Natural Disturbances

Wilderness managers are encouraged to allow natural disturbance processes to shape and control wilderness ecosystems. However, due to current and past management (such as fire suppression), impacts from human use, and influences from outside the wilderness boundaries, natural disturbance regimes may not be adequately functioning in their natural ecological role and may even pose unacceptable risks or risks that require some human intervention to protect other high value resources.

Wilderness managers need to know whether natural disturbance regimes have been altered in wilderness, by how much, and what the consequences are for wilderness character and ecosystem function. Ultimately, wilderness managers need to know whether, when, where, and how to intervene to restore natural disturbance processes. Science plays a critical role in the overall decision process to manage for or restore natural disturbance processes within the context of preserving all the qualities of wilderness character.

Wilderness has unique value for the scientific study of natural systems and natural disturbance processes. As a setting that is minimally confounded by human activities, the causes and consequences of environmental change caused by disturbance are more easily discerned than more managed settings. In this way, Wilderness serves as a useful benchmark or reference point for comparison with more human impacted environments to better understand the degree to which we have altered other lands. Finally, the remoteness of many wilderness areas affords the opportunity to allow and observe natural disturbances that occur without human interference.

The ecological literature defines disturbance as “any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment1” (Pickett and White 1985). Natural disturbances include fires, insect outbreaks, disease epidemics, droughts, floods, hurricanes, windstorms, landslides, avalanches, and volcanic eruptions. In terms of frequency and area affected, the two major natural disturbances affecting wilderness areas are fire and insect outbreaks. These two natural disturbance regimes are responsible for much of the variation we see in vegetation structure and composition.

The Leopold Institute and its partners conduct research to determine if, and to what degree, natural disturbance regimes have been altered and whether wilderness has departed from a natural baseline condition. Our science also informs wilderness managers of the options that are available to successfully accomplish scientifically sound goals. The Leopold Institute’s natural disturbance research program has focused primarily on fire.

It’s a challenge to manage the natural role of fire in wilderness. Wildfire was historically one of the most important natural processes across the United States. Many species evolved with wildfire and, subsequently, many ecosystems have adapted to fires. Humans have altered these natural fire regimes in many ways, but most dramatically by suppressing fires. Ecosystems and landscapes that were adapted to periodic wildfire have experienced vegetation type changes and tree density increases, making these landscapes more susceptible to uncharacteristically large and severe wildfire.
Starting in the late 1960s, federal land managers allowed some lightning-caused fires to burn as a natural ecosystem process in a few national parks and wilderness areas. Today, several large and/or remote parks and wilderness areas are often allowed to burn freely. These areas hold a wealth of fire history data free of human influence and, as such, provide opportunities to learn how to use fire beneficially.

The Leopold Institute’s fire research program seeks to uncover wilderness lessons about fire to apply across a broad spectrum of lands from wilderness to the wildland urban interface. Current research includes:

• learning how fire frequency, severity, and size are related to climate and other environmental factors;
• predicting how fire regimes will change as the climate changes and human footprint enlarges; and,
• investigating the ability of past wildfires to act as fuel treatment by reducing the severity, size, and occurrence of subsequent wildfires.

Fire is suppressed in wilderness for many reasons. Lands that border wilderness may contain houses or roads. Or vegetation within a wilderness area may have grown up without the stimulus of fire. As the wildland-urban interface expands and ecological changes increase the likelihood of more frequent and more severe fires, the decision to let wildfires burn is increasingly difficult.

Wilderness managers need to understand their options for restoring fire as a natural process and they need to know when active restoration is needed and justified. Leopold Institute researchers and their collaborators are developing knowledge to support fire and fuels management decision-making and planning. Research in this area includes:

• quantifying the hidden consequences of suppressing fires;
• incorporating the benefits of wildland fire into risk analysis frameworks so that comprehensive tradeoffs can be made among fire management strategies; and,
• mapping the probability of burning, and the likelihood that a wilderness fire will spread into front-country areas, will facilitate maps of predicted burn areas.

Despite an increasing recognition that fire management can adopt alternative management responses to fire, a strong inclination toward fire suppression remains within land management agencies and society at large. The Leopold Institute has studied what influences the authorization of fire in wilderness, public attitudes toward wilderness fire management, and methods for engaging the public and monitoring public support. Past research has included:

• identifying what helps and hinders the management of fire for its benefits in wilderness;
• examining trends over time in attitudes of wilderness visitors toward the use of fire;
• investigating agency practices for public engagement that lead to success in fuels management at the wilderness/non-wilderness interface; and,
• developing methods for public collaboration in planning for fire and fuels management.