Response of high-latitude forests to a warmer and CO2-enriched atmosphere: tree rings in a process-based model

Temperatures in Arctic and subarctic North America have been rising in recent years and are projected to continue to rise. Furthermore, atmospheric carbon dioxide is increasing around the globe. This project will evaluate the response of white spruce to these ongoing changes. It will use archived samples from ten sites, standard tree-ring methodologies supplemented by novel chemical analyses, and numerical models to understand tree growth response to changing environmental drivers. The Alaskan timber industry has been in decline in recent years. Successful outcomes from this project will provide useful information to forest managers and planners. Workforce development will be promoted as this would be the first NSF award to the principal investigator. It will also provide support for the training of a post-graduate scholar. Finally, it will involve undergraduate students in the research activities. Educational outreach will be accomplished through workshops to be offered to high school students from a school serving a population that is under-represented in science and engineering fields. The project will advance the use of tree-ring data in understanding forest growth responses to natural and anthropogenic forcings. Extending traditional tree-ring width and maximum latewood density records, the principal investigators will establish a high latitude network of stable carbon (del13C) and oxygen (del18O) isotope measurements, which provide an independent constraint on such changes relative to traditional dendroclimatological measurements. This project represents an interdisciplinary opportunity to combine three distinct disciplines: (1) basic dendrochronological techniques, which allow for precisely-dated, quantitative and verifiable long-term tree-ring records; (2) low temperature geochemical tools to measure del13C and del18O ratios that will independently reflect environmental variables including temperature, precipitation, relative humidity and long-term physiological information on water use efficiency in natural forests; and (3) the joint use of a process-based mechanistic model, MAIDENiso, to distinguish between the confounding effects of increases in temperatures and atmospheric CO2 and to predict boreal forest response under different scenarios, and the NASA GISS ModelE2 general circulation model to provide inputs to MAIDENiso.