Forests are a crucial component of the world's ecology, providing a wealth of biological diversity. Although trees are the most visible component, within the woodland and forest biomes that cover about 30% of the world's ice-free land surface, there are other animal and plant species as well. Forest trees provide a huge number of products upon which human society depends, including fuel, fiber, paper, materials for construction and building, food, and medicines. They also play a vital role in many ecosystems, such as maintaining the structure and fertility of forest soil, and preventing soil erosion and floods. In addition, forests provide the invaluable ecological function of absorbing carbon dioxide and releasing oxygen through photosynthesis. Through this process, forests control greenhouse gas levels, which help maintain global temperatures, and produce the atmosphere upon which all living things depend.

Trees began their evolution more than 400 million years ago. Botanists believe the...