The forest and the abiotic environment in the space are organically combined to form a complete ecosystem. Forest is the largest terrestrial ecosystem on 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 decline, animal communities, regulating hydrological turbulence and consolidating soil. They are one of the most important habitats in the earth's biosphere.