Swine Invade Redwoods : Serious Threat to Muir Woods Monument Seen as Hardy Wild Pigs Multiply and Imperil Ecology of Area

The wild swine breeding in the rolling hills of mellow Marin County have gone too far. They’re now threatening the most popular groves of ancient redwood trees in California.

About 1.3 million people annually trek through Muir Woods National Monument, where redwoods thousands of years old reach high into the sky only 15 minutes from San Francisco’s Golden Gate Bridge.

The National Park Service finds itself in great need of funds to prevent an invasion in Muir Woods of feral pigs that have already torn up creek beds and other property in nearby areas of the nation’s largest greenbelt, the Golden Gate National Recreation Area.

Rangers say the first pigs were spotted in the parklands in 1981. Once the ordinary domestic pig variety, they either escaped from nearby farms or were released purposely by sportsmen and thrived in the mild climate. Glenn Fuller, Park Service manager for Muir Woods, said signs of the pigs have been seen in the popular Bohemian Grove stand of redwoods in the heart of the monument and along roadways and hiking trails outside the 520-acre park.

The giant redwoods, resistant to diseases and insects, are vulnerable because the pigs grub around the roots of the trees, destroy ferns and ground cover and root up the creek beds, a major source of nutrients and water.

“It’s a very real danger and as the pressure is increased on the woods, the problem will become very dramatic,” said Fuller, adding that it takes years to repair hillsides ravaged by the swine.

Population estimates range up to 200 or more over a 50-square mile area and, with the fecundity of the female pigs, the population can double every four months.

Although redwood groves are older and taller in Yosemite National Park and at the Redwoods National Park near the Oregon border, the 10-mile valley floor of Muir Woods is where visitors to San Francisco can gasp at the giant trees without traveling long distances.

The Park Service has requested $160,000 to fence off the valley floor section of Muir Woods, which the rapidly breeding pigs, still mainly in the hills, could destroy in a matter of months. Other options are increased hunting and trapping of the pigs, possibly with specially trained dogs.

Park rangers are already engaged in a limited program of baiting, trapping and shooting the pigs with the help of a contract hunter. The pigs, which make good eating, are donated to charitable and nonprofit organizations.

At the Audubon Canyon Ranch in nearby Stinson Beach, the wild pigs have rooted up acres of stream beds looking for salamanders, newts, slugs, worms and bugs. Conservationists fear that erosion will result when the winter rains hit, sending tons of sediment into the already silt-filled and ecologically threatened Bolinas Lagoon wildlife sanctuary.

“These pigs are strong, healthy, vigorous, slim animals and they’ll eat anything,” said Skip Schwartz, manager of the Audubon property overlooking the lagoon.

Jud Howell, natural resources specialist for the recreational area, said that although skittish around people, the male boars are tusked and dangerous. They also carry diseases that could get into the water supply of a vast area of Marin County. Their only natural predators, he said, are mountain lions that still roam the more remote regions.

“Pigs are just everywhere,” said Howell, who works with volunteers to monitor the animals’ movements and numbers. “They’re on the south side and north side of Mt. Tamalpais, on the Bolinas Lagoon side of the Bolinas ridge and in the national seashore. They’re even wandering down into Mill Valley.

“If we don’t do anything, obviously we’ll have this problem forever and it will make significant changes in the ecosystem of the lagoon and the entire recreational area.”