A cloud forest, also called a tropical montane cloud forest, is a generally tropical or subtropical evergreen forest, usually found on mountains, that experiences persistent, frequent or seasonal cover by low-lying cloud; the International Cloud Atlas formally recognizes clouds of this kind as a distinct type, formed directly by the vegetation beneath them. Most tropical cloud forests lie within about 25 degrees of the equator, typically between 500 and 4,000 meters in elevation, where moist ocean air is forced upward against mountain slopes, cools and condenses as it rises. Annual rainfall in the biome ranges from around 500 to 10,000 millimeters, with average temperatures generally between 8 and 20 degrees Celsius, and much of the moisture reaching the forest floor arrives as fog drip condensing directly onto leaves and trunks rather than as rain, which can double the water reaching the ground in seasonally dry climates. The trees tend to be shorter and more gnarled than in lowland tropical forest, with leaves that shrink and thicken with increasing altitude, and their branches often carry more weight in mosses, ferns, bromeliads, orchids and other epiphytes than in the trees' own foliage. Cloud forests cover only about one percent of the world's woodland, spread across roughly 736 known sites in 59 countries, concentrated in Central and South America, Southeast Asia, East and Central Africa, Hawaii and the Caribbean, yet they hold about 3,700 species of birds, mammals, reptiles, amphibians and tree ferns between them, some fifteen percent of global diversity in those groups, with about half of those species found nowhere else. They are also a critical freshwater source for downstream communities, in places such as coastal Peru and northern Chile essentially the only water supply there is, even as roughly 2.4 percent of the world's cloud forest cover was lost between 2001 and 2018, with losses over 8 percent in some regions, and rising temperatures are expected to push the climate conditions the forest needs further upslope in the decades ahead, shrinking the habitat available to it.