How does environmental context influence the leaf phenology of tree species in Maritime Canada?

Hemiboreal forest encompasses the shifting optimal distribution limits of both boreal and temperate forest types, providing an opportunity to develop insights for the potential effects of global change on each forest type. Leaf phenology, the timing of leaf life cycle events, serves as a dynamic indicator of biological response to climate change and signifies the potential robustness or susceptibility of particular species to future change. In order to better understand how environmental context influences the leaf phenology of hemiboreal tree species we installed a network of 34 leaf phenocam stations across Maritime Canada encompassing a range of 3° latitude and 2 °C in annual average temperatures. The most common broadleaf species observed were red maple (Acer rubrum) and paper birch (Betula papyrifera), while the most common needleleaf species we observed were red spruce (Picea rubens) and balsam fir (Abies balsamea). Our phenocam stations consist of a solar-powered consumer grade cellular time-lapse camera and colour reference panel, and were installed prior to and throughout the 2019, 2020, and 2021 growing seasons. We dissected image field of views into regions of interest corresponding to discernable individuals and used green chromatic coordinate curve fitting and threshold extraction approaches. We found that most species had a high degree of plasticity in phenological response to varying site conditions, though some had a conserved response to varying site conditions relative to other species. We also observed an unusually early fall green-down for paper birch at one site in July of 2021. This suggests that climate change may have differential effects on hemiboreal tree species due to phenology triggers being distinct among species. This work demonstrates the complexity of environmental influence upon leaf phenology, as well as the utility of phenocams in monitoring leaf phenology in remote regions of Maritime Canada.