We stopped and rested at 130 feet. Blozan was standing on a small limb. “When these trees die, the nearby streams turn brown,” he said. “The water gets full of tannic acid. As long as I’ve been coming here, these streams were crystal clear. Now they look like they’re coming out of a bog.” Many insects and fish that live in hemlock streams, such as the stone fly and the brook trout, are also threatened by sunlight and heat pouring into stream environments that were once shady and cool.
Blozan loosened his rope and climbed straight to the top. I followed him, moving more slowly. We spent a while lolling in the top of the tree. A bird landed near my face. It looked at me, hopped toward me, and let out a string of territorial cries. It was a red-breasted nuthatch, a species that feeds in hemlocks. Birds don’t always seem to recognize a human in the top of a tree. Whatever this bird thought I was, it didn’t seem to like having me there. A ruby-throated humming-bird began hovering around us, seemingly attracted to my red shirt. It throbbed off into the distance.
From the top of Jim Branch No. 10, we could see that the forest canopy was a ruin. The crowns of the dead trees were still encrusted with living material—a hemlock rain-forest canopy without the hemlocks. It was a scaffold of lichens and other organisms. The trees that harbored them had died so recently and so suddenly that they were all carrying on, for the moment, as if nothing had happened.
WHEN IT BECAME APPARENT that the eastern hemlock might nearly cease to exist, Blozan and his partners founded the Tsuga Search Project, an effort to identify and measure the world’s tallest and largest eastern hemlocks before they were gone. They spent more than $100,000 of their own money on it. Brian Hinshaw, one of the partners, told me, “We just want to try to understand what we once had in these hemlocks.” In the Cataloochee Valley, Blozan walked into groves where he found what had been among the world’s tallest hemlocks. They were already dead, but he and his partners climbed the skeletons and measured them anyway. “The data are for someone someday,” he said. In October 2007, Blozan and one of his partners, Jason Childs, went into a cove in the Cataloochee to check on the health of the world’s tallest hemlock, Usis. Blozan had treated Usis with the chemical, and they wanted to see how it was doing. It was dead.
Three flagship species of migrating birds make their nests in hemlocks: the Blackburnian warbler, the black- throated green warbler, and the solitary vireo. In spring, they arrive in the Cataloochee before leaves come out on hardwoods; the evergreen hemlocks offer them cover, food, and a place to nest. No one knows what will happen to them when they arrive in the spring. Many other birds feed in hemlocks or nest in them, including the Acadian flycatcher, the Louisiana waterthrush, the winter wren, and the red-breasted nuthatch. The flying squirrel lives in hemlocks, and it feeds on fungi around their roots; the flying squirrel seemed to have gone into a decline. When an old hemlock falls, a world passes away. As for the Cataloochee Valley, most of the eastern hemlocks there were dead.
The Search for Ebola
1. Disturbed Forest
MONTHS LATER, when the epidemiologists finally arrived, they traced the threads of the horror back to one man, Patient Zero, who became known only by his initials, G.M. The threads converged on one little spot in the world. It was a sinuous patch of forest called Mbwambala. Mbwambala is a fragment of disturbed woodland about three miles long and half a mile wide that wanders along a small stream about six miles southeast of the city of Kikwit, in the Democratic Republic of the Congo. G.M. was forty-two years old at the time of his death. He lived with his extended family in Kikwit, in a family compound consisting of huts made of wattle. Each day, G.M. commuted on a bicycle to his place of work in the little forest of Mbwambala.
Kikwit is situated on the banks of the Kwilu River, 250 miles east of Kinshasa, the capital of Congo. Kikwit stands on a rolling, grassy plateau that is dissected by streams the color of chocolate milk. The streams meander through valleys filled with gallery forest, narrow, snakelike stands of trees nestled along the streams. Most of the plateau had once been covered with tropical rain forest, but 90 percent of it had been cut down in recent decades.
Nobody had a clear idea of how many people lived in Kikwit. Some experts felt that the city had a population of around 150,000, while others had a feeling that the city might contain closer to half a million people. Kikwit had grown into a sprawling agglomeration of houses made of wattle and cinder block, with roofs made of grass or sheets of metal. The city was a transportation center of a sort. Overland trucks passed through the city, moving along the Trans-Africa Highway, a system of dirt roads that crosses Africa from the Atlantic Ocean to the Indian Ocean. This is the same system of roads along which the human immunodeficiency virus, HIV, seems to have moved across Africa after its trans-species jumps from unidentified animal hosts—most likely monkeys and chimpanzees—into the human species.
Congo had been ruled for many years by the dictator Mobutu Sese Seko, who’d maintained control using a corrupt, chaotic army. Many things that had once worked reasonably well in Congo now did not. At one time, it had been possible to drive an automobile from Kikwit to Kinshasa in just four hours over a paved road. Now the drive to the capital lasted anywhere from twelve hours to several days, when the road was passable. It had developed ruts up to ten feet deep.
Kikwit had no running water, no sewage system, no telephone network, no newspaper, and no radio station. At night, the city went dark; there was very little electricity. The city’s main hospital, Kikwit General Hospital, had a diesel generator. It also had an X-ray machine, but the hospital didn’t have running water or toilets. It didn’t even have bed-pans: a family member would provide a clay jar to collect the patient’s body waste. Many people who lived in Kikwit commuted by foot or bicycle to fields of cassava and maize outside the city. The people practiced slash-and-burn agriculture, moving their crops from place to place. The abandoned fields grew up in Christmas bush, an invading shrub from Florida and Central America. People also hunted small animals and gathered wood in the remaining patches of forest.
Just after dawn one day around Christmas 1994, G.M. got on his bicycle and pedaled through the city and down to the Kwilu River, and he crossed it on a bridge. He turned right and followed the river upstream through a valley. It was the rainy season. The weather was hot and wet, and the road was muddy; he threaded his way around puddles. After five miles he parked his bicycle, leaning it against a hollow stump near the road. Then he walked away from the road and away from the river, going uphill toward the east, following a footpath that went through thickets of Christmas bush and through fields of maize and cassava. He crossed a low ridge. The path descended. In about a mile, he came to a chocolate-colored stream. It wound among low hills through the forest of Mbwambala.
Mbwambala was a type of natural habitat that biologists call an ecotone. An ecotone is a transitional zone where two different ecosystems touch and mix. One sort of ecotone, for example, is the dividing line between wild forest and cleared agricultural land. Another ecotone is the meeting of sea with land, along a seashore. Ecotones
