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Insects can certainly be pests, but one invasive group is threatening to wipe out a ubiquitous species of trees in Western North Carolina, a process conservation groups are fighting to stop.
The hemlock woolly adelgid arrived in the U.S. from Japan in the 1920s. The pest feeds off sap or starches in the hemlock tree. An adelgid stays stationary, disrupting the flow of nutrients to a tree’s needles and causing the hemlock to die within four to 10 years, according to the Foothills Conservancy of North Carolina.
The woolly adelgid cannot move on its own and relies on wind, animals, people and traffic to propel it.
The woolly adelgids were first spotted in the Great Smoky Mountains National Park in the early 2000s, according to the Hemlock Restoration Initiative’s Sara Defosset. The program is part of Asheville-based WNC Communities and was created in 2014 through money from the N.C. Department of Agriculture and Consumer Services and the U.S. Forestry Service.
“They’re pretty much anywhere there are hemlocks,” said Foothills Conservancy conservation associate Ryan Sparks. “It’s well established.”
But the hemlock woolly adelgid is not the only force behind the loss of hemlock tress.
“Our trees are in worst shape than trees in neighboring states,” Defosset said. “That invasive bug coupled with the drought caused a double whammy with our big mature hemlocks.”
Two types of hemlocks reside in the eastern U.S., according to the N.C. Forestry Service, the eastern hemlock and the Carolina hemlock, both of which can live for hundreds of years.
The Carolina hemlock is mostly in Western North Carolina and also neighboring states. It has a height of 40 to 60 feet and is primarily found on ridge tops, according to the Hemlock Restoration Initiative.
The eastern hemlock can grow as tall as 170 feet and live for 500 years. They tend to grow in moist, shady groves. The foliage of the eastern hemlocks are dark green, nitrogen-rich and available year round since they are an evergreen. This can also be an important source of food in the eastern forest in the winter when hardwoods are dormant.
The Great Smoky Mountains National Park has 35,000 acres with a significant hemlock presence, according to the Hemlock Restoration Initiative.
Park personnel are using three methods to control the woolly adelgid. They are releasing beetles as a form of bio-control, treating trees with an insecticide that protects them for five to seven years, and spraying the canopy and branches.
According to a website from the N.C. Forestry Service, the hemlock was once one of the largest and most common tree in the state’s mountains.
While the loss of the tree would not have a tremendous effect on humans, it would certainly affect hiking and recreation.
“There’s no other tree to replace it,” Sparks said. “Once these things go away, forests change. We really don’t know what the impact could be.”
While the direct impact on humans might be minimal, the loss of the trees could have a large impact on animals.
Several animals thrive in the hemlock ecosystem. Trout also thrive in the watersheds and the trees serve as a habitat for many birds, according to the N.C. Forestry Service.
The trees provide much needed shade and streams can be two to four degrees cooler under hemlock canopies compared to other forests. But shade is not the only advantage hemlocks can provide as even the tallest ones keep low branches, which can provide a ladder that helps animals move to other trees, according to the Great Smoky Mountains National Park.
To help stymie the spread of the hemlock woolly adelgid, Patrick Horan, founder of Sapphire-based Saving Hemlocks, was recently at the Foothills Conservancy’s Cane Brake property to release a predator Sasi beetle that feed on the hemlock woolly adelgid. Using biological control and chemicals are two of the ways to save the hemlock trees.
Horan has been releasing the Sasi beetles for 10 years and has done it in Georgia, Tennessee, Kentucky and both Carolinas.
That predator-prey relationship is critical, according to the Hemlock Restoration Initiative. In Asia and the Pacific Northwest part of the U.S., the hemlock woolly adelgid does not have the same impact as it does in North Carolina since a predator-prey relationship already exists between the woolly adelgid and native insects.
Some 3 million Sasi beetles produced in U.S. Department of Agriculture labs have been released in national and state parks, according to the Burke County-based Foothills Conservancy. But other areas have to rely on private groups to implement biological control.
However, the Sasi beetle is just one means of combating the hemlock woolly adelgid.
“We welcome any management strategy to the table,” Defosset said. “We’re trying to recreate the predator-prey balance that keeps these insects in check.”
Another means of fighting the woolly adelgid is chemicals, which are now a cost-effective means of killing the insect, according to the Transylvania County office of the N.C. Cooperative Extension. The county’s office also runs a cost-share program and reimburses property owners up to 50 percent.
The most cost-effective method for controlling the woolly adelgid for homeowners, according to the Great Smoky Mountains National Park is soil drenching with chemicals available at most hardware or garden supply stores.