Adaptive Silviculture for Climate Change—San Juan National Forest

Preparing forests for a changing climate is a growing concern for forest managers. To provide examples of how to integrate climate change adaptation into on-the-ground forest management, the Adaptive Silviculture for Climate Change (ASCC) project established a series of experimental silvicultural trials in different forest ecosystem types. By implementing site-specific treatments based on local conditions and management objectives, the trials are designed to help future forests respond to a changing climate.
The San Juan National Forest in Colorado is a dry, mixed-conifer forest with a historical fire interval of about 30 years. It has been selectively logged in past decades and has experienced various insect and disease outbreaks. The forest’s dense understory contributes to ladder fuels that increase the threat of extreme fires. Climate change is expected to increase average annual temperatures, decrease snowpack, cause earlier snowmelt, increase drought and insect outbreaks, and change the composition and abundance of the forest’s tree species.
A team of natural resource specialists and researchers developed a set of desired future conditions, objectives, and tactics for the San Juan National Forest based on three climate adaptation approaches.
For the resistance option, management strategies include thinning while maintaining even and consistent tree spacing, retaining the existing stand structure, and retaining the same species composition to maintain relatively unchanged conditions over time. For the resilience option, management strategies include favoring fire-adapted and drought-tolerant species, and creating variable stand openings to allow changes in current conditions, but to encourage an eventual return to prior conditions. Finally, under the transition option, management strategies include retaining the most fire-adapted and drought-tolerant species, removing white fir (which serves as a ladder fuel), and creating high variability in canopy openness. Subsequent monitoring that focuses on tree regeneration, forest growth, and forest health will evaluate the forest’s response to these treatments as the climate changes, and will inform future forest management.

To help inform forest managers who are coping with the vagaries of a changing climate, a team of scientists, land managers, and collaborators formed the Adaptive Silviculture for Climate Change (ASCC) project, which has established a series of experimental silvicultural trials in a network of different forest ecosystems across the U.S and Canada. Each trial is focused on understanding and evaluating management options designed to enable forests to respond to a changing climate. The silvicultural treatments that prepare forests for these different scenarios are tailored to the local conditions of the ecosystem in which each forest is located.
The San Juan National Forest ASCC site is a dry, mixed-conifer forest in southwest Colorado. The warmer, drier conditions that climate change is likely to bring will make this forest more vulnerable to catastrophic fires, as well as to insect and disease outbreaks. To deal with these eventualities, silvicultural prescriptions focus on reducing ladder fuels and creating more open stands. The response of the various treatments to actual climate conditions in the coming years will help inform future forest management for this type of forest.

To begin to answer ASCC Network’s core question—what actions can be taken to enhance an ecosystem’s ability to adapt to change while still meeting management goals and objectives—the group brought together a core team of scientists and managers interested in integrating climate change adaptation into their silvicultural planning and management. To accommodate the uncertainty of climate change impacts, the ASCC experiment looks at a spectrum of adaptation options. Each ASCC Network site begins with a workshop to familiarize local managers and scientists with adaptation approaches and tactics for forest management and design specific climate change adaptation experimental treatments for their ecosystem. While experimental elements are consistent across all study sites, management activities at individual sites are tailored to achieve desired future conditions and to meet local management goals.

The ASCC Network process provides scientists and managers with the necessary tools for integrating climate change considerations into their decision-making. The Network also helps managers to address locally appropriate adaptation actions to address the uncertainties of climate change. In the case of the San Juan National Forest, various prescriptions are being implemented to reduce the potential for extreme wildfire and insect and disease outbreaks in the face of a warming and drying climate. The treatments and resultant findings from the San Juan National Forest’s climate-related management activities along with those of other ASCC Network sites are based on a robust experimental design and will provide a suite of adaptation actions that managers can use in future silvicultural planning.