Species variability in growth response to light across climatic regions in northwestern British Columbia

We characterize variation in radial and height growth of saplings of 11 tree species across a range of light levels in boreal, sub-boreal, subalpine, and temperate forests of northwestern British Columbia. Shade-tolerant species had the greatest response to an increase in light at low-light levels but had low asymptotic growth at high light. Shade-intolerant species had weaker responses to increases at low light but had the highest growth rates at high light. The effects of climate on intraspecific variation in sapling response to light were also related to shade tolerance: across different climatic regions, the most shade-tolerant species varied in their response to low light but not high light, while shade-intolerant species varied only in their high-light growth. Species with intermediate shade tolerance varied both their amplitude of growth at high light and the slope of the growth response at low light. Despite the interspecific trade-offs between high- and low-light growth, there was a striking degree of overlap in the light response curves for the component species in virtually all of the climatic regions. Successional dynamics in these forests appear to be more strongly governed by interspecific variation in sapling survival than growth.

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