Plant diversity and determinant factors across smallholder agricultural management units in Central Ethiopia

Abstract

Forests in the highlands of Ethiopia have declined considerably, and the supply of forest-based ecosystem services is eroding. Managing agricultural landscapes as well as enhancing plant biodiversity in agro-ecosystems is and will continue to be one possible strategy to preserve biodiversity, ensure an ecosystem service supply and sustain agricultural productivity. This study investigated the current status and prospects of plant diversity and its determinants in an agricultural landscape dominated by smallholder farmers in Southern Ethiopia. Specifically, the study investigated effects of land use, altitudinal gradient, wealth status and household attributes on plant diversity in agricultural landscapes. A complete count, Y-frame transect sampling method and household interviews were used for the study involving 39 households and 115 sample plots. A total of 166 plant species belonging to 134 genera and 56 families were recorded in all land use types. Of these, 101 were woody plant species (51 trees and 50 shrubs), while 65 were cultivated herbs and grasses. Land use, altitude and household wealth status significantly influenced tree and shrub species richness. Among land uses, home gardens hosted the highest number of tree and shrub species. Upper altitudes and rich households also had the highest tree and shrub species richness compared to others. Plant diversity indices (Shannon, Simpson and Margalef) were affected by altitude, wealth status and land use types. Household location, wealth status, the household attributes of landholding and family size had strong and positive influences on the tree species diversity and woody stem density of households, while educational background and off-farm income were negatively related with household-owned tree stem density. Species preference ranking, seedling demand and importance value index computations indicated the dominance of exotic tree species, which may suggest their economic importance over indigenous tree species. In the long term, this might lead to dominance of exotic tree species in the landscapes, which could cause a potential future threat to the remnant indigenous plant diversity that is currently finding refuge in the agricultural landscapes.