Invasive Species

woolly adelgid on a hemlock tree branch
The woolly adelgid is the scourge of many hemlock trees at the Obed.

Many non-native species have set up residence in the Obed Wild and Scenic River. A non-native is any species that occurs outside its native range as a result of deliberate or accidental introduction by humans. Non-natives compete with native species for habitat and food and often take over specialized ecosystems that rare plants or animals need to survive.

The non-native species are not natural components of the ecological system and, as a result, have not evolved in concert with the native species. Often, non-native species will not have natural predators, so their numbers will grow alarmingly. In fact, most of the successful non-natives seem to be pre-adapted to our area. This could be explained by the biological similarity between the Obed WSR and regions of Europe, East Asia, and western North America. The presence of non-native species in the Obed WSR is a detriment to the park because of the reduction in biological diversity as native populations are forced out of their environmental niches.

Hemlock Woolly Adelgids
The hemlock woolly adelgid (pronounced ah-DEL-jid) is a tiny aphid-like insect that poses a very serious threat to the ecology of the Obed WSR. Without successful intervention, the hemlock woolly adelgid is likely to kill most of the hemlock trees in the national park. Hemlocks play an important role by providing deep shade along creeks, maintaining cool micro-climates critical to survival of trout and other cold water species. The impact of widespread loss of hemlock could trigger changes more significant as those that followed the demise of the American Chestnut in the 1930s and 40s.

Wild Hogs
Rooting and wallowing wild hogs (Sus scrofa) threaten natural ecological communities. The hogs will eat just about anything, including the roots and foliage of wildflowers that often take years to mature and bloom.

Managing Non-native Species
National Park Service policy states that manipulation of populations of non-native plant and animal species, up to and including total eradication, will be undertaken whenever such species threaten the resources being preserved in the park. The Obed WSR is following this policy as long as the programs to control non-native species do not result in significant damage to native species, natural ecological communities or processes, or historic objects. Management procedures vary for the non-native species mentioned above. The park is trying to totally eradicate some non-native plant species through the use of herbicides that do not harm the ecosystem.

Last updated: April 14, 2015

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