Soil erosion, iron smelting and human settlement in the Haubi Basin, north-central Tanzania. (Special section).

Soil erosion, iron smelting and human settlement in the Haubi Basin, north-central Tanzania. (Special section). The Haubi Basin, situated in the Irangi Hills of Kondoa District,Dodoma Region, Tanzania (FIGURE 1), exhibits some of the most extremeexamples of erosion and associated sedimentation in the region(Christiansson 1981; Payton et al. 1992) (FIGURE 2). The severity of theproblem, with its consequent loss of productive land, has been knownsince the beginning of the 20th century (Kannenberg 1900; Obst 1915).Recognition of the extent and severity of the issues encouraged theBritish colonial government to introduce a variety of measures aimed atsoil conservation in the 1930s (Fosbrooke 1950). These included theconstruction of check-dams, contour bunds and contour planting withsisal. After independence, a second programme of soil conservationmeasures was launched. These were initially similar to those employedunder colonialism, but later included de-stocking, resulting in theremoval of some 90,000 livestock from the most severely eroded areas. Asin the colonial period, recent overexploitation of land resources bylocal populations was regarded as the primary explanation for thecontinuing soil erosion. [FIGURES 1-2 OMITTED] Recent investigations involving a combination of geomorphological ge��o��mor��phol��o��gy?n.The study of the evolution and configuration of landforms.geo��mor studies with OSL OSL Open Source LabOSL Office of Student LifeOSL Open Source LicenseOSL Oregon State LibraryOSL Order of St Luke the PhysicianOSL Optical Stimulated LuminescenceOSL Oud Strijders Legioen (Dutch)OSL Order of Saint Luke dating of sediments, however, have identified two mainphases of erosion, both of which commenced well before the mid 19thcentury, and are therefore unrelated to recent land use practices(Eriksson 1998). The first occurred between 14,500 and 11,400 BP,coinciding with the end of the Pleistocene. Proxy environmental datafrom throughout the region indicate that this period was significantlywetter than today. The second phase appears to have commenced around 900years ago, with a new phase of gullying being initiated sometime afterAD 1400. Since farming and herding were well established across the regionby 2000-1800 BP, an increase in human settlement, iron smelting and/ orlivestock grazing could have contributed to the initiation of the secondmajor phase of soil erosion some 900 years ago. In an effort to assessthese hypotheses, a programme of survey and test-excavations was begunin 1999, aimed at collecting data on the dating, distribution andtopographical locations of sites of different periods, and recovery ofsamples that would allow the reconstruction of subsistence strategiesand metal-producing technologies. Three seasons of archaeological fieldwork have been completed. Afourth is scheduled for 2002. Over 50 separate artefact See artifact. scatters havebeen located, which range in date from the ESA to the 19th century.Three rock-shelters containing archaeological deposits, two with rockpaintings, have also been found. Over 70% of the scatters can beattributed to the Iron Age (i.e. post 2000 BP). These comprise surfacespreads of pottery, iron slag and tuyeres, with occasional pieces ofhouse daub. Most occur on the middle pediment pediment,in architecture, the triangular gable end on a building of classic type or a similar form used decoratively. It consists of the tympanum, or triangular wall surface, enclosed below by the horizontal cornice and above by the raking cornice, which follows the slopes above Lake Haubi;have been cut by gullying up to 30 m deep; and are severely deflated.The only securely dated Early Iron Age site (Haubi 16) occurs at thehead of the gully system on the upper pediment slopes, whereas the bulkof the Later Iron Age (c. 1000-200 BP) sites are found lower down. Sitesdated after AD 1800 occur on both the middle slopes and lake basinfloor. A suite of radiocarbon assays on charcoal from in situ depositsor lumps of iron slag recovered from the Haubi and adjacent Mwisangabasins, when calibrated using the OxCal programme, tends to support theimpression gained from the survey data that there was a marked increasein settlement and smelting activity after c. AD 1300. Whether this apparent upsurge in activity was responsible fortriggering soil erosion remains uncertain, however. While there wascertainly an increase in iron smelting, metallurgical analysis ofsmelting debris suggests that the technology was very fuel efficient. Inaddition, former local iron-smelters claim to have used only three tofour hardwoods for charcoal (FIGURE 3). As these species make up