°C and have annual humidity exceeding 77%. They occupy about seven per cent of the Earth's land surface and harbour more than half of the planet's terrestrial plants and animals. Tropical evergreen forests are dense, multi-layered, and harbour many types of plants and animals. The trees are evergreen as there is no period of drought or frost. The canopy tree species are mostly tall hardwoods with broad leaves that release large quantities of water through transpiration, in a cycle that is important in raising as much mineral nutrient material as possible from the soil.