Aquatic and terrestrial are the two main types of ecosystems, and each has various sub-ecosystems. Forest, desert, grassland and mountain are four subtypes of terrestrial ecosystems, and marine and freshwater are aquatic ecosystem subtypes.
Forest ecosystems come in several types as well. For example, the tropical evergreen ecosystem possesses heavy plant and tree life, with each tree level serving as home to various animal types. Desert ecosystems get less than 25 inches of rain per year and account for about 17 percent of Earth's land.
The largest ecosystems are the marine ecosystems, which account for about 71 percent of Earth's surface and almost all of its water. The marine ecosystems are classified into divisions, such as coral reefs and estuaries.