Threats to the Spruce-Fir Forest
Threats to the Spruce-Fir Forest of Great Smoky Mountains National Park
Dead Trees from Clingmans Dome by Larry Sossamon
Dead Trees from Clingmans Dome by Larry Sossamon
A Unique Forest Type
On the crest of the Great Smokies is a forest of red spruce and Fraser fir trees that looks more like a Canadian forest than what you would expect to find in the South. Fraser fir grows only in the highlands of the southern Appalachians, and the Smokies are the southernmost limit of the red spruce’s range. In fact, 74% of all the spruce-fir forest in the southern United States is within the boundaries of Great Smoky Mountains National Park. This unique forest type, with its rich diversity of plants and animals, helped the park earn recognition as a United Nation’s International Biosphere Reserve—an area deemed to have world-wide significance.
The Adelgid Arrives
The Fraser fir is adapted to high winds, intense rain and fog, cool temperatures and the short growing season that characterize this harsh, high country environment. But mature Fraser firs are being eliminated from the park by a tiny European import, the balsam woolly adelgid. This insect is difficult to see with the naked eye, yet it can kill a fir in as little as three years.
The balsam woolly adelgid was introduced on nursery stock into New England around 1900. The adelgid and many other “exotics” reproduced virtually unchecked because natural enemies were not imported with them or failed to function as they did in former settings. In addition, host trees had little genetic resistance to the newcomers. The adelgids eventually spread to the southern Appalachians. They were first detected in the Smokies in 1963 on Mt. Sterling, near the park’s northeast boundary.
The insect has infested all Fraser fir stands within the park. During the last 30 years, over 70% of the mature fir in the park have been killed by the adelgid. Of those that remain alive, most are infested by the insect. The adelgid usually does not affect individual trees until they are old enough to produce roughened bark, which is about the same time trees begin to produce cones.
An adelgid population consists of wingless females that rely on wind currents to spread from tree to tree. Adelgids are found on the surface of the bark, often covering it so heavily with their white “woolly” mass that the trees appear whitewashed. As many as 50,000 adelgids may infest a single tree. Each adelgid finds a suitable feeding site, inserts its mouthparts into the bark and stays for the rest of its life. As the adelgid feeds on the tree's sap, it injects a hormone that causes the tree’s cells to harden, interfering with the flow of water and nutrients. The normal growth function is disrupted, and the tree dies in a few years.
The National Park Service exercises active control measures against the "exotics" causing the most disruption to the native ecosystem. In 1982, the park’s Resource Management and Science Division began an initiative, co-sponsored by the U.S. Forest Service, to treat several areas. Trees are individually sprayed with a fatty acid soap derived from plant and animal fats and oils. This soap is toxic to the adelgid, but presents no harm to humans or the environment.
The entire trunk of each tree must be saturated, which makes aerial application impractical. Trucks with high pressure sprayers do the job, so control is limited to areas along roads where the trees are accessible.
If adelgid counts on trees show that soap treatment is necessary, Resource Management crews spray the trees in mid-July and/or September when the maximum number of adult adelgids are exposed. The soap affects the adelgid's waxy, protective coating and the insect dies. A control area is currently established at Purchase Knob to preserve the genetic diversity of the fir and provide future seed sources.
Balsam woolly adelgids are not the only threat to the high elevation forests. In recent years, scientists in the Northeast have reported a decline in red spruce, including high mortality and a decrease in growth rate. In our southern Appalachian mountains, there have been a few signs of reduced red spruce health, including a deterioration of canopy vigor reported in the late 1980s. Current primary stressors of red spruce include the death of surrounding fir trees
due to the adelgid, gradual climate change, and atmospheric deposition or air pollution.
High elevation forests are more vulnerable to damage from pollutants because they receive greater amounts of both dry and wet acid deposition and are frequently enveloped in acidic clouds.
Researchers have found a link between acid precipitation, aluminum uptake by the trees, and slower growth of spruce. However, the problem is highly complex and will take several years to fully understand.
Climate change could also profoundly affect the future of the spruce-fir forest. Since spruce-fir habitats in the South are cut off from similar habitats to the north, higher temperatures would likely “squeeze species off the mountain tops,” leading to extirpation or extinction.
If both spruce and fir trees continue to decline, there is little doubt that other organisms will also perish. Ecological relationships that have been functioning for thousands of years are now being altered. The spruce-fir forest is home to dozens of species of plants and animals that live nowhere else on earth. Seven subspecies of birds, 45 species of plants, and the spruce-fir moss spider live only in spruce-fir forests. Many of the plants are listed as rare or endangered and some, like Rugel's ragwort, occur only in the national park.
Several mosses and liverworts that live only on the bark of fir trees are in jeopardy. Plants that are dependent on fir to shade them are beginning to decline. Blackberries and other species that are sun loving are invading and choking out other species. It is likely that important pollinators and other crucial links in the system are being reduced or eliminated by the loss of spruce and fir.
Hope for the Future
There is hope for the rugged alpine environment of the high southern Appalachian peaks. Because of the biological importance of the spruce-fir forest and the immediacy of the threats to the ecosystem, the spruce-fir zone is receiving increasing research attention. Agencies have combined forces to intensively study this high elevation ecosystem. Recent research efforts have focused on setting up permanent study plots to examine the decline of fir and the longterm prognosis for its survival, and to delineate and study remaining stands of mature fir.
Although spraying the fir forest is not feasible on a large scale, researchers still hope to discover a strain of Fraser fir that is resistant to adelgids or to find biological controls for the adelgids. Natural regeneration of young fir continues to be good in many areas. Continuing research and management efforts are extremely important if this rare ecosystem is to survive.