Rock Outcrop
JB: This is Earth and Sky on a unique habitat – what scientists call “high elevation rock outcrop.”
DB: This might be a high elevation cliff face, granite dome, boulder field or even a single boulder. Some plant and animal communities thrive on dry, sunny, exposed rock outcrops. But – in the southern Appalachian Mountains of the eastern U.S. – certain rock outcrop species are becoming imperiled – those that require the cool, moist conditions under a canopy of spruce and fir trees.
JB: The retreat of the last ice age left only small, isolated “islands” of spruce and fir forests on the highest mountaintops in the Southern Appalachians. During the last century, these remaining stands have gotten smaller and weaker because of past logging and burning, disease, air pollution, acid rain and climate change. There’s also a non-native insect – a kind of aphid that’s caused massive mortality of Fraser firs throughout the Southern Appalachians.
DB: As trees die, the forest canopy opens – and that’s trouble for plant and animal species that need the moist habitat under the canopy. Consider the fate of the spruce-fir moss spider. It can only survive on the forest floor of boulder and rock outcrops on the highest mountain peaks – and these are drying out.
JB: Our show today was made possible by the National Fish and Wildlife Foundation, in cooperation with the U.S. Forest Service. We’re Block and Byrd for Earth and Sky.
The following individual(s) were interviewed for today’s show. Our thanks to:
Dr. Frederick Coyle
Professor of Biology
Western Carolina University,
David Danley
Botanist
US Forest Service
John Fridell
US Fish and Wildlife Service
Asheville, NC
Author’s Notes:
In the southeastern US, spruce-fir forest is typically only found above 4,400 feet in elevation, with a relatively pure zone of spruce-fir generally beginning only above 5,000 feet in elevation. Red spruce usually dominates the forests at the lower elevations and Fraser fir-dominated forests are typically found near the mountain summits. Approximately 75% of the remaining spruce-fir forest in the Southern Appalachians occurs in the Great Smoky Mountains National Park.
The role of atmospheric pollution in the decline of the high elevation spruce-fir forest ecosystem in the southern Appalachians is a controversial and highly complex topic. While opinions vary and more research is needed, there are studies that implicate atmospheric pollution as possibly a significant factor contributing to the deterioration of the health of high elevation red spruce in the southern Appalachians. Others argue that it is the loss of the fir. Whether, and to what degree, atmospheric pollution may be affecting Fraser fir is also still being studied, but it has been suggested that the effects of air pollution may stress the fir, making them more susceptible to insect and other damage.
The balsam woolly adelgid is a nonnative insect pest that is believed to have been introduced into the Northeastern United States from Europe around 1900. It has caused massive mortality of Fraser fir throughout the Southern Appalachians. It was first discovered in North Carolina on Mount Mitchell around 1957, though it is believed to have been established at that site as early as 1940. From Mount Mitchell, the adelgid spread to the Fraser fir stands throughout the Southern Appalachians. All ages of fir trees are attacked by the adelgid, but damage is generally minimal until the trees reach maturity, at around 30 years of age. Most mature Fraser firs are easily killed by the adelgid, with death occurring within 2 to 7 years of the initial infestation. The death of the fir trees and the resultant opening of the forest canopy causes the remaining trees to become more susceptible to wind and other storm damage. The adelgid is transported and spread primarily by the wind but may also be spread by contaminated nursery stock; on the fur or feathers of animals; or by humans on contaminated clothes, equipment, or vehicles. All efforts to control the spread of the adelgid and treat the infested trees have thus far been largely unsuccessful.
Additional Teacher Resources
U.S. Fish & Wildlife Service: Rock Gnome Lichen in North Carolina
This site provides a brief overview of the rock gnome lichen including status, family, habitat, distinguishing characteristics, species distribution, and threats.
U.S. Fish & Wildlife Service, Division of Endangered Species: Rock Gnome Lichen,
This report includes a brief natural history of the rock gnome lichen and the reasons for its current status, including its dependence of spruce and fir “islands” for a precise amount of moisture and light.
