A COMPARISON OF RAINFALL IN DIFFERENT WOODLANDS

At Bedgebury the rainfall in thirteen forest plots planted withdifferent tree species has been compared with that in the open.In all these forest plots the trees have closed canopy within20 years of planting and the canopies differ considerably intheir structure. From 6 to 93 per cent. of the gross rainfallmay be retained on the tree canopies and lost to the soil. Theproportion of precipitation intercepted is greatest in lightrains and least in heavy rains. During light showers considerablymore moisture is retained on the conifer than on the hardwoodcanopies. In the heavier showers rainwater flows down the stems,but stem flow represents a small proportion of the total waterreaching the forest floor. The amount of water which reachesthe ground along the trunks varies with the species and thecharacter of branching. Some raindrops penetrate directly throughthe canopy, but many are intercepted by the canopies and coalesceto fall as large drops on the forest floor. These large waterdropstend to fall continuously on the same spot so that in the plantationsthe water is distributed unevenly. In the winter months, whenthe deciduous species have shed their leaves, snow penetratesmore easily through their canopies than those of the evergreenconifers.     

A COMPARISON OF LIGHT IN DIFFERENT WOODLANDS

At Bedgebury, a comparison has been made between the light intensitiesin fifteen forest plots and five open areas during the widerange of light conditions found in spring and summer. Lightdistribution under a tree canopy is extremely variable so thatit was essential to make a large number of random observationswithin each plot. The percentage of light penetrating the diversecanopies has been found to differ considerably both from plotto plot and from season to season. Some of the factors whichdetermine the amount of light passing through the canopy andtheir effects on the ground flora and natural regeneration arediscussed.     

THE CHEMICAL COMPOSITION OF PRECIPITATION IN ADJACENT FOREST AND OPEN PLOTS

The chemical composition of the precipitation in three openplots and under thirteen different forest canopies is comparedfor a 2-year period at an experimental forest in south-eastEngland. The average contents of sodium, potassium, calcium, and magnesiumin the precipitation in the open are 19, 3, 11, and less than4 Kg./Ha./annum respectively, compared with 33, 24, 24, and10 under the forest canopies. Only very small quantities ofphosphorus were present in the precipitation. The data are discussed with particular reference to the nutrientcycles of forest stands, the removal of nutrients by logging,and the maintenance of soil fertility.     

THE COMPOSITION OF TREE LEAVES

Tree leaves have been collected from three series of forestplots, each series with a wide range of tree species establishedon a fairly uniform soil type. The contents of sodium, potassium,calcium, magnesium, iron, manganese, silica, phosphorus, ash,carbon, and nitrogen in the tree leaves are given. The chemicalcompositions of the leaves are related to soil conditions andthe tree species selected for afforestation. When hardwood leavesare compared with softwood leaves some consistent differencesin chemical composition occur between the two groups at allthree localities. The ecological and silvicultural applicationsof foliar analysis are considered.