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Worsening wildfires expected to hamper fisher recovery

ODFW Photo New research by Oregon State University indicates the recovery of the fisher, a forest carnivore, is affected by the increasing frequency and intensity of wildfires.

Researchers at Oregon State University have found that the increasing frequency and intensity of wildfires will likely hamper the recovery of the Pacific fisher, an elusive forest carnivore in the Mustelidae family with badgers, otters and minks.

Looking at six years of data from a long-term monitoring program covering a portion of the fishers’ range along the Oregon-California border, the fisher population declined by an estimated 27% after three “mixed-severity” wildfires and salvage logging altered the region, according to lead researcher David Green of the OSU Institute for Natural Resources. The study was published in Ecosphere Jan. 10.

The largest population of fishers in the western U.S. inhabits 50,000 square kilometers known to scientists as the Klamath-Siskiyou Ecoregion. The “fierce and secretive” animals are native only to Canada and the northern United States, and became the subject of conservation efforts as a result of extensive 19th- and 20th century fur trapping and logging that threatened the population, Green said.

According to a U.S. Forest Service article from 2017, the agency identified 26 fishers in the Ashland Watershed, where a sculpture of the animal by Jeremy Criswell has greeted visitors on the Bandersnatch Trail since 2015. The Ashland Watershed is in the fishers’ northernmost range, Green said.

In the OSU study, researchers monitored fishers and gray foxes in a 465-square-kilometer section of the Klamath-Siskiyou Ecoregion and studied the effects of the Beaver, Gap and Happy Camp Complex wildfires that burned 26% of the area between the summers of 2014 and 2016 — the unburned areas within the study site and years of study prior to the fires served as controls for the fire impact research, Green said.

The study area hosts 20-60 fishers, which generally average six individuals per 100 square kilometers across the ecoregion, he said.

Researchers started studying the population in 2006, allowing for greater understanding about the impact of specific landscape disturbances, Green said. The study presents work from 2011-2016, capturing pre- and post-wildfire data. The team plans to review the latest six years of data shortly, he said, and return to the area in the fall to keep monitoring going.

“It becomes really important to have these long-term studies so that you can see what’s natural variation, like what is the normal birth and death rate that occurs in that population, let alone when something big comes through like a wildfire,” he said. “We were really fortunate in our research that we could say with some certainty what it looked like before.”

The combination of baseline population data and fresh information captured through on-the-ground monitoring quickly initiated after the summer fires of 2014 (in September) allowed for a balanced and bolstered determination of cause and effect, Green said.

Intense fires can make vegetation uninhabitable, and salvage logging and replanting add variables that complicate understanding of wildlife’s response to wildfire, he said.

Ecological thinning and intentional fire use have been identified as necessary to rectify a decline in forest health in the West due to a century of fire suppression, according to the latest published research in forest and wildfire science.

The OSU study presents a reflection on short-term effects, while long-term effects and new factors such as calls to restore forests to natural low-severity fire regimens will sustain researchers’ attention going forward.

Certain elements of the fishers’ ecology benefit from mature forests, namely the need for dens and cavities where the animals give birth and keep their kits safe from predators, Green said.

Ongoing research focuses on how the short-term negative impacts to fishers of techniques intended to mitigate wildfire severity — such as prescribed burning, debris clearing and thinning — stack up against the long-term effects of major wildfires, and paves the way for informed forest management recommendations, he said.

As industry stakeholders weigh the costs and benefits of forest and wildlife management, Green said public-private partnerships support the balance of ecosystem health, threatened species conservation and sustainable change.

Collaborators and stakeholders in the study included North Carolina State University, U.S. Forest Service, U.S. Fish and Wildlife Service, California Department of Fish and Wildlife, Oregon Department of Fish and Wildlife, Fruit Growers Supply Company, Timber Products Company, Sierra Pacific Industries and the National Council for Air and Stream Improvement.

In addition to the expected negative effect on fisher populations, worsening wildfires will, in a broader sense, influence the overall composition of the medium-size predator community, according to the research.

Fishers are preyed upon by bobcats and cougars, and gray foxes and fishers compete for prey. Fishers require a lot of food to sustain themselves day-to-day, making them “opportunistic” eaters that prefer to prey on small mammals, but tolerate berries and mushrooms, Green said.

Reintroduction efforts in recent years have been crucial to population recovery, Green said, and researchers are captivated by the puzzle of why the animals have not repopulated areas of their historic range independently. He hypothesized competition with gray foxes, a more resource “generalist” cousin, may play a part.

“Some of our previous research has shown that when fishers were removed from a site to be translocated, to be reintroduced to an area in Northern California, we actually saw an increase in the number of gray foxes in that region,” Green said. “It could be for prey and resources; it could also be direct competition, but what we found is that fishers act as the dominant competitor.”

In the recent fire impact study, the effect was similar: Gray fox populations benefitted from the negative effect of fires on fishers, he said.

The next phase in research analysis focuses on defining elements of fisher recovery across the landscape, Green said, including the long-term roles of salvage logging, replanting, reproduction trends and competitor species.

Reach reporter Allayana Darrow at adarrow@rosebudmedia.com or 541-776-4497.