A-Level Geography: Distribution and Influencing Factors of Biomes | A-Level 地理：生物群系的分布与影响因素

📚 A-Level Geography: Distribution and Influencing Factors of Biomes | A-Level 地理：生物群系的分布与影响因素

Biomes are large-scale ecological communities shaped by climate, soil, and living organisms. Understanding their global distribution and the factors that control it is a core requirement of A-Level geography, linking physical systems with human-environment interactions.

生物群系是由气候、土壤和生物共同塑造的大尺度生态群落。理解其全球分布及控制因素是 A-Level 地理的核心要求，它将自然系统与人类-环境相互作用联系起来。

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1. What is a Biome? | 什么是生物群系？

A biome is a major community of plants and animals occupying a broad climatic region. Each biome is defined primarily by its dominant vegetation, such as tropical rainforest, savanna, desert, temperate grassland, Mediterranean shrubland, and tundra.

生物群系是占据广阔气候区域的动植物主要群落。每个生物群系主要由其优势植被定义，例如热带雨林、稀树草原、沙漠、温带草原、地中海灌木丛和苔原。

Biomes are not uniform; they show variation within themselves due to local conditions. However, their global pattern broadly follows climatic zones, which is why climate is often described as the first-order control on biome distribution.

生物群系并非均匀一致；由于局部条件，它们内部存在变化。然而，其全球格局大致遵循气候带，因此气候常被描述为生物群系分布的一级控制因素。

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2. Global Distribution of Major Biomes | 主要生物群系的全球分布

Imagine a world map of biomes: tropical rainforests hug the equator; tropical savannas lie north and south of the rainforests; hot deserts occupy subtropical high-pressure belts; temperate grasslands and deciduous forests appear in mid-latitudes; and tundra fringes the Arctic.

想象一张全球生物群系地图：热带雨林紧贴赤道；热带稀树草原位于雨林的南北两侧；热带沙漠占据副热带高压带；温带草原和落叶阔叶林出现在中纬度；而苔原环绕北极边缘。

This pattern reflects the Earth’s energy balance and atmospheric circulation. Equatorial regions receive intense solar radiation, producing high rainfall and lush forests, while subtropical high-pressure zones bring descending dry air, generating deserts.

这种格局反映了地球的能量平衡和大气环流。赤道地区接收强烈的太阳辐射，产生高降雨量和茂密森林，而副热带高压带带来下沉干燥空气，形成沙漠。

Biome	Typical Latitude	Key Feature
Tropical rainforest	0°–10°	High temperature and rainfall year-round
Savanna	10°–20°	Wet and dry seasons
Desert	20°–30°	Very low precipitation
Temperate grassland	30°–50°	Moderate rainfall, hot summers, cold winters
Tundra	60°–75°	Permafrost, very short growing season

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3. Climate as the Primary Control | 气候作为主要控制因素

Climate determines the amount of energy and water available to plants, and therefore controls the structure and productivity of biomes. The two most important climatic variables are temperature and precipitation, which together define the growing season and water availability.

气候决定了植物可获得的能量和水量，从而控制生物群系的结构和生产力。两个最重要的气候变量是温度和降水，它们共同决定生长期和水分可用性。

For example, tropical rainforests occur where mean monthly temperatures exceed 18°C and annual rainfall exceeds 2000 mm. In contrast, hot deserts occur where annual rainfall is below 250 mm and temperatures are extremely high in summer.

例如，热带雨林出现在月均温超过18°C、年降雨量超过2000毫米的地区。相比之下，热带沙漠出现在年降雨量低于250毫米、夏季气温极高的地区。

Biome distribution = f (temperature, precipitation, seasonality)

Seasonality matters too. Savannas experience alternating wet and dry seasons, creating fire-adapted grasslands with scattered trees, whereas a Mediterranean climate has winter rainfall and summer drought, producing sclerophyllous shrubs.

季节性也很重要。稀树草原经历干湿季交替，形成适应火灾的草原和散生树木，而地中海气候则是冬雨夏旱，产生硬叶灌木。

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4. Temperature: The Thermal Boundary | 温度：热量边界

Temperature limits plant growth through enzyme activity, cell division, and water uptake. Below a certain threshold, photosynthesis slows dramatically; above another threshold, respiration rates may exceed photosynthesis, causing stress.

温度通过酶活性、细胞分裂和水分吸收限制植物生长。低于某一阈值，光合作用大幅减慢；高于另一阈值，呼吸速率可能超过光合作用，造成胁迫。

This is why tundra biomes are treeless: the growing season is too short (often less than 50 days) and permafrost blocks root penetration. Conversely, tropical rainforests have no thermal seasonality, allowing continuous growth.

这就是苔原无树的原因：生长期太短（通常不足50天），且永久冻土阻碍根系下扎。相反，热带雨林没有热力季节性，允许持续生长。

In mountainous areas, temperature decreases with altitude (the lapse rate), producing vertical biome zones: tropical at the base, montane forest, then alpine grassland, and finally ice and snow. This is called altitudinal zonation.

在山地地区，温度随海拔升高而降低（垂直递减率），产生垂直生物群系带：山麓为热带植被，然后是山地森林、高山草甸，最后是冰雪带。这称为垂直地带性。

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5. Precipitation: The Moisture Constraint | 降水：水分制约

Precipitation determines which biome can survive in a region. Deserts occur where dry descending air dominates; rainforests occur where moist ascending air and intertropical convergence bring heavy rainfall.

