Biomes are major ecosystem types characterized by similar climates, soil conditions, and biological communities. Temperature and precipitation largely determine what kind of biome would occur in a place, in the absence of human disturbance.
Understanding biome distribution is important in environmental science because resource availability and biological productivity differ greatly among biomes. Consequently, humans use biomes differently, and ecological resilience differs among biomes.
Among the major terrestrial (land-based) biomes are deserts, tundra, grasslands, temperate deciduous forests, temperate coniferous forest, tropical moist forest, and tropical seasonal forest.
Grasslands, shrublands, savannas, and thorn scrub are among the biomes occurring where temperatures are extreme and precipitation is too slight to support forests. Frequent fires and drought tend to keep trees from growing.
Forests, consisting of trees and the complex, layered communities on the ground and in the soil, occur where there is enough moisture to support trees and tree seedlings. Tropical (low-latitude) rainforests and temperate (midlatitude) rainforests are extremely tall because of abundant rainfall. Tropical forests have relatively poor soils, so cutting them removes most organic matter from the forest.
Grasslands have been lost through conversion to farmlands, overgrazing, and fire suppression. Forests have been lost through logging and conversion to agriculture.
Marine environments can be described by depth and by proximity to shore. Shallow, light-rich environments are usually the most biologically productive because they include many photosynthetic organisms. Near-shore and onshore environments include intertidal zones, estuaries, coral reefs, and mangrove swamps.
Marine environments play key roles in global systems because of photosynthetic activity and biomass production.
Freshwater aquatic systems, including lakes, rivers, and wetlands, are major centers of biodiversity in terrestrial systems.
Wetlands provide essential ecosystem services, including floodwater storage and water purification. Even so, wetlands continue to be converted in North America and worldwide.
Human alteration of ecosystems has been most extensive in forests, grasslands, and wetlands. Many islands have lost nearly all their original habitat. Arctic environments are the least directly altered by human actions, although indirect effects are extensive.
