The latest incident happened in May, when an 8 x 10-foot burl was cut from the base of a redwood tree near the Redwood Creek Trail in Redwood National Park.
Weeks before the May discovery, a park scientist located a pile of small burls lying on the ground that had been cut from park trees.
Another incident this year involved an old-growth redwood tree being cut down for its burl in Prairie Creek Redwoods State Park.
Anyone with information about the cutting of the Redwood Creek Trail burl is asked to call NPS Ranger Laura Denny at 707-465-7750. A $1,500 reward is being offered for any information that garners an arrest and conviction of the culprits.