- The most valuable and the richest ecosystem on Earth. It plays a critical part in the Earth's life support systems and house 50%, and possibly as much as 90%, of all the species on Earth. It is a key storehouse of foods, oils and minerals, and a source of ingredients that make up a range of medical treatments. It also represents home and livelihood for many people. However, more than half of the rainforests have disappeared, chopped down for valuable tropical hardwoods, or cleared to provide areas for cattle grazing or human habitation. The forests play an important part in climate patterns, and deforestation is thought to be responsible for 18% of global warming. Furthermore, as they disappear there is also an albedo effect - a damaging increase in the sunlight reflected - which affects wind and rainfall patterns.