Forests and Rainfall

Abstract

THE question of the influence of woodland upon rainfall is a very old one, yet it cannot be said even now to be fully answered. While there is indisputable evidence from all parts of the globe that the reckless destruction of forest-growth has brought progressive desiccation in its train, it has only comparatively recently come to be realised that the problem is essentially hydrological rather than meteorological. When, indeed, one reflects that a forest is itself primarily an adaptation to rainfall and other climatic conditions, it is somewhat surprising that the earlier investigators should have expected to find anything more than a secondary reaction of the forest upon rainfall. No doubt the characteristic type of forest prevailing in moist regions like Europe helps by maintaining the humidity of the atmosphere to equalise, if not slightly to increase, the rainfall over the year as compared with denuded tracts; but, on the other hand, recent research by Quayle in Australia (Proc. Roy. Soc. Victoria, vols. 33 and 34, 1921 and 1922) has shown that where forest and scrub are composed of drought-resisting species, reducing transpiration to a minimum, a distinct increase of rainfall has followed deforestation in the interests of settlement and the replacement of xerophilous vegetation by grass and crops.