northern Asia) got into the Fraser fir, a native American species growing on the higher ridges and peaks of the southern Appalachian Mountains; this parasite killed from 70 to 90 percent of the mature wild Fraser firs, making the mountains look as if they were covered with driftwood. (Today the wild Fraser firs in the Appalachians often don’t get much taller than a person before they die from adelgid infestation.) A fungal disease of unknown origin has killed off the vast majority of the wild flowering dogwoods in North America. Another disease, sudden oak death, has killed hundreds of thousands of oaks in California and may get into Eastern oaks. A European insect carrying a European fungus has lately caused a mass dying of the American beech tree, and the American beech’s future as a species in the wild is uncertain. An Asian beetle called the emerald ash borer arrived in Michigan in 2001 in packing wood from China. It is devastating to a number of species of American ash trees. Despite strong efforts to control it, the emerald ash borer keeps appearing in different places, and it seems capable of not only wiping out the ash but threatening the classic major-league baseball bat (which is commonly made of ash). Another invader, the Asian long-horned beetle, had its North American debut in Brooklyn, where it showed up in a park near warehouses that held large amounts of packing wood from China. The Asian long-horned beetle has infested tens of thousands of trees in New Jersey and Long Island, and it has shown up Sacramento. It could take out the sugar maple. In effect, the trees of North America have been hit with all sorts of Ebolas of their own.
When a parasite moves to a new habitat, it can find new hosts through a process called the trans-species jump. Often the new host has no resistance; the host and the parasite haven’t had time to adjust to each other through natural selection. (It is frequently not in the best interest of a parasite to kill its host quickly.) One example is the human immunodeficiency virus, HIV. It appears to have once lived in chimpanzees, though it doesn’t make them sick—the chimp’s immune system is well acquainted with the virus and has learned how to deal with it. In Africa, at various times and places in the twentieth century, HIV made trans-species jumps into humans—probably through hunters who killed and butchered chimps, and so were exposed to infected chimp blood. Once the virus had escaped the chimpanzee’s immune system, it amplified itself freely in its new hosts.
Another example of an invasive species is the Ebola virus. Ebola is a parasite with a known tendency to make trans-species jumps into new hosts. Ebola lives naturally in some unknown type of host in central Africa—possibly a bat, possibly a wingless fly that lives on a bat, or quite possibly some other creature. Ebola probably doesn’t make its natural host very sick. Ebola makes primates incredibly sick. This means that primates are
Outbreaks of Ebola in humans tend to burn out fairly quickly, but Ebola is a far more serious matter for gorillas. In recent years, roughly a third of the gorillas in protected areas in central and west Africa have died from Ebola virus. The virus is spreading unchecked in the gorilla population of central and western Africa, and it kills around 90 percent of the gorillas it infects. No one knows how Ebola has been getting into gorillas; possibly some disturbance in the ecosystem has put the animals into contact with the unknown host of Ebola.
I sometimes wonder if the unknown natural host of Ebola is itself an invasive species—some sort of rodent or insect, perhaps—that’s moving into disturbed habitats in the African rain forest. If so, this might explain why Ebola seems to be jumping into gorillas more frequently these days. Ebola’s host might be moving into new niches that have opened up in a rain forest that’s being changed by logging and human invasion. The Ebola host might be bringing itself and its parasite—Ebola—into close contact with gorillas. The World Conservation Union recently put the western gorilla on its critically endangered list; the Ebola virus, together with poaching, could push the western gorilla to extinction in the wild (some gorillas would persist in captivity). In other words, what happened to the American chestnut could also happen to the western gorilla: functional extinction due to a species-jumping parasite.
Global climate change has become entangled with the problem of invasive species. A warmer climate could allow some invaders to spread farther, while causing native organisms to go extinct in their traditional habitats and making room for invaders. The earth’s biosphere can be thought of as a sort of palace. The continents are rooms in the palace; islands are smaller rooms. Each room has its own decor and unique inhabitants; many of the rooms have been sealed off for millions of years. Now the doors in the palace have been flung open, and the walls are coming down.
