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Growth of Pseudotsuga menziesii and Tsuga heterophylla seedlings along a light gradient: resource allocation and morphological acclimation

Summary

Published in Canadian Journal of Botany 75: 1424-1435

Silvicultural alternatives that differ in the degree of overstory removal may create shady environments that will be problematic for the regeneration of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Gradients of light in the field were used to compare mortality, growth, and leaf morphological acclimation of two conifer species of contrasting shade tolerances: Douglas-fir and western hemlock (Tsuga heterophylla (Raf.) Sarg.). Results after two growing seasons indicated that Douglas-fir mortality occurred mainly at relative light intensity (RLI) below 20%, while western hemlock mortality was evenly distributed along the light gradient. Height, diameter, and biomass of the planted seedlings increased with increasing light for both species but at different rates, and maximum biomass accumulation always occurred in the open. Douglas-fir allocated more resources to stem biomass than western hemlock, which accumulated more foliage biomass. Increases in specific leaf area for Douglas-fir seedlings occurred at RLI £ 0.4 and red / far red (R/FR) ratio £ 0.6, which appear to be the minimal optimum light levels for growth. Conversely, western hemlock seedlings adjusted their leaf morphology in a more regular pattern, and changes were less pronounced at low light levels. These results, along with early mortality results for Douglas-fir, suggest that the most successful way to artificially regenerate this species may be by allowing at least 20% of RLI for ensuring survival and at least 40% RLI for optimum growth.

Sector(s): 

Forests

Categorie(s): 

Scientific Article

Theme(s): 

Forestry Research, Forests, Silviculture

Departmental author(s): 

Hébert, François

Author(s)

MAILLY, Daniel and James P. KIMMINS

Year of publication :

1997

Format :

Paper

Keywords :

conifer, Pseudotsuga menziesii, Tsuga heterophylla, light, light quality, leaf morphology, acclimation, biomass, mortality, western hemlock, Douglas fir, silviculture of natural forests, lumière, qualité de la lumière, morphologie des feuilles, acclimatation, sapin de Douglas, pruche de l'Ouest, sylviculture des forêts naturelles résineuses, sylviculture des forêts naturelles, silviculture and yield of natural forests – softwood stands

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