Estimates of numbers of species in tropical forests vary. However, statements that tropical forests harbor a great bulk of the Earth's species are relatively common. For example, Erwin (1988) and Wilson (1992) stated that while cov ering just 6% of the Earth's land surface, tropical forests are estimated to contain at least 50%, possibly 70%, or even 90% of the Earth's total number of species. It is estimated that about 170,000 plant species, or two-thirds of all plant species on earth, occur in tropical forests (Raven 1988). More recent estimates yield even higher numbers with more than 200,000 species of flowering plants alone (Prance et al. 2000).
Wilson (1992) gives a well-known example of the species richness in tropical forests: a single small tree in the Peruvian Amazon contained as many species of ants as the British Isles. Alwyn Gentry set the world record for tree diversity at a site in the rain forest near Iquitos, Peru. He found about 300 species in each of two 1-ha plots (Wilson 1992). A 1-ha plot in lowland Malaysia contained as many as 250 or more species of trees larger than 10 cm in diameter (Whitmore 1984). Peter Ashton discovered over 1,000 species in a combined census of ten selected 1-ha plots in Borneo (Wilson 1992). Comparisons of number of species between tropical and temperate regions help to illustrate the point: for example, half a square kilometer of Malaysia's forests had as many tree and shrub species as the whole of the USA and Canada (Myers 1996). As forests disappear, so do their species, and most extinctions occurring today happen in tropical forests (Myers 1994).
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