So what's so scary about this bug whose name is literally longer than it is? Here are a few numbers to consider: In one year, a single female can produce 90,000 young. (And they're ALL female.) In less than 20 years, HWA have killed 90% of the hemlock trees in Shenandoah National Park and 80% of the hemlocks on the Blue Ridge Parkway, and are quickly working their way through the forests in the Great Smoky Mountain National Park, where they were found in 2002.
“The ecological extinction of the eastern hemlock will be the most dramatic impact on the eastern mixed deciduous forests since the chestnut blight,” observed Dean Henson, the naturalist at Pine Mountain, where he spotted HWA in July of 2006. Jenny Beeler, Natural Resource Management Specialist at Cumberland Gap, agrees and takes that comparison one step further. “It doesn't matter how old or how young the tree is - the HWA makes it difficult for the trees to reproduce - it can affect little trees. That's what's scary about this,” said Beeler, who found HWA in the national park in November of last year.
The HWA is not a native species of this country - if it were, the trees would have had time to adapt to the threat. It was introduced on the west coast of the U.S. in the early 1920s, when it is believed to have come in on ships from Asia, and it had made its way to the east coast by 1951. Wind and birds traveling from tree to tree are the primary culprits in the migration of the HWA, though unwitting hikers who brush up against infected branches are also responsible for some of its dispersal.
Why is the hemlock so important in forest ecology? Its nickname, the “redwood of the East,” gives a hint. They are known as the most shade-tolerant and long-lived trees in the forest. That means they can grow with as little as 5% of full sunlight and can live up to 800 years. They are a popular habitat for songbirds and some raptors, and since they grow in riparian zones (streams), they provide vital cover for water species.
“If we lose the hemlocks, that will dramatically affect the streams - they provide the moderation of temperatures,” Beeler explained. “Fish and insects could be affected by higher temperatures in the summer.” Consequently, mammals and birds that depend on the streams for life will be affected. The loss of the hemlock as habitat will also adversely affect many forms of life in the park, not least the hikers and picnickers who enjoy the cool shade and filtering rays of sunlight on the trails.
Of the 20,000 acres that comprise the national park, some 940 are either hemlock forest or hemlock-cove forest (hemlock mixed with hardwood trees) - almost five percent of the park's trees. At the present time, evidence of light infestation HWA has been found on the Sugar Run Trail, in the Brownie's Creek/Brush Mountain Road area, and on the Banner Field Trail in Tiprell, with a heavier infestation located at Shillalah Falls. At Pine Mountain State Resort Park, there are two known light infestations within the park and one near the park border, not to mention other occurrences in Kentucky Ridge State Forest. (Presently, the only two counties in Kentucky known to have HWA are Bell and Harlan counties, where it has been seen at the Pine Mountain Settlement School and possibly Blanton Forest.)
The next question is a much harder one to answer - what can be done? At Cumberland Gap, they are still in the process of monitoring the park to discover the extent of the problem, after which, according to Beeler, funding sources will be explored. At Pine Mountain, several goals have been set to combat the problem. These include minimizing the loss of the more susceptible old-growth trees by soil injection or drenching with insecticide, and treating to reduce spread by applying soap sprays. Henson adds, “These goals may change or expand as the infestation spreads and as better information becomes available.” Planned treatments for the national park are the same, with the possible addition of importing predator beetles that eat only HWA; the Great Smoky Mountains National Park is currently seeing good results with this treatment.
Any of these procedures will be costly and time-consuming, and the lack of available funding and manpower at both the state and federal levels is discouraging. Henson admits that “there is presently no known ‘silver bullet' for this problem and any treatments undertaken will have to be repeated every two-three years until better technology comes into being, if ever.” As for what can be done on the local and individual level, both Henson and Beeler ask that visitors to the parks report sightings to the staff.
But perhaps the best thing anyone can do, for now, is to take a walk through a hemlock grove - the opportunity may not be around for much longer.
For more information on HWA and how you can help the parks, visit www.saveourhemlocks.org or either park's naturalist staff.
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