Species Invaders

By Maureen Halsema

Southern Appalachia is under attack. Half of the imperiled species in the region are at risk from invasive species. Some particularly damaging species include, the hemlock woolly adelgid, the emerald ash borer, the gypsy moth, the tree-of-heaven, and Japanese stilt grass.

The hemlock woolly adelgid threatens the majestic hemlock trees in the Smokies and Shenandoah by sucking the sap from the base of the trees’ needles. Within a few years of infestation, these trees are often damaged and even killed. The loss of hemlock trees could have severe ramifications throughout the forest ecosystem, including affecting the Smokies’ diverse salamander population. Park rangers are struggling to combat this invasive insect, originally from Asia, through a variety of means including introducing a natural predator, biocontrol beetles from British Columbia called the Laricobius nigrinus They have also used chemical controls, such as the Merit 75W formula designed for soil application. This type of control can eliminate a hemlock woolly adelgid tree infestation within two years. The chemical must be carefully monitored, however, to avoid introduction into nearby water resources.

The emerald ash borer’s larvae pose an enormous threat to ash tree populations. The larvae eat the inner bark of the ash trees and interfere with the tree’s ability to transport water and nutrients. The adults render are less devastating because they simply eat the foliage. This Asian native beetle has killed millions of ash trees across the United States and Canada.

Insecticides and quarantines have been used to try to control the emerald ash borer population.
The gypsy moth caterpillar is an extremely invasive species that attacks the foliage millions of acres and hundred of species in the United States, particularly targeting oaks and aspen. Southern Appalachia is home to one of the highest concentrations of gypsy moths. Efforts to suppress gypsy moth population include, pesticides, natural predators, small mammals, birds, fungus species, and even viruses. Rangers have also been countering the effects by replanting the forest with trees that are less likely to be on the gypsy moth’s menu.

Tree-of-heaven, an invasive species native to China, grows rapidly in a variety of conditions. It can survive in poor soil, thrives in the sun, but can sustain a population in the shade as well. In addition to growing ubiquitously wherever it takes up residence, the tree-of-heaven also produces an allelopathic chemical that prevents other plants from growing in its vicinity. This plant utilizes roads as a migration route. In order to control populations, rangers target large female fruit bearing trees in order to reduce seed distribution. Chemical controls are a controversial but somewhat effective means of population control.

Japanese stilt grass can also survive in a diverse range of habitats. It is most commonly found in shaded floodplains or in closed forest canopies with low lighting conditions, but it can also live in drier areas in direct sunlight. This plant poses a serious threat to the natural landscapes that it inhabits as it encroaches on land and nutrients displacing native species. Land managers try to combat their thriving and damaging populations through a variety of means. They attempt to manually remove these species, to mechanically remove them with a mower, or to apply herbicide treatments, such as Round Up.