Resisting climate change by creating forest refugia

Models of the state’s future climate do not favor the survival of some of Minnesota’s tree species. However, that doesn’t mean these species don’t hold intrinsic ecological, cultural or economic value.

We need to work to retain these species in our landscape and protect them from the impacts of climate change. On the climate adaptation spectrum, resistance-focused management approaches aim to maintain the current conditions of the ecosystem in the face of a changing climate. Resistance approaches improve the defenses of the forest against the impacts of climate change and other disturbances.

One resistance strategy involves creating refugia. Refugia are areas that remain buffered from climate change over time and can protect vulnerable species from the impacts of warming temperatures and more variable precipitation.

In the long term, climate refugia create key areas of biodiversity critical for maintaining ecosystem health and productivity.

Some tree species are particularly vulnerable due to less favorable climate projections or critical forest health risks. They need management focused on protection and retention. 

Some species are particularly at risk due to major forest health threats, such as ash species due to the invasive emerald ash borer (EAB). If you are caring for trees that are currently or predicted to be impacted by forest health threats, work with a natural resource professional who can help you identify your goals, quantify risk and your risk tolerance, and determine appropriate management strategies.

Regardless of which species you are managing, we encourage you to work with a natural resource professional since decisions related to climate adaptation are site-specific, nuanced, and complex. 

Reduce stressors as much as possible

To nurture vulnerable species and improve forest health, focus on reducing and mitigating stressors that may impact the ecosystem. This includes protecting soil health, reducing competition, and increasing resilience to disease, insects, and severe disturbances. These practices are critical to maintaining a healthy forest, regardless of whether any vulnerable species are present.

Management strategies include, but are not limited to:  

• Promote a diversity of species, age classes, and stand structures to increase resilience to pests, diseases, and severe disturbances.
• Thin stands to reduce competition between trees for growing space. 
• Harvest sites with clay-heavy soils only during frozen conditions to prevent compaction and rutting. 
• Prevent and mitigate invasive plants by promoting a diversity of understory plant species.
• Use prescribed fire or thinning to reduce fuel load and risk of catastrophic fires.
• Promote healthy riparian areas to protect water and maintain habitat for wildlife.

Additional in-depth management strategies can be found in this adaptation resource by the USDA Forest Service.

Protect unique, sensitive, and at-risk sites and communities

The first step to creating refugia involves identifying 1) sensitive or at-risk species and communities you wish to protect, and 2) unique sites that can buffer the impacts of climate change.

Woodland stewards have different goals and objectives and may wish to protect or preserve different species or ecological communities. If a species you care about is listed as a “refugia” species in the recommended trees lists, align your management decisions to protect that species. You may also be interested in protecting a community of species, such as the unique plants and wildlife that grow in forested peatlands in northern Minnesota. 

Woodland stewards can create hotspot areas of biodiversity that are sheltered from the impacts of climate change. These sites foster biodiversity and promote ecosystem resilience as the climate continues to change.  Sites that are naturally buffered from the impacts of climate change include: 

• Areas that are cooler than the surrounding area, such as north-facing slopes and along the North Shore of Lake Superior.
• Areas with wetter soil conditions, such as sites with clay-heavy soils or groundwater-connected wetlands.

Manage and prevent significant forest health threats

Significant forest health issues threaten the state’s entire population of certain tree species. This includes ash, oak, and elm, which are impacted by emerald ash borer (EAB), oak wilt, and Dutch elm disease (DED), respectively.

Implement management strategies that mitigate the impacts and prevent the spread of forest health issues if these species are found in your woodland and you are located within the current range of these forest health threats.

Proactively improve the resilience of your woodland and keep an eye open for any signs of major forest health issues even if you are not currently threatened by these insects and diseases.