The inherent clinal responses of four quantitative traits thought to be adaptive for trees in cold-limited environments (i.e., height-growth cessation, growth rate, resource allocation to aboveground and belowground tissues, and resource allocation to photosynthetic and nonphotosynthetic tissues in the shoot) were characterized under nonlimiting conditions in a controlled glasshouse study for seedlings of three ecologically distinct and co-occurring northern tree species (Pinus contorta Dougl. var. latifolia Engelm. (lodgepole pine), Picea glauca (Moench) Voss x Picea engelmannii Parry ex Engelm. (interior spruce), and Abies lasiocarpa (Hook.) Nutt. (subalpine fir)). For each species, clinal trends were quantified among populations adapted to increasingly cold-limited climates across an elevation gradient approaching the tree line. In subalpine fir seedlings, strong clinal variation for all the quantitative traits indicated an increasingly conservative response to climate moving toward harsher conditions. Variation in lodgepole pine and interior spruce seedlings suggested a more plastic strategy, favoring competitive traits across a wide range of climate conditions. Study findings suggest that ecologically distinct species may exhibit different strategies in adapting to local climates.
