Divergent leaf phenology trends between boreal and temperate species in the Acadian Forest Region

The Acadian Forest Region is a temperate-boreal transitional zone in eastern North America. Therein, both forest types are vulnerable to environmental changes due to their proximity to biogeographical range limits. Using four growing seasons of phenocam-derived leaf phenology observations for the species Acer rubrum, Betula papyrifera, and Abies balsamea from across the Acadian Phenocam Network as well as multiple growing season observations from the North American PhenoCam Network we parameterized eight leaf emergence and six leaf senescence models for each species which together span a range in process and driver representation. With climate models from the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5) we simulated future patterns in leaf emergence, senescence, and season length (senescence minus emergence) for these species at sites within the Acadian Phenocam Network. Model performances were similar across models. By the late 21^st century, leaf emergence could be about two to three weeks earlier for both boreal and temperate species. The timing of leaf senescence may become continuously delayed for boreal species like Betula papyrifera and Abies balsamea, though remain relatively constant for temperate species like Acer rubrum. This has important implications for carbon uptake, nutrient resorption, ecology, and ecotourism for the Acadian Forest Region. Phenocams have the potential to rapidly advance process-based model development and predictions of leaf phenology in the context of climate change.