A comparison of rainfall in different woodlands

Abstract

At Bedgebury the rainfall in thirteen forest plots planted with different tree species has been compared with that in the open. In all these forest plots the trees have closed canopy within 20 years of planting and the canopies differ considerably in their structure. From 6 to 93 per cent. of the gross rainfall may be retained on the tree canopies and lost to the soil. The proportion of precipitation intercepted is greatest in light rains and least in heavy rains. During light showers considerably more moisture is retained on the conifer than on the hardwood canopies. In the heavier showers rainwater flows down the stems, but stem flow represents a small proportion of the total water reaching the forest floor. The amount of water which reaches the ground along the trunks varies with the species and the character of branching. Some raindrops penetrate directly through the canopy, but many are intercepted by the canopies and coalesce to fall as large drops on the forest floor. These large waterdrops tend to fall continuously on the same spot so that in the plantations the water is distributed unevenly. In the winter months, when the deciduous species have shed their leaves, snow penetrates more easily through their canopies than those of the evergreen conifers. © 1954 Oxford University Press.