16. Climate Change and Your Woodland: Assessing Risk and Adapting to Change

Stephen Handler, Climate Change Specialist, USDA Forest Service

Kris Tiles, Natural Resources Educator, University of Wisconsin-Extension

Jennifer Teegarden, Cooperative Forest Management Outreach Specialist, Minnesota Department of Natural Resources

As a woodland owner, you want to ensure that your woods stay healthy, resilient, and productive for years to come. The management actions that you take in your woods today will play out over decades, and your decisions will be realized and appreciated by future generations. Woodland stewardship requires this long-term perspective, and we know that the future is going to look a lot different than today. In fact, it is increasingly clear that changing climate conditions will present new challenges for woodlands in the future. This is why it is increasingly important to consider climate change as you develop your plans for woodland stewardship. This chapter covers information on assessing risks to your woods (and opportunities) from climate change, as well as some practical ways to adapt to change.

Climate Change Definitions

“Weather” is the term we use to describe short-term conditions in the atmosphere—conditions that can last for minutes, days, weeks, or even years. This includes the regular variation and unpredictable changes in day-to-day conditions, as well as the extreme conditions that stick in our memories. The summer heat wave, the “polar vortex” in the winter of 2019, the drought of 2012—these are all examples of weather events, because they occurred over short periods of time.

The “climate” is the long-term average in weather conditions in an area. The key difference between weather and climate is time. The usual standard is that it takes a minimum of 30 years of information to say anything reliable about the climate of an area, or to define a long-term trend that is meaningful. It is crucial to look at a long stretch of time when you’re trying to sum up the climate of an area, because we know that the Earth’s weather patterns can be erratic and unpredictable. Weather-related cycles like El Nino can repeat in semi-regular cycles over many years, so it’s important to account for these swings when you’re trying to describe the average of an area.

“Climate change,” similarly, is a long-term change in weather patterns that occurs over multiple decades. Climate change includes shifts in both the average weather conditions (average winter minimum temperature or average rainfall during the growing season, for example) as well as extreme weather events (frequency of tornadoes or 5-inch rain events, for example). Weather events such as heavy rainstorms, seasonal droughts, or late spring frosts can clearly have major impacts on woodlands in the Midwest, but these events are random and unpredictable. Climate change, on the other hand, indicates a long-term shift in the conditions of an area. We know that the climate ultimately controls what kinds of plant and animal life can survive in a particular area, and so a changing climate means that woods of the future may be living and growing under a different set of conditions than they are today.

On-going Evidence of Climate Change

Climate change has already been underway for several decades, and more changes are expected to occur. The overwhelming amount of evidence points to the fact that climate change is real, and the Midwest has not been immune to the effects. The National Climate Assessments from 2014 and 2018 list several on-going trends that have already been documented across the region:

• Annual average temperatures have increased about 1.3°F over the past century. The rate of increase has tripled in recent decades.
• Winters have been warming faster than other seasons.
• Nighttime temperatures have been warming faster than daytime temperatures.
• The growing season has lengthened by about 9 days since 1901 because winter is getting shorter.
• Multi-day heat waves have become more frequent since 1950.
• Annual precipitation has generally increased over the past century, by as much as 20 percent in some parts of the Midwest.
• Heavy rainfall events have become more common, and a larger percentage of our overall rain comes from heavy rain events.

Future Expectations

Understandably, there is uncertainty involved with making long-term future predictions of climate change. A large part of this uncertainty exists because the amount of future warming will depend on global decisions about the use of fossil fuel and renewable energy. But we have enough information to anticipate many changes that are likely to happen, especially if we plan across a range of potential outcomes. The National Climate Assessments also list several projected future impacts of climate change for the Midwest region:

• Annual average temperatures will rise by 6°F to as much as 9°F by the end of the century. Winter will continue to experience more warming than other seasons.
• As the 21^st century continues, winters will likely bring less ice cover and snowfall, and more winter precipitation will come as rain rather than snow.
• The growing season may increase by as much as one month by the end of the century.
• A greater share of our rainfall will come in large storms, with heavy rainstorms becoming 2 to 3 times more frequent by the end of the century.
• The Midwest may experience decreased soil moisture in the summer because of warmer conditions and longer growing seasons.

