Desired REgeneration through Assisted Migration (DREAM)

Overview of DREAM project sites in Wisconsin, USA and Quebec, Canada.

Climate change is altering conditions across the planet. Increasing temperature and variations in amount and seasonality of precipitation throughout the year will continue to impact how species respond. The future is uncertain. Thus, natural resource managers need climate-informed decision support tools to effectively plan for and counteract these changes to sustain long-term forest health and resilience.

Projections indicate changes in climate may outpace the rate of natural plant adaptation and migration. This mismatch presents a significant challenge for resource managers as they make decisions on what tree species to select, grow, and plant during reforestation and restoration projects. 

How can land managers be sure that trees planted today will meet the climatic challenges of tomorrow? One strategy that holds promise is assisted migration. Assisted migration is defined as the human-assisted relocation of species in response to climate change and may include one of the following components:

• Assisted population migration involves the movement of seed sources or populations to new locations within a historical range of variability.
• Assisted range expansion is the movement of seed sources or populations from their current range to suitable areas just beyond their current range, facilitating or mimicking natural dispersal. 
• Assisted species migration is the movement of seed sources or populations to a location outside of the established range of a species, beyond locations accessible by natural dispersal.

Approach

Conceptual model of how the Desired REgeneration through Assisted Migration (DREAM) framework incorporates approaches climate and forest dynamics modelling, plant physiology, and silviculture in a structured, complementary, and self-strengthening manner.

The Desired Regeneration through Assisted Migration (DREAM) project is an international collaboration that seeks to diminish these uncertainties through a structured process that uses basic and applied forest research to derive climate-informed planting approaches. Our approach includes four steps to safeguard success in assisted tree migration:

1. Create management tools using bioclimatic models to identify when and where to source tree seed.
2. Test the ecophysiology of putative climate-adapted seedlings to determine temperature and moisture tolerances.
3. Study climate-informed plantings’ response to silvicultural treatments to identify sustainable practices.
4. Model dynamics of climate-informed planting scenarios using tested physiological tolerances.

Climate Analog Models

Climate analog models are increasingly used to forecast potential future climate change impacts on ecological systems. Specifically, climate analogs match projected future climates with contemporary climates on the landscape. For example, if an ecosystem is projected to experience a warmer and drier climate, climate analog models locate locations elsewhere on the landscape that are also similarly warm and dry now. The locating of climatic analogs relative to future conditions supports identification of source populations and/or novel tree species that may be potentially future adapted to climate change in assisted migration applications.

Northern Research Station researchers are developing next generation climate analog models by incorporating tree species range information with climate analog models, thus easing the decision process in developing assisted migration action. After identification of analog locations, our next two components begin to tease apart the influence of environmental variation on physiological tolerances.

Testing Physiological Tolerances

Every species has a set of environmental conditions within which it can best survive and reproduce. Abiotic conditions, such as temperature and soil chemistry and biotic conditions, such as browsing and competition, influence growth and population.

By testing the physiological tolerances of tree species, Northern Research Station scientists are working to identify species that have a higher ability to cope with extreme conditions (e.g., drought tolerance) as well as how changing environmental factors may impact tree growth and vigor. Testing the physiological tolerances of tree species can provide answers to land managers on what species may thrive in future conditions before costly investment and waiting decades to monitor outcomes.

Silvicultural Scenario Planting

Sourcing seedling stock from the appropriate climate analogs and testing them for their physiological tolerances alone will not guarantee planting success. Experimental plantings are necessary to observe seedling survival, growth, and condition as they occur under a wide range of environmental conditions known to strongly affect seedling success.

Our researchers are conducting experimental planting trials. The DREAM approach differentiates itself from other assisted migration trials in that planting trials explicitly consider and manipulate three factors known to strongly affect seedling success: light levels, competing vegetation, and deer browsing (Figure 2). By planting future-adapted seedling stock under a broad set of conditions, the DREAM approach will provide guidelines on how to maximize climate-adaptive success efficiently and cost-effectively.

Forecast Modeling

Given the pace of climate change there is urgency to discerning whether assisted migration approaches will bolster climate resiliency in the long-term. In this phase of DREAM we will use the forest landscape model, LANDIS-II, to explore how climate-adaptive seed sourcing and climate interact to influence future tree performance and broader forest landscape dynamics under contrasting climate scenarios. By parameterizing tree species’ vital attributes (e.g., growth, survival, drought tolerance) with data obtained in our physiological and silvicultural trials, we will be able to evaluate whether climate-informed management will sustain forest productivity and ecosystem goods and services under increasing climate change better than conventional management over long-term timeframes.

Expected Outcomes

Given the high level of uncertainty in the timing and intensity of climate change and the resulting impact on forests, land managers need access to the best available science to support strategies that confer resilience to a broad range of climatic futures.

This research will build a foundation of identifying tree species and nursery stock that could perform well as climate continues to change as well as develop the silvicultural tools that will help managers plant the forests of tomorrow, today.