Upon an urgent need for evaluating forest resilience and stability under changing climate, we investigated tree species changes in New England forests and what they mean to the future forests in the region. In this study, we used the USDA Forest Service forest inventory and analysis (FIA) data between 1995 and 2016 to explore forest biodiversity patterns along climate gradients and changes over the decades. FIA provides periodic data of sampled plots and trees for the region, including ~6,000 plots and more than 33,000 individual trees. We applied biodiversity models to develop indices for analyzing data. As some species play important roles in determining ecosystem functioning and processes, we selected a few species including sugar maple (Acer saccharum) and eastern hemlock (Tsuga Canadensis) for special inspection regarding concerns about their declines due to environmental or pathological stresses. We also examined red maple (Acer rubrum) and black birch (Betula lenta) in the region because some studies considered them to be the species replacing sugar maple and hemlock, respectively.
Results/Conclusions
Along the latitudinal gradient of New England, tree species diversity increases from the north to the south at a rate about 2-3 species per latitudinal degree. Sugar maple and eastern hemlock have relatively narrow distribution centers but responded differently to changing climate. As sugar maple prefers cold winters and well-drained deep soils, its center has retreated to mountainous areas of Vermont and northern New Hampshire. Eastern hemlock, often found in lowland and riparian zones, has its center moved northward from Connecticut and Massachusetts to New Hampshire. Hemlock woolly adelgid (Adelges tsugae) that has killed hemlock trees in CT and MA could have been benefited by warmer winters. Red maple and black birch prefer warmer climate without distribution center in New England. Black birch shares a moist habitat with eastern hemlock and has moved in when the latter declined. Red maple, an opportunist, has adapted to places left by sugar maple. As sugar maple has an important ecological role in northern hardwood forests and eastern hemlock a significant impact on riparian ecosystems, they are vulnerable to changing climate. The potential replacements could affect resilience and stability of ecosystem functioning in New England forests and many ecosystem services we have relied on.