Woody species diversity in a changing landscape in the south-central highlands of Ethiopia

Ethiopia hosts one of the richest flora and fauna resources in tropical Africa. However, this rich bioresource is decreasing due to extensive deforestation. The objectives of this study were to (i) investigate woody species diversity on smallholder cultivated land (crop fields and homegardens) and its implication for biodiversity changes over time: (ii) assess the dynamics of woody species diversity, density and structure with age of crop fields since conversion from natural forest using a chronosequence of farm fields; and (iii) assess the effects of some household and homegarden characteristics on woody species diversity around homegardens in the south-central highlands of Ethiopia. Woody species diversity in the adjacent natural forest was used as a reference. Systematic sampling was used to collect vegetation data from crop fields and natural forest, while simple random sampling within wealth categories was used to select sample households and their homegardens. In total, 70 woody species were recorded. The highest number of woody species (64) was recorded in homegardens, followed by crop fields (32) and the lowest number (31) in remnant natural forest. Despite the low species number, natural forest showed higher Shannon and Simpson diversity indices and Shannon evenness than crop fields and homegardens. This was due to the uniform distribution of species in natural forest compared with homegardens or crop fields. The diversity and density of woody species declined with increasing age of crop fields, while diversity of woody species increased with increasing age and size of homegardens. Wealth status of the households also affected species diversity in homegardens. Rich households kept a greater number of woody species, probably due to their larger-sized homegardens. Generally, the study showed that conversion of natural forest into cultivated land (mosaics of homegardens and crop fields) typical of the smallholder system in the highlands of Ethiopia does not result in a dramatic loss of species but that the spatial distribution, density and species composition may be altered. (c) 2008 Elsevier B.V. All rights reserved.