Oak tree with epiphytes; Bali, Indonesia.

When one thinks of tropical forests, images of tall giant trees come to mind, with shrubs and groundcovers struggling in the dense shade below the all-encompassing canopy. The air is still and vexingly humid, filled with bugs and ravenous mosquitoes. This is the popular idea of the lowland rain forest.

More images of cloud forests Tree ferns in Oaxaca, Mexico. Leptospermum flavescens on Mt. Ophir, Malaysia. Mt. Santo Tomas, Philippines.

Cloud forests, a type of rainforest, occur on high mountains in the tropics, generally between 2,000 and 3,500 meters, and experience very different environmental conditions. As one ascends in elevation, the hot steamy lowlands are left behind and several distinct vegetation zones occur, including lower montane forest, cloud forest or upper montane forest, and even an alpine zone if the mountain is high enough. The height of the trees is much lower, and in fact, the trees usually appear crooked and stunted, due to exposure to wind, sun, and cold. Cloud forests are so named because they are often shrouded in mist and fog. The high moisture level and cool year-round temperatures foster plant communities rich in mosses, ferns, and epiphytes, a habitat that scientists are beginning to study and catalog with increasing interest.

Monochaetum humboldtianum, native to Venezuela.

How is it possible for tropical cloud forest plants to thrive out-of-doors in Coastal California? If one looks into the origins of familiar local garden plants like Fuchsia or Begonia one will find that many of the species we grow are native to higher elevations in the tropics, in these cases the Andean foothills. Section Vireya Rhododendron and Aeschynanthus (lipstick plants) come from the montane tropics of Southeast Asia, particularly New Guinea. These plants can grow here because of striking similarities between coastal California's climate and that of mountainous areas in the tropics. The temperature variation between day and night and between summer and winter is not very great in the tropics, even on tropical mountains. Coastal California also has moderate temperatures year round due to the ocean's strong influence - San Francisco is sometimes referred to as "the air-conditioned city." Cloud forests are found at elevations where water in moist rising air masses condenses creating a shroud of mist and fog. The high moisture levels are comparable to northern California's wet winters while a cool ocean current off the coast creates summer fog which softens our Mediterranean summer drought to the extent that it moves inland. Views from atop tropical mountains are remarkable in their resemblance to panoramic summer views of the Bay area with thick fog advancing and retreating below higher hills and mountains.

Major areas in the world where cloud forests are still found include southern Mexico, Central America, and all countries in tropical South America. On the other side of the globe, cloud forests can still be found in SE Asia, New Guinea, tropical Africa, Madagascar, and some islands in the South Pacific.