Acclimation of trees and ecosystems to higher temperature and altered water sources

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Human activities are altering the concentration of atmospheric carbon dioxide with consequences such as warmer air temperatures and altered precipitation and snow melt patterns. I propose to initiate a series of new lab and field studies to investigate the acclimation and adaptation of northern conifer trees and whole ecosystem response to altered environmental conditions. Lodgepole pine (Pinus contorta) and Douglas-fir (Pseudotsuga menziesii) trees dominate the eastern slopes of the Rocky Mountains in southern Alberta at the sharp transition zone between grassland and forest ecosystems. This is an ideal area and set of species to use in studies of tree and ecosystem physiology because this transition zone should be very susceptible to anticipated climate changes, including warmer temperatures and shifts in the availability of water sources (altered snow melt patterns, change in spring/summer precipitation). My planned studies will investigate the response of photosynthesis, respiration, transpiration and water-use efficiency to increases in temperature and the physiological mechanisms controlling the observed responses. We will study the linkages between the efficiency of water transport through tree stems and tree sensitivity to high temperature-induced declines in photosynthesis and growth. Stable isotope tracers will be used to measure variation in the uptake and use of snow melt water and spring/summer precipitation by trees. Our measurements will be compared to predictions of physiological models to gain further understanding of the mechanistic controls and the reasons for potential differences in sensitivity between species in their response to environmental changes. Finally, our measurements will be used to initialize and test a detailed ecosystem model under current conditions, so that the model can be used to predict tree and ecosystem physiological responses under proposed scenarios of future climate change.