma, M., Glaser, B., Lesur, J., Schmidt, J., Akçar, N., Bekele, T., Beldados, A., Demissew, S., Hadush, T., Nash, B.P., Nauss, T., Negash, A., Nemomissa, S., Veit, H., Vogelsang, R., Woldu, Z., Miehe, G. (2019). Middle Stone Age foragers resided in high elevations of the glaciated Bale Mountains, Ethiopia. Science, 365(6453), 583–587.
Ossendorf G., Alemseged, B., Ralf, V., Lars, O., Joséphine., L Minasie, G., Zinash, L. (2017). Archaeological Research Report for Authority for Research and Conservation Field Work Report1–6.
Kabukcu, C. (2018). Wood Charcoal Analysis in Archaeology. In: E. Pişkin et al. (eds.), Environmental Archaeology. Springer Nature, 133–154.
Reber, D., Fekadu, M., Detsch, F., Vogelsang, R., Bekele, T., Nauss, T., & Miehe, G. (2018). High-Altitude Rock Shelters and Settlements in an African Alpine Ecosystem: The Bale Mountains National Park, Ethiopia. Human Ecology, 46(4).
Scheel-Ybert R. (2018). Anthracology: Charcoal Analysis. In: Smith C. (eds) Encyclopedia of Global Archaeology. Springer, Cham.
Vogelsang, R., Bubenzer, O., Kehl, M., Meyer, S., Richter, J., & Zinaye, B. (2018). When Hominins Conquered Highlands an Acheulean Site at 3000 m a.s.l. on Mount Dendi/Ethiopia. Journal of Paleolithic Archaeology. 1(4).
Zimmer, C. (2019). In the Ethiopian Mountains, Ancient Humans Were Living the High Life, The New York Times.