Effects of light and intraspeci®c competition on growth and crown morphology of two size classes of understory balsam ®r saplings

This paper characterizes the growth and crown morphology of young balsam ®r saplings naturally regenerated under a gradient of understory light environments and intraspeci®c competition densities for two size classes (50±100 cm and 100± 200 cm). Most growth and crown morphological parameters investigated were strongly related to the natural light gradient investigated (3±83% full sunlight), but the relationship tended to plateau at around 25% full sunlight. The relationships were generally better for the larger size class. Intraspeci®c competition did not signi®cantly affect growth and crown morphology of saplings receiving less than 25% full sunlight, but it affected relative height growth, relative radial growth and the apical dominance ratio for those receiving more than 25% full sunlight (Rˆ0.506; p<0.001; Rˆ0.403; p<0.002; Rˆ0.348; p<0.001, respectively). These results suggest that live crown ratio, apical dominance ratio and the number of internodal branches can provide, alone or in combination, useful indicators of vigour for understory ®r. Such a study provides the basic data inputs required for the development of empirically-derived mechanistic models that can predict understory tree growth and survival. # 2001 Elsevier Science B.V. All rights reserved.