By ROGER HAMILTON, Mamirauá, Brazil

Tito Cavalcante Martins silently propels his dugout canoe around tree trunks and thorny branches protruding from the dark water. Two months ago, he said, a person could walk through this forest and not get his feet wet. But now, it is home for the tambaqui, a fish that fattens on fruit that drops into the water. It is home for many other creatures as well, and Martins points them out in the canopy above: troops of monkeys, sloths placidly munching on leaves, noisy flocks of parrots, a toucan, and the brilliant flash of a scarlet macaw.

But Martins' hand-made harpoon never leaves its perch on the gunwale. Come back during the dry season, he says, when the fish are massed together in shrunken channels and lakes, making easy targets not only for fishermen, but for caimans and great flocks of birds.

Everything gets tougher when the water rises. People hurry to harvest their cassava before the river inundates their garden plots. They refurbish floating corrals and begin the tedious job of cutting grass and foliage to feed their cattle. They make floating gardens.

Everyone travels by canoe or motorized launch--to school, to visit neighbors, even to the outhouse. Some take a riverboat downstream to find seasonal work in the closest city, Tefé.

The water continues its rise. People living in floating houses check the ropes that tether their dwellings to trees. Those with houses perched on stilts worry that the water will rise above their floorboards, and that they will have to lay down palm leaves to keep their feet dry, piling them higher and higher as the water rises, sometimes to the point where they have to crouch to walk around.

It is hard to imagine another place in the world like Mamirauá. Although its environment constrains human affairs, Mamirauá (which means baby manatee in the local indigenous language) harbors a remarkable ecosystem of plants and animals that have evolved ingenious ways to cope with seasonal changes. Many species are found here and nowhere else, such as the white uacari monkey and the blackish squirrel monkey, both endangered species.

In fact, it was the white uacari that drew Brazilian biologist José Márcio Ayres to the area in 1983 to carry out his doctoral studies. He was the first person to make a scientific description of this monkey since the middle of the last century.

Would he be the last? Ayres soon realized that the future of the white uacari depended on the preservation of its habitat, which was being threatened by logging. He started a protection campaign, and in 1990, the governor of the State of Amazonas designated a 1,124,000-hectare swath of lakes and forest as the Mamirauá Ecological Station. It was Brazil's first reserve to protect the flooded forest, or várzea, ecosystem.

In 1992, the Mamirauá Civil Society was created to administer the new reserve. Although its initial efforts would be concentrated in a 260,000-hectare focal area, the long-term aim is to extend management to the entire reserve.

While Ayres and his associates were drawn to Mamirauá by its natural treasures, they came to the conclusion that conservation cannot take place in isolation from the people who were already there. Ecology teaches the interdependence of plants and animals, and early on they decided that the key to preserving this ecosystem was the participation of one species in particular: man.

People have been a part of the várzea ecosystem for many centuries. While they modified the environment in many ways, they did not destroy it. But in recent years, pressures had begun to mount. Commercial fishermen from Manaus and Colombia were decimating the local fish populations, loggers were making inroads in the forest, and commercial hunting was threatening the region's manatees, aquatic birds, caimans and turtles.

Equally threatened were the local people who depended on these disappearing resources for their sustenance. Therefore, reasoned Ayres, the local people should be involved in drawing up protective rules and regulations, and then enforcing them.

Ayres again went to the state government with a proposal to create a new kind of legal entity, an environmental reserve where man and biodiversity would coexist. In 1996, the legislative assembly classified Mamirauá as a "sustainable development reserve" that would reconcile three objectives: biodiversity conservation, natural resource use by local communities and research.

It was a bold and trendsetting move that won support from many national and international agencies and organizations, including Brazil's National Environmental Fund, which is financed by the IDB (see "Money where it counts" on this page).

The flat-bottomed aluminum skiff slapped the waves as it planed off the main stem of the river into a channel leading to the flagship of the Mamirauá Sustainable Development Reserve's fleet of floating houses, a two-story base of operations for staff and visiting scientists.

Marise Reis leaned against a stack of boxes filled with flour, sugar, fruit and rapidly thawing chickens. Lanky, laid back and perfectly at ease getting in and out of boats, she was taking a break from her desk duties at the reserve's headquarters in Tefé to visit community leaders prior to an assembly set for the next month. The assembly would be a major event, the culmination of years of meetings, negotiations with governmental authorities, research and the tireless efforts by the reserve's staff to draw up a management plan for Mamirauá that would combine biodiversity conservation, sustainable resource use and activities to improve the lives of local inhabitants. The plan, which was subsequently approved nearly in its entirety, would already be thoroughly familiar to the local people, since they were closely consulted during its preparation.

With its community-based approach, Mamirauá has made a clear break with past attempts to protect biodiversity in the Amazon, says Reis. In developed countries, the first step in creating parks and reserves is to separate man and nature, like breaking up a fight between two antagonists. But in the Amazon, relocating or prohibiting the entry of people, even if it were desirable, would be too costly. Just finding the money to enforce basic regulations is very difficult. And unlike people in developed countries, residents of Mamirauá must harvest fish, timber, wildlife and other forest products for their livelihood.

For all of these reasons, things had to be done differently in Mamirauá.

"When we looked at this area and started thinking about assigning uses to different areas, we never lost sight of the needs of the communities for fish and wood," says Reis.

She and others gathered extensive data on the area's population structure, patterns of migration to and from urban centers, family customs, health and education, and economic activities. Meanwhile, Reis visited the area's 60 communities to explain the objectives of the reserve and solicit ideas.

Most importantly, she guided the communities in creating a representative body that would take the lead in shaping the reserve in the future. At first, two general assemblies were held semiannually. Three riverboats spent three days visiting each community to pick up the 100 delegates, who would meet for three days in Tefé or another location. Later, the assemblies were cut back to one a year. "Nobody could stand meeting so often, neither them nor us," recalls Reis.

The plan hammered out in 1997 was far-reaching and tough, building on regulations already in place. Among its provisions were closing the reserve's focal area to commercial fishing boats from urban centers and assigning lakes to a three-tiered classification system: strict protection, sustained use and special management for selected species. Restrictions were placed on fishing gear, and rules were passed for hunting manatees, turtles, birds and other species. While local communities can continue to fell trees, special provisions now spell out which can be cut, with what equipment, and when.

The reserve's long-term objective is to put in place a zoning system that will totally protect some areas, leave others open for sustainable uses, and designate still others for specific objectives, such as ecotourism, management of turtles, manatees, and caimans, and bird nesting habitat.

Meanwhile, scientists from Brazil and around the world will continue to gather data on species' life cycles, population dynamics, migratory patterns and interactions with other species to give planners the information they need to design management plans.

Reis acknowledges that the new conservation measures and regulations will represent a short-term loss for the communities. But these costs will be partially offset by better health care services, septic tanks and treating drinking water. Project personnel will also help community members to improve fish processing methods, market ornamental fish, produce honey, cultivate fruit trees and sell nontimber forest products. Also, plans are underway to open the area up to low-impact tourism, which would provide jobs for guides, tour operators, cooks and lodging personnel.

Despite a promising start, Mamirauá's future as a place where man and nature can coexist is far from assured. Conservation has meaning only over the long term, and building a lasting relationship between people and their environment takes time. "Old habits die hard," says Reis. "Sometimes the people think that things can be changed over night. But we know it's not like that."