I evaluated the relationship between trees and grasses in semi-arid savannas in South Africa and reviewed the role of trees on human-managed lands in dry areas of Africa. Trees transport water and nitrogen via their roots from deeper soil to upper layers of the soil, from where the grasses take these up. The water and nutrients from deeper layers of the soil would otherwise not be available to the grasses, so in a way trees help the transfer of these unavailable resources to grasses. Grasses under trees also have higher nitrogen content in their root,s an important nutrient for plants. I illustrate the crucial role of trees in two human-used landscapes in areas with low rainfall in Africa: Agroforests and Rangelands. Trees not only prevent soil erosion, invasion by weeds, aid in better water and nutrient management but also provide additional economic benefit to the associated human communities.