American marten detection rates in Sierra Nevada mountains fall by 60%, possibly caused by habitat loss, fragmentation from logging, say scientists
October 24, 2011
– Scientists tracking the reclusive American marten in the Sierra Nevada mountains have estimated that detection rates of marten have declined by 60 percent compared to historical surveys in the 1980s – and one possible cause, they say, is habitat loss from logging.
The findings, announced this week in the Journal of Wildlife Management, are important because previous research had demonstrated that marten populations had become increasingly fragmented in northeastern California and this new study offers an explanation for the pattern.
Martens also are considered an “indicator” species that reflect beneficial conditions for other animals that occupy old forests.
Katie Moriarty, an Oregon State University doctoral student and lead author on the study, says martens typically utilize large home ranges with patches of dense trees, large snags, downed logs, and decadent trees for resting and denning. Martens are often found in areas where these patches are connected, which may allow them to safely travel from one area to the next without being predated by large carnivores including bobcats, coyotes and goshawks.
Timber harvests and recent fires have reduced some of the available habitat or created gaps that fragment the landscape, the authors say. In addition, efforts to reduce the risk or severity of fire – including the removal of “fuel” in the form of downed woody material – may contribute to habitat loss.
“In the Sierra Nevada and Cascade mountain ranges, martens are associated with older forests above 5,000 feet and are usually found in wooded areas that contain red and white fir, or lodgepole pine, and riparian areas,” Moriarty said. “Marten numbers may be declining throughout this range as the highest densities of detections have been in isolated and unmanaged areas.
“Preserving marten habitat is important,” Moriarty added, “because what is beneficial for martens is presumably good for other species that thrive in old forests at high elevations. Marten habitat is associated with favorable conditions for spotted owls, pileated woodpeckers, northern goshawks, northern flying squirrels, red-backed voles and other species.”
Martens are one of the smaller members of the weasel family, weighing between one and two-and-a-half pounds – and they look something like a cross between a fox and a mink. Martens are “smaller than a Chihuahua,” Moriarty said, “but have the attitude of a pit bull.”
Small but fierce predators, martens feast on snowshoe hare, chipmunks, voles and other small mammals, and also consume bird eggs and berries. They can survive rugged winters with snow more than a dozen feet deep.
Moriarty’s study focused on the Sagehen Experimental Forest, which is located on the eastern slope of the Sierra Nevada mountain range. The Sagehen Creek Field Station, established in 1951 and operated by the University of California, is located about 30 miles north of Lake Tahoe. The Sagehen Creek study area is particularly important it is the only place in the United States where martens have been surveyed, using similar methods, for more than a quarter-century.
The marten detections in the study were recorded in part by using “track plates” – long, rectangular black boxes that are set in the woods and baited. When the martens enter them they leave tracks on contact paper. Other methods include snow tracking, cameras and hair snares, which are devices that snag bits of hair off the animal as it tries to reach a piece of bait. The hair can then be used to identify individual martens based on DNA analysis.
Nine previous surveys of martens had been conducted from 1980 to 1993, using similar methods on the same grid, giving the scientists an ideal basis for comparison. The focus of the Journal of Wildlife Management study was a series of surveys in 2007-08, which found 60 percent fewer detections than previous surveys – a decline the authors suggest may be due to habitat fragmentation and loss.
“We’ve estimated that there has been about a 25 percent loss in suitable habitat for martens since the 1980s,” Moriarty said.
Moriarty and her co-authors recommend three strategies for retaining marten habitat at Sagehen Creek:
Resource managers should consider retaining the remaining contiguous patches of closed-canopy and old forest, which are thought to be the highest quality marten habitat;
Corridors of dense, late-seral forest should be retained among thinned areas to provide corridors that martens and other animals can use to travel between patches of closed-canopy forests;
Managers should strive for a “silvicultural paradigm” that retains large snags, diverse tree structure, large downed woody material, and patches of decadent trees as potential resting and denning habitat.
Moriarty has been studying martens in northern California for several years and gained attention in 2008 when she and her field crew photographed a wolverine during this marten research – the first wolverine seen in California in three-quarters of a century.
Co-authors on the Journal of Wildlife Management study are William Zielinski, of the U.S. Forest Service’s Pacific Southwest Research Station in Arcata, Calif., and Eric Forsman, of the U.S. Forest Service’s Pacific Northwest Research Station in Corvallis, Ore.
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