Effects of transformation processes on plant species richness and diversity in homegardens of the Nuba Mountains, Sudan

Abstract

Traditional homegardens (HGs) are considered to harbor high levels of plant diversity and have been therefore characterized as sustainable agro-ecosystems suitable for on-farm (incl. circa situm) conservation of plant genetic resources. While the functional structure of traditional HGs is poorly understood specifically for semi-arid and arid regions, their plant species richness and diversity is increasingly threatened by recent and fast evolving agricultural transformation processes. This has been particularly claimed for traditional jubraka HG systems of Sudan. Therefore, sixty-one HGs in four villages of the Nuba Mountains, South-Kordofan Province, Sudan, were randomly selected, geographically recorded and plant richness and abundance determined and plant diversity parameters calculated. In addition, socio-economic household data were assessed by interviews and soil samples taken to allow a comprehensive analysis of putative factors affecting HG plant diversity across different villages, levels of commercialization and plant species composition based clusters. A total of 110 species from 35 plant families were grown in the HGs along with 71 ornamentals. Perennial species accounted for 57 % including 12 indigenous fruit tree (IFT) species and six exotic fruit tree species. Mean species richness of useful plant species (excluding ornamentals) per HG was 23 (range 6–46). On average, 41 % of the 23 species per HG were of exotic origin, however, with a large range (21–83 %) among locations. Mean diversity and evenness indices were 1.46 (range 0.49–2.42) and 0.48 (0.15–0.87), respectively. The level of commercialization of HGs only marginally affected species diversity measures although the species richness was significantly higher for commercial than subsistence HGs. Species richness was higher on lower (6.6–7.2) pH soils. IFT richness was highly variable, but non-significantly different across the four locations. Plant species richness and diversity was high in comparison with other HG systems in semi-arid regions. Cluster analysis was found to be a valuable tool to classify HGs and to extract homogeneous HG types with low, intermediate and high richness and diversity. In addition, the share of exotic and ornamental species in HGs indicated a trend towards the loss of traditional farming practices, particularly in areas with good market access. The data did not indicate the hypothesized loss of inter-specific diversity due to commercialization and species richness was numerically even higher for market-oriented HGs compared to subsistence ones.