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Fisher populations will struggle to survive increasing wildfires

A new study published in the journal Ecosphere has found that the recovery of the fisher, an endangered forest carnivore native to Canada and northern United States, will likely be hindered by the increasing frequency and severity of wildfires. Scientists led by Oregon State University (OSU) discovered that fisher abundance declined significantly after three mixed-severity wildfires from the summers of 2014 and 2016.

A fierce and secretive animal, the fisher is a member of the Mustelidae family, which also includes badgers, wolverines, minks, and otters. They are roughly the size of a large house cat. With hind feet that rotate almost 180 degrees, fishers can not only scale trees, but can also climb down head first. These abilities help them attack prey from above or carry offspring in their mouths as they climb up and down trees.

Fisher populations have persistently declined during the 19th and 20th centuries due to fur trapping and logging. With the recent wildfires affecting the Klamath-Siskiyou Ecoregion, a 50,000-square-kilometer area straddling the Oregon-California border and hosting the largest fisher populations, their numbers have dwindled even more.

“The fisher has a limited distribution, and rapid changes to forest structure could threaten its long-term persistence,” said study lead author David Green, a conservation ecologist at OSU. “We estimated a 27 percent reduction in the total number of fishers within our study area following the fires.” 

Strangely, Dr. Green and his colleagues have found that, while fisher density decreased regardless of wildfire intensity, gray fox populations showed a significant decline after medium-severity wildfires, but actually increased after high-severity fires.

“Our results suggest that increased severity, extent and frequency of wildfires in the western United States will have negative impacts on fisher populations and change community composition for medium-size predators. We found that the wildfires that occurred in the Klamath-Siskiyou Ecoregion affected fisher density negatively regardless of burn severity, while gray fox density decreased in areas that burned at medium severity and increased in areas that burned at high severity.”

Further research is needed to understand why the different wildfire severity levels had different impacts on the two species of animals studied.

“Understanding the effects of wildfire on the species that live in forests, and the interactions among species, is important for making the most effective conservation and management decisions. The short- and long-term consequences are unclear for wildlife amid the calls for restoring forests to their natural regimes of frequent, low-severity fires,” Dr. Green concluded.

By Andrei Ionescu, Staff Writer

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