Water relations of tree crops: a comparison between Corsican Pine and Douglas Fir in south-east England.
In further work [cf. F.A. 27 No. 106], the annual cycle of water movement has been studied over five growing seasons in adjacent semi-mature stands of Corsican Pine and Douglas Fir, growing on deep porous soils in Bramshill Forest, Hampshire. Periods of soil water deficit in the two stands have been identified from records of gypsum-block resistance measurements of soil moisture tension. Rainfall over this period has been equated with total evaporation and compared with values of open-water evaporation calculated from climatic records. Estimates have been made of water use by the two species, and the site factors affecting these estimates BIOLOGY-ODC 18 269 have been examined. It is concluded that Corsican Pine, which dries the soil more deeply and intensely than Douglas Fir, uses more water during the period of deficit. The causes of these differences are not fully understood, but it is possible that wind may interact with the distinctive canopy structure and leaf pattern of the species and thereby affect transpiration, though the rates of loss of intercepted rainfall seem to be similar. There may be differences in the rate of uptake of water as affected by rooting pattern, and in its subsequent movement to the transpiring surfaces, and the effects of the bracken understorey and humus layers should also be considered.KEYWORDS: Pinus nigra var. maritima P.n. var. calabrica water relations, hydrological \ Pseudotsuga menziesii water relations, hydrological \ Soil moisture \ soil water requirements \ different species \ Water relations \ plants effects \ deficit