A biome is a large-scale ecological area characterized by a common climate and the resulting dominant plant and animal communities. Terrestrial biomes specifically refer to land-based ecosystems, classified by the vegetation and life forms adapted to the climate of that geographic area. The distribution of these environments is shaped by large-scale geographical and meteorological processes.
Environmental Factors Driving Biome Formation
The distribution of terrestrial biomes is primarily governed by two factors: temperature and precipitation. These variables define the long-term weather patterns, or climate, of a region, controlling which life forms can survive. The combination of average annual temperature and total yearly precipitation dictates the availability of liquid water and the length of the growing season. For example, high temperatures and abundant rainfall support lush, productive forests. Low year-round temperatures, even with moderate precipitation, restrict life because water remains frozen and unavailable to plants, resulting in biomes like the tundra.
Characteristics of Major Terrestrial Biome Types
Tundra
The Tundra biome is characterized by a cold climate and a short growing season, typically found in high northern latitudes. A defining feature is permafrost, a layer of permanently frozen subsoil that restricts the growth of deep-rooted plants. This frozen substrate limits vegetation to low-lying species like mosses, lichens, and dwarf shrubs. Animals living here, such as caribou and arctic foxes, exhibit adaptations like thick coats and layers of insulating fat to survive the extreme cold. Alpine Tundra occurs at high elevations worldwide and shares a similar cold, windswept environment but lacks permafrost. The absence of trees is due to low temperatures, intense solar radiation, and poor soil drainage.
Forests
Forests are categorized by their dominant tree types and the climate conditions that support them. The Boreal Forest, or Taiga, is the largest terrestrial biome, situated just south of the Arctic Tundra. It experiences long, cold winters and short, cool summers. The landscape is dominated by coniferous trees like pine, spruce, and fir. These evergreen trees have needle-like leaves with waxy coatings, which reduce water loss when water is frozen and unavailable.
Temperate Deciduous Forests are found in mid-latitude regions that experience four distinct seasons with moderate temperatures and ample rainfall. They are dominated by broadleaf trees, such as oak, maple, and beech, that shed their leaves annually in the autumn. This seasonal leaf drop helps trees conserve water during the cold winter months. The decomposing leaves contribute to rich, fertile soil that supports a diverse understory and animal life, including deer, bears, and various bird species.
Tropical Rainforests are situated near the equator, receiving consistently high temperatures and the highest annual rainfall of any biome. This stable, warm, and wet climate supports the greatest biodiversity on Earth. Plant life is characterized by broad-leaved evergreen trees and a complex vertical structure. The dense canopy creates low light conditions on the forest floor, forcing many plants to develop adaptations, such as growing as epiphytes on tree branches, to reach sunlight. Rapid decomposition means the soil is often poor in nutrients despite the lush growth.
Grasslands
Grasslands are characterized by continuous cover of grasses and herbaceous plants, with trees sparsely scattered or absent.
Tropical Grasslands (Savannas)
Tropical Grasslands, or Savannas, are found in warm climates with pronounced wet and dry seasons. The vegetation consists of scattered trees and tall grasses. The ecosystem is maintained by seasonal fires and the grazing of large herbivores like zebras and giraffes.
Temperate Grasslands
Temperate Grasslands, known as Prairies or Steppes, experience hot summers and cold winters with moderate precipitation, often insufficient to support extensive tree growth. The dominant vegetation is shorter grass. The fertile soil is rich in organic matter from the deep, dense root systems of the grasses. Historically, these areas supported vast herds of grazing animals, such as bison, which shaped the ecosystem.
Deserts and Shrublands
Deserts are defined by extremely low precipitation, typically receiving less than 25 centimeters of rain per year, and can be either hot or cold.
Deserts
Hot deserts, such as the Sahara, experience high daytime temperatures and significant temperature drops at night. Plant life, including cacti and succulents, has evolved adaptations like thick, water-storing tissues, reduced leaf surface area, or deep roots to maximize water retention. Desert animals are often nocturnal or burrowing to avoid the intense heat.
Chaparral (Shrublands)
Chaparral is characterized by hot, dry summers and mild, wet winters. Found in small patches globally, such as the Mediterranean Basin and coastal California, the vegetation is dominated by dense, spiny, evergreen shrubs. These plants are highly adapted to fire, with many species requiring the heat or smoke from wildfires to germinate their seeds.
How Latitude and Altitude Influence Biome Location
The global pattern of terrestrial biomes is largely a result of how latitude, the distance north or south of the equator, affects solar energy input. Regions near the equator receive the most direct sunlight, leading to consistently high temperatures and supporting tropical biomes. As latitude increases toward the poles, temperatures drop, leading to temperate and then polar biomes. This creates broad, horizontal bands of biome types across the continents.
Altitude, or height above sea level, influences biome distribution in a manner that mirrors the effects of latitude. As elevation increases, the air cools due to the atmospheric lapse rate. For every thousand-meter rise in elevation, the temperature drops significantly, mimicking the climatic shift experienced toward the poles. This results in vertical zonation on mountains, where a sequence of biomes changes from deciduous forest at the base to coniferous forest, then alpine tundra, and finally permanent snow and ice at the summit.