Woodland characterized by lush vegetation and comparatively high temperature and rainfall throughout the year. Rain forests are the world's most biologically diverse ecosystems. Although they account for less than 7 % of the land surface on Earth, they contain more than 50 % - some scientists estimate as high as 90 %- of its plant and animal species. One hectare (about 2.5 acres) of tropical rain forest may contain more than 600 species of trees. By comparison, the forests of the United States and Canada combined contain only around 700 tree species.  Rain forests also play a critical role in global climate regulation by absorbing carbon dioxide, a gas believed to be partially responsible for global warming. Plants naturally absorb carbon dioxide and give off oxygen gas in the process of photosynthesis, and tropical rain forests absorb more carbon dioxide than any other terrestrial ecosystem on earth. Global emissions of carbon dioxide have increased nearly 30% in the last century. There is general agreement among the scientific community that by absorbing some of the gas, rain forests play a vital role in lessening its impacts.

  Temperature 

Rain forests are typically hot and steamy- the average annual temperature is 25° C (77° F). Temperature near the equator varies little over the course of a year, so rain forest temperatures are about the same year round- the average minimum monthly temperature in a rain forest is a balmy 18° C (64° F). 

  Rainfall 

Rain forests can average as little as 1.8 m (6 ft), or as much as 9.0 m (30 ft), of rainfall a year. What distinguishes a true rain forest is the distribution of precipitation throughout the year. There are no dry seasons. Every month, typically more than 100 mm (4 in) of rain falls. If a rain forest does have dry periods, they are usually short and unpredictable.

  Soil 

Despite their incredible lushness and high diversity, one of the peculiarities of rain forests is that the  soil is poor in nutrients that can be absorbed by plant roots. The nutritious minerals have been washed out of the soils by heavy rainfall and high temperatures over thousands of years. To compensate for the nutrient-poor rain forest soils, most tropical trees absorb the nutrients they can find and hold them in their living tissue. When tropical trees die, nutrients are released into the soils by decomposition. Rather than remaining in the soil reservoir as they would in a temperate forest, in the rain forest, the nutrients are rapidly absorbed again by other living organisms.