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Photo by P.J. Perea
The loss of black walnut would be devastating for wildlife and forest management, not to mention the loss of quality wood for furniture, gun stocks, turkey calls and more. |
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Photo by P.J. Perea
A black walnut's distinct fruit encases a nut favored by small mammals. Its wood is prized by craftsmen.
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The battle for black walnut trees
One of the most coveted timbers in the world is also a favored source of food and shelter for a variety of wildlife. Yet its standing as one of the most premium of fine hardwoods and importance to wildlife are at risk as these highly prized giants are falling prey to the devastating effects of a tiny beetle.
The black walnut (Juglans nigra) is easily recognized by its deeply furrowed black-brown bark and large compound leaves between 1 to 2 feet long. It grows throughout most of North America, though its native range lies mostly in the Central and Eastern states. Trees are usually found on the forest edge or scattered among other trees in moderately moist forests. Known associates include sugar maple, silver maple, black oak, white oak, northern red oak, yellow poplar, American elm, beech and sassafras.
Why they're important
A mature black walnut can tower to 100 feet tall, offering large limbs that serve as ideal roosting trees for wild turkeys and the eastern screech owl. Many species of woodpeckers, swallows, wrens, nuthatches and owls use black walnut cavities, and deer browse its leaves, twigs and buds.
It's coveted prize is a hard-shelled, richly flavored nut that is surprisingly sweet. It takes about 10 years for trees to produce nuts, with best crops beginning at 30 years. The nuts have nearly twice the protein of English walnuts and are a favorite of squirrels, rabbits and other rodents as it takes strong teeth and persistence to gnaw through the extremely hard shells. Woodpeckers also consume the nuts , as do other resourceful birds such as ravens, which fly high in the air with walnuts in their beak, then drop them to the ground to crack the shells.
The feral hog is one of the few larger mammals that readily seek and eat the protein-rich nut . Any bits and pieces that remain after hogs or squirrels have cracked them open become a first-come, first-served buffet for other birds, including wild turkeys.
What makes it thrive?
The long-lived black walnut (sometimes exceeding 200 years) does best in deep and moist, well-drained soil high in organic matter. This tree must be dominant or codominant where it grows to thrive and regenerate, as the black walnut is intolerant of shade during all stages of growth. Areas that offer abundant light, such as clearcuts and patch clearcuts, are ideal.
One way this tree tips the survival scale in its favor is by secreting the growth-inhibiting substance juglone. The chemical is lethal to or prevents the growth of certain plants within the tree's rooting zone. While juglone is found in all parts of the tree, the flower buds, nut hulls and roots, which can extend three to four times the diameter of the tree canopy, are especially potent. Juglone combined with extensive root competition make black walnut a bad companion for planting near flower or vegetable gardens.
What's causing the decline?
The walnut twig beetle (Pityophthorus juglandis), a yellowish-brown bark beetle smaller than a grain of rice, can be the tree's worst enemy. The beetle, which bores through the bark of the twigs, then mates and lays eggs, is hard to detect.
"They damage the cambium (the living layer of the tree), and then bore back out through the bark as adults," said Gary Burger, a biologist and registered forester with the NWTF.
The walnut twig beetle, however, comes with some pretty toxic baggage.
"While their abundance and physical activity damage the tree, the fungus (Geosmithia) they carry and introduce into the cambium layer is really the agent that leads to the tree's demise," Burger said.
A tree can host millions of fungus-ridden beetles. The fungus eventually girdles the tree with cankers, starving the tree. Known as thousand cankers disease, the outcome is a progressive decline that kills a tree within two to three years after initial infection.
The disease is generally found in eight states west of Kansas. Many experts now believe that TCD has the potential to develop into an uncontrollable outbreak similar to Dutch elm disease or chestnut blight. TCD was recently discovered in Knox County, Tenn., the first state east of the Mississippi River with a known infection.
TCD is difficult to control due to the tree's high susceptibility to the fungus along with no known means of control through insecticides or fungicides. Other factors include the beetle's spread from its original range in the Southwest and parts of Mexico, and the ability of both beetle and fungus to invade new areas and survive under a wide range of climatic conditions.
Another complicating factor is the generally slow detection of new infestations.
"The beetle's presence is difficult to detect due to its tiny size and the corresponding tiny entry hole," Burger said. "Once dieback is noticed, the beetles have almost always completed their lifecycle in an infested tree and moved on to new, healthy trees."
Taking action
According to Burger, at least eight states (North Carolina, Indiana, Oklahoma, Missouri, Tennessee, Kansas, Michigan and Nebraska) have issued quarantines on the transportation of any black walnut with some bark component, such as firewood, logs, slabs and mulch.
"The NWTF, through its communications network and regional biologists (particularly in the Midwestern and Mississippi River states) is spreading the word about this new threat to encourage individuals and forest products companies alike to adhere to quarantines and gain at least a basic understanding of the disease and identification of infestations," Burger said.
The NWTF also has an ongoing partnership with the National Association of State Foresters, whose members have worked to bring this issue to state foresters across the country and provide the latest information to help state forestry agencies do all they can to prevent the spread of TCD.
Preventing its spread is the best way to ensure the survival of a tree that is vital to many species. And that's encouraging news to those who use the tree, from wildlife to cabinetmakers, gunsmiths and connoisseurs of its sweet and tasty nuts. — Kris Wetherbee