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We studied growth, crown architecture, and specific leaf area acclimation of a shade-intolerant species, Pinuscontorta Dougl. ex Loud. var. latifolia Engelm., and a moderately shade-tolerant species, Pseudotsugamenziesii var. glauca (Beissn.) Franco, using naturally regenerated saplings along a wide range of light conditions. Study sites were located within a dry-summer, cool-temperate climate represented by the Dry Cool Interior Douglas-fir biogeoclimatic subzone near Williams Lake, British Columbia, Canada. In an open light environment, Pinuscontorta had a greater growth increment in both terminal and lateral shoots than did Pseudotsugamenziesii. With decreasing light availability (i) terminal increment, mean lateral increment, and total lateral increment decreased in both species (although Pinuscontorta reduced lateral growth significantly faster than Pseudotsugamenziesii); (ii) the ratio of mean lateral to terminal increment in Pinuscontorta did not change, but significantly increased in Pseudotsugamenziesii; (iii) the ratio of total lateral to terminal increment in Pinuscontorta decreased, but increased in Pseudotsugamenziesii; and (iv) specific leaf area in both species increased (in Pseudotsugamenziesii, it was always higher and increased marginally faster than in Pinuscontorta). We concluded that the less shade-tolerant Pinuscontorta was less plastic in crown architecture and specific leaf area than the more shade-tolerant Pseudotsugamenziesii.

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To evaluate the variation in trembling aspen (Populus tremuloides Michx.) productivity at a large geographic scale, we examined the relationships between site index and environmental factors from 142 even-aged, fully stocked stands located on a variety of sites across interior British Columbia. Site index was derived from stem analysis and the environmental measures included climate surrogates (latitude, longitude, and elevation), biogeoclimatic zone, slope– aspect, actual soil moisture regime (SMR), and soil nutrient regime (SNR). The spatial gradients (latitude, longitude, and elevation), slope–aspect, SMR, and SNR affected aspen site index, but their relationships greatly varied with biogeoclimatic zone. At the provincial scale, these relationships were weaker than on the zonal scale. Among the models developed for predicting aspen site index, we recommend the zone-specific all-factor model for application, which explained 82% of the variation of site index and provided unbiased and precise predictions.