In temperate Europe, the wild cherry tree (Prunus avium L.) produces highly valued wood and is well suited to agroforestry conditions by its high light requirements. However, it is extremely sensitive to intra- and inter-species competition, which impairs its growth. We studied water competition between ten-year-old wild cherry and grass in a silvopastoral plot where trees were planted in a grazed pasture. Tree diameter and height increments, grass and tree predawn and midday leaf water potentials, volume soil water content, and grass and tree root elongations measured using rhizotrons were compared in four conditions: tree with grass, tree without grass, grass alone, and bare soil. The trees with grass clearly suffered more from water deficit than the trees without grass. Observations of root development and volume soil water content suggest that this resulted from severe root competition with grass for water.