When is a terrace not a terrace? The importance of understanding landscape evolution in studies of terraced agriculture

Abstract

Before the invention of modern, large-scale engineering projects, terrace systems were rarely built in single phases of construction, but instead developed gradually, and could even be said to have evolved. Understanding this process of landscape change is therefore important in order to fully appreciate how terrace systems were built and functioned, and is also pivotal to understanding how the communities that farmed these systems responded to changes; whether these are changes to the landscape brought about by the farming practices themselves, or changes to social, economic or climatic conditions. Combining archaeological stratigraphy, soil micromorphology and geochemistry, this paper presents a case-study from the historic and extensive terraced landscape at Konso, southwest Ethiopia, and demonstrates - in one important river valley at least - that the original topsoil and much of the subsoil was lost prior to the construction of hillside terraces. Moreover, the study shows that alluvial sediment traps that were built adjacent to rivers relied on widespread hillside soil erosion for their construction, and strongly suggests that these irrigated riverside fields were formerly a higher economic priority than the hillside terraces themselves; a possibility that was not recognised by numerous observational studies of farming in this landscape. Research that takes into account how terrace systems change through time can thus provide important details of whether the function of the system has changed, and can help assess how the legacies of former practices impact current or future cultivation.

Usable Pasts Forum: Critically Engaging Food Security

“…Geoarchaeological, archaeobotanical, and ethnobotanical work at Konso, Ethiopia, for example, suggests that risk mitigation rather than yield maximization is the primary concern across this extensive terraced landscape, with farmers interplanting a wide range of crops across different types of fields in different topographic locations and then removing or encouraging those species most suited to that year's rainfall (Thornton-Barnett 2019). Importantly, the recognition that this landscape includes different types of fields, forming what are in effect different ecological niches, was only achieved by charting the development of the agricultural system over approximately 600 years, including the identification of artificial sediment traps (Ferro Vázquez et al 2017).…”

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

“…The term terrace is used generally here and includes sediment traps, and terraces built for a variety of purposes, such as soil retention, water retention, and soil creation or improvement (Ferro-Vázquez et al 2017). The construction and maintenance of agricultural terraces requires substantial labor and time input from the community, and has a significant effect on local landscape processes (Ciampalini et al 2012;Tarolli, Preti and Romani 2014).…”

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

“…Research undertaken at Konso in Ethiopia offers an example of this, because here the construction of very similar sediment traps to those at Engaruka was facilitated by the loss of all of the topsoil and most of the subsoil from adjacent hillsides (Ferro-Vázquez et al, 2017). The improvement in economic productivity gained by the deliberate capture of fine clays and silts in irrigable sediment traps located next to rivers was thus achieved at the expense of wide-scale soil erosion nearby.…”