How do temperature and precipitation determine where the major terrestrial biomes occur?
Topic 1.2 Terrestrial Biomes: describe the global distribution of the major terrestrial biomes and explain how temperature and precipitation determine the type of biome found in a region.
A focused answer to APES Topic 1.2, covering the major terrestrial biomes, how temperature and precipitation define them, latitude and altitude patterns, and biome shifts under a changing climate, with a worked climograph question.
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What this topic is asking
The College Board (Topic 1.2) wants you to describe the major terrestrial biomes and explain what determines where each one occurs. The key idea is that two abiotic factors, temperature and precipitation, set the conditions that decide which plants can grow, and the plants in turn define the biome. You should be able to read a climograph and match a climate to a biome.
What a biome is
The same biome can appear on different continents wherever the climate matches, because organisms with similar adaptations evolve under similar conditions.
Temperature and precipitation control biome type
In general, higher temperature and more precipitation support more plant growth and more complex vegetation, while cold or dry conditions support sparse, low-growing vegetation.
The major terrestrial biomes
- Tropical rainforest: warm and very wet year-round; highest biodiversity and productivity; nutrient-poor soils because nutrients are held in living biomass.
- Savanna: warm with a pronounced wet and dry season; grasses with scattered trees; shaped by fire and grazing.
- Desert: very low precipitation (under about 250 mm/year); plants and animals adapted to conserve water.
- Temperate grassland: moderate temperatures, seasonal rainfall too low for forest; deep fertile soils.
- Temperate forest: moderate temperature and precipitation; deciduous or mixed trees with four seasons.
- Taiga (boreal forest): cold with short summers; coniferous evergreen trees.
- Tundra: very cold, low precipitation, permafrost, short growing season; mosses, lichens and low shrubs.
Latitude and altitude patterns
Because temperature falls from the equator toward the poles, biomes form bands by latitude: tropical forests near the equator, then deserts and grasslands, then temperate forests, taiga and tundra toward the poles. The same sequence appears going up a mountain with altitude, because temperature also drops with elevation, so a single tall mountain in the tropics can pass through several biome-like zones from base to summit.
Because vegetation is limited mainly by warmth and water, biome boundaries are not fixed. A sustained change in climate, whether natural or driven by human-caused warming, can shift where a biome can exist. Warming may push the tundra-taiga boundary poleward, expand deserts where precipitation falls, or let forests advance up mountainsides. This is why temperature and precipitation are the master variables in Topic 1.2: change them, and the whole distribution of life on land responds.
Try this
Q1. Identify the biome with the highest net primary productivity and biodiversity. [1 point]
- Cue. Tropical rainforest.
Q2. Explain why tundra has low plant biomass despite covering a large area. [2 points]
- Cue. Very low temperatures and a short growing season limit photosynthesis, and permafrost restricts root growth and drainage, so only low-growing vegetation can survive.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2021 (style)4 marksSection II (FRQ). A region has an average annual temperature of 25 degrees C and receives 250 mm of precipitation per year, falling mainly in a short wet season. (a) Identify the biome most likely found in this region. (b) Describe two adaptations of organisms that allow them to survive in this biome. (c) Explain how a sustained increase in annual precipitation could change the biome over time. (d) Identify the two abiotic factors that most strongly determine terrestrial biome type.Show worked answer →
A 4-point FRQ on biome identification and climate controls.
(a) Identify (1 point): a desert (hot desert), because precipitation is very low (250 mm/year) with high temperature.
(b) Describe (1 point): any two adaptations, for example water-storing tissues or waxy coatings in plants to reduce water loss, deep or shallow spreading roots, nocturnal behavior or burrowing in animals to avoid daytime heat.
(c) Explain (1 point): more reliable precipitation would allow grasses and then shrubs or trees to establish, shifting the area toward grassland or savanna, because vegetation type is limited mainly by water availability.
(d) Identify (1 point): temperature and precipitation.
Markers reward a correct biome from the climate data, two valid drought adaptations, a logical link from increased water to greater vegetation, and naming the two controlling abiotic factors.
AP 2019 (style)1 marksSection I (multiple choice). Which biome is characterized by permafrost, low temperatures, low precipitation and a short growing season? (A) Taiga (B) Tundra (C) Temperate grassland (D) Savanna. Justify your choice.Show worked answer →
A 1-point MCQ on biome characteristics. The answer is (B).
The tundra has permanently frozen subsoil (permafrost), very cold temperatures, low precipitation and a very short growing season, supporting low-growing vegetation such as mosses and lichens. Taiga (A) is the colder boreal forest but lacks permafrost as a defining feature and supports conifers; temperate grassland (C) and savanna (D) are warmer with more precipitation. The trap is confusing tundra with taiga.
Related dot points
- Topic 1.1 Introduction to Ecosystems: explain how species interactions, including predation, symbiosis and competition, shape ecosystems and influence the survival of organisms.
A focused answer to APES Topic 1.1, covering ecosystems, predator-prey relationships, the three symbioses (mutualism, commensalism, parasitism), competition and resource partitioning, with a worked FRQ on interpreting interaction data.
- Topic 1.3 Aquatic Biomes: describe the major freshwater and marine biomes and explain how abiotic factors such as salinity, depth, light, temperature and nutrients shape them.
A focused answer to APES Topic 1.3, covering freshwater and marine biomes, salinity, the photic and aphotic zones, estuaries, coral reefs and wetlands, and the abiotic factors that control aquatic productivity, with a worked dissolved-oxygen question.
- Topic 1.7 The Hydrologic (Water) Cycle: describe the processes of the water cycle and explain how human activities alter the storage and movement of water.
A focused answer to APES Topic 1.7, covering evaporation, transpiration, condensation, precipitation, runoff, infiltration and groundwater, and how deforestation, paving and irrigation alter the cycle, with a worked water-budget calculation.
- Topic 1.8 Primary Productivity: define gross and net primary productivity, explain the factors that control them, and calculate net primary productivity from data.
A focused answer to APES Topic 1.8, covering gross and net primary productivity, respiration, the GPP-NPP relationship, limiting factors, productivity across biomes, and ecological efficiency, with a full worked NPP calculation.
- Topic 2.4 Ecological Tolerance: describe the range of tolerance of organisms and explain how tolerance limits determine the distribution and survival of species.
A focused answer to APES Topic 2.4, covering the range of tolerance, optimum range, zones of stress, limits of tolerance, the law of tolerance and how tolerance varies between species and life stages, with a worked tolerance-curve question.
Sources & how we know this
- AP Environmental Science Course and Exam Description — College Board (2020)