Climate Change Impacts to Woodlands

Climate change will directly and indirectly affect the woods in our region (Table 16-1). For example, the timing of leaf expansion is directly controlled by warming in the spring, and researchers have observed that the length of sugar maple’s growing season has already increased by 11.5 days over the past few decades in Michigan. There will also be indirect effects of climate change. For example, longer growing seasons mean that insect pests can complete more life cycles in one year, and milder winters mean that more insects are able to survive over the winter. These factors can work together and lead to increased insect pest damage, such as the multi-year outbreak of native eastern larch beetles that are affecting northern Minnesota’s tamarack.

A tool used to estimate changes in suitable growing conditions for tree species is the Climate Change Tree Atlas. The Tree Atlas uses climate models to assess whether individual species might have more or less suitable growing conditions in the future. Table 16-2 shows the Tree Atlas results for 16 common Midwestern tree species, projected across a range of future climate scenarios at the end of the 21^st century. The following characteristics can help in interpreting the table,

• An Increase indicates suitable growing conditions for the species is expected to increase more than 20 percent by the end of the century.
• A Decline indicates suitable growing conditions for the species is expected to decline more than 20 percent by the end of the century.
• A Mixed change indicates suitable habitat projections are mixed across a range of mild and extreme climate scenarios.
• These changes are averaged values across the regions indicated in the columns:
  • Midwest Region includes the states of Minnesota, Wisconsin, Michigan, Iowa, Illinois, Indiana, Ohio, and Missouri.
  • Northern Minnesota includes the Laurentian Mixed Forest Province in Minnesota.
  • Southern Wisconsin includes the southern half of Wisconsin below the “tension zone” line of the Laurentian Mixed Forest Province.
  • Southern Illinois includes the Central Interior Broadleaf Forest Province in Illinois.

Models like the Tree Atlas are only tools, and are not perfect. Models do not account for some factors that could be modified by climate change, like droughts, wildfire activity, and invasive species. These factors, and others, could cause a particular species to perform better or worse than a model projects. Despite these limits, models provide useful information about future expectations. It may be best to think of the output from tools like the Tree Atlas as an indicator of potential change.

Tree species with easily dispersible seeds, such as red maple, will likely occupy new habitat more quickly than other tree species. Trees will have a harder time migrating in highly fragmented or developed landscapes. Planting programs can help move tree species adapted to future conditions into new locations, but that will depend on decisions of individual woodland owners.

Assessing Risk in Your Woods

Impacts from climate change will not be spread evenly across the landscape. A variety of factors, such as soils, forest health, and past management, can influence how your woods will be affected by climate change. So you can think about “risk factors” that might make your woods more or less vulnerable to climate change. This is similar to the way a doctor might think about risk factors for heart disease when meeting with a patient. No one factor will automatically predispose a woodland to decline, but it certainly makes good sense to control as many risk factors as you can. It will be helpful to talk with a consulting forester or other professional to get their input on how these risk factors relate to your woods.

Here are some general risk factors for you to consider as you think about climate change and your woods, also represented in Figure 16-1. These will not apply to each and every woodland, but they are generally consistent across the Midwest.

1. Tree species diversity – Woods with a diverse mix of native species will have many options to respond to climate stressors, even if some species decline. Woods dominated by only one or two species are at higher risk of decline. Also, woods dominated by boreal species like balsam fir, black spruce, and quaking aspen may find future conditions less favorable than woods with species adapted to warmer, drier climates such as oaks and hickories.
2. Structural diversity – Woods with a diverse mix of age classes, multiple canopy levels, and complex features (standing and downed dead trees, for example) will have many microsites that can provide growing conditions for different species as conditions change. Woods with a simplified structure, such as even-aged trees, are less adaptable to future stress.
3. Regeneration – Woods with abundant and diverse tree regeneration, or with good regeneration potential, are prepared to cope with changes to the overstory. Woods with limited regeneration potential may be in serious risk if the overstory declines. Several factors can limit regeneration potential, including lack of overstory seed sources, browse pressure from deer, or competition from invasive plants.
4. Disturbance regime – Woods may be in a better condition if they have experienced natural disturbances, or if management has been designed to mimic natural disturbances. For example, a fire-dependent forest type may be overstocked with trees and stressed by competition if natural wildfire or thinning haven’t knocked back shade-tolerant species and reduced trees that could be fuel for wildfire.
5. Management history – Woods that have been enhanced through management will be more vigorous and able to tolerate future stress, such as a red pine stand that is regularly thinned to reduce competition and stress. Woods with past management that has removed the best trees, reduced diversity, or damaged the soils will be at greater risk of decline.
6. Pests and diseases (including earthworms) – Woods with minimal damage or no looming threats from pests and diseases may be better able to tolerate future stress from climate change. Woods that are already compromised by insect outbreaks, earthworm damage to soils, or disease may be less vigorous and more prone to increased damage.
7. Drought risk – Woods on moist soils, a north-facing slope, or with close connection to the groundwater will be at less risk of future drought stress. Woods on drought-prone soils, a southern aspect, or with a high stocking level may be more affected by future droughts.
8. Flood risk – Low-lying woods connected to a larger complex of wetlands may be less at risk from a high water event. For example, a riparian corridor connected to wetlands and backwater areas can more easily distribute water during a flood. Low-lying woods that are isolated, such as a small perched bog, may be more at risk of excessive flooding and water table fluctuations.
9. Local hydrology – Woods where natural hydrology has been maintained may be better able to cope with precipitation changes in the future. Woods with dikes, ditches, rutting, culverts, and other features that have altered how water moves may be at greater risk of excessive drying or swamping.
10. Harvest access and operability – Woods that can be accessed by heavy equipment at different seasons of the year will have greater management flexibility in the future. Woods with sensitive soils may require frozen ground or deep snow for logging equipment to operate safely and without causing damage. As winters continue to get warmer, there will be less operating time in the winter to access these sites so it may be harder to perform management actions.

