A biome is a large-scale community of organisms classified primarily by the dominant vegetation and characterized by adaptations to that particular environment. Tropical rainforests have high biodiversity, warm temperatures year-round between 25 and 30°C, heavy annual rainfall exceeding 200 cm, and a dense canopy structure with multiple vertical layers. In contrast, the tundra is characterized by extremely cold temperatures, a short growing season, permafrost, low precipitation, and vegetation limited to mosses, lichens, and low shrubs.
Other major terrestrial biomes include the temperate deciduous forest, with its moderate rainfall, distinct seasons, and trees like oaks and maples that shed their leaves in autumn. The taiga, or boreal forest, features long cold winters, short summers, coniferous trees such as spruce, pine, and fir, acidic soils, and relatively low biodiversity. Desert biomes receive less than 25 cm of annual precipitation, experience extreme temperature fluctuations, and support organisms with specialized water-conservation adaptations. Grasslands are dominated by grasses rather than trees, have moderate rainfall between 25 and 75 cm per year, and include temperate prairies as well as tropical savannas, which feature scattered trees, distinct wet and dry seasons, and large herbivore populations such as zebras and wildebeest. A terrestrial ecosystem is any land-based community of organisms and their environment, encompassing forests, deserts, grasslands, and tundra.
Aquatic ecosystems are equally diverse. Marine ecosystems cover about 71% of Earth's surface, contain saltwater, and support diverse life from phytoplankton to whales across habitats including coral reefs, open ocean, and deep-sea environments. Coral reefs are marine structures built by colonies of coral polyps, supporting roughly 25% of all marine species and protecting coastlines from wave erosion. An estuary is a partially enclosed coastal body of water where freshwater from rivers mixes with saltwater from the ocean, creating a highly productive ecosystem. Freshwater ecosystems include bodies of water with low salt concentration, such as lakes, rivers, streams, ponds, and wetlands. Within freshwater systems, lentic ecosystems consist of still or slow-moving waters like lakes, ponds, and wetlands, while lotic ecosystems consist of fast-moving habitats like rivers and streams, characterized by continuous water flow and high dissolved oxygen. Wetlands are areas where land is saturated with water permanently or seasonally, supporting hydrophytic vegetation and serving as natural water filters.