TROPICAL ALPINE PLANT ECOLOGY

Tropical refers to areas within the tropics above the natural elevation limit of contiguous, closed-canopy forest. The habitat occurs in Central America, South America, Africa, Papua New Guinea, Irian Jaya, Borneo, Java, Sumatra, and Hawaii. Tenerife, in the Canary Islands, although subtropical, has an alpine zone ecologically similar to that in Hawaii, just inside the tropics. Treeline often occurs at 3400 to 3900 m (but see 60), and the upper limit of plant life is often at 4600 to 4800 m (25, 35, 36, 43, 45, 48, 56, 92, 94, 109, 136, 146, 147, 152, 155). The lower limit of the alpine habitat is poorly defined both in areas where human disturbance has lowered or eliminated treeline (as in some parts of the Andes and Papua New G(uinea; 32, 62, 106, 132, 152), and in very dry areas (such as the western slopes of the central Andes and the northern slope of Mount Kenya; 25, 157) where treeline forest is naturally lacking. In these cases alpine vegetation merges gradually with montane scrub, pasture, or desert vegetation. The general term tropical includes regional terms such as (mesic areas of the northern Andes), (drier areas of the central Andes), jalca (mesic areas in the transitional zone between the paramo to the north and the puna to the south), zacatal (the Mexican volcanoes), afroalpine