Crown-stem dimension relationships in two New Zealand native forests

The relationships between crown and stem dimensions of trees in two South Island, New Zealand, natural forests were investigated to determine whether they might explain differences in tree species composition estimates based on canopy area and basal area. Dacrydium cupressinum, a common canopy emergent at the lowland podocarp forest site, had the strongest relationship between crown and basal area and a significantly shallower slope than two common understorey trees at that site, Weinmannia racemosa and Quintinia acutifolia. Nothofagus solandri, the only canopy species at the montane beech forest site, showed an intermediate slope and level of correlation. We conclude that differences in estimates of species composition can be at least partly explained by species-specific differences in the relationship between crown area and basal area and that caution is required in interpreting species relative abundances where different methods have been used to quantify abundance. However, the relationships are not strong enough to warrant the calculation of equations for the prediction of crown area from basal area, as has been done for several open-grown tree species.