1. Rainforests are forests characterized by high rainfall
Rainforests are forests characterized by high rainfall. This often results in poor soils due to leaching of soluble nutrients. Minimum normal annual rainfall between 175 cm (69 in) and 200 cm (79 in) occurs in this climate region. Mean monthly temperatures exceed 18 °C (64 °F) during all months of the year.[3] The monsoon trough, alternatively known as the intertropical convergence zone, plays a significant role in creating the climatic conditions necessary for the Earth's tropical rainforests. Rainforests are also often called the "Earth's lungs"; however, there is no scientific basis for such a claim as tropical rainforests are known to be essentially oxygen neutral.[4][5] Around 40% to 75% of all biotic species are indigenous to the rainforests.[6] Rainforests are home to half of all the living animal and plant species on the planet.[7] The rainforests are home to more worldwide species than all other biomes added together. About 80 percent of the world's known biodiversity could be found in forests.[8] It has been estimated that there may be many millions of species of plants, insects and microorganisms still undiscovered in tropical rainforests. Tropical rainforests have been called the "jewels of the Earth" and the "world's largest pharmacy", because over one quarter of natural medicines have been discovered there.[9] Tropical rainforests are currently fragmenting due to human activity. Habitat fragmentation caused by geological processes such as volcanism and climate change have occurred in the past, and have been identified as drivers of speciation.[10] However, fast human driven habits destruction is suspected as being one of the major causes of species extinction. Tropical rain forests have been subjected to heavy logging and agricultural clearance throughout the 20th century, and the area covered by rainforests around the world is rapidly shrinking. 資料來源: