Almost imperceptibly, as the air thickens, the ichu grass gives way to small shrubs and dwarf trees and suddenly one is amazed to see the ragged gray edges of clouds approaching from below rather than above.
As blankets of mist rise up, the bus turns a hairpin bend and one finds oneself high up on the edge of the Andes, having literally disappeared into a cloud. The descent and the switchbacks continue, the clouds opening momentarily from time to time to display fleeting glimpses of sheer cliff faces, waterfalls and stupendous green, sunlit gorges. The clouds are here for a simple reason.
As the earth rotates towards the east, trade winds are generated across the Amazon, which carry the moisture-laden air westward. As the air rises, clouds are formed and, like fleets of wind-blown galleons, they move in an endless and stately procession across the Amazon. When the warm air finally strikes the Andes, it cools, condenses, and a wreath of cloud forms, swirling, drizzling, and cloaking the mountainside and its forest in a perpetual sheet of mist. Within this mist - from roughly 8,200 to 11,500 feet (2,500 to 3,500 meters) - emerges the cloud forest, an expanse of stunted, evergreen trees whose limbs are festooned with thick coatings of lichens, mosses, orchids and epiphytic ferns.
With each change in altitude the climate also shifts. So, too, do the patterns of plants and animals. The cloud forest - home to the rare spectacled bear, the brilliant red Cock-of-the-Rock and numerous iridescent hummingbirds - is the least studied and also one of the most biologically diverse habitats in the world. Almost 50% of the plants here are endemic, meaning they are found nowhere else on Earth. One of the Manu Biosphere Reserve's many distinctions is that it currently protects the largest area of undisturbed cloud forest in the world.