The Amazon is synonymous with rainforest, so the patches of cerrado scattered through Campos Amazonicos are startling. These savanna enclaves -- grasslands, campos sujos (scrubby fields), and cerradao (dense woodland savanna) -- exist as relics of a drier climatic era, persisting in pockets where soil conditions favor open vegetation over closed-canopy forest. Gallery forest lines the wetlands, and 42 percent of the park remains dense rainforest, but the 28 percent classified as savanna-pioneer contact zone is what draws biologists. These enclaves may represent fragments of a once-continuous savanna belt, isolated as the climate shifted and the forest closed in. Understanding how species adapted to these shrinking islands helps researchers model how Amazonian biodiversity formed in the first place.

The Roosevelt River enters from the south, winding through flat terrain laced with slow meanders. The Jiparana (also called the Machado River) forms the park's southern boundary in Rondonia. Together with the headwaters of the dos Marmelos and Manicor rivers, these waterways define the park's hydrology and its isolation. Roosevelt and Colonel Candido Rondon mapped the river's course during their harrowing 1913-1914 expedition, a journey that cost several lives and left the former president with health damage he never fully recovered from. The park lies south of the Trans-Amazonian Highway, that ambitious and controversial road carved through the forest in the 1970s to connect the Amazon to the rest of Brazil.

Few detailed studies of the park's flora and fauna have been completed, which is itself a telling fact -- the area remains that remote. But what researchers have found is compelling. The Manicore marmoset was discovered here, a primate new to science. Mixed groups of woolly monkeys and white-nosed saki have been observed foraging together, an unusual interspecies behavior rarely documented elsewhere in the Amazon. Protected species include the oncilla, the margay, the jaguar, and the giant otter. The park's forests may serve as breeding grounds for commercially important fish species, connecting aquatic ecosystems across a watershed that drains into the Madeira River far downstream.

Campos Amazonicos is not simply a standalone park. It forms part of an ecological corridor stretching from the Xingu Indigenous Park in Mato Grosso and Para, through the Terra do Meio Mosaic and the Juruena National Park, to the Apui Mosaic in Amazonas. This chain of protected areas is designed to block agricultural expansion into the central Amazon. The park was created by decree in June 2006 and expanded by a net 133,000 hectares in 2012 -- a rare case of a Brazilian national park growing rather than shrinking. But threats press in from every direction: land grabbers burn cleared forest along the Trans-Amazonian Highway, the planned Tabajara Dam would flood portions of the buffer zone, and settlers from northern Mato Grosso push northward along the Tin Highway. The Chico Mendes Institute administers the park, supported by the Amazon Region Protected Areas Program, but funding remains a persistent challenge.