降水决定了一个地区能够生存的生物群系。沙漠出现在干气流下沉主导的地方；雨林出现在潮湿上升气流和热带辐合带带来强降雨的地方。

Rainfall seasonality creates vegetation patterns. In tropical savannas, a long dry season prevents dense forest and favours deep-rooted grasses and fire-resistant trees. In contrast, temperate rainforests require reliable rainfall across many months.

降雨季节性形成植被格局。在热带稀树草原，漫长旱季阻止茂密森林形成，有利于深根草本植物和耐火树木。相反，温带雨林需要在多个月份有稳定降雨。

Water availability also depends on evapotranspiration. Effective precipitation (rainfall minus evaporation) is a better ecological indicator than raw rainfall. Thus, some regions with moderate rainfall still experience drought-like conditions if evaporation is high.

水分可用性还取决于蒸散量。有效降水（降雨量减去蒸发量）是比原始降雨量更好的生态指标。因此，一些降雨量中等的地区若蒸发量高，仍可能经历类似干旱的条件。

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6. Non-Climatic Abiotic Factors | 非气候非生物因素

While climate is dominant, soil, parent material, topography, and fire can modify biome boundaries. For example, serpentine soils are poor in calcium and rich in magnesium, producing sterile grasslands even where forest is climatically possible.

虽然气候占主导，但土壤、母质、地形和火灾可以改变生物群系边界。例如，蛇纹岩土壤钙少镁多，即使在气候适宜森林的地方也会产生贫瘠草原。

Topography influences drainage, aspect, and shelter. North-facing slopes in the northern hemisphere receive less sunlight, so they remain cooler and wetter, supporting different vegetation from south-facing slopes. Valley bottoms may accumulate cold air, creating frost pockets.

地形影响排水、坡向和庇护条件。北半球的北向坡接收阳光较少，因而更凉爽湿润，支持与南向坡不同的植被。谷底可能积聚冷空气，形成霜穴。

Fire is a natural ecological factor. Seasonal fires remove dead litter, recycle nutrients, and prevent woody encroachment. Savannas and Mediterranean shrublands are fire-adapted, with species like eucalyptus and cork oak possessing thick bark or resprouting ability.

火灾是一种自然生态因素。季节性火灾清除枯枝落叶、循环养分并防止木本植物侵入。稀树草原和地中海灌木丛适应火灾，例如桉树和栓皮栎具有厚树皮或再萌生能力。

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7. Biotic Factors | 生物因素

Plants and animals also shape biomes. Grazing herbivores, such as wildebeest in savannas, control grass height and nutrient cycling; without them, grass biomass may accumulate and more frequent fires may occur.

植物和动物也塑造生物群系。放牧食草动物，如稀树草原的角马，控制草的高度和养分循环；如果没有它们，草本生物量可能累积，并可能发生更频繁的火灾。

Mutualism is also visible in biomes: mycorrhizal fungi enhance nutrient uptake for many trees, while nitrogen-fixing bacteria allow legumes to colonise low-nitrogen soils. Species competition drives succession and biome dynamics.

互利共生在生物群系中也很明显：菌根真菌增强许多树木的养分吸收，而固氮细菌使豆科植物能够在低氮土壤中定殖。物种竞争驱动演替和生物群系动态。

Introduced species can disrupt biome structure. For example, invasive grasses in dry regions can alter fire regimes, converting shrublands into continuous grassland, with major impacts on native biodiversity.

引入物种可以破坏生物群系结构。例如，干旱地区的外来草本植物可以改变火灾状况，将灌木丛转变为连续草原，对本地生物多样性产生重大影响。

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8. Human Influence and Biome Modification | 人类影响与生物群系改造

Humans have transformed biomes through agriculture, urbanisation, deforestation, and climate change. The tropical rainforest biome has been heavily logged, while temperate grasslands have become the world’s breadbaskets.

人类通过农业、城市化、森林砍伐和气候变化改变了生物群系。热带雨林生物群系遭到大量砍伐，而温带草原已成为世界粮仓。

Climate change is shifting biome boundaries. Warmer temperatures are causing tundra to shrink as treeline moves poleward and upward, while increased aridity may expand subtropical deserts. Such shifts create migration pressure on species.

气候变化正在改变生物群系边界。气温升高导致苔原收缩，因为树木线向极地和高海拔移动，而干旱加剧可能使副热带沙漠扩张。这种变化给物种带来迁移压力。

Conservation efforts, such as biosphere reserves and wildlife corridors, aim to preserve biome integrity. Yet the pace of global change often exceeds the ability of ecosystems to adapt, making this a critical geography exam topic.

诸如生物圈保护区和野生动物廊道等保护措施旨在维护生物群系完整性。然而，全球变化的速度往往超过生态系统适应的能力，因此这是一个关键的地理考试主题。

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9. Case Study: Tropical Rainforest vs Tundra | 案例研究：热带雨林 vs 苔原

Tropical rainforest and tundra represent the two extremes of global biome distribution. They differ enormously in biodiversity, biomass, and nutrient cycling, yet both are controlled by the same fundamental climatic principles.

热带雨林和苔原代表全球生物群系分布的两个极端。它们在生物多样性、生物量和养分循环方面差异巨大，但都受相同的基本气候原则控制。

In the tropical rainforest, high solar input drives high evapotranspiration and rapid nutrient cycling. Soils are often deeply weathered and poor, because nutrients are stored in vegetation rather than in the soil. The tundra, by contrast, has slow decomposition and stores large amounts of carbