Homegarden agroforestry system is recognized as inclusive and ecologically sound system. However, the recently observed change from enset-coffee based homegardens to cash crop khat, is expected to cause decline in tree species diversity and soil organic carbon. Thus, this study aimed at assessing the effect of traditional homegarden system change to khat based system on tree species diversity and soil carbon in Wondo Genet district, Sidama Region. Wondo Genet district was purposively selected as it is the main area of homegarden system change towards khat based system and Atotal of 4 kebeles were selected using systematic sampling method in which 120 households were randomly selected using systematic sampling method. The households were sampled along transect lines established in target kebeles. A sub-sample was taken for soil sampling and tree species diversity assessment in a plot size of 10 m x 10 m. Analysis of variance (ANOVA) was used to analyze the means of different fields for tree species diversity and soil organic carbon contents. Results revealed that, a total of 32 tree species were recorded in enset, enset and coffee and khat fields. Cordia africana, Persea americana, Carica papaya, Milletia ferruginea were the most abundant species. The traditional homegarden componets (enset and enset and coffee) fields had significantly higher (p<0.05) in terms of tree species diversity, richness, and density than the newly evolving khat field. Similarly, enset and enset and coffee fields had significantly higher (p<0.05) soil organic carbon content and stock at both surface soil depth (0-20 cm) and sub-surfaces soil depth (20-40 cm). Generally, the shift from enset and enset and coffee-based systems to khat was at the expenses of tree species diversity and organic carbon of the soil. Thus, development options which could enhance tree species diversity, soil organic carbon need to be designed.

Keywords: Agroforestry; Enset and coffee; Tree species; Diversity