Geoarchaeological evidence for the construction, irrigation, cultivation, and resilience of 15^th--18^th century AD terraced landscape at Engaruka, Tanzania

Abstract

Agricultural landscapes are human-manipulated landscapes, most obviously in areas modified by terracing and/or irrigation. Examples from temperate, arid, and desert environments worldwide have attracted the attention of many disciplines, from archaeologists, palaeoecologists, and geomorphologists researching landscape histories to economists, agronomists, ecologists, and development planners studying sustainable resource management. This article combines these interdisciplinary interests by exploring the role archaeology can play in assessing sustainability. Our case study is Engaruka, Tanzania, archaeologically famous as the largest abandoned irrigated and terraced landscape in East Africa. The site has been cited as an example of economic and/or ecological collapse, and it has long been assumed to have been irrigated out of necessity because agriculture was presumed to be nearly impossible without irrigation in what is now a semiarid environment. Geoarchaeological research refutes this assumption, however, demonstrating that parts of the site flooded with sufficient regularity to allow the construction of more than 1000 ha of alluvial sediment traps, in places greater than 2 m deep. Soil micromorphology and geochemistry also record changes in irrigation, with some fields inundated to create paddylike soils. Geoarchaeological techniques can be applied to both extant and abandoned agricultural systems, thereby contributing to an understanding of their history, function, and sustainability.

Diversification, Intensification and Specialization: Changing Land Use in Western Africa from 1800 BC to AD 1500

“…The construction of terraced field systems occurs in several locations in Africa (Grove and Sutton 1989;Lang and Stump 2017;Stump 2010;Widgren 2000Widgren , 2010, but within our area and period of interest (western Africa up to AD 1500) this system appears to be limited to the Mandara Mountains of northern Cameroon. Other terraced regions of western Africa, such as the Kofyar in Nigeria (Netting 1993), were likely terraced some time after our study period, and several of these are documented by AD 1800 (Widgren 2018).…”

Drivers of increased soil erosion in East Africa’s agro-pastoral systems: changing interactions between the social, economic and natural domains

“…This often led to communal usage and conservation of those ecosystems with strong local controls to safeguard continued services (Conte 1999;Haugerud 1989;Lawi 2002;Tengö and Hammer 2003;Thornton 1980). In response to the challenging East African conditions, farming systems developed in a way to build and sustain productive soils (Lang and Stump 2017;Widgren and Sutton 1999). For example, intercropping in fertile and wet areas, where a permanent and extensive cover with multiple crop types protected the soil from erosion and regenerated the productivity, as well as providing farmers a more divers output secured from crop failures.…”

“…However, East Africa's agro-pastoral systems are shaped by millennia of coadaptation, reciprocal influencing and feedback mechanisms between communities and ecosystems. It is argued that agropastoral communities could only persist by developing systems which were able to conserve or improve the soil properties (Berkes et al 2000a;Gual and Norgaard 2010;Lang and Stump 2017;Tengö and Hammer 2003;Widgren and Sutton 1999). In this review, the drivers of increased erosion rates in East Africa are studied through the lens of the three domains of sustainable development: natural, social and economic (Brundtland 1987;Griggs et al 2013), and their interactions in complex adaptive agro-pastoral systems as illustrated by Fig.…”

Conservation through Biocultural Heritage—Examples from Sub-Saharan Africa

“…Landscape memories can be understood as forms of materialised human practice, such as built environments and archaeological sites, including settlement systems and land-use systems linked to user and property rights-what Widgren [98,99] has called 'landesque capital'. Across the continent, there are many examples of irrigation or terracing system landscapes that are relict (see for instance Engaruka in Tanzania [100][101][102], Nyanga in Zimbabwe [103] and Mpumulanga in South Africa [104]).…”