adapting the temperature-driven hypotheses of ecophysiological models predicting leafout to include spring frost probability.

The fast rate at which climate change operates (Loarie et al., 2009), paired with the increase in frequency and intensity of extreme climatic events (Bonsal, Zhang, Vincent, & Hogg, 2000), can desynchronize the annual dormancy-growth cycle of trees with air temperature (Parmesan & Yohe, 2003). Climate warming-induced earlier dormancy release in spring and later autumn hardening of tree tissues could extend the growing season and increase forest

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Climate change affects timings, frequency, and intensity of frost events in northern ecosystems. However, our understanding of the impacts that frost will have on growth and survival of plants is still limited. When projecting the occurrence of frost, the internal variability and the different underlying physical formulations are two major sources of uncertainty of climate models. We use 50 climate simulations produced by a single-initial large climate ensemble and five climate simulations produced by different pairs of global and regional climate models based on the concentration pathway (RCP 8.5) over a latitudinal transect covering the temperate and boreal ecosystems of western Quebec, Canada, during 1955–2099 to provide a first-order estimate of the relative importance of these two sources of uncertainty on the occurrence of frost, i.e. when air temperature is < 0 °C, and their potential damage to trees. The variation in the date of the last spring frost was larger by 21 days (from 46 to 25 days) for the 50 climate simulations compared to the 5 different pairs of climate models. When considering these two sources of uncertainty in an eco-physiological model simulating the timings of budbreak for trees of northern environment, results show that 20% of climate simulations expect that trees will be exposed to frost even in 2090. Thus, frost damage to trees remains likely under global warming.