Biologists once said, "forests are the lungs of the earth." Forest and human development are closely related to the ecological balance of nature.

Through the photosynthesis of green plants, forests can not only convert solar energy to form a variety of organic matter (forests provide 2.83 billion tons of organic matter each year, accounting for 53.4% of the total output of 5.3 billion tons of organic matter produced by land plants), but also absorb a large amount of carbon dioxide and release oxygen through photosynthesis, maintaining the balance of carbon dioxide and oxygen in the atmosphere, purifying the environment, and enabling human beings to continuously obtain fresh air.

In 1903, the forester G. F. Morozov proposed that the forest is a complex of trees, associated plants, animals, and the environment. Forest community, botany and vegetation are called forest plant community, and ecology is called forest ecosystem. In forestry construction, forest is a kind of natural resource that is protected, developed and renewable. It has three major economic, ecological, and social benefits.

The forest and the abiotic environment in the space are organically combined to form a complete ecosystem. Forest is the largest terrestrial ecosystem on the earth and an important part of the global biosphere. It is the gene pool, carbon pool, water pool and energy pool on the earth. It plays a vital role in maintaining the ecological balance of the whole earth. It is the resource and environment for human survival and development. Forest is an area with high density of trees (or historically, forest is a wasteland reserved for hunting), covering about 9.5% of the earth's surface (or 30% of the total land area). These plant communities cover a large area of the world, and play an important role in carbon dioxide reduction, animal communities, regulating hydrological turbulence and consolidating soil. They are one of the most important habitats in the earth's biosphere.

The forest is a clean-living environment and a green treasure house for human beings. However, the destruction of the forest by human beings makes the ecological environment worse and worse, and disasters are frequent. Natural and man-made disasters have reduced the forest area of about 8million square kilometers in the world to 2.8 million square kilometers. Moreover, the forest area is still disappearing at the rate of 200000 square kilometers per year.