Effects of light and intraspecific competition on growth and crown morphology of two size classes of understory balsam fir saplings

This paper characterizes the growth and crown morphology of young balsam fi r saplings naturally regenerated under a gradient of understory light envir onments and intraspecific competition densities for two size classes (50-10 0 cm and 100-200 cm). Most growth and crown morphological parameters invest igated were strongly related to the natural light gradient investigated (3- 83% full sunlight), but the relationship tended to plateau at around 25% fu ll sunlight. The relationships were generally better for the larger size cl ass. Intraspecific competition did not significantly affect growth and crow n morphology of saplings receiving less than 25% full sunlight, but it affe cted relative height growth, relative radial growth and the apical dominanc e ratio for those receiving more than 25% full sunlight (R-2=0.506; p<0.001 ; R-2=0.403; p<0.002; R-2=0.348; p<0.001, respectively). These results sugg est that live crown ratio, apical dominance ratio and the number of interno dal branches can provide, alone or in combination, useful indicators of vig our for understory fir. Such a study provides the basic data inputs require d for the development of empirically-derived mechanistic models that can pr edict understory tree growth and survival. (C) 2001 Elsevier Science B.V. A ll rights reserved.