Forests of the Great Lakes region will likely experience some of the most dramatic changes in response to climate change in the continental U.S. In northeastern Minnesota, forests are vulnerable to declines in signature canopy tree species at the southern edge of their ranges—including Betula papyrifera, Populus tremuloides, Abies balsamea and Picea glauca. Empirical data shows temperate tree species such as red maple have a competitive advantage over boreal tree species as the climate continues to warm. Simulation modeling indicates that temperate tree species (“climate-ready”) that currently occur in the region at low abundance levels (e.g., Quercus rubra, Q. macrocarpa and Pinus strobus) will be well-adapted to future climate conditions, but also demonstrates that the natural colonization rates of these species cannot keep pace with the rapidly changing climate leaving many suitable niches unrealized. In the first facilitation project of its kind, we tested the efficacy of within-range planting of climate adapted species. In 2013 and 2014 we planted a total of 4,400 climate-ready seedlings using both local and seed sources from further south or west where climate conditions are warmer. We assessed seedling growth, survival and phenological responses to a range of planting conditions, including regional climate variation.
In the early years of the project, Q. rubra and Q. macrocarpa had good (>90%) overall survival rates. Q. rubra and Q. macrocarpa sourced from central Minnesota showed higher survival rates compared with northern seed sources. Q. rubra showed greater height growth across all site temperature-moisture conditions compared to Q. macrocarpa. Central Minnesota Q. rubra had the lowest specific leaf area along with the greatest diameter and height growth. Although Minnesota P. strobus survival did not vary by temperature or precipitation levels at the planting sites, northern sourced seedlings survived better overall. Mean annual height growth (cm) was higher overall at moist, relative to dry sites for Minnesota seedlings. Northern Minnesota seedlings maintained growth over the range of site temperature and moisture conditions, while seedlings from a central Minnesota seed source showed reduced growth at cool sites and had 9% lower survival, overall. Field responses to facilitation plantings were consistent with our understanding of the native range of each of the experimental tree species. Early results suggest that the facilitation model using within range planting of climate-adapted temperate zone tree species may be an effective strategy for maintaining key forest functions in a changing climate.