In 1996, the biologist Robert Timmins was walking through a market in Thakhek, the provincial capital of Khammouane, and bought a dead rodent. Villagers called it kha-nyou. It had a long furry tail, short legs and a skull that did not match anything in the literature. When Paulina Jenkins and colleagues formally described it in 2005 as Laonastes aenigmamus, they judged it strange enough to need an entirely new family. A year later, palaeontologists argued they had gone the wrong way: the animal was not new at all, but a surviving member of the Diatomyidae, a family last seen in the fossil record roughly eleven million years ago. It had been living in these limestone hills the whole time.
Phou Hin Poun covers about 1,801 square kilometres of tower karst in the Annamite Range, and the striking thing about it is how little of it is soil. More than half the area is estimated to be bare rock - fluted, pitted, blade-sharp limestone rising in towers and ridges, drained from within by caves and fissures so that surface water simply leaves. What grows on the remainder is dry evergreen forest and scrub, shaped as much by a tropical savanna climate as by the porous ground beneath it. This is not lush country. It is vertical, hot, thin-soiled and almost impossible to walk across, which is exactly why so much has survived in it.
The kha-nyou was not the only surprise. Another rodent found here, described in 2005 by Musser, Smith, Robinson and Lunde, was given the genus name Saxatilomys - from the Latin saxatilis, among the rocks, and the Greek mys, mouse. The name is a description of a lifestyle. Saxatilomys paulinae has been recorded only in forested, rocky limestone, and it represents a new genus within the Murinae, the Old World rats and mice, a subfamily zoologists had every reason to think was thoroughly catalogued. The karst does this repeatedly. Isolation on a landscape of stone islands is a machine for producing species that exist nowhere else and that nobody thought to look for.
Surveys have counted 113 species of mammal here, along with 160 birds, 81 reptiles, 47 amphibians and 145 fish. Forty-one bat species have been recorded, and a single cave, Tam Houay Si, is used by twenty-two of them - a nightly exodus of a scale that is hard to picture until you have stood beneath one. The mammal list reads like a wishlist for Southeast Asian conservation: Indian elephant, Indochinese tiger, the critically endangered saola, giant muntjac, Assam macaque, Francois' langur clinging to sheer limestone, and the black giant squirrel moving through the canopy below. Among the birds are the wreathed hornbill, the grey peacock-pheasant, the hill myna, the red-collared woodpecker, and the sooty babbler, a species that E. C. Stuart Baker described in 1920 and that has kept a low profile ever since.
Phou Hin Poun is one of twenty-one National Biodiversity Conservation Areas in Laos, and the protection this status confers is largely nominal. The annual budget for each is about five hundred dollars. That figure is not a typo and it is not an exaggeration for effect. Spread across 1,801 square kilometres - an area larger than Greater London - it works out to well under a dollar per square kilometre per year. Designation on a map, without staff or vehicles or salaries behind it, is a promise the state has not been in a position to keep.
Nearly thirty thousand people live inside the conservation area - 29,603 at last count. They are not intruders in it; their villages predate the designation, and their livelihoods come from the same forest, fish and stone the surveys are counting. Any honest account of Phou Hin Poun has to hold both facts at once: that this is one of the richest karst ecosystems in Asia, and that its future will be decided by the daily economic arithmetic of the families living in it, not by a line on a ministry map or a budget that would not cover a month of fuel. The kha-nyou survived eleven million years without anyone's help. What happens next is a different kind of question.
Phou Hin Poun National Biodiversity Conservation Area centres on 17.75N, 104.80E in Khammouane Province, central Laos, covering roughly 1,801 sq km of limestone tower karst in the western Annamite foothills. From the air the boundary is invisible but the terrain is unmistakable: a dense field of grey pinnacles and knife-edge ridges, with dark forest confined to the fissures between them and almost no surface drainage. Best viewed from 8,000-12,000 ft AGL in low sun, when the towers cast the shadows that reveal their relief. Route 8 forms the northern edge of the region and Route 13 runs down the Mekong plain to the west; the Nam Hin Bun is the main watercourse. Nearest airports: Thakhek (VLTK) to the southwest, Nakhon Phanom, Thailand (VTUW) across the Mekong, Savannakhet (VLSK) to the south, and Vientiane Wattay (VLVT) to the northwest. Haze from agricultural burning cuts visibility badly in March and April; November to February offers the clearest air.