Abiotic factors and biomes at Higher Level: The same ideas as SL, with different places: Queensland to Alice Springs, Darwin, Yakutsk, Hawaii and Tenerife. HL goes on to biomes that do not match the prediction (2.4.9).
Practise this as you read
- Plot a place on the biome graph from its two numbers.
- Link each abiotic factor to a named biome.
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The climate decides the biome: Abiotic factors decide which biome develops on land. It is the climate, the long-term average, not one day's weather, that does it.
The points to remember
- Abiotic factors are the determinants of where land biomes are found.
- The main ones are temperature and precipitation, with insolation (sunlight energy).
- Together they set the water and energy available for photosynthesis.
- They decide the soil and the plants; the plants decide which animals can live there.
- For any temperature and rainfall pattern, one natural ecosystem type is likely to develop.
- Warm and wet: dense forest. Dry: grassland or desert. Cold: slow growth, tundra or taiga.
Remember it as: Water and warmth decide the plants; the plants decide the animals.
Real example: from the Daintree rainforest on the Queensland coast (over 2,000 mm of rain a year) inland to Alice Springs (about 280 mm), Australia's biome changes from tropical rainforest to savanna to hot desert, as rainfall falls.
Factor plus effect: Name the factor and what it does: 'low temperature slows photosynthesis', not just 'temperature'. If temperature or rainfall changes, the biome boundaries shift too.
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The biome graph puts the two main factors together. Each area is one biome.
How to use the biome graph
- Across: mean annual temperature (°C). Up: annual precipitation (mm).
- Plot the place's two numbers: the area the point falls in is its likely biome.
- Hot and very wet: tropical rainforest. Hot and dry: hot desert.
- Coldest: tundra; a little warmer: boreal forest. Mild and wet: temperate forest.
- Mean annual temperature = the 12 monthly means added up, divided by 12.
Real example: Darwin, Australia, averages 27.6 °C and about 1,730 mm, mostly in a wet season, so it plots in tropical seasonal forest and savanna. Alice Springs averages 20.9 °C and 280 mm: hot desert.
Name it in full: Give the biome's full name from the chart, and only one answer. Near a boundary, quote both values to show which side the point falls on.
Each abiotic factor can be a limiting factor. Where one is scarce, productivity is low and the biome is simple.
How the climate limits productivity
- Low temperature slows enzymes and photosynthesis, and the growing season is short.
- Below 0 °C water freezes, so roots cannot take it up; permafrost blocks roots and drainage.
- Low precipitation gives too little water for photosynthesis: plants are small and far apart.
- Low insolation (a low sun and short winter days) gives little energy for photosynthesis.
- Warm, wet and sunny all year gives the highest productivity: tropical rainforest.
| Factor | Yakutsk, Siberia | Effect |
|---|---|---|
| Temperature | About -38 °C in January | Growth only in a short summer |
| Water | About 240 mm a year; frozen in winter | Little water plants can use |
| Insolation | About 5 hours of daylight in December | Little energy in winter |
| Ground | Permafrost hundreds of metres deep | Shallow-rooted larch trees only |
Real example: Yakutsk lies in the taiga. Its larch trees drop their needles for the frozen winter and grow only in the short summer, so productivity is far lower than in a temperate forest.
Use the data you are given: Tie each way to the data: 'below 0 °C for five months, so water is frozen'. 'High rainfall' is never a reason a cold biome is unproductive.
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Water is the factor that differs most from region to region. How much falls, how much evaporates, and how much stays frozen decide the biome.
Water and the biome
- Tropics with high rainfall and transpiration all year: tropical rainforest.
- Where evaporation exceeds precipitation, water limits growth: desert.
- Near the poles most water is frozen (ice, permafrost), so little is left for plants: tundra.
- Mid-latitudes with moderate rain and transpiration: temperate forest or grassland.
- Where water inputs exceed outputs, or the water table is high: wetland.
- Mountains: the windward side is wet (forest); the leeward side is in a rain shadow (dry).
| Place | Rain a year | Biome |
|---|---|---|
| Hilo (east, windward) | About 3,200 mm | Tropical rainforest |
| Kawaihae (west, leeward) | About 250 mm | Dry grassland and scrub |
Real example: on Hawaii's Big Island, trade winds rise over the eastern slopes and drop their rain on Hilo. The west coast lies in a rain shadow, so the land there is dry scrub.
Link every point to a biome: In a longer answer, pair each water fact with the biome it produces: 'evaporation exceeds precipitation, so water limits growth and a desert forms'. Facts with no biome score less.
On a mountain the temperature falls as you climb, so the vegetation changes in bands. A vegetation map read with an elevation map shows it.
Altitude and maps
- Climbing a mountain is like travelling towards a pole: it gets colder, so biomes change in bands.
- The highest land has the coldest biome: alpine grassland, scrub, or bare rock and ice.
- Use two maps together: find the highest zone on the elevation map, then read its vegetation.
- Name the vegetation exactly as the key does: 'subtropical rainforest', not 'rainforest'.
Tenerife, Canary Islands, from coast to summit
Coast
Dry scrub of spurges and cactus-like plants.
600-1,200 m, north side
Laurel forest in the belt of cloud.
1,200-2,000 m
Canary pine forest.
Above 2,000 m
High-mountain broom scrub.
Teide, 3,715 m
Bare volcanic rock.
Real example: Tenerife climbs from dry coastal scrub to the bare rock of Mount Teide. The laurel forest grows only on the north side, where the trade winds bring a belt of cloud.
Copy the key exactly: If the highest zone is 'grassland and woodland', give both words. 'Forest' alone, or 'rainforest' when the key says 'subtropical rainforest', is too vague.
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You may be asked to draw a climate graph for a biome from a table of monthly data. It uses the same layout as the graphs in the papers.
Drawing a climate graph
- Draw 12 bars for monthly precipitation, on a left axis in mm.
- Plot 12 points for mean monthly temperature on a right axis in °C, and join them.
- Label the months, both axes with units, and give a title naming the place.
- Add the total precipitation and the mean temperature: they place it on the biome graph.
Real example: Alice Springs's graph shows the hot desert pattern: short bars in every month, only 280 mm a year, and a line rising to 29.4 °C in the southern summer.
Two axes, two scales: Choose a scale for each axis that uses most of the height, and start the temperature axis below zero if any month is below freezing.
How this comes up: Paper 2, Section B (a): distinguish two named biomes and the factors that cause their distribution [4].
Hot deserts and temperate deciduous forests cover large areas of the Earth.
Distinguish between hot desert and temperate deciduous forest and the factors that cause their distribution.
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