The effects of climate change will be more serious for some trees and in some places on the landscape. Thinking specifically about the risk factors in your woods can help you reduce your level of risk through time. Woodlands may respond slowly to climate change, so do not expect changes to occur all at once. This means you have time to gradually improve the health and vigor of your woods. The remaining portion of this chapter focuses on actions you can take to help your woods adapt or tolerate the changes that lie ahead.

Helping your Woods Adapt to Climate Change

Climate change adaptation means taking action to prepare for current and expected impacts of climate change. Given all the potential impacts from climate change, this can seem like a huge job. But you can take a deep breath because there is no single best answer of how to adapt to climate change. Adaptation decisions will vary by forest type, site conditions, landowner goals, and other factors. The overall purpose of adaptation is to give your woods the best chance for success, not to come up with the “perfect solution.” This means that you can identify new and different management actions to address climate impacts, but also recognize how the work you are already doing might help address climate change.

Begin with Your Goals

Clearly stating your goals and values through a stewardship plan is an important step that you can take toward climate change adaptation (Chapter 1). This sounds basic, but it is fundamental to planning an appropriate and site-specific adaptation response. A concrete set of goals and values gives you a place to begin evaluating the risks that climate change may pose to your woods. If your goal is to maintain a certain mix of existing species or a particular kind of habitat, you may opt for more defensive tactics designed to resist change for the short-term. This mindset toward climate adaptation is called “Resistance,” and it may be a suitable option for you for the short-term, especially in situations where you have high-value woods or you are focused on maintaining the status quo (Table 16-3). If your goal is to maintain healthy woods that can tolerate a wide range of future conditions, you may opt for tactics that emphasize diversity and forest health. This is considered a “Resilience” mindset, which allows some flexibility and change as long as the woodland generally remains the same. If your goal is to maximize the value or productivity of your woods for a future harvest, you may consider planting new species that are projected to be more productive under future conditions. This “Transition” mindset is based on intentionally making changes that are designed to reduce long-term risk. Having an overarching set of goals in place will help guide you through the range of possible climate change impacts and potential responses.

Woodland owners will naturally have different viewpoints on how to judge climate change risks and opportunities. In many cases, preparing for climate change offers “win-win” opportunities because many adaptation actions are already good forestry practices. Also, many adaptation actions can address stressors that woodland owners already consider, such as drought and pests. So you will likely find that addressing climate change matches well with your overall goals for your woods.

Diversity is a Smart Bet

Trees live for a long time—several decades to centuries, depending on the species—so managing and conserving your woods requires careful long-term planning. In a lot of ways, managing a woodland is like managing a retirement portfolio. Woods are assets that mature slowly over time, just like you expect your retirement investments to grow over decades. Your attitude toward risk in your woods can change over time, just like your investment strategy might change depending on whether you are 30 or 80 years old. Changing climate conditions and unpredictable weather events will add risks for your woods, similar to the uncertainties in our chaotic and interconnected economic system.

So what can your retirement portfolio tell you about how to take care of your woods? Well, regardless of whether you’re a risk-taker early in your career or cautious nearing retirement, it always makes sense to keep a diverse investment portfolio. As the old saying goes, “don’t put all your eggs in one basket.” It is a losing bet to have all your retirement savings pooled into slow-growing securities, and it is also a risky bet to invest all of your savings in the next “hot stock.” Diversifying your investments reduces the chance that any one bad year (or series of bad years) will ruin your savings, and it increases the chance that you will reap the benefit of a good year.

