Impacts of size and competition on tree form and distribution of aboveground biomass in Scots pine

Abstract

Studies on tree allometry have often focused on the average tree of a representative stand across an age gradient. Another dimension of change in tree form is the variation caused by differences in competitive status, evident between trees of one stand or between stands of comparable age but different stocking densities. This study compares the structural relationships of dominant Scots pine (Pinus sylvestris L.) trees over a wide age range with those in young trees of similar age but different competitive status. Allometric relationships are developed between biomass components and diameter, and crown structure is analysed in terms of crown allometry, pipe model relationships, and foliage density. The differences in allometry seem to be largely due to the rise of the crown base, which is positively correlated with size in the age series and negatively correlated with size in the cross-sectional data. The allometric relationships of the crown are less variable, but differences are found in the crown size to foliage biomass ratios between the two data sets. In the age series, foliage biomass is proportional to crown surface area, while in the cross-sectional data, it is proportional to crown volume. It is concluded that the reaction to competition for light is twofold: (1) to allocate new foliage higher up and, consequently, to lift the crown base, and (2) to grow sparser crowns.