Like a green lifeline, tropical forests stretch through 50 countries around the equator between the Tropic of Cancer and the Tropic of Capricorn. Two-thirds of these forests, 1.5 billion acres, receive 4 to 10 m (13.2-33 ft.) of rain a year and average 26.6°C (80°F) at the forest floor. These are the true rain forests.
Further away from the equator, semi-deciduous forests receive less rain, only 1 to 4 m (3.3-13.2 ft.). Many trees loose their leaves during the drier seasons. Because these seasonal forests are more open to sunlight part of the year, the understories have denser plant growth.