The effects of seed dispersal and seedling establishment limitations on climate-driven tree species range shifts in the northeastern U.S.

The Northern Forest is maintained mostly by natural regeneration, but assisted migration may be required as climate changes. However, our ability to predict tree species’ establishment under changing climate in this complex mountainous region is still rudimentary. While the regeneration of the boreal cold-tolerant conifers species (red spruce, balsam fir) appears to be shifting upslope, this is not true for the dominant temperate deciduous species (sugar maple, American beech). Although edaphic factors (soil pH, mycorrhizae) explain some of this deciduous species’ ‘failure to migrate’, an empirical model is needed to integrate fine- scale seedling establishment with intermediate-scale seed dispersal to better understand tree regeneration under changing climate. We propose to develop species regeneration models by integrating field and greenhouse experiments with field observations across a large, well- established network of sites spanning all four U.S. states containing Northern Forest (previously funded by NSRC and NSF awards to the lead PI). We will quantify how regeneration of the four dominant species can be limited by (1) seed dispersal and (2) seedling establishment by conducting (a) seed addition experiments on plots in the network and (b) seedling establishment experiments in greenhouse and field settings. Our models will provide quantitative guidelines on target densities and site conditions (preparation) for adaptive forest management and conservation using assisted migration along regional climate-edaphic gradients. The project will train an early-career (post-doctoral) scientist, a graduate student, and several undergraduates. Our collaborators will help facilitate workshops to disseminate project findings to appropriate stakeholder groups across the region