Ghanaian farmers have been practicing farming since time immemorial and trees are a normal component of farmlands. However, the choice of particular tree species and their population on the farms is greatly influenced by the farmers’ preferences and therefore, the utility value placed on particular tree species. This study was conducted to determine the number of trees per unit area of farmland, the diversity of the tree species, and the factors that influence farmers’ decision to leave trees on their farms in three districts of the Upper East region of Ghana. It also seeks to determine any relationship between tree density and the yields of commonly cultivated crops in the study area. The area falls within the Guinea and Sudan savanna zones, characterized by a short unimodal rainfall regime (about 5 months) and a rather long dry season. Twelve communities (4 per district) were randomly selected and farmers were interviewed on their reasons for allowing trees on their farmlands as well as the yields of major crops cultivated. Ten farms in each community were also randomly selected and inventories of trees were conducted, where trees were identified, and enumerated. Farm sizes were also measured. Mean tree population densities on farms were 18.5, 18.4 and 25.9 trees per hectare in the Garu-Tempane, Bawku West and Kassena Nankana West districts respectively. A Shannon Weiner diversity index of 1.563, 1.195 and 1.551 were calculated for Garu-Tempane, Bawku West and Kassena Nankana West districts respectively. Forty-two (42) different tree species belonging to 23 families were encountered in Garu-Tempane district, 28 species from 18 families were encountered in the Bawku West district and 37 species belonging to 21 families in the Kassena Nankana West district. Azadirachta indica, Combretum molle, Diospyros mespiliformis were the commonest on all farms. Factors that influenced farmers’ decision to allow trees on their farms were shade (22%), fuelwood (18%), food (15%), medicine (13%), housing (13%), soil improvement (10%), erosion control (7%), fodder (1%) and others (1%). Crop yields were generally high in the Bawku West district and there was no significant relationship between tree population density and the yields of crops.

Keywords: Population density; species diversity; species richness; agroforestry; tree-crop interaction.