Woody species diversity and traditional knowledge of tree ecosystem services and disservices in homegardens in Southern Ethiopia

Homegarden agroforestry systems (HGAFS) in sub-Saharan Africa provide essential ecological and socioeconomic benefits. Their high tree and shrub diversity results in a complex interplay of trade-offs between the ecosystem services (ESs) and the potential ecosystem disservices (EDs) provided by trees and shrubs. Here we focused on HGAFS in the lowlands of the Southern Ethiopian Rift valley, and drawing on data from vegetation surveys of 191 homegardens, key informant and household interviews, focus group discussions, and species rankings, we aimed to (i) quantify geographical variation in tree and shrub species composition and diversity across HGAFS, (ii) identify the drivers behind this variation, and (iii) reveal traditional ecological knowledge (TEK) regarding the ESs and EDs provided by the tree and shrub species present. We recorded a total of 43 woody species from 37 genera and 27 families, with Moringa stenopetala (95%) and Mangifera indica (83%) the most frequent. We found that species composition and species richness significantly varied across villages and was also affected by the frequency of farmer’s contacts with development agents, whereas we found no impact of farmland ownership, farmer’s experience or training in agroforestry practices. Farmer’s ranking of the species according to nine categories of ESs and four categories of EDs showed that many of the most dominant species simultaneously provided both important ESs and EDs but that the former outweighed the latter. Despite HGAFS being a long-standing indigenous practice, there is an increasing reliance on development agents-based agricultural extension, which may inadvertently reduce the integration and transmission of TEK. Integrating Homegarden agroforestry systems into national conservation and agricultural policies, strengthening capacity-building for farmers and development agents, and reinforcing TEK transfer can enhance their sustainability.