Major Terrestrial Biomes (College Board AP® Environmental Science): Study Guide

What are biomes?

Biomes definition

• A biome is a group of similar ecosystems that have developed in similar climate conditions

  • Biomes are large-scale ecological communities or ecosystem types

  • They are characterised by their dominant vegetation, climate and other abiotic factors

  • These factors shape their biotic communities

• Biomes cover large geographic areas

  • Multiple ecosystems can be found within a single biome

• Biomes can be categorised into groups, including:

  • Freshwater biomes

  • Marine biomes

  • Forest biomes

  • Shrubland biomes

  • Grassland biomes

  • Desert biomes

  • Tundra biomes

• Each of these groups has characteristic abiotic limiting factors, productivity and biodiversity

• These groups can be divided further into:

Forest biomes

• Forest biomes are dominated by trees and can be further divided into:

  • Taiga (boreal forests)

  • Temperate rainforests

  • Temperate seasonal forests

  • Tropical rainforests

Shrubland biomes

• Shrubland biomes are characterised by dense, low-growing woody shrubs, scattered trees, as well as grasses and herbs

• Shrubland is usually classified as a distinct biome and does not fit neatly into either the forest or grassland biome

  • However, it can share characteristics with both

• Some classification systems group shrublands into one of these broader categories depending on the specific ecosystem and dominant vegetation

• For example:

  • Mediterranean shrublands (e.g. chaparral) can be similar to temperate forest biomes

  • Semi-arid shrublands (e.g. savanna-type landscapes) are closer to some grassland-type biomes

Grassland biomes

• Grassland biomes are characterised by grasses and herbaceous plants and can be further divided into:

  • Temperate grasslands

  • Savannas

Desert biomes

• Desert biomes are characterised by low rainfall and are dominated by cacti and other drought-resistant plants—they can be further divided into:

  • Hot deserts

  • Cold deserts

  • Coastal deserts

  • Semi-arid deserts

Tundra biomes

• Tundra biomes are found in high latitudes and are characterised by low temperatures and permafrost—they can be further divided into:

  • Arctic tundra

  • Alpine tundra

Distribution of terrestrial biomes

• Insolation, precipitation and temperature determine where a biome is located on Earth

  • Insolation affects temperature and the rate of photosynthesis in plants

  • Precipitation affects the availability of water

    • This is a key limiting factor for the plants in many biomes

  • Temperature affects the rate of photosynthesis and respiration in plants

    • It also affects the metabolic rates of animals

• The combination of temperature and precipitation is the main factor that determines the distribution of biomes around the world

Characteristics of major terrestrial biomes

Forest biome characteristics

Taiga (boreal forest) characteristics

• Location

  • Between 50°–60° latitude (north and south of the equator)

  • Example locations: Canada, Russia, Scandinavia

• Annual precipitation

  • 300–900 mm (spread throughout year)

• Temperature range

  • Winter: -30°C

  • Summer: Up to 20°C

• Seasons

  • Two main seasons—winter and summer

• Growing season

  • 2–3 months

• Soils

  • Not very fertile: often acidic, with permafrost

  • Shallow soil with a thick litter layer due to slow decomposition

• Biodiversity

  • Less biodiversity than temperate forests

  • Example flora: coniferous trees

  • Example fauna: squirrels, bears, reindeer, wolves

Temperate rainforest characteristics

• Location

  • Between 40°–60° latitude

  • Example locations: Pacific Northwest (USA), New Zealand, Chile

• Annual precipitation

  • 2000–3500 mm (mostly in winter)

• Temperature range

  • 5°C to 20°C

• Seasons

  • Mild winters and cool summers

• Growing season

  • 6–12 months

• Soils

  • Fertile but nutrient-poor due to leaching

• Biodiversity

  • High biodiversity

  • Example flora: mosses, ferns, evergreen trees

  • Example fauna: black bears, elk

Temperate seasonal forest characteristics

• Location

  • Between 30°–50° latitude

  • Example locations: Eastern USA, Europe, China

• Annual precipitation

  • 750–1500 mm (spread throughout year)

• Temperature range

  • Winter: -10°C

  • Summer: 30°C

• Seasons

  • Four distinct seasons

• Growing season

  • 4–7 months

• Soils

  • Fertile, enriched by leaf litter decomposition

• Biodiversity

  • Moderate biodiversity

  • Example flora: deciduous trees (oak, maple)

  • Example fauna: deer, foxes, squirrels

Tropical rainforest characteristics

• Location

  • Within the Tropics (0–23.5° latitude)

  • Example locations: Amazon (South America), New Guinea, Southeast Asia, Zaire Basin

• Annual precipitation

  • Over 2000 mm

• Temperature range

  • 26°C to 28°C

• Seasons

  • No seasons—hot and wet all year round

• Growing season

  • All year round

• Soils

  • Relatively infertile due to leaching

  • Rapid uptake of nutrients by plants

• Biodiversity

  • Very high biodiversity

  • Approx. 50% of the world's plant and animal species

  • Example flora: mahogany, teak trees, lianas, orchids

  • Example fauna: toucans, jaguars, frogs, snakes

Shrubland biome characteristics

• Location

  • Between 30°–40° latitude

  • Example locations: Mediterranean Basin, California

• Annual precipitation

  • 200–1000 mm (mostly in winter)

