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To test the isolated and combined effects of drought and defoliation on biomass partitioning and water relations, four-year-old saplings of Quercus robur L. and Q. petraea (Matt.) Liebl. were investigated under controlled conditions. It was hypothesized that defoliation leads to a reduction of late wood and that, as a consequence, subsequent drought stress will more rapidly lead to desiccation damage due to the loss of reserves in water transport capacity. Alternatively, defoliation could have a negative effect on water relations via a growth reduction of the fine-root system, thereby diminishing the trees capacity for water uptake. Four treatments were applied to each species:(1) control C,(2) defoliation in two consecutive years De,(3) drought stress in the second year Dr,(4) a combination of (2) and (3) DeDr. Drought-stressed trees showed a decrease of predawn and midday water potentials and of maximum stomatal …