USA: Forest management research to help fight effects of climate change

Forests and their ecosystems face increased threats to health as temperatures rise

By Mike Wolterbeek

Prolonged drought, landscape-level bark beetle mortality and catastrophic wildfire have been increasing in frequency, extent and severity over the past few decades, and western forests will be increasingly stressed as temperatures rise and climate change effects intensify.

Leading a team of scientists and forest managers, Sarah Bisbing, a forest ecology assistant professor and researcher from the University of Nevada, Reno, is building a Sierra Nevada-wide study, the Sierra Nevada Adaptive Management Experiment, known as AMEX, to identify alternative forest management treatments that will improve conifer forest resistance and resilience to climate change.

Bisbing, a faculty member in the Department of Natural Resources and Environmental Science, received a $2.8 million grant from CAL FIRE's Forest Health Grants Program to implement this large-scale, replicated experiment in collaboration with state and federal land management agencies.

Over four degrees latitude from the northern to southern Sierra Nevada (Shasta to Tulare counties), this long-term, multi-decade study will compare treatments representing fundamentally different climate change impact scenarios and a suite a potential approaches forest managers may take to mitigate impacts on the ecological, economic and social services provided by forest ecosystems.

The project is designed to support silviculture research, which is applied forest ecology or the act of managing a forest to meet a desired set of ecological, economic and social conditions.

"This research will help inform what forest managers will do in the long run to increase carbon sequestration, combat drought mortality, and make forests more resistant and resilient to catastrophic wildfires and insect damage," Bisbing said. "Climate change is and will be increasing the severity of ecological disturbances in forests, which will not only have devastating impacts on forest ecosystems but also turn these carbon sinks to carbon sources, leading to increases in the release of carbon into the atmosphere. This study will guide forest managers as they build resilience and resistance to those disturbances and attempt to mitigate the impacts of climate change on forest ecosystems."

Ongoing and predicted impacts to forests include regeneration failures, shifts in species' ranges, drought mortality, and increasing severity of disturbances such as bark beetle outbreaks and/or fire. These changes are creating uncertainty in how forests will function in the future and concerns around sustaining ecosystem goods and services.

The AMEX project is designed to be a long-term assessment of the effectiveness in common and novel silvicultural tools for climate change mitigation and to track forest response under changing conditions. Multiple treatments will be implemented, as no single activity will reduce these threats, and research will help identify solutions and target structures to support climate change mitigation while also informing seed zone regulations for reforestation efforts.

All project actions will lead to immediate short-term carbon sequestration through release of large-diameter trees and long-term carbon storage through reforestation efforts and regular maintenance of proposed conditions. Forest health improvement treatment types are defined as resilience, resistance, and transition treatments and include fuels reduction, pest management, biomass utilization and reforestation coupled with mechanical treatments to provide diversity in species, age classes and structures at the landscape and regional scales.

Forest treatments

Resilience treatments closely mimic forest structure under historic fire conditions and are designed to prepare the forest for disturbance by creating tree stand conditions that will help recovery of pre-disturbance composition and structure.

Resistance treatments are aimed at reducing fuel loading and will prepare the forest to resist a disturbance by creating stand structure that is open, park-like and forces fire to stay on the ground.

Transition treatments will help the forest adapt to changing climate, representing the scenario where resistance and resilience treatments are not effective and the forest cannot recover without intervention. Treatments mimic a disturbance that fundamentally changes the composition and structure of the forest, requiring foresters to plant species better adapted to the new conditions of the climate change-impacted system.

Project activities will support a suite of ecosystem services across the western Sierra Nevada by creating forest age and plant community diversity at multiple scales, including:

• Diverse age stands will help facilitate wildlife movement via patch diversity and intact corridors while supporting habitat for a wide range of species.

• Resistance treatments, reductions in basal area and removal of understory fuels will support increased diversity in the understory plant community and associated herbivores.

• Resilience treatments will create the greatest compositional and structural diversity, supporting a wider range of plant and animal species under both current and future conditions.

• Transition treatments are aimed at insuring continued forest cover under future conditions, maintaining carbon sequestration over a 100-year rotation while also providing for continued forest cover for wildlife.

• Fuels reduction activities will have a wide-reaching impact on watersheds and downstream users by reducing sedimentation, maintaining water quality and providing a continued source of upland water for downstream users.

• Biomass removed via harvest will be stored long-term in wood products produced by local mills, such as Sierra Forest Products in the southern Sierra Nevada.