Global climate change may be helping the hemlock adelgids spread both north and south. Winters in the north are becoming steadily warmer, and the insects are not likely to be hit as often with deep cold. Summers in the southern Appalachians have lately become drier and hotter, and drought stress makes infested hemlocks far more susceptible to parasites. Climate change may also mean that the adelgids will be more active when birds are flying south. Recently, the woolly adelgid has turned up in Ohio, Michigan, Vermont, New Hampshire, and Maine— approaching the northern limits of the hemlock range. Wherever it goes, it seems to get into every hemlock. It kills saplings before they can produce seeds, and so, in every place it arrives, it stops the hemlock species from reproducing. Many experts have concluded that the insect could kill nearly all the eastern hemlocks; if so, the species would essentially disappear from the wild.
ON DECEMBER 3, 2001, an arborist named Will Blozan discovered woolly adelgids on the branches of a wild hemlock in the Ellicott Rock Wilderness, on the Blue Ridge in South Carolina, near the extreme southern end of the hemlock range. No one had expected to see the insect this far south so soon. “It was a spear through the heart,” Blozan told me. He phoned Rusty Rhea, an entomologist and the forest-health specialist for the Forest Service in Asheville, North Carolina. Rhea was surprised. He sent out a bulletin to all rangers in the area warning them to look for adelgids. Within two weeks, Rhea was getting reports. The insect had gone all over the mountains.
Will Blozan is a tall man in his thirties with dark blue eyes that can take on a guarded look, and he has a laconic way of speaking. Blozan has wide shoulders and powerful-looking hands, but his hands move with a sensitive, precise quality—they’re the hands of a professional tree climber. He is the co-owner of a tree-care company called Appalachian Arborists, based in Asheville. (Arborists, who used to be known as tree surgeons, get around in trees using ropes.) He is also the president of the Eastern Native Tree Society, a small organization dedicated to discovering giant trees in the East. Since 1993, he had been spending his spare time exploring patches of old-growth forest in the Appalachians from New Hampshire to Georgia. Will Blozan became well known among tree biologists for having discovered and measured many of the tallest and largest trees in eastern North America. He often found them while he was bushwhacking through remote valleys in the southern Appalachians; he got into places that may not have had human visitors in years or decades.
In the Great Smokies in summer, the heat can be Amazonian. The land can slope sixty degrees, and in many places the undergrowth consists of a mesh of rhododendrons. “It’s total suckage in there,” Blozan said. “‘Rhodo wrestling’ may be the appropriate term for movement in the Smokies.”
When he found a big tree, he would get an estimate of its height using a laser device. Later, he would climb to the top, using ropes, and would send a measuring tape down along the trunk—this is the only way to determine the height of a tree to the nearest inch.
As he explored around, measuring tall trees, Blozan spent a lot of time around the southeastern tip of Great Smoky Mountains National Park, in a place called the Cataloochee Valley. It is a rain-forest wilderness, “well known for making you wet,” Blozan said. The Cataloochee Valley is centered on a rumpled drainage dissected by hundreds of small upland coves and divided by ridges and mountains. A few hiking trails wander through the Cataloochee, but many parts of it are very difficult to enter.
Blozan eventually discovered that the Cataloochee Valley has the highest average tree height—more than 160 feet—of any watershed in eastern North America. The Cataloochee contains more than 80 percent of the world’s tallest eastern hemlocks. It also contains the world’s largest yellow poplar and four of the world’s tallest white pines, including the tallest tree in eastern North America, a white pine that Blozan discovered in 1995 and named the Boogerman Pine. In January 2007, he found what turned out to be the world’s tallest eastern hemlock, growing in a cove in the Cataloochee. He and Jason Childs, another arborist, climbed it and measured it with a tape, and got 173.1 feet. Blozan named the world’s tallest hemlock Usis, which is the Cherokee word for “antler.” “The Cataloochee is the epicenter of the eastern hemlock species,” Blozan said. “The valley has the largest and best groves of eastern hemlock in the world.” In effect, the Cataloochee Valley is the Notre Dame cathedral of the eastern forests.
By the summer of 2002, the woolly adelgid had been found in the Cataloochee. Few national parks have a
