© 2000 Heron Publishing—Victoria, Canada
Light absorption and bole volume growth of individual Douglas-fir
trees
Andreas Brunner (1) and Gordon Nigh (2)
1. Danish Forest and Landscape Research Institute, Hørsholm Kongevej 11, DK 2970 Hørsholm, Denmark (abr@fsl.dk) / 2. Research Branch, British Columbia Ministry of Forests, P.O. Box 9519, Stn. Prov. Govt., Victoria, B.C. V8W 9C2, Canada / Received September 30, 1998
Summary
Empirical growth and yield models for forest management are evolving toward individual-tree models that are capable of simulating
the growth of mixed and uneven-aged stands. Spatially explicit (i.e., distance-dependent) models usually modify the growth
of trees by means of competition indices; however, these competition indices rarely simulate the light available for tree
growth explicitly. We used tree growth data from an even-aged, unthinned, 50-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stand in British Columbia to test the hypothesis that the amount of absorbed light is a good predictor of
diameter at breast height, height, and bole volume growth of an individual tree. We also explored the relationships between
these variables. A spatially explicit light model was used to simulate photosynthetically active radiation absorbed by individual
trees during a growth period (APAR) based on detailed canopy architecture information. For the purpose, we used a weighted
leaf area (WLA) that is linearly related to APAR. Because of the integration of light absorption by a tree crown, estimates
of WLA were highly correlated with leaf area for dominant trees. For suppressed trees, leaf area was a poor estimator of WLA.
The relationship between WLA and bole volume growth was nonlinear, indicating a higher light-use efficiency in suppressed
trees than in dominant trees. This relationship was strong enough to be useful for growth modeling. Only height growth of
suppressed trees was affected by WLA. We conclude that single-tree WLA can be used as a process-oriented competition index
in growth models for forest management.
Keywords:
APAR, canopy architecture, competition, growth model, leaf area, Pseudotsuga menziesii.
