Studies of the water relations of Pinus sylvestris in plantation conditions. V. Responses to variation in soil water conditions.
On the Dry plot, rain was prevented from entering the soil; on the Irrigated plot, the soil was kept near field capacity by irrigation; the Normal plot represented normal forest conditions. In 1958, the Dry plot attained a soil-water deficit of 25 cm by September with no effect on transpiration. In 1959, transpiration on the Dry and Normal plots fell below that on the Irrigated plot when the soil-water deficits exceeded 22 cm. Transpiration on the Dry plot was 70% and on the Normal plot 80% of that on the Irrigated plot throughout September 1959; the soil-water deficit on the Dry plot then was 30-35 cm and was numerically a little less than the storage capacity of the soil for available water as estimated by moisture-release experiments.