4 Biome Distributions and Environmental Controls
Learn how climate and local conditions shape terrestrial biomes, and how water depth, light, salinity, temperature, and movement organize aquatic communities.
What shapes distributions
A is a broad region with recurring environmental conditions and characteristic communities of life. Biomes do not have sharp borders: they transition into one another, and the same type can occur in distant places with similar conditions. Climate is the main influence on terrestrial distribution, while aquatic biomes are strongly shaped by water depth, light, salinity, temperature, and water movement.
Climate and terrestrial life
Temperature and are two key features of climate. Temperature affects growing-season length and the rates of biological processes. Water availability affects photosynthesis, plant growth, and organisms’ ability to avoid drying out.
Together, temperature and influence which plants can dominate a region. Those plants, in turn, provide food and habitat for animals. Warm temperatures and abundant rainfall support dense, multilayered tropical forests. Very low rainfall is associated with sparse desert vegetation, whose plants tend to be adapted to conserve or store water. Cold temperatures and short growing seasons favor low-growing tundra plants, while seasonally dry tropical regions commonly support grasslands or savannas with scattered trees.
Latitude, elevation, and local controls
Sunlight is more direct near the equator than near the poles, contributing to broad patterns of temperature and seasonal change. Temperatures generally fall as elevation increases, so mountain slopes may contain vegetation zones resembling those at progressively higher latitudes.
Biomes do not form perfect bands. Oceans, winds, mountain ranges, and local topography modify regional conditions. Mountains can force moist air upward, producing wetter conditions on the windward slope and drier conditions in the on the leeward side.
Local controls include soil depth and nutrients, drainage, exposure, and disturbance. A fire regime can help maintain grassland or savanna by limiting tree growth. Soil and water conditions can also create wetlands or other local communities within a wider regional .
Major terrestrial biomes
Terrestrial biomes are broad patterns rather than rigid rules. A particular site’s soil, elevation, water supply, and disturbance history can make its plant community differ from the typical description.
Tropical wet forest: Warm year-round with abundant rainfall. Tall broadleaf evergreen trees, vines, epiphytes, and diverse animals are characteristic.
Savanna: Warm, with distinct wet and dry seasons. Grasses grow with scattered trees, alongside grazing animals and their predators.
Desert: Very low ; temperatures may be hot or cold. Plants are widely spaced and drought-adapted, while animals often avoid heat or conserve water.
Temperate grassland: Seasonal temperatures and moderate, often seasonal . Grasses and herbs occur with grazing animals and burrowing species.
Temperate forest: Moderate and marked seasonal temperature changes. Broadleaf deciduous trees or, in some regions, evergreen trees grow with varied understory life.
Chaparral (Mediterranean shrubland): Mild, wetter winters and hot, dry summers; fires recur in many areas. Drought- and fire-adapted shrubs and small trees are characteristic.
Boreal forest (taiga): Long, cold winters and a short growing season. Mostly evergreen conifers grow alongside mammals and birds adapted to cold and seasonal food supply.
Tundra: Very cold conditions and a short growing season; the ground is often underlain by permafrost. Mosses, lichens, sedges, and low shrubs occur with animals adapted to cold and brief summers.
Environmental gradients in aquatic biomes
Water absorbs light, so depth and clarity determine where photosynthesis can occur. The sunlit supports algae, aquatic plants, and phytoplankton, which form the base of many aquatic food webs. Below it, light is too limited for photosynthesis; organisms there depend on food produced elsewhere or on other energy sources.
Water temperature affects organismal activity and the amount of dissolved oxygen available. In some lakes, surface waters warm and separate from deeper, cooler water during part of the year. Seasonal mixing can redistribute oxygen and nutrients.
Salinity distinguishes freshwater, marine, and brackish habitats, and organisms must tolerate the salt conditions they experience. Currents, waves, tides, and river flow transport nutrients and organisms, shape habitats, and affect how firmly organisms must attach or how they move.
Freshwater and marine settings
Aquatic habitats differ in their water conditions, flow, and available light, which shape their communities.
Lakes and ponds are standing freshwater habitats. Communities vary with depth, light, temperature, and nutrient supply. Phytoplankton and rooted aquatic plants grow where light reaches; fish, invertebrates, and decomposers occupy different parts of the water body and its bottom.
Rivers and streams are flowing freshwater habitats. Current speed and variation in flow favor organisms able to cling to surfaces, swim against currents, or live in slower-flowing margins. Flow also carries nutrients and sediments downstream.
Wetlands have soils that are saturated or flooded for at least part of the year. Emergent plants such as reeds and sedges tolerate waterlogged soils, and wetlands support many aquatic and terrestrial animals.
Estuaries occur where freshwater meets seawater. Salinity changes with tides and river flow, so organisms must tolerate fluctuating conditions. Nutrient-rich waters and sheltered habitats support productive communities, including plants, algae, fish, and shellfish.
Coastal and shallow marine habitats receive enough light for photosynthesis in suitable areas. Kelp forests and coral reefs are examples with distinctive communities; their distributions depend on factors such as light, temperature, substrate, and water conditions.
The open ocean includes sunlit surface waters and vast deep regions with little or no sunlight. Phytoplankton support food webs in sunlit waters; deep-water communities rely largely on sinking organic matter or, in some locations, chemical energy.
Comparing land and water
On land, temperature and largely determine the vegetation that defines broad patterns. In water, important gradients often change over much shorter distances: light, pressure, temperature, salinity, oxygen, and flow can shift with depth, distance from shore, or position along a river.
Both terrestrial and aquatic biomes reflect interactions among physical conditions and living organisms. In each, producers capture energy, and the availability of water, light, nutrients, and suitable habitat influences which organisms can persist. Climate—especially temperature and —sets major limits on terrestrial vegetation and helps explain the global distribution of forests, grasslands, deserts, and cold-region biomes. Latitude, elevation, terrain, soils, and disturbance modify those patterns; aquatic communities are shaped by light and depth, temperature, salinity, water movement, and nutrient availability.