YAKUSHIMA, Japan — A mysterious pestilence has befallen this island’s primeval forests, leaving behind the bleached, skeletal remains of dead trees that now dot the dark green mountainsides. Osamu Nagafuchi, an environmental engineer with a passion for the island and its rugged terrain, believes he knows the culprit: airborne pollutants from smog-belching China, hundreds of miles upwind.
For years, Mr. Nagafuchi’s theory was ignored by fellow scientists and even mocked by bureaucrats in the national government who administer the forests on this southwestern island. But Japan has begun taking his warnings more seriously, as the nation has been gripped by a national health scare over rising levels of potentially dangerous airborne particles that have swept into other parts of Japan and that many now believe were produced by China, its huge and rapidly industrializing neighbor.
These fears have reached a new level recently as China itself has issued more public warnings about the growing health risks from its cities’ gray, soupy air. While Mr. Nagafuchi and a small number of collaborators say their research is not politically motivated, they admit that they may be finding more receptivity among a public that already resents China for supplanting Japan as Asia’s largest economy, and for what is seen as its haughty attitude in a territorial dispute over islands both countries claim.
Japanese officials still dispute whether airborne pollutants are responsible for killing the pine trees. But they and other scientists have at least begun to view Yakushima, which is far from Japan’s own industrial centers, as a pristine laboratory for understanding how China’s growing environmental problems could be affecting its neighbors.
Many islanders are already believers, and they worry that the pollutants may be threatening their health.
“We are starting to feel like the canary in a coal mine,” said the island’s mayor, Koji Araki. “Our island is right downwind from China, so we get the brunt of it.”
Whatever the cause, the tree die-off is a worrisome turn for this small, mountainous island off Kyushu, the southernmost of Japan’s main islands, whose moss-carpeted forests provide a rare patch of primitive nature in an otherwise densely populated nation. There are fears here that a growing smog problem could scare off the hikers and other ecotourists upon whom many of the island’s 14,000 residents depend for their livelihoods.
Most visitors come to see Yakushima’s majestic cedar trees, which have so far been unaffected by the mysterious ailment killing the pines. The cedars won the island the distinction of a Unesco World Heritage site in 1993.
The cedars were logged for centuries to build some of the great Buddhist temples in the ancient capital, Kyoto. The biggest remaining tree, the gnarled Jomon cedar, measures 16 feet around at the base and is estimated to be at least 2,600 years old.
The dying trees are from an endangered species of pine that is found only on Yakushima and a neighboring island. Mr. Nagafuchi, a professor of ecosystem studies at the University of Shiga Prefecture in central Japan, said he noticed the problem when satellite photographs showed a large increase in the number of dead trees between 1992 and 1996.
Mr. Nagafuchi, then a public employee for a city in Kyushu, had already found blackened snow while hiking to Yakushima’s mountaintops in 1992. He started collecting and analyzing the snow as a sort of weekend hobby. To his surprise, he found it contained silicon, aluminum and other byproducts from the burning of coal, which is used to heat homes in China. Using maps of winds, he theorized that the pollutants were carried here from China, across the East China Sea.
The discovery drove Mr. Nagafuchi to quit his city job and eventually become a university professor, doing much of his research on Yakushima. He has set up small monitoring stations around the island to measure levels in the air of ozone and sulfur emissions, which are typically the byproducts of burned coal or automobile exhaust.
On a recent afternoon, Mr. Nagafuchi climbed to the highest of those stations, atop Mt. Kuromi, a windswept peak that rises 6,000 feet above the sea below. After hooking up his laptop to download data from the station’s small digital recorder, he pointed out the thin, gauzy haze that clouded what he said should have been pristine air.