Just west of Chattanooga, Tennessee Department of Environment and Conservation scientists are defending towering hemlock trees in coves along the Cumberland Plateau from a tiny, fuzzy white pest dubbed the hemlock woolly adelgid.
The tiny insect, a type of aphid introduced into the East Coast of the United States from Asia in 1951, has been moving slowly westward from parts of the Great Smoky and Appalachian mountains that are closer to the coast. A similar infestation began along the West Coast in 1924.
Nymph and adult forms of the pest insert a stylet – a contraption similar to a hypodermic needle – on the branches of the evergreen trees, sucking in the sap and nutrients that are supposed to be feeding the trees.
Scientists believe the insect may actually be injecting their own saliva into the tree to disrupt plant growth, and enhance their feeding. The trees lose their vigor and eventually die, usually within 3 to 7 years after the aphids begin their attack.
There are no natural predators for this invasive aphid, and thus they multiply rapidly, and spread by hitching rides on birds.
Halfway down the trail at Fiery Gizzard Cove in the Grundy Forest State Natural Area, a patch of paint on the side of a nearly 100-foot-tall, mature hemlock indicates that state scientists have injected it with the pesticide Imidacloprid. The pesticide will travel through the trees’ circulatory system and kill any of the aphids attempting to feed. It's the same pesticide used to kill Formosan termites in live oak trees along streets in New Orleans.
There are none of the aphids on this tree yet, said Todd Crabtree, Tennessee state botanist.
“We know they are not here yet,” Crabtree told members of the Society of Environmental Journalists during a Thursday tour of the wilderness area on the downslope of the cove. “But there’s zero chance that they’re not going to be here, so we’re going to be prepared.”
“We did some (geographic information system) work to figure out where the hemlocks are, and targeting areas where people are going to be was the first priority – and near stream corridors,” Crabtree said. “This big tree protects this area from being opened up to erosion, and there are very few other species that can grow in this environment and get that large, and provide the same protection.”
The hemlocks are part of a complex ecosystem along the Cumberland Plateau that supports one of the most diverse collection of plants and animals in the world, scientists say. And its an ecosystem under a variety of human-made threats.
Just west of Fiery Gizzard Cove, scientists of Sewanee: University of the South have identified more than 1,100 species of vascular plants on the school’s 13,000-acre campus.
“That’s more (species) than many small European countries,” said Jon Evans, who holds the unique title of assistant provost for environmental stewardship and sustainability, in addition to being a botanist and biology professor.
“We are on the very edge of the Cumberland Plateau,” Evans said. The plateau is the western part of the southern Appalachian Mountains, the range of mountains that runs inland up the East Coast.
“It’s a major hot spot for many biodiversity groups in the temperate zone of the world,” Evans said, including salamanders, trees, land snails, and a variety of North American mammals.
“We are part of that broader region, but here, because we interface with the highland rim (which drops down into valleys along the Tennessee and Cumberland rivers), and, as you go west, you get prairie remnants (of traditional prairie lands of the Midwest) and their ecosystems in middle Tennessee, some of that also spills over into the western escarpment of the plateau.”
“We have all this natural land on this campus that gives us the unique opportunity to train students in the area of environmental stewardship,” he said. “We are finding new species every year on the Cumberland plateau.”
Students learning how to use geographical information systems to help conduct scientific research have mapped the hemlocks on campus, a baseline resource for tracking the invasive aphids as they eventually move west, said Christopher Van de Ven, manager of the university's Landscape Analysis Lab.
"In the near future, we'll redo the survey and find out how much damage the aphids are doing," he said.
The university's GIS system, dubbed the Sewanee Forest History Project, allows students or other researchers to use a computer to review a wealth of documents for locations throughout the campus, everything from past logging operations to archaeological digs.
Sewanee students are collecting new information on the area's ecological diversity through a biodiversity fellow program for selected junior and seniors and through a new program that is developing an online app that all students can use to collect data on species found on and near campus.
“We want to make this amazing diversity of the campus come alive to students on their iPhones,” Evans said. Using its partnership with iNaturalist.org, students will be able to use the app to take photos in the field of plants or animals and either have experts identify them, or use pre-loaded photos and descriptions on the site to find out the identity themselves.
“We just had a herpetology blitz and found over 60 species,” Evans said. “Each one was recorded with a camera and a GPS point that will go up on our iNaturalist site.”
The university’s own herbarium is part of the research resource, with hundreds of dried plant specimens that are being loaded into the app to help with identifications.
Students also have been using their skills in Fiery Gizzard Cove, Evans said. The richness of its plant and wildlife mix stems from the area being a refuge for species during the Pleistocene epoch of geological history, which lasted from about 22.6 million years ago to about 11,700 years ago. It was a time dominated by glaciers that marched south over much of what is now the United States. But those glaciers spared the cove, and when the glaciers marched north into Canada and then mostly disappeared, the plant and animal life in the cove and similar protected spots emerged and spread.
“There are species down there that are still hanging out after having arrived there during the Pleistocene,” Evans said.
The rock that makes up the plateau predates the Pleistocene, dating back to the Mississippian epoch, some 300 million years ago. Over time, rivers and stream have eroded an upper layer of sandstone, as well as a lower layer of limestone, creating the cuts that locals call coves.
At the top of the plateau, the land is acidic, good for trees, but not the best for farming.
One cove on Sewanee land is called Shakerag Hollow, supposedly named for the moonshine stills that were hidden in the woods on its slope – buyers of the liquor would shake a rag at the top of the slope, put their money on a stump, and return later for their bottles.
From the top, its easy to see the farmland below that sits on much less acidic, thus more fertile land spreading out into Georgia and Alabama.
Shakerag Hollow is the location of another invasive threat to southeastern biodiversity, Evans said. A fungus that entered the United States in the late 1970s, probably on horticultural plants from Asia, caused a blight that has wiped out flowering dogwoods in the hollow’s understory.
“The dogwood anthracnose blight infects leaves, and its more likely to kill a tree if the leaves hold water for a longer period of time, so down here in the cove, its shadier and that’s what happened,” Evans said
Evans participated in a research project in the 1990s that documented the ecological consequences of the blight, including several alarming issues.
“Its fruit was extremely important to migratory birds and that food source is now completely gone from the ecosystem,” he said. The birds have had to turn to other fruits and nuts that less of the fats and nutrients so important for migratory songbirds, some of which must fly all the way to south America to winter.
“We also know that dogwood are real important in entraining calcium,” Evans said. Instead of the calcium being stored in the tree’s trunk, it is kept in the dogwood leaves and stems, which would fall to the ground and be available for other wildlife.
“It turns out these dogwood trees were hotspots for invertebrates to find the calcium they need to survive, snails and other kinds of invertebrates, and that’s where the birds would go for their calcium needs as well.”
“So this snowball effect of the importance of dogwoods in the ecosystem, in the food web, is one of these stories of the environmental consequences of our actions,” he said.
Environment reporter Mark Schleifstein wrote this story while attending the 23rd annual conference of the Society of Environmental Journalists in Chattanooga, Tenn., last week. The 2014 conference will be in New Orleans from Sept. 3 to 7.