Natural ecosystems can be classified as large and distinct areas where specific organisms live owing to habitation variables such as temperature, moisture and the availability of sunlight. There are six major types of natural ecosystems: tundra, grassland, forest, desert, marine and freshwater. Tundra is the coldest of all biomes, with low biological diversity and a short growing season. Grasslands are characterized by moderate temperatures and biological diversity. Forests are known for rainy weather, while deserts have little moisture.
Marine and freshwater are the two types of natural water ecosystems. Marine ecosystems include oceans and coral reefs. Both oceans and coral reefs are known for their large amount of genetic diversity. Freshwater ecosystems include lakes, rivers and wetlands. Temperatures vary greatly in freshwater when compared with those of marine ecosystems, and genetic diversity is not as pronounced.
Man-made ecosystems are ecosystems humans have created intentionally or unintentionally. Urban ecosystems include most large cities. Dams, orchards, farms and villages are also synthetic ecosystems. These ecosystems were not created with the sole intention of becoming an ecosystem and generally have poor genetic diversity. Scientists have also created ecosystems intentionally, such as coral reefs for endangered aquatic species.