We report a study on water competition between eleven-year-old wild cherry and a permanent sward in a silvopastoral plot where trees were planted at wide spacing (6 ´ 8 m), which prevents intrusion of other competing trees. We compared the growth and water status of unweeded trees against weeded ones, particularly in terms of sward and tree root elongations as observed using rhizotrons. Complementary measurements were volumic soil water content, grass and tree predawn and minimum leaf water potentials and tree diameter and height increments. The weeded trees showed twice the diameter growth increase of the unweeded ones. The unweeded trees clearly suffered more than the weeded ones from water deficit as shown by the values of leaf water potential. Decreases in soil water content were greater for the association "tree+sward" than for the weeded trees. The observations of root development through the rhizotrons showed that the soil space was relatively shared between tree roots and those of sward though there was not a total exclusion. Sward roots were and grew rather in the upper horizons (0-40 cm) while tree roots were and grew rather in the deepest horizons (40-80 cm). At time of water deficit, the sharing of the soil space by tree and sward roots led to a severe water stress of trees through a progressive drying of the deepest horizons : sward roots extracted almost the whole available soil water from rainfall, resulting in drought maintenance in the deeper soil layers. Tree root growth was not directly influenced by that of sward root as globally the weekly root elongation rates were the same for the weeded and unweeded trees. Tree root growth appeared to be more influenced by the soil water potential (computed from the values of measured volume soil water contents). A relationship was put in evidence between the weekly elongation rate of tree roots (WER in m week-1) and the soil water potential measured at the end of the corresponding week (ysoil in -Mpa) in the following form : WER = [a ´ |(ysoil| / (|(ysoil | - b)] where a and b are two parameters. Consequently, tree root elongation is reduced as the soil water potential becomes more and more negative. As the uptake of water by sward roots in the upper horizons led to a progressive drying of the deepest horizons where the tree root system was in majority, tree in association with sward was in a situation of water stress, with small possibilities of root elongation and consequently limited possibilities to prospect wetter soil horizons.