OOS 28-3 - Survival, growth, and physiological performance of forest adaptation plantings across a range of canopy conditions in northern hardwood ecosystems

Background/Question/Methods
Recent and projected changes in climate and disturbance regimes are expected to shift suitable habitat conditions for numerous canopy tree species in north temperate ecosystems; however, there is limited ability for natural tree migration rates to track the rapidity of these changes. Given potential misalignment of current species assemblages with future climate conditions, there is a burgeoning interest in the application of adaptation strategies that deliberately adjust species composition through the planting of tree species adapted to future climates and other novel stressors, such as introduced insects and diseases. Nevertheless, these plantings are occurring in current ecosystems and management contexts, creating a need for operational evaluations of adaptation plantings especially in the context of ecological memory and working forest landscapes.

In this study, we examined the four-year survival and growth of future-climate adapted seedling transplants within co-produced operational-scale experiments across northern hardwood forests in northeastern US. Nine species were evaluated based on projected future importance under climate change and potential functional redundancy with species currently found in these ecosystems. We investigated how adaptation planting type (“population enrichment” vs. “assisted range expansion”) and local site conditions reinforce interference interactions with existing vegetation at filtering adaptation strategies focused on transitioning forest composition.

Results/Conclusions
Our results show performance of seedling transplants is based on species (e.g., functional attributes and size), strength of local competition (e.g., ecological memory), and adaptation planting type, a proxy for source distance. These findings were consistent across regional forests but modified by site-specific conditions such as browse pressure and extreme climate events, namely drought and spring frost events. Measurements of physiological performance reinforced the importance of drought in serving as a key filter that may limit the potential of isohydric species in future adaptation planting applications.

Our results highlight that managing forests for shifts in future composition represents a promising adaptation strategy for incorporating new species and functional traits into contemporary forests. Yet, important barriers remain for the establishment of future climate-adapted forests that will most likely require management intervention. Nonetheless, the broader applicability of our findings demonstrate the potential for adaptation plantings to serve as strategic functional nodes for establishment of future-adapted species across complex, connected landscapes.