Treating Landscapes
The northern spotted owls that reside in the forests of the Pacific Northwest prefer dense, multistoried, old-growth forests. Unfortunately for the owls, so do wildfires. A recent study showed that wildfires accounted for 75% of the loss of owl habitat between 1994 and 2003.
Hazardous fuels built up after decades of fire suppression have many forests preparing for unusually large and severe fires. Forest managers are looking for the most efficient approaches to thinning and reducing fuels.
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Threatened and endangered species habitat, research areas, recreational sites and wilderness are just some of the forest areas with specific conservation aims and related management restrictions. Unfortunately, wildfire doesn't recognize conservation or management area boundaries, and it can play havoc with policies such as the Northwest Forest Plan designed to create reserves and buffers around owl habitat.
Ager has been looking at the question of what type of management approach is most effective in mitigating fire risk while preserving remaining owl habitat, as well as other habitat such as riparian conservation reserves for salmon.
Working with Finney, Ager has begun using burn probabilities to identify areas of the forest that are sources and sinks for fire. Every national forest is carved into different management areas with layers of forest and land management and conservation objectives.
Along with land managers on the Deschutes National Forest in Oregon, researchers designed a relatively simple risk assessment process to examine wildfire risk among and within an array of conservation reserves and other land management designations on the forest. The process can be applied to any national forest and provides detailed risk profiles and rankings for resources of concern. In this study, they examined three questions:
What is the relative wildfire risk among the array of management designations and conservation reserves on the forest?
Are specific conservation reserves contributing to wildfire risk and to the loss of other highly valued resources?
How do fuel treatments reduce wildfire risk when conservation reserves are excluded from treatment?
The researchers started by estimating burn probabilities through simulations of 50,000 wildfires on a 6 million-acre area that encloses the forest. The burn conditions replicated recent severe wildfire events on the forest. The burn probabilities represented the chance that a specific 90-square-meter "pixel" on the forest would burn given a random ignition within the study area and a "problem fire" event. For each polygon within selected management designation and conservation reserves, they calculated average burn probability, expected flame length and the average size of fire generated by an ignition within the polygon.
In general, the researchers found wide variation in burn probability and expected flame length within and among conservation reserves and other land designations.
Ager believes that the concept of competing risks needs to be addressed in these highly fragmented conservation reserve networks. "If fuel treatments and restoration activities are prohibited in, for instance, owl habitat and riparian areas, we take on added risk of reserves burning each other," he says.
He adds that the questions raise more questions regarding future threatened and endangered species listings. "Before someone proposes another listing or new conservation reserve," Ager says, "we need to ask how this will increase fire risk to existing reserves. We may list something that contributes to the demise of existing habitat reserves."
"How do you determine the relative value of a pair of spotted owls versus a salmon? I don't know," adds Calkin. "These are the type of trade-offs that we need to make explicit in these frameworks by developing loss functions, but computing those types of values is difficult."
However, land and fire managers are starting to see the value in these analyses.
"Spatially, this is helping us a lot," says Dave Owens, a fire planner with the Central Oregon Fire Management Service. "We want to lay out different land management objectives and look at the values in the area and see where the real hazards are."
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