Fishers ‘n’ Fire

In keeping with this weeks California wildlife theme, this was in E&E news the 22nd of December.

Thinning forests in the southern Sierra Nevada mountains may cause some harm to key habitat for an isolated population of fishers, but such fuel reduction treatments likely will benefit the weasel-like mammals over the long run by reducing the risk of severe wildfire, a recent study concludes.

Forest managers have targeted dense stands in the Sierra National Forest and other public lands in the region for thinning in recent years, but they’re also required to help protect the fisher, which is a candidate for protection under the Endangered Species Act.

The study, published in the most recent issue of the journal Landscape Ecology, used computer models to simulate how different fuel reduction scenarios, including a no-treatment scenario, would affect fisher habitat over 60 years, compared with the potential effects of a major wildfire on the same habitat area. The authors concluded that while thinning could cause some damage to the fisher’s habitat, a high-intensity fire is a greater threat.

Description: Pacific fisher

Rare Pacific fishers rely on downed trees for denning, prompting questions about the effects of forest thinning on the animals’ habitat. But a recent study suggests that reducing the risk of destructive forest fires through fuel treatments will benefit the animals over the long run. Photo courtesy of Fish and Wildlife Service.

“Our simulations suggest that the direct, negative effects of fuel treatments on fisher population size are generally smaller than the indirect, positive effects of fuel treatments, because fuels treatments reduced the probability of large wildfires that can damage and fragment habitat over larger areas,” the study concludes.

Fuel treatments typically involve removing dead wood, which fishers use for denning, from the forest floor, said Robert Scheller, an assistant professor of environmental sciences and management at Portland State University in Oregon and the lead author of the study.

“It’s pretty important for them to have a safe place to raise a litter,” he said.

But a major fire would also damage the population’s habitat, “potentially over much broader areas than the treatments intended to reduce wildfire risks,” the study states. A large, super-hot fire would likely kill larger trees, shrink the forest canopy and burn up dead wood, all of which could adversely affect fishers.

“The long, relatively narrow arrangement of suitable habitat means that one or more large fires could burn across it and isolate fishers on either side of the burn,” the study states. “Because both fuels treatments and wildfires can negatively impact fisher habitat, this system exemplifies a probabilistic, risk-minimizing balancing act for forest and wildlife managers.”
Small, isolated population

Biologists estimate the southern Sierra Nevada fisher population at about 300 adults, most of which live in a narrow, isolated band across the western slope of the Sierras, south from Yosemite National Park to the mountain range’s southern tip.

Scheller added that while the study found that the overall benefits of fuel treatments probably outweigh the risks, such treatments are still something of a gamble: If no fire ever scorches the area, then the damage to the habitat from the fuel treatments would be for naught.

“The question is, ‘What are the odds of a fire coming through those areas that have been treated?’” he said.

The study is part of a broader effort from the Forest Service to figure out how to protect fishers while allowing for timber harvesting and fuel treatments in Sierra National Forest. Under the National Forest Management Act and Sierra Nevada Forest Plan, the Forest Service is to help maintain viable, well-distributed fisher populations.

The fisher once roamed from British Columbia to the southern Sierra, but historic fur trapping and logging reduced its range to three native populations — the southern Sierra Nevada, Northern California and southwestern Oregon — as well as a reintroduced population in Washington’s Olympic National Park.

Environmental groups say that logging continues to threaten the remaining fisher populations. Several groups have filed a lawsuit to try to force the Fish and Wildlife Service to add the West Coast population of the fisher to the endangered species list.

“Without protection from continued logging on private and federal lands, the fisher will go extinct,” said Craig Thomas, executive director of Sierra Forest Legacy.

Here’s a link to the study. I was looking around on the web for other information and ran across this look at the impacts of fuel treatments with some potential mitigation of their impacts by Truex and Zielinksi….

Also this one from May:

Kings River Fisher Project — Progress Report

Researchers Craig Thompson, Kathryn Purcell, James Garner and Rebecca Green from the Sierra Nevada Research Center of the U.S. Forest Service have just released a progess report on 72 radio-collared fisher which they have been studying since 2007. The project area is located in the Kings River area, west of Shaver Lake in the High Sierra Ranger District of the Sierra National Forest.

The purpose of this study is to learn more about fisher ecology including their habitat requirements, and to increase understanding about the effects of timber harvest and fuels treatments on select response variables of interest, including fishers and their habitat.

The report is too large to post here (30 MB) but it can be downloaded from this website until June 22. Here’s an excerpt from the summary:

“Using a combination of telemetry and scat dog data, we generated a preliminary density estimate of 13.4 fishers per 100 km². We observed reproductive activity for 79% of the adult females monitored during two breeding seasons, with 45 kits observed at 31 natal dens. We located an additional 64 maternal dens in a variety of structures. Survival rates ranged from 0.61 for subadult males to 1.0 for juvenile females, and predation accounted for 81% of all mortality. Genetically confirmed predators include mountain lion (40%), bobcat (40%), and coyote (20%).

We generated 95% kernel home range estimates of 1,113 ha for females and 4,522 ha for males. In agreement with most published literature, fishers were found in areas of higher canopy cover. However they were also found more often in areas with higher number of small (<20” dbh) trees, indicating that these trees may provide requisite structure and canopy. Fishers avoided edges, particularly with respect to resting sites, and were found on the lower portions of north facing slopes more often than any other topographic position. Fishers used a variety of tree species and structures for resting, with the most common choices being cavities in black oak and white fir. Diet was dominated by mammalian remains, though we documented a large diversity in food consumed including plants, birds, reptiles, and insects."

I wonder if fishers and Sierra red foxes (also in consideration as endangered species here) might be in competition for the same prey species?

Very interesting to me was the structure of the Sierra Nevada Adaptive Management Team here. With the public involved and the public discussion forum here. It is an intriguing approach and may be a good deal for $12 million over 7 years.