Trees on farms play a vital role in providing diverse goods and services to those farmers practicing agroforestry in Kenya. Other than the environmental advantages of agroforestry such as carbon sequestration and species conservation, trees provide soil and microclimate enhancement, deliver fruits, medicines, fodder, timber and fuelwood. (Akinnifesi et al. 2010). . Tree diversity help to diversify income , lower production risk and optimise the management of tree resources (Anorld and Dewees 1995). Promotion of on-farm tree planting activities requires detailed knowledge on these driving forces. Tree richness and diversity analysis is an important tool for selecting priority areas for tree growing and rehabilitation. However, tree species richness and diversity are influenced by numerous socio-economic and biophysical factors. The interaction of different biophysical and socio-economic factors help in conservation of species and prevent extinction. The purpose of this study was to assess the effects of different socio-economic and biophysical factors on tree richness and diversity in smallholder farms in the study area.