Projects per year
Rain forests are usually ‘old-growth forests’ par excellence, but they are not generally ‘virgin forests’, having been colonised by indigenous peoplexe 1 indigenous people in former times and undergone re-growth for several hundreds of years. They occupy the warm and wet regions of the Earth, occurring where the temperature of the coldest month is at least 18°C, and where every month has 100 mm of rain or more. They are no more leafy than old temperate forests (leaf area index 5–7.5), and, like temperate forests, their leaves show a continuous vertical profile. Also their gas exchange rates are not different from those of temperate forests except inasmuch as they continue to operate all year round. However, they differ from temperate forests by their broader range of life forms, the tendency of trees to be tied together with lianas, and their high species richness. Several lines of evidence suggest they are acting as carbon sinks, except when they are disturbed, although this may be a transient response to the general increase in CO2 concentrations. However, it is likely that they will decline if climatic warming and drying progresses, and they will then be carbon sources to the atmosphere. In the meantime, they perform an important range of environmental services, and their protection will probably be included in whatever international agreement succeeds the Kyoto Protocol.