This study characterized the height growth and crown form of 14-year-old balsam fir regenerated naturally under a light gradient varying from 3 to 83% of photosynthetic photon flux density (PPFD). After 14 years, total height growth was correlated with percent PPFD (R2 = 0.766; p < 0.001). From 3 to 25% of PPFD, balsam firs went from a suppressed stage with an umbrella type crown shape to a full grown stage with a cone type crown shape. This morphological change was caused by a greater increase in leader length compared to the mean nodal branches length. The number of nodal and internodal branches increased with PPFD. Balsam fir crown morphology showed a strong plasticity with a light gradient going from 3 to 83% of PPFD.
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Parent et al. (1995) studied this question.