The caatinga is one of Brazil's great biomes, and also one of the least famous abroad. Where the Amazon gets the attention, the caatinga covers roughly 800,000 square kilometers of the Northeast - an area larger than France - with a unique dryland ecosystem found nowhere else on Earth. The name comes from Tupi and means roughly "white forest," because in the dry season the trees and shrubs lose their leaves and the landscape fades to a pale gray-white. When the rains arrive, sometimes briefly and all at once, the entire biome explodes back into green. Hyperxerophilic plants - adapted to extreme drought - dominate. Cacti stand between twisted trees that have evolved wax-coated leaves. In the Castanhão Ecological Station, this biome is the subject of strict protection and scientific study.

The station sprawls across three municipalities in eastern Ceará: Jaguaribara holds 84.04 percent of the reserve, Iracema 15.2 percent, and Alto Santo just 0.75 percent. The terrain is gentle - smooth to gently undulating, part of the Sertaneja Depression that spreads across the Sertanejos Residual Plateaus. Rivers through the area drain into the Jaguaribe basin, which itself covers just over 51 percent of the state of Ceará. The reserve sits about 270 kilometers from Fortaleza, far enough inland to escape the coastal climate entirely. The Chico Mendes Institute for Biodiversity Conservation (ICMBio), Brazil's federal agency for protected areas, administers it - the same agency named for the rubber tapper and environmental activist murdered in 1988 in Acre.

The climate here is tropical semi-arid. Average annual temperatures run around 27 °C. Annual rainfall varies considerably year to year but hovers around 750 millimeters in a typical season, concentrated almost entirely in a brief wet period. During the 2012-16 drought that nearly emptied the adjacent Castanhão reservoir, the station received far less than that. In normal years, the rains arrive, the caatinga turns green for weeks, the rivers flow, and the animals emerge. Then the ground dries, the leaves drop, the watercourses go to stone, and the biome goes quiet again. It is a boom-and-bust ecology, and the creatures that live in it are built for cycles of abundance followed by patience.

In 2006, after the station had been open for five years, federal authorities announced plans to nearly double its size to 23,000 hectares, adding the Serra da Micaela highlands to the reserve. The logic was straightforward: the sources of the rivers that feed the Castanhão basin lie in those higher elevations, and protecting river sources protects water supplies downstream. IBAMA, the Brazilian environmental enforcement agency, planned to install an office in Nova Jaguaribara - the new town built for families displaced by the reservoir - to conduct caatinga research and manage the expanded area. But by 2017, the ICMBio website still listed the station at its original 12,574.44 hectares. The expansion, for whatever combination of bureaucratic, financial, and political reasons, had not happened.

The station protects what it can, but the numbers are sobering. Within its boundaries, roughly 36 percent of the area is used for agriculture - a holdover from pre-reserve land use still being unwound. Another 15.7 percent is entirely devoid of vegetation, stripped bare by previous human activity. Only 18.2 percent of the reserve still holds original native vegetation. The rest is in various states of recovery. The pioneer species that dominate in disturbed areas - Mimosa acustipula and various Crotoneae - are exactly the plants that show up first when the caatinga is trying to heal itself. They are an encouraging sign and a sobering one at the same time: encouraging because nature moves back in when given room, sobering because without this strict reserve there would be nowhere for it to start. The quiet work of the ecological station is to keep giving the caatinga that room, indefinitely.