A forest is an undulating area of land typically dominated by trees. Hundreds of different definitions of forest are commonly used around the globe, adding variable factors like tree density, tree species, land usage, legal status and ecological role to the mix. Forests can also be defined in biological terms as a community of plants and animals with reproductive capacity, including both plant and animal life. There are many types of forest, ranging from deciduous (which lose their leaves in the autumn) to evergreen (which grow back anew each year). The types of forests can often be inferred from a geographical location, with temperate and tropical forest being the most common.

In addition to the types of forest mentioned above, the types of trees also differ depending on the type of forest. For instance, there are two distinctly separate types of trees: coniferous forests which usually produce nuts and seeds, and deciduous forests which produce foliage and other products like fruit. There are also tropical forest trees, which feature low temperatures and high humidity, unlike other types of forest which feature similar features but different climates. The climate of a forest often affects the structure and distribution of trees, influencing how much carbon dioxide is released into the atmosphere and thus influencing climate change.

A large amount of carbon dioxide is released from tropical rainforests and other coniferous forests annually. The main threat to these ecosystems is illegal logging; although this has been limited in some countries, recent years have seen increasing cases of illegal timber harvesting in Latin America and Asia. The threat of deforestation has been highlighted by the fact that in many developing countries, farmers grow much more forested timber than the available soil can support. This is leading to a sharp increase in CO2 emissions from burning wood for domestic and commercial purposes. An increasing number of governments are now trying to put measures in place to protect tropical rainforests and other coniferous forests by putting in place legal protection, better enforcement measures and stricter regulations on how they manage the forestry industry.