So, if diversity is crucial for long-term risk management, how will you encourage diversity in your woods, and how will it benefit your woods under changing conditions? Here are a few suggestions:

Species diversity: Woodlands naturally contain mixes of different tree species, and these species have different levels of risk with climate change. Northern or boreal species like quaking aspen, black spruce, and balsam fir are expected to decline across a range of climate scenarios, while some species like red maple, white pine, and white oak are projected to do well. Each forest type also has an inherent amount of species diversity. For example, jack pine forests have fewer species than northern hardwoods. Maximizing the natural diversity potential of a given forest type can help woodlands be resilient to both current and future pressures and provide more options for the future. As a landowner, you should look for opportunities to maintain a diverse mix of species.

If you’re going to plant some new trees on your property, you may want to focus on species that are projected to tolerate future climate conditions. If you’re more cautious, you can plant native tree species that are already common but expected to do well in the future. If you’re willing to take risks, you can try planting tree species that are currently uncommon but expected to do well—perhaps even some long-distance migrants from one or two hundred miles to the south!

Genetics: Forest management tends to favor high-quality genes by retaining trees that have resisted pests and stress and removing trees that have succumbed to these factors. As a woodland owner, you might also notice that a certain pocket of aspen has withstood a drought better than another pocket, or that certain individuals of other species just seem to be superior. You can try to favor these high-performers through management.

If you’re going to plant trees but do not want to use new tree species, you may be able to introduce some genetic diversity by getting seedlings from locations that match future climate conditions. Tools like the Seedlot Selection Tool can help with this task. The idea is that populations of trees that currently live in areas exposed to more heat and drought might have genetic adaptations that allow them to tolerate those conditions.

Structure:  The structure of a woodland includes the horizontal spacing among trees (including gaps in the canopy) as well as the number of layers of vegetation (dead trees, forest floor, tree seedlings, young trees, sub-canopy trees, and dominant canopy trees). Keeping a diverse structure provides a variety of site conditions with different amounts of moisture, temperature, shade, and ground cover. This kind of diversity can help different tree species to find their optimum growing conditions. For example, encourage a wider tree species mix in northern hardwoods by harvesting groups of trees rather than single-trees. Gaps can be placed near less common tree species currently present in the stand, such as yellow birch, white pine, red oak, or hemlock to provide open ground for their seedlings to establish.

Additionally, keeping several different age classes of trees in your woods is another way to reduce risk because trees are more susceptible to certain risks at different ages. For example, young trees are more susceptible to drought, while older trees might be more susceptible to insect pests. Keeping a few different age classes will reduce the chance that any one event will cause a lot of damage.

More Detailed Adaptation Ideas

You might be asking yourself, “Diversity is nice, but what else should I be doing to help my woods adapt to climate change?” Fortunately, more detailed resources are available for landowners and foresters. The Forest Adaptation Resources book includes a list of forest management strategies and approaches that can be applied to help woodlands cope with future change. A “Top 10 List” of adaptation actions for woodland owners includes the following:

Ten Things You Can Do to Keep Your Woodland Healthy:

1.       Protect water and soils on your land.
2.       Improve the ability of your trees to resist insects and diseases.
3.       Prevent and control non-native plants that threaten native plants and animals.
4.       Manage damage to young trees from excessive deer browsing.
5.       Protect rare or sensitive plant and animal communities.
6.       Promote a diversity of tree species.
7.       Promote a diversity of tree sizes.
8.       Respond quickly after big disturbance events to help your woods bounce back.
9.       Consider how your current trees, and trees that you may plant, will react to future conditions.
10.       Monitor your woods and the effect of different management tactics.

The Forest Adaptation Resources book also includes an Adaptation Workbook to help foresters and landowners consider climate change. This workbook starts with identifying management objectives, and includes separate steps for considering climate change risks and opportunities. You can also select adaptation actions from a menu that will help achieve your management objectives (Figure 16-2).

Going through a structured process like the Adaptation Workbook can help break down your thought process of climate adaptation into manageable steps. It also helps connect your fundamental goals and values for your woods to the adaptation ideas that make the most sense for your situation. Landowners across the Midwest have used the Adaptation Workbook to develop their own customized adaptation plans. Many example plans are available online at www.ForestAdaptation.org.