In a move that wildlife biologists say has spared an African Eden, a German logging company said Friday that it had given up its lease on a tract of swamp-fringed rain forest in the Congo Republic.
The Congo Republic government said the land, the 100-square-mile Goualogo Triangle, would be added to the adjacent Nouabale-Ndoki National Park.
Biologists at a news conference at the Bronx Zoo, where the deal was announced, called the tract an untouched ecosystem set in a fast-deteriorating landscape. They said it was one of the few places left in Central Africa where animals showed no fear of humans, because few humans have ever set foot there.
African conservation experts said this was the first time a logging company had voluntarily given up land rights without some trade-off.
The agreement, by Congolaise Industrielle des Bois of Germany, was announced by executives from the company, officials from the Congo Republic government and scientists from the zoo's parent organization, the Wildlife Conservation Society, which worked with the company to survey the region's wildlife.
The Goualogo tract, in the Congo Republic's remote north, is bordered by two unbridged rivers and flooded forests. People who venture in "feel like you're violating a place, like you don't belong," said Paul Elkan, a biologist who spent two years surveying the holdings of the logging company for the conservation society.
Elkan described the moment last year when he realized there was something special about the area.
In Central Africa, when chimpanzees spot humans, the chimps' reaction, honed by long experience with meat-hunting crews, is to shriek and vanish.
After crossing the Ndoki River, establishing a camp and then cutting a trail, Elkan and the other surveyors heard chimps nearby, he said. A storm swept in and the surveyors raced back toward camp. But the sound of the chimps did not fade.
"They were following me," he said. "I went back and met them."
As the team explored the area, they found that many chimpanzees, gorillas, forest antelope, red colobus monkeys and other animals showed little fear and in many cases showed almost as much curiosity as the humans. Elkan described trails created by herds of forest elephants as "boulevards."
Preservation of the tract was the fruit of a new relationship between African loggers and conservationists, who until now have tended to battle each other.
"Logging companies are here to stay in Central Africa," said Jean-Gael Collomb, a biologist who maps logging leases for the World Resources Institute, a private group in Washington. "At some point you have to give up and realize that to reach your objectives you have to be a bit more creative" in how you work with them.
Giuseppe Topa, the chief forestry specialist for the World Bank, said, "The big news here for me is simply that there is a place in Congo that had never seen a man."
Officials of the German-owned company, Congolaise Industrielle des Bois, or CIB, said that once the biological riches in this particular tract were evident, it was clear the land had to be set aside, even though they estimated the timber was worth $40 million.
Hinrich L. Stoll, the president of the company, said: "There was no compensation to us for this. This decision came from a mutual understanding to give up part of a forest with great value."
The company, the largest employer in Congo Republic, with 1,200 workers, is privately held and does not release its earnings.
Stoll said the decision was part of an intensifying effort to shed the long-standing image of tropical loggers as despoilers of fragile ecosystems. Like most logging companies in Africa, CIB has long been the target of boycotts and criticism, particularly by European environmental groups.
The company retains leases on more than 5,000 square miles of forest land in northern Congo Republic, but in 1999 reached agreement with the government and the Wildlife Conservation Society to limit hunting by its cutting crews and to plan its harvest in ways that would limit environmental damage.
The decision to set aside the Goualogo tract came after a four-month survey last year of its wood and wildlife by scientists and experts from the conservation group, the company and the Congo Republic Forestry Ministry.
At the news conference, Henri Djombo, the forestry minister, said his country was hoping for assistance from wealthy countries in return for protecting this tract and many others. Eleven percent of Congo Republic's land is set aside as parks.
Topa, of the World Bank, said the Congo Republic's government was doing a good job of trying to build respect in a region where most governments are either shattered or riddled with corruption.
"We've been bashing African governments because they don't do enough for conservation," he said. "We should recognize such efforts when they occur."
Some private environmental groups were not as quick to hail the announcement.
The partnership between CIB and the Wildlife Conservation Society has long been criticized by some groups, particularly in Europe, that see the efforts as a possible attempt by the company to polish its image without changing its practices.
On Friday, Simon Counsell, the director of the Rainforest Foundation in Britain, said, "It's very hard to know whether CIB should be deserving of any green plaudits because apart from selected people from WCS, the company has refused to allow independent environmental observers into their logging areas."
John G. Robinson, the Wildlife Conservation Society's vice president for international conservation, said other outside groups, including a television crew from the BBC, had recently toured the region.
"The company has been a constructive partner," he said. "The net result for conservation has been good, and the Goualogo Triangle by itself is an amazing step."