The summer water balance in a Danish oak forest was studied during a period of 5 years. Interception reduces rainfall inside the forest by about 15%. Variations of the saturated soil moisture amount to some 10% of the water available to plants. Nevertheless, in most summers low soil moisture only restricts evapotranspiration during July. Insufficient leaf area is a major factor in restricting evapotranspiration: oak leaves develop late, and defoliation by insects also has a noticeable effect. The difference between potential and actual evapotranspiration normally ranges between 50 and 100 mm but reached 150 mm in 1976. Yet even in this dry year the vegetation recovered at once as soon as the water stress had been removed.

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