Mount Bintumani -- also called Loma Mansa, meaning "king of the Loma" -- rises to 1,945 meters above sea level, the highest point in Sierra Leone and the second-highest peak in the entire Guinea Highlands after the Nimba Range to the east. The massif is a geological outlier, an ancient granitic plateau that has resisted the erosion shaping the lower terrain around it. Its elevation creates conditions found almost nowhere else in Sierra Leone: montane evergreen forest extends to about 1,680 meters, above which the plateau opens into high-altitude grassland swept by cool winds. At these heights, temperatures drop noticeably from the tropical lowlands below, and the vegetation shifts from dense canopy to open grass and scrub. The reserve encompasses 33,201 hectares of this varied terrain, from lowland gallery forest and wooded savanna at the base to the windswept grasslands on top.

The Loma Mountains support ten primate species, a remarkable concentration for a single protected area. Western chimpanzees are the headline residents, and the mountains hold Sierra Leone's largest population. But the primate list extends to red colobus monkeys, black-and-white colobus, sooty mangabeys, and Diana monkeys -- several of them threatened across their range. Beyond primates, the mountains shelter some of West Africa's most elusive large mammals. Forest elephants move through the lower forests. Pygmy hippopotamuses -- smaller, reclusive cousins of the common hippo, found only in the forests of West Africa -- inhabit the waterways. Leopards, Jentink's duiker, and water chevrotain round out a fauna that would be remarkable anywhere but is extraordinary for a reserve this small. BirdLife International has designated the Loma Mountains an Important Bird Area, recognizing its significance for multiple bird species whose habitat is disappearing elsewhere in the region.

Between 2002 and 2023, the Loma Mountains lost six percent of their primary forest cover. The clearing is driven by forces familiar across tropical Africa: farmers and ranchers who say there is not enough agricultural land in surrounding communities, who see the forest as unused potential. Illegal marijuana cultivation has also pushed into the park's boundaries. The pressures are not abstract or distant -- they are the pressures of poverty, of communities with few livelihood options and little reason to value a forest reserve whose benefits accrue to the global biodiversity ledger rather than to local dinner tables. Sierra Leone's civil war, which devastated the country from 1991 to 2002, disrupted conservation efforts and displaced populations into previously undisturbed areas. Recovery has been slow. The infrastructure for enforcement barely exists, and the political will to prioritize a remote mountain over more immediate development needs is perpetually thin.

The vegetation of the Loma Mountains tells a story of altitude and water. At the base, Guinea-Congo lowland forest forms the foundation -- dense, species-rich canopy typical of the West African forest belt. Gallery forests trace the watercourses, threading green corridors through the wooded savanna that occupies drier ground. As elevation increases, the character of the forest changes. Montane evergreen forest takes over, its trees shorter and more gnarled than the lowland giants, adapted to cooler temperatures and thinner soils. Mosses and epiphytes thicken on branches where clouds regularly settle. Above 1,680 meters the trees surrender entirely to montane grassland, a landscape that looks more like Scotland than West Africa -- open, wind-raked, and improbably green. These high grasslands are rare in the region, and their ecological isolation has produced plant communities found nowhere else. The Loma Mountains are, in ecological terms, a sky island: high ground surrounded by a sea of lower, warmer, different terrain.