Champion black walnut overcomes 2002 injury

Standing 79 feet tall with a 90 foot crown spread, and estimated to be 150 to 200 years old, the State Champion black walnut tree spreads its regal arms into the sky behind the manor house at Tanglewood Park. State Champion trees are the determined giants of their species in each state. There are also National Champions, individuals of a species that are the largest known in the country.

The black walnut was once a common tree in Piedmont North Carolina, but its value as a fine-furniture and nearly indestructible hardwood has not left many with the stature of the one at Tanglewood.

As desirable as it is for its wood, it is a messy landscape tree, dropping nuts the size of eight-balls covered in a green husk that is notable for its ability to stain. In fact, a tan-colored dye is produced from the husk. The tree is also allopathic: It produces a toxin from its leaves that discourages the growth of many other plants, and as a result is rarely planted in landscape situations.

Tree surprises the experts

Tanglewood's tree was struck by lightning back in 2002, leaving a scar of fractured bark spiraling down its trunk. David Lusk of Lusk Tree Service performed a risk assessment of the tree to determine whether it posed a public danger. To his surprise, he found the tree to be healthy and vital.

"When I first looked at the tree, I thought there is just no way we are going to be able to save it," Lusk said. How the tree has repaired itself from its wound is an object lesson in a tree's response to injury, one that Lusk illustrated in an article he had published in this month's issue of Tree Care Industry magazine, a publication of the association of the same name.

Lusk found that despite the tree's appearance it is actively recovering from this wound and annually producing nuts and a heavy crop of vegetation each year since the injury.

Lusk said that all trees "overlap themselves with a new tree every year." Essentially, the living, growing component of the tree is a band of wood growing outward each year. New wood is growing to surround the wounded wood on the tree. Lusk drilled several small holes into the trunk wood that had been exposed by the lightning strike and is now dead and decaying. He found that the wood was hard and difficult to penetrate but eventually revealed a darker inner wood indicating that the wood had hardened rather than rotted.

Arborists refer to this condition as compartmentalization of decay. The tree has isolated the wound and grown healthy wood around it. In the case of the walnut tree, the inherent superior strength of the wood only adds to its ability to withstand the insult. Lusk said that the first stage of walnut decay produces a hardened wood rather than a soft rotting wood as occurs in many trees.

Lusk recommended some measures that will help shore up the injured tree, including crown-reduction through pruning and removal of a lower limb that has sustained an unacceptable level of damage. A system of cabling was installed to insure the strength of the tree. Known by the industry name of Cobra cabling, this system was introduced to the U.S. tree industry from Germany and requires no drilling or bolting into the tree. Shock absorbers in the cable system prevent what Lusk referred to as the "karate chop" effect, of snapping a branch above the point of cabling.

Lusk sought the help of Wearflex Slings, a local manufacturer, to design a ratchet controlled binding to help stabilize the trunk and avoid vertical cracking of the trunk surface. The ratchet will be adjusted manually to compensate for the trunk's growth.

"This is a fairly nontraditional approach, and it has to be considered that you don't want to disrupt the tree's plumbing," Lusk said.

The injured areas of the tree will continue to decay though, and this may one day leave the tree with a substantial hollow where the injured wood has fallen away and the new tree rings have formed around it. Lusk said that this is how hollows are formed and that many old and towering trees stand today with this exact condition.

Lusk said that the Forsyth County Parks and Recreation Department should be credited for its efforts to save this historic tree. In an era when the cheapest and the quickest are often considered the only measures to take, it is refreshing to see this recognition of authentic value.

■ If you have a gardening question or story idea, write to David Bare in care of Features, Winston-Salem Journal, P.O. Box 3159, Winston-Salem, NC 27101-3159, or send e-mail to his attention to gardening@wsjournal.com.