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Productivity potential of high-elevation forests in British Columbia is poorly understood despite continuing harvesting operations. We examined how site index of three principal tree species, subalpine fir (Abies lasiocarpa (Hook.) Nutt.), Engelmann spruce (Picea engelmannii Parry ex Engelm.), and lodgepole pine (Pinus contorta var. latifolia Dougl. ex Loud.), were affected by climatic and edaphic conditions in the Engelmann spruce–subalpine fir zone. We deliberately selected naturally established stands with a wide range in site quality, which are described by subzones, latitude, longitude, elevation, soil moisture regime (SMR), and soil nutrient regime (SNR). Site index varied among subzones for all three species, particularly between the parkland and the forested subzones. Increasing latitude and elevation resulted in a significant decrease in site index for all study species. Site index of subalpine fir and Engelmann spruce significantly increased with SNR from very poor to very rich while site index of lodgepole pine increased with SMR from moderately dry to moist and then decreased on very moist sites. The models developed accounted for 63–70% of variation of site index. These models, tested by independent data, were unbiased with mean prediction error of ±2.3, ±2.6, and ±1.8 m in predicting site index of subalpine fir, Engelmann spruce, lodgepole pine, respectively. They are recommended for estimating site index of the study species to assist in making silvicultural decisions in the interior subalpine forest. |
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