A Path Forward for Forests: Our Forests in a Warmer and Drier World

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“How did you go bankrupt?” Bill asked.

“Two ways,” Mike said.

“Gradually and then suddenly.” -Ernest Hemingway, The Sun Also Rises

Forests are dynamic ecosystems, always changing and evolving. Sometimes change is slow: a seedling dropped last spring might sit on the forest floor for decades before germinating. Sometimes change is rapid: in a matter of seconds, a wildfire can dramatically transform a forest. When viewed in isolation, these changes might seem random. However, when considered together, it becomes clear that the changes in a forest follow a pattern influenced by various factors. Among these, climate plays a crucial role in guiding the many small and large changes within a forest.

A newly germinated Engelmann spruce came from a tree less than 600 feet away; the seed tree may have germinated in the same manner over 500 years ago. The natural cycles of a forest are events set in motion long ago. Climate frequently provides the timing for these events, and timing is essential. For example, leaves that emerge before the final spring freeze will die and fail to photosynthesize. Forests have evolved to thrive in a stable and predictable climate, and any abrupt changes can disrupt these fine-tuned cycles.

CSU student hanging a temperature sensor.

Climate, like forests, is dynamic: it is always changing and evolving. Any long-term change in climate is associated with species extinctions. If the change is slow, species may adapt, slowly moving to once again find climatic pockets where they are able to thrive. Faster change results in more species going extinct. Over the past 500 million years, there have been at least five mass extinction events, periods in which over 75% of Earth’s species have gone extinct. Many of these events are associated with rapid climate change.

Over the past 150 years, Earth’s climate has been changing as a result of human carbon dioxide emissions. With changes in climate come novel changes in our forests. Persistent drought and above-average temperatures weaken trees, making them more susceptible to bark beetle outbreaks, wildfire, and pathogens. To respond to these changes we need to change how we manage forests.

Photo by Karin Teague, Independence Pass Foundation.

For as long as humans have inhabited North America, we have played some role in managing forests. Native Americans used fire to rejuvenate forests and preserve hunting grounds. Europeans initially managed forests for resources, primarily timber and water. In the 1960s, this management changed to equally value wildlife, grazing, recreation, and wilderness. While many management techniques have been employed (to varying degrees of success or failure), all management has been predicated on the concept of stationarity. Stationarity says that future conditions will be similar to past conditions. Extreme events, such as wildfires and beetle outbreaks, will happen but are predictable in the sense that they are similar in size and severity to previous events. Climate change breaks stationarity and makes management much more challenging. To effectively manage forests in a nonstationary world, we need to manage for uncertainty. In any situation with uncertainty, one of the best tools we have is diversity. In the case of forests, this includes diversity of species, diversity of age, and a diversity of genetics within a species. Doing this isn’t as complicated as it sounds.

Managing for diversity starts with a diversity of management approaches. It is neither practical nor advisable to attempt to actively manage all forests. We need to identify areas where we allow forests to respond to climate change with minimal human intervention. Locally, this will primarily take place in federally designated wilderness and roadless areas. Other forests that have a history of disturbance and are closer to roads and communities are good candidates for more active management.

The 2022 Hunter Creek prescribed burn.

Forest management doesn’t attempt to build an ecosystem from the ground up, but rather guides and influences the natural processes within an ecosystem. This can be done with tools such as controlled burns, mechanical treatments (including selective logging, patch cuts, or even clear cuts in some areas), or invasive species management. Locally, ACES in partnership with Aspen Fire Protection District, the City of Aspen, Pitkin County Open Space and Trails, and the U.S. Forest Service has taken many of these steps in the Hunter Creek Valley. As climate change impacts forests, managers are considering assisted migration, which involves introducing non-native trees that are better suited to the new climate. While this technique has potential success it also has significant risk: humans have a long history of introducing new species with very unpredictable and undesirable ecosystem results.

Unfortunately, no amount of management can truly prepare forests for the dramatic changes in climate caused by human actions. For any management to be successful, we need to decarbonize our economy and rapidly reduce greenhouse gas emissions. We also need to accept that forests will be changing. In many areas, we already see these changes: aspen groves on south-facing slopes are being replaced by shrubs, or conifer trees killed by bark beetles or wildfires are not regenerating. When we make profound changes to the climate, we cannot expect ecosystems to remain the same.

ACES Forest & Climate Director Adam McCurdy leading a “Stories Told by Trees” walk.