Rainforests are not really Earth's lungs, but they may be its pharmacy
Somewhere between 40 and 75 percent of all living species may be native to rainforests, and more than a quarter of natural medicines were found there. Yet the popular idea that these forests supply the planet's oxygen is wrong: they add very little net oxygen to the atmosphere.
What makes a rainforest is not just rain. The defining traits are an unbroken, closed canopy, constant humidity, a damp carpet of leaf litter, plants that depend on moisture, abundant epiphytes and climbing lianas, and no wildfire. Most are tropical or temperate, but ecologists also recognise subtropical, littoral and cloud forests, vine thickets and even dry rainforest.
Tropical rainforests usually lie within about 10 degrees of the equator, often tied to the monsoon trough known as the Intertropical Convergence Zone. Every month averages above 18 °C, and there is no real dry season. Rainfall is at least 168 cm a year, usually 175 to 200 cm, and can top 1,000 cm. They stretch from Myanmar through Malaysia, Indonesia and Papua New Guinea, across Africa from Cameroon to the Congo, through the Amazon and Central America, and out to Australia and Hawaii. Millions of plant, insect and microbe species there may still be undescribed.
Temperate rainforests are far rarer. They grow along the Pacific Northwest from Alaska to California and in the Appalachians, on the coasts of Ireland and Scotland, in southern Norway, along the Adriatic and the eastern Black Sea, in Japan, Korea, Taiwan and southern China, and in southern Chile, Australia and New Zealand.
Dry rainforests break the pattern with a more open canopy and only 630 to 1,100 mm of rain, typically in the rain shadow of mountains. In Australia their plants cope with shedding leaves in dry spells, smaller or thick leathery leaves, and thorns or prickles, forming types such as Araucarian vine forest and semi-evergreen vine thicket. Across all types, rainforests and the species found nowhere else are vanishing fast through deforestation, habitat loss and air pollution.
Source: Rainforest
