Leaf phenology in 22 North American tree species during the 21st century

Discusses a model developed to predict tree species leaf out under two climate change scenarios. An illustration of research use of phenological event data.

"Recent shifts in phenology are the best documented biological responseto current anthropogenic climate change, yet remain poorly understoodfrom a functional point of view. Prevailing analyses arephenomenological and approximate, only correlating temperature recordsto imprecise records of phenological events. To advance ourunderstanding of phenological responses to climate change, wedeveloped, calibrated, and validated process-based models of leafunfolding for 22 North American tree species. Using dailymeteorological data predicted by two scenarios (A2: +3.2 °C and B2:+1 °C) from the HadCM3 GCM, we predicted and compared range-wide shiftsof leaf unfolding in the 20th and 21st centuries for each species.Model predictions suggest that climate change will affect leafphenology in almost all species studied, with an average advancementduring the 21st century of 5.0 days in the A2 scenario and 9.2 days inthe B2 scenario. Our model also suggests that lack of sufficientchilling temperatures to break bud dormancy will decrease the rate ofadvancement in leaf unfolding date during the 21st century for manyspecies. Some temperate species may even have years with abnormalbudburst due to insufficient chilling. Species fell into two groupsbased on their sensitivity to climate change: (1) species thatconsistently had a greater advance in their leaf unfolding date withincreasing latitude and (2) species in which the advance in leafunfolding differed from the center to the northern vs. southern marginsof their range. At the interspecific level, we predicted thatearly-leafing species tended to show a greater advance in leafunfolding date than late-leafing species; and that species with largerranges tend to show stronger phenological changes. These predictedchanges in phenology have significant implications for the frostsusceptibility of species, their interspecific relationships, and theirdistributional shifts." [Abstract]