Adaptability of natural regeneration in red pine-dominated ecosystems following experimental climate adaptation treatments

Background/Question/Methods

Tree regeneration is fundamental to ensuring future forest function, and uncertainty about future conditions, particularly climate, challenges forest managers to regenerate tree species that establish successfully under current conditions and will also tolerate the range of conditions (and potential change) anticipated long-term. The Adaptive Silviculture for Climate Change (ASCC) long-term study site at the Cutfoot Experimental Forest in north-central Minnesota, USA is assessing the impacts of three climate adaptation approaches (resistance, resilience, transition) and a no action, passive treatment in Pinus resinosa Ait. (red pine)-dominated forest ecosystems. In the fifth growing season following the initial treatments, we evaluated how these climate adaptation approaches have influenced natural regeneration and the understory woody community in terms of species abundance, community composition and diversity, and whether or not silviculture can be used to encourage natural regeneration that is more adaptable to changes in future climate. Natural regeneration of trees and shrubs were sampled May-August, 2019 across five replicates of the four treatments (total area about 200 ha). Using biomass calculated from field measurements and existing indices of species-specific climate adaptability ratings we calculated a community-weighted mean of adaptability, along with species diversity (H’) and species richness. Differences among treatments were tested with ANOVA.

Results/Conclusions

Relative to the passive treatment in which no management activities took place, each adaptation treatment (resistance, resilience, and transition) raised tree species diversity and richness significantly (F=10.71, p<0.001; F=7.352, p=0.004 respectively). The resilience treatment also contained the greatest overall woody species diversity (F=6.42, p=0.008) relative to the other three treatments. Following community weighted mean analysis, the transition treatment resulted in the greatest difference (a significant increase) in mean adaptability of natural tree regeneration over the passive treatment compared to the resistance and resilience treatments (F=7.138, p=0.017). While resistance, resilience, and transition treatments all increased naturally regenerated tree species diversity and richness relative to the passive control, they offered different benefits (e.g. species diversity vs. adaptability) in terms of climate adaptation. The greater levels of diversity within the resilience treatment may confer greater resiliency to the included stands following future disturbances while the greater adaptability within the transition treatment may help those stands avoid an undesirable state shift as climate continues to change and some species decline. Lastly, our work suggests that climate adaptation objectives may be achieved through natural regeneration in addition to or in lieu of artificial regeneration when resource constraints exist.