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Evidence that higher [CO2] increases tree growth sensitivity to temperature: a comparison of modern and paleo oaks
Citation:
Voelker, S., M. Stambaugh, J. Renee Brooks, F. Meinzer, B. Lachenbruch, AND R. Guyette. Evidence that higher [CO2] increases tree growth sensitivity to temperature: a comparison of modern and paleo oaks. OECOLOGIA. Springer, New York, NY, 183(4):1183-1195, (2017).
Impact/Purpose:
As global atmospheric carbon dioxide concentrations ([CO2]) continues to rise over the next centuries, many regions across the globe are projected to undergo climate change that will cause key forest physiological functions to be impacted by warmer temperatures. Given the importance of forests to the global carbon cycle and the unknown magnitude to which [CO2] and temperature interactions may affect forest productivity, there is a need for a keen understanding of how tree growth responds to temperature and [CO2]. To test the growth-sensitivity to temperature under different ambient CO2 concentrations, we determined paleo ([CO2] 230 ppm) tree growth rates as they relate to variation in temperature during the last deglacial period, and compare these to modern ([CO2] 330 ppm) tree growth rates as they relate to spatial variation in temperature across the modern species distributional range. Modern and paleo tree growth rates were both positively related to temperature but greater [CO2] strengthened the relationship, suggesting tree growth will be increasingly sensitive to temperature under projected global warming and high-CO2 conditions.
Description:
Aim: To test the growth-sensitivity to temperature under different ambient CO2 concentrations, we determined paleo tree growth rates as they relate to variation in temperature during the last deglacial period, and compare these to modern tree growth rates as they relate to spatial variation in temperature across the modern species distributional range. During the deglacial period, [CO2] averaged about 230 ppm, whereas modern [CO2] averaged about 330 ppm.Location: Paleo oaks were sampled from Northern Missouri, USA. The paleo temperature reconstruction was from a lake in Northern Illinois, USA. Data used to quantify the growth-sensitivity to temperature for modern oaks were collected across the Great Plains, Midwest and Upper Great Lakes regions.Methods: Growth data were from 53 paleo bur oak log cross-sections collected in Missouri that were preserved in river and stream sediments. These oaks were radiocarbon-dated to between 10.5 and 13.3 cal kyr BP, which spans rapid warming during the last deglaciation. Growth data from modern bur oaks were obtained from increment core collections paired with USDA Forest Service Forest Inventory and Analysis data. Paleotemperatures were obtained from a high-resolution pollen-based reconstruction and modern temperatures were obtained from gridded meteorological data. Results: Growth-sensitivity to temperature (i.e. the slope of growth rate versus temperature) was significantly greater for modern oaks growing at an average [CO2] of 330 ppm compared to paleo oaks growing at an average [CO2] of 230 ppm. The relative frequency of modern oaks first increased then decreased with increasing temperatures along their distributional range, whereas that of paleo oaks increased steeply to an asymptote with increasing temperature.Main Conclusions: Modern and paleo tree growth rates were both positively related to temperature but greater [CO2] strengthened the relationship, suggesting tree growth will be increasingly sensitive to temperature under projected global warming and high-CO2 conditions.
