Radial growth response of four dominant boreal tree species to climate along a latitudinal gradient in the eastern Canadian boreal forest

To address the central question of how climate change influences tree growth within the context of global warming, we used dendroclimatological analysis to understand the reactions of four major boreal tree species - Populus tremuloides, Betula papyrifera, Picea mariana, and Pinus banksiana - to climatic variations along a broad latitudinal gradient from 46 to 54 degrees N in the eastern Canadian boreal forest. Tree-ring chronologies from 34 forested stands distributed at a 1 degrees interval were built, transformed into principal components (PCs), and analyzed through bootstrapped correlation analysis over the period 1950-2003 to identify climate factors limiting the radial growth and the detailed radial growth-climate association along the gradient. All species taken together, previous summer temperature (negative influences), and current January and March-April temperatures (positive influences) showed the most consistent relationships with radial growth across the gradient. Combined with the identified species/site-specific climate factors, our study suggested that moisture conditions during the year before radial growth played a dominant role in positively regulating P. tremuloides growth, whereas January temperature and growing season moisture conditions positively impacted growth of B. papyrifera. Both P. mariana and P. banksiana were positively affected by the current-year winter and spring or whole growing season temperatures over the entire range of our corridor. Owing to the impacts of different climate factors on growth, these boreal species showed inconsistent responsiveness to recent warming at the transition zone, where B. papyrifera, P. mariana, and P. banksiana would be the most responsive species, whereas P. tremuloides might be the least. Under continued warming, B. papyrifera stands located north of 49 degrees N, P. tremuloides at northern latitudes, and P. mariana and P. banksiana stands located north of 47 degrees N might benefit from warming winter and spring temperatures to enhance their radial growth in the coming decades, whereas other southern stands might be decreasing in radial growth.