• Temperature range

  • Winter: 0°C

  • Summer: 35°C

• Seasons

  • Mild, wet winters and hot, dry summers

• Growing season

  • 4–6 months

• Soils

  • Nutrient-poor due to frequent fires

• Biodiversity

  • Moderate biodiversity

  • Example flora: shrubs, small trees

  • Example fauna: foxes, lizards, rodents

Grassland biome characteristics

Temperate grassland biome characteristics

• Location

  • Between 40°–60° latitude

  • Example locations: 'veldts' (South Africa), 'pampas' (Argentina), 'steppes' (Russia), 'plains' (USA)

• Annual precipitation

  • 250–750 mm

• Temperature range

  • Winter: -20°C

  • Summer: 30°C

• Seasons

  • Four distinct seasons—cold winters and warm summers

• Growing season

  • 3–4 months

  • During summer (temperature-dependent)

• Soils

  • Fertile soil with nutrients near the surface

• Biodiversity

  • Large number of species

  • Example flora: grasses, wildflowers

  • Example fauna: bison, antelopes, rabbits

Savanna biome characteristics

• Location

  • Between 5°–30° latitude

  • Example locations: Central Africa (Tanzania, Kenya)

• Annual precipitation

  • 800–900 mm

• Temperature range

  • 15°C to 35°C

• Seasons

  • Wet and dry seasons

• Growing season

  • During the wet season (4–5 months)

• Soils

  • Free-draining with a thin layer of humus

  • Fertile but prone to erosion

• Biodiversity

  • Wide range of species

  • Example flora: grasses, baobab, acacia trees

  • Example fauna: zebras, elephants, giraffes

Desert biome characteristics

• Location

  • Between 15°–30° latitude

  • Example locations: Sahara (North Africa), Kalahari and Namib (Southern Africa), Australia, Middle East

• Annual precipitation

  • Below 250 mm

• Temperature range

  • Daytime: Up to 50°C, average 25°C

  • Night-time: Below 0°C

• Seasons

  • Summer and winter

• Growing season

  • Very short, after rare rainfall

• Soils

  • Infertile, dry

  • Sandy or rocky, low in organic matter

• Biodiversity

  • Relatively low biodiversity

  • Example flora: cacti, yucca

  • Example fauna: spiders, scorpions, camels, meerkats

Tundra biome characteristics

• Location

  • Between 60°–75° latitude

  • Example locations: North of the Arctic Circle

• Annual precipitation

  • Less than 250 mm (mostly snow)

• Temperature range

  • Winter: -30°C

  • Summer: 10°C

  • Below 0°C for 6–10 months

• Seasons

  • Winter and summer

• Growing season

  • 1–2 months

• Soils

  • Thin, infertile (low organic matter)

  • Permafrost present

• Biodiversity

  • Low biodiversity

  • Example flora: small grasses, mosses, lichen

  • Example fauna: snowy owls, snow buntings, tundra swans, arctic foxes, hares, wolves, polar bears, musk ox, caribou

Distribution of nonmineral terrestrial natural resources

• Nonmineral terrestrial natural resources are resources like freshwater and trees for lumber

  • These resources are essential for human use

• The distribution of these resources varies due to multiple environmental factors:

Climate

• Temperature and precipitation patterns directly impact water availability and vegetation growth

  • For example, rainforests are abundant in water, while deserts are arid

Geography

• Landforms such as mountains and proximity to oceans can influence rainfall and resource distribution

  • For example, rain shadow effects create dry areas on the leeward side of mountains

Latitude and altitude

• Higher altitudes and latitudes tend to have colder climates, reducing vegetation density and diversity

  • For example, tundra biomes at high latitudes have fewer trees than tropical forests

Nutrient availability

• Nutrient-rich soils support denser vegetation

• Nutrient-poor soils limit growth

  • Despite their nutrient-poor soils (particularly in deeper soil layers), tropical rainforests remain dense due to the rapid recycling of nutrients in the ecosystem

  • The constant decomposition of plant material and the efficient nutrient cycling in the upper soil layers support vegetation growth

Soil composition

• Soils with good drainage and nutrient retention support more vegetation compared to sandy or rocky soils

Changing distribution of terrestrial biomes

• The global distribution of biomes is dynamic

Past biome shifts

• Natural climate variations, such as ice ages, caused shifts in biomes

  • For example, tundra regions expanded during glacial periods

Current and future biome changes

Global warming

• Rising temperatures are causing shifts in biome boundaries

  • For example, tundra biomes are retreating as forests expand northward in polar regions

• Biome shifts can occur in two ways:

  • Range shifts—when species move to new areas to find suitable conditions as their current habitats become less hospitable

  • Biome type changes —when a biome transitions to a different type, such as a forest becoming a savanna or a tundra becoming a forest

• The distribution of biomes is primarily determined by temperature and precipitation

  • As global temperatures rise due to global warming, the boundaries between biomes are shifting:

    • Poleward

    • Upward in elevation (i.e. to higher altitudes)

• This means that:

  • Warmer biomes, such as tropical rainforests and savannas, are expanding

  • Colder biomes, such as tundra and boreal forests, are contracting

Desertification

• Increased droughts and human activities are expanding deserts into once-productive lands

Deforestation and habitat loss

• Human activity is reducing forested biomes, such as the Amazon, impacting biodiversity and carbon storage

Sea-level rise

• Coastal biomes, such as mangroves and wetlands, are shrinking due to rising sea levels

Impacts of biome shifts

• The impacts of biome shifts are significant

  • As species move to new areas or experience changes in their habitats, they may face new competition, predation, or disease

  • This can lead to declines in population numbers and even extinction in some cases

  • Biome shifts can also have impacts on the vital services that ecosystems provide to living organisms (including humans)

    • E.g. water regulation, nutrient cycling and carbon sequestration