only afraction of local forests, iron smelting by the late 19th centuryprobably had only minimal impact on the environment. Establishing theantiquity of such `species selectivity' will be a focus of the nextphase of research. Equally important will be to account for the increasein smelting activity from c. 1500 AD, and whether this was associatedwith an intensification of regional trade. One possibility, as yetunverified but suggested by similarities in pottery, is that the ironsmelters of the Irangi Hills were part of a network which linked themwith grain-producing areas over 100 km to the north around Engaruka,where extensive fossil fields and irrigation irrigation,in agriculture, artificial watering of the land. Although used chiefly in regions with annual rainfall of less than 20 in. (51 cm), it is also used in wetter areas to grow certain crops, e.g., rice. systems dating mostly tothe 15th-17th centuries still survive (Sutton 1998). [FIGURE 3 OMITTED] Acknowledgements. We are grateful to the Tanzania Antiquities Unitand COSTECH COSTECH Commission on Science and Technology for permission to undertake the archaeological research,which has been funded by the British Institute in Eastern Africa. Wewould like to thank all members of the MALISATA programme who havefreely shared their data with us, especially Dr Robert Payton andProfessor E.K. Shishira, along with Stephan Woodborne and the Quaternary quaternary/qua��ter��nary/ (kwah��ter-nar?e)1. fourth in order.2. containing four elements or groups.qua��ter��nar��yadj.1. Consisting of four; in fours. Dating Research Unit, Pretoria. The metallurgical analyses wereconducted by Bertram Mapunda at the Institute of Archaeology The Institute of Archaeology is an academic department of University College London (UCL), in the United Kingdom. The Institute is located in a separate building at the north end of Gordon Square, Bloomsbury. , London,while on a Commonwealth East African Visiting Scholarship organised bythe School of Oriental & African Studies. We are especially gratefulto the Institute's director, Professor Peter Ucko for having helpedfacilitate this. We would also like to thank all of the British,Tanzanian and Swedish students who have assisted with this work, and theresidents of Haubi for being so accommodating. References CHRISTIANSSON, C. 1981. Soil erosion and sedimentation in semi-aridTanzania: studies of environmental change and ecological imbalance.Uppsala: Scandinavian Institute of African Studies and Department ofPhysical Geography, University of Stockholm. ERIKSSON, M.G. 1998. Landscape and soil erosion history in CentralTanzania: a study based on lacustrine la��cus��trine?adj.1. Of or relating to lakes.2. Living or growing in or along the edges of lakes.[French or Italian lacustre (from Latin lacus, lake) + , colluvial and alluvial deposits.Stockholm: Department of Physical Geography, University of Stockholm.Dissertation series 12. FOSBROOKE, H. 1950. The fight to rescue a District, East AfricanAnnual for 1950: 61. KANNENBERG, H. 1900 Reise durch die Hamitischen Sprachgebiete umKondoa, Mitteilungen von Forschungsreisenden und Gelehrten aus denDeutschen Schutzgebeiten 13: 144-72. OBST, E. 1915. Das abfluBlose Rumpfscollenland im nordostlischenDeutch-Ostafrika. Bericht fiber eine im Auftrag der HanburgischenGegraphischen Gesellschaft in der Jahren 1991/12 usgefuhrteForschungsreise, Mitteilungen der Geographischen Gesellschaft inHamburg, Band 29. PAYTON, R.W., C. CHRISTIANSSON, E.K. SHISHIRA, P. YANDA & M.G.ERIKSSON. 1992. Landform land��form?n.One of the features that make up the earth's surface, such as a plain, mountain, or valley.landform?A recognizable, naturally formed feature on the Earth's surface. , soils and erosion in the north-eastern IrangiHills, Kondoa, Tanzania, Geografiska Annaler 74A: 65-79. SUTTON, J.E.G. 1998. Engaruka: an irrigation agricultural communityin the northern Tanzanian Rift Valley before the Maasai era, Azania 33:1-37. Mats Eriksson, Lane, British Institute in Eastern Africa, PO Box30710, Nairobi, Kenya. pjlane@insightkenya.com Mapunda, ArchaeologyUnit, University of Dar es Salaam The University of Dar es Salaam is a university in the Tanzanian city of Dar es Salaam. The university was born out of a decision taken in 1970 to split the then University of East Africa into three independent universities; Makerere University (Uganda), University of Nairobi , PO Box 35050, Dar es Salaam Dar es SalaamLargest city (pop., 1995 est.: 1,747,000), capital, and major port of Tanzania. Founded in 1862 by the sultan of Zanzibar, it came under the German East Africa Co. in 1887. ,Tanzania. bbbmapu@udsm.ac.tz Eriksson, Dept for Natural Resources andthe Environment, SIDA, 10525 Stockholm, Sweden. mats.eriksson@sida.se