The Atlantic Forest is not a single forest. It is a mosaic of habitats glued together by geography and moisture gradients. On stabilized coastal dunes, restinga forests grow low and dense. Inland, tropical moist forests climb into submontane and montane zones, their canopies dripping with epiphytes. Further west, where the rain thins, the Atlantic dry forests form a transition toward the semi-arid Caatinga. Mangroves occupy the river mouths. Campos rupestres rise on rocky highlands. Araucaria moist forests spread across the cool southern reaches, their odd candelabra pines looking more like a drawing than a tree. The biome spans tropical moist broadleaf forests, tropical and subtropical grasslands, and mangrove ecosystems. Ninety-two percent of it lies in eastern Brazil, with the remainder in Paraguay and Argentina.

Approximately 40 percent of the Atlantic Forest's vascular plants and up to 60 percent of its vertebrates are endemic - they exist nowhere else on Earth. Biologists have cataloged over 3,000 tree species, 98 bat species, 94 medium-to-large mammal species, over 2,000 epiphytes, 26 primate species, 528 amphibians, 124 small mammals, and over 800 bird species in what remains. Between 1990 and 2006, researchers described more than a thousand new flowering plants. Some species thought lost returned from near extinction - the black-faced lion tamarin, rediscovered in a small population in 1990 after being presumed extinct; the butterfly Actinote zikani, declared extinct in 1981 and found again in 1991. A new blonde capuchin (Cebus queirozi) was identified in northeastern Brazil in 2006. The forest keeps producing surprises, even as it disappears.

The Atlantic Forest that Portuguese colonists encountered was not pristine. Researchers now estimate that Indigenous land management had shaped 60 to 80 percent of the forest landscape by 1500. For thousands of years, Indigenous peoples practiced slash-and-burn agriculture, transforming biological corridors into food resources and reshaping plant and animal communities in the process. Portuguese colonists then exploited Indigenous labor and knowledge to harvest Paubrasilia echinata - the brazilwood tree whose red-dye trunks gave the country its name. Sugar plantations, called engenhos, followed in the sixteenth and seventeenth centuries and did more damage to the forest than any previous human activity. The deforestation has continued ever since, but the pattern of heavy human use long predates Europeans. What changed after 1500 was scale, tools, and export economies.

The golden lion tamarin is a small primate with a face framed by a fiery red-gold mane. By 1970 it was on the edge of disappearing. A few hundred individuals remained in fragmented patches of forest near Rio de Janeiro. The tamarin's plight sparked international attention, and conservation efforts began in earnest - zoo breeding programs, habitat corridors, protected areas. The species is still threatened, but it has rebounded. The tamarin became the animal face of the Atlantic Forest. Its survival story is also the ecosystem's. So is the story of the maned sloth, Bradypus torquatus, endemic to these forests and named for its long dark hair. So is the story of Dendropsophus branneri, the small hylid tree frog that lives in the canopy and calls through the evening.

Today about 28 percent of native vegetation cover remains. Deforestation continues at roughly 0.5 percent a year, higher in urban areas. Agricultural conversion leads the pressure - sugarcane, coffee, tobacco, soybeans, biofuel crops - followed by logging and hunting. When a forest fragments, larger animals disappear first, which cascades through seed dispersal networks and alters the plants themselves. One study found biomass reduced to 60 percent of normal in fragments smaller than 25 hectares. Against these trends, the Pact for Atlantic Forest Restoration has assembled more than 100 businesses, nonprofits, and government agencies behind a target of restoring 15 million hectares by 2050. The Pontifícia Universidade Católica do Rio Grande do Sul maintains a 3,100-hectare private reserve called Pró-Mata. São Paulo state created the 9,300-hectare Restinga de Bertioga State Park as a wildlife corridor. In 2007, two volunteers named Joao Milanez and Joanne Stanulonis planted 5,500 new trees in the mountains around Gravata. Every hectare returned to forest is a hectare that might support a tamarin, a tree frog, a capuchin. The Atlantic Forest persists in fragments, but the fragments are still there. That is the narrow margin on which biodiversity now depends.