The Influence of Neighbours on the Growth of Trees I: The Demography of Buds in Betula pendula

The growth of primary branches of four-year-old silver birch trees growing close to neighbours was followed over a period of three years. Branches were divided into three groups: those entering closely into each other's canopy, those growing into zones with no neighbour, and an intermediate category. On each branch the following variables were measured: total number of buds, number of living buds, number of lateral branches, gross and net bud production, and bud mortality. Before the start of the study the trees had been growing without neighbours. There were no significant effects of neighbours after one year of the experiment but by the third year all variables were showing some response. Fewer buds were `born' and a greater proportion died in the areas of the crown most subject to interference from the branches of neighbouring trees and this was reflected in smaller mean branch size in these areas. The age of a branch was also an important factor affecting performance. Significant interactions between branch age and interference zone for the number of living buds, gross and net bud production and bud mortality indicated that the effect of neighbours varied with branch age. The behaviour and fate of a bud appear to be conditioned more by its local environment than by its position on the tree of which it is a part.