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Terrestrial
Biomes

Explore the major land-based ecosystems on Earth: their climate patterns, characteristic organisms, and the environmental factors that define each biome.

AP Environmental Science

What Is a Biome?

A biome is a large-scale community of organisms defined primarily by the dominant vegetation type and characterized by the organisms that have adapted to that particular environment. Biomes are determined mainly by climate: temperature and precipitation patterns over long periods.

Climate Drives Biome Distribution

The two most critical climate variables that determine biome type are average annual temperature and average annual precipitation. Together, these create a "climate space" where each biome occupies a distinct zone.

Precipitation (cm/yr) Average Annual Temperature (°C) 0 100 200 300 400 -10 0 10 20 30 Tundra Taiga Temperate Forest Desert Tropical Rainforest Grassland Savanna

The Major Terrestrial Biomes

Ecologists recognize several major terrestrial biomes. While classification systems vary, the AP Environmental Science framework focuses on these key types:

Tundra
Permafrost, low shrubs, extreme cold
Taiga
Coniferous forest, long winters
Desert
\( < 25 \) cm rain/yr, extreme temperatures
Grassland
Grasses dominate, seasonal drought
Temperate Forest
Deciduous trees, four distinct seasons
Tropical Rainforest
Highest biodiversity, warm and wet year-round
Savanna
Scattered trees, wet/dry seasons
Chaparral
Mediterranean climate, fire-adapted

Climate and disturbance shape vegetation, roots and soil across biomes

Four representative vegetated regions expose soil and roots. Scenic transitions are illustrative, not a single real geographic transect or common depth scale.Climate, disturbance, soils and local history shape vegetation and belowground structure across biomes. Compare the plant forms and soil features that accompany different environmental conditions.

Biomes: vegetation above and below ground

Biomes: vegetation above and below ground. Climate, disturbance, soils and local history shape vegetation and belowground structure across biomes. Compare the plant forms and soil features that accompany different environmental conditions.Climate, disturbance, soils and local history shape vegetation and belowground structure across biomes. Compare the plant forms and soil features that accompany different environmental conditions.

Net Primary Productivity Across Biomes

Net Primary Productivity (NPP) measures the rate at which producers in an ecosystem create useful chemical energy. It is calculated as:

Biomes with high temperature and high precipitation (like tropical rainforests) have the highest NPP. Cold or dry biomes (tundra, desert) have the lowest. This relationship is fundamental to understanding energy flow through ecosystems.

The Climate-Biome Rule

1
Temperature decreases with increasing latitude and altitude. Moving poleward or upward mimics moving through biomes.
2
Precipitation patterns are driven by atmospheric circulation, rain shadows, and proximity to oceans.
3
Altitude mimics latitude: climbing 1,000 m in elevation is roughly equivalent to traveling 600 km toward the poles.

Altitude Mimics Latitude

Tropical/ Deciduous Coniferous Forest Alpine Meadow Tundra Snow/Ice 0-30° 45-55° 55-65° 65-90° Altitude Latitude

A climate envelope climbs toward a vanishing summit

A forested mountain rises through open alpine meadow to a rocky finite summit, with a winding lower-flank road and a small upper flowering-plant patch.A climate band moving upward can intersect a smaller portion of a mountain as it approaches the summit. Habitat suitability and species occupancy also depend on precipitation, terrain, dispersal and barriers.

A climate envelope approaches a finite summit

A climate envelope approaches a finite summit. A climate band moving upward can intersect a smaller portion of a mountain as it approaches the summit. Habitat suitability and species occupancy also depend on precipitation, terrain, dispersal and barriers.A climate band moving upward can intersect a smaller portion of a mountain as it approaches the summit. Habitat suitability and species occupancy also depend on precipitation, terrain, dispersal and barriers.

Tundra vs. Desert: Both Extreme, Very Different

Students often confuse tundra and desert because both have low biodiversity and harsh conditions. The key difference is the limiting factor:

Tundra Desert
Limiting Factor Temperature Water
Avg. Temperature \( -25^\circ\text{C} \) to \( -5^\circ\text{C} \) Variable (hot or cold)
Precipitation 15-25 cm/yr \( < 25 \) cm/yr
Soil Permafrost present Sandy or rocky, no permafrost
Vegetation Mosses, lichens, low shrubs Cacti, succulents, sparse shrubs
Latitude High (\( 60\text{-}90^\circ \)) Any (often \( 30^\circ \) N/S)

How to Identify a Biome

1
Check latitude/altitude: Is the location near the equator, mid-latitudes, or the poles? At sea level or high elevation?
2
Determine temperature range: What is the average annual temperature? Does it have seasonal variation?
3
Assess precipitation: How much rain or snow falls annually? Is it seasonal or year-round?
4
Look at dominant vegetation: Coniferous trees → taiga. Broadleaf deciduous → temperate forest. Grasses → grassland or savanna.
5
Check for special features: Permafrost → tundra. Fire dependence → chaparral or savanna. Epiphytes → tropical rainforest.

