1. Forests, oceans and wetlands are called the three major ecosystems of the earth, among which wetlands are the "kidney of the earth" and forests are the "lungs of the earth".

2. Forest ecosystem. Forest ecosystem is a unified system in which forest organisms interact with environment and forest organisms to produce energy conversion and material circulation. It can be divided into natural forest ecosystem and artificial forest ecosystem. Compared with terrestrial ecosystem, it has the following characteristics: rich biological species, richer hierarchical structure, more complex food chain and higher photosynthetic productivity, so the biological productivity is also higher. It has the functions of climate regulation, water conservation, soil and water conservation, wind prevention and sand fixation in terrestrial ecosystem.

3. Wetland ecosystem. Wetland ecosystem belongs to water ecosystem. Its biological community is composed of aquatic and terrestrial species, with active material circulation, energy flow, species migration and evolution, and high ecological diversity, species diversity and biological productivity.

4. Marine ecosystem. Marine ecosystem is a natural system composed of biological community and its environment interaction in the ocean, which consists of two parts: marine biological community and marine environment, and each part contains many elements.