PS 42-50 - Assisted migration as adaptative and rehabilitation tool for degraded forests

Background/Question/Methods

Rehabilitation of degraded forests can mitigate the effects of global change through enhanced carbon sequestration. It can also improve the forests adaptive capacity by promoting resilience to disturbances through functional diversity. In this project, we assessed assisted migration, the deliberate displacement of tree species or populations to locations with suitable future climate conditions, as both adaptive and rehabilitation tools in degraded mixedwood forests.

To do so, we studied seedling survival and growth of 9 species through the abiotic (e.g. microclimate) and biotic (e.g. browsing, competing vegetation) filters in mixedwood plantings. We set the experiment in 2018 in high graded yellow birch (Betula alleghaniensis) – conifer stands, 120 km northwest of Quebec City, Canada. The factorial experimental design comprised canopy cover (clearcut vs partial cut), cervid exclusion (excluded vs non-excluded) and competing vegetation (removed vs non-removed) treatments. We planted species expected to have unfavorable (Picea glauca, Picea rubens, Thuya occidentalis), and favorable (Pinus strobus, Pinus resinosa, Acer saccharum) future habitat conditions, and species with potential new habitat in the area (Quercus rubra, Prunus serotina, Carya ovata). Seedlings were grown from seeds of locations associated to three climate analogues: current climate, projected climates for mid-century and end of century.

Results/Conclusions

Seedlings of all species, except for Acer saccharum and Carya ovata, grew 18 to 120% larger in basal diameter in open conditions than under partial cover after 3 growing seasons. The understory vegetation control treatment by mechanical release benefited the conifers and Quercus, although the magnitude of effects was smaller than that of canopy treatments with an increase of 9 to 15% in basal diameter. Planting under partial cover contributed to acclimate southern species such as Quercus rubra, which suffered frost damage during the Springs 2020 and 2021, mostly in clearcuts. The high survival rates (89%) observed in the first three years suggest assisted migration plantings may be a viable approach in degraded forests, however longer-term monitoring will be necessary to robustly evaluate practicality.