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Biogeographic variation in jack pine in contrasting climates: Implications for tree response to global change.
Tjoelker, Mark1, Oleksyn, Jacek2,3, Reich, Peter2, 1 2 3
ABSTRACT- Genetic and environmental sources of variation in traits underlying survival and growth of trees across large climate gradients are poorly quantified, yet critical to predicting responses to climate warming. We tested the hypotheses that biogeographic patterns in traits are genetic in origin, associated with long-term adaptation of local populations to climate, and reflect tradeoffs that mediate response to climate warming. We measured survival, growth, and needle traits in trees of 20 geographically diverse jack pine (Pinus banksiana) populations (44 to 57 °N) grown in common-garden plantations in northwestern Ontario, Minnesota, and Michigan, spanning much of the climatic range of the species (0.5 to 9.0 °C). Growth and survival declined with climate warming based on transfer distances between populations and planting sites. Populations originating in cold climates had shorter needles with a lower specific needle area, lower relative water content, and higher water-use efficiency compared to populations from warmer climates. At the colder sites these traits were associated with increased needle longevity and plant survival. Rates of net photosynthesis, nitrogen concentration, and longevity in needles exhibited both genetic and environmental variation. For northern populations grown in a warmer climate, lower rates of photosynthesis coupled with a shorter needle lifespan were associated with reduced tree growth and survival. Selection for trait combinations that confer greater survival in cold climates has likely resulted in constraints on growth that limit responses to climate warming. Tradeoffs in traits and their genetic and environmental variation suggest that population differences will be important in predicting large-scale responses of this boreal species to climate change.
KEY WORDS: jack pine, biogeography, climate change, needle traits