Effects of Forest Restoration on Mesocarnivores in the Northern Redwood Region of California
Martens are agile, 2-foot-long members of the weasel family. They need ancient forests—and used to thrive in the coast redwoods of California. Today the Humboldt marten, the coastal subspecies of the Pacific marten in California, has vanished from more than 95 percent of its former range. A single population of about 100 remains on the coastal edge of the Six Rivers National Forest, roughly between Crescent City and Arcata.
To expand their numbers, Humboldt martens need a way to get from their last stronghold in ancient forests to other ancient forests to the north and west. But young, logged forests lie in-between. In 2009–2010 a team from the US Forest Service studied how those young forests could be managed to regain old-growth characteristics (such as huge redwoods and diverse plants and animals) as soon as possible. The team looked at three factors: shrubs, roads and rest sites.
A dense cover of native shrubs such as rhododendron and evergreen huckleberry turns out to be essential for the species. “Martens are just the right size to hunt underneath that layer,” says US Forest Service Ecologist Keith M. Slauson, who led the study. That cover is degraded in clear-cut forests. But removing some young trees can bring it back in one to three decades, the researchers found.
Roads, on the other hand, cut through shrub cover and may attract marten predators. To test that idea, the researchers placed pairs of cameras within 1,600 feet of each other (about one-third of a mile) — in each case, one on a stream and one on a road. After two months, they found that 80 percent of the carnivores not specifically adapted for forests, such as bobcats, mountain lions and gray foxes, were photographed on roads. Eighty percent of the forest specialists, such as martens and fishers, were along the streams.
Another essential for martens—rest sites—are typically provided by live and dead trees. But it can take more than two centuries for trees such as redwoods to develop the cavities that martens use. A practical substitute is marten “rest boxes,” like large bird boxes, which have proven successful with the European pine marten.
Given their population size, martens can’t wait a century or two for the forest to heal itself. Humans can help, Slauson said, by installing rest boxes, strategically removing roads and thinning young forests to restore shrub cover.