REDWOOD NATIONAL AND STATE PARKS, Calif. — It was an unlikely crime scene: a steep trail used by bears leading to a still, ancient redwood grove. There, a rare old-growth coast redwood had been brutally hacked about 15 times by poachers, a chain saw massacre that had exposed the tree’s deep red heartwood.

The thieves who butchered this and other 1,000-year-old arboreal giants were after the burls, gnarly protrusions on the trees that are prized for their intricately patterned wood. Although timber theft has long plagued public lands, a recent spate of burl poaching, with 18 known cases in the last year, has forced park officials to close an eight-mile drive through old-growth forests, the Newton B. Drury Scenic Parkway, at night to deter criminals. More closings are expected.

While some burls are small and barnacle-like — perfect for souvenir salt-and-pepper shakers — others weigh hundreds of pounds and can fetch hundreds or thousands of dollars per slab.

The poachers, known locally as the “midnight burlers,” are motivated by a sluggish local economy and expensive methamphetamine habits, park officials say, and they have been targeting ever-bigger burls and using increasingly brazen tactics. Last year, a redwood estimated to be 400 years old was felled by thieves who wanted access to a 500-pound burl 60 feet up. It was the first time an entire tree was cut down for a burl, said Brett A. Silver, the state park’s supervising ranger.