The water balance components of Mediterranean pine trees on a steep mountain slope during two hydrologically contrasting years

•A water balance method was developed for open forests on shallow soil.•Sapflow measurements allow quantification of bedrock water uptake.•Sapflow was highly correlated with the Voronoi polygon area around the tree.•Bedrock water uptake can cover up to 100% of Pinus brutia transpiration in summer.•Hydrologic models need to consider bedrock water dynamics.