Example: Tropical Rainforest

Emergent Layer (40-70 m) Canopy (25-35 m) Understory (5-20 m) Forest Floor (0-2 m)
Temp: \( 25\text{-}28^\circ\text{C} \)  |  Precip: \( 200\text{-}400+ \text{ cm/yr} \)  |  NPP: \( \approx 2{,}200 \text{ g C/m}^2/\text{yr} \)
Contains ~50% of all terrestrial species

Example: Taiga (Boreal Forest)

Climate
Long, cold winters (\( -40^\circ\text{C} \) to \( -20^\circ\text{C} \)). Short, cool summers (\( 10\text{-}15^\circ\text{C} \)). Precipitation: 30-85 cm/yr, much as snow.
Vegetation
Dominated by coniferous (evergreen) trees: spruce, fir, pine. Needle-like leaves reduce water loss and withstand snow.
Adaptations
Animals: thick fur, hibernation, migration. Trees: conical shape sheds snow. Acidic, nutrient-poor soils (podzols).
Significance
Largest terrestrial biome on Earth. Major carbon sink storing ~30% of terrestrial carbon in soils and biomass.

Use seasonal climate evidence to justify a biome identification.

Use this illustration to explore the concept described in its caption.

A boreal forest is shown in summer and winter. A vertical temperature range marks warmest monthly mean 16, annual mean minus 3, and coldest monthly mean minus 25 degrees Celsius. Annual precipitation is 55 centimetres.
The selected climate summary has a −3 °C annual mean, a 16 °C warmest month mean, a −25 °C coldest month mean and 55 cm annual precipitation. These values support a boreal-forest interpretation but do not supply a monthly climograph.

Example: Savanna

Wet Season Dry Season Fire Season Savanna: Tropical Grassland with Scattered Trees
Temp: \( 20\text{-}30^\circ\text{C} \)  |  Precip: \( 50\text{-}130 \text{ cm/yr} \)  |  Strong wet/dry seasonality
Fire maintains grassland by preventing tree enclosure

Grassland vs. Savanna

Both biomes are dominated by grasses, but they differ in climate zone, tree density, and seasonal patterns:

Temperate Grassland Tropical Savanna
Latitude Mid-latitudes (\( 30\text{-}55^\circ \)) Tropics (\( 5\text{-}20^\circ \))
Temperature Hot summers, cold winters Warm year-round
Precipitation 25-75 cm/yr 50-130 cm/yr
Trees Nearly absent Scattered, widely spaced
Soil Deep, rich (mollisols) Thin, laterite-rich
Examples Great Plains, Pampas, Steppe Serengeti, Cerrado

NPP by Biome

2500 2000 1500 1000 0
\( \text{NPP (g C/m}^2/\text{yr)} \)
Trop. 2200 Temp.F 1200 Taiga 800 Savanna 900 Grass. 600 Tundra 140 Desert 90

Common Mistakes

✕ Deserts Are Always Hot
Not all deserts are hot. Cold deserts (Gobi, Antarctic interior) are defined by low precipitation (\( < 25 \) cm/yr), not temperature.
✕ Confusing Biome and Ecosystem
A biome is a global-scale category. An ecosystem is a specific local community. The Yellowstone forest is an ecosystem within the taiga biome.
✕ Savanna = Grassland
Savannas have scattered trees and are tropical. Temperate grasslands (prairies) have almost no trees and experience cold winters.

Biome Summary Table

Biome Temp (\( ^\circ\text{C} \)) Precip (cm/yr) Key Feature
Tropical Rainforest \( 25\text{-}28 \) 200-400+ Highest biodiversity
Savanna \( 20\text{-}30 \) 50-130 Wet/dry seasons, fire
Desert Variable \( < 25 \) Water is limiting factor
Temperate Grassland \( -20 \) to \( 30 \) 25-75 Deep, fertile soil
Temperate Forest \( 5\text{-}20 \) 75-150 Deciduous, four seasons
Taiga \( -40 \) to \( 15 \) 30-85 Largest biome, conifers
Tundra \( -25 \) to \( -5 \) 15-25 Permafrost
Chaparral \( 10\text{-}18 \) 25-75 Mediterranean, fire-adapted

Question 1 of 5

Which two climate variables are most important in determining the type of terrestrial biome at a given location?

Question 2 of 5

A researcher measures an annual precipitation of \( 20 \) cm/yr with a mean temperature of \( -15^\circ\text{C} \) and finds permafrost beneath the surface. Which biome is this?

Question 3 of 5

Which of the following best explains why tropical rainforests have the highest net primary productivity (NPP) of all terrestrial biomes?

Question 4 of 5

A student claims that because both the Gobi Desert and the Sahara Desert receive \( < 25 \) cm of rain per year, they must have identical temperatures. What is wrong with this reasoning?

Question 5 of 5

Fire suppression in a savanna ecosystem would most likely lead to which of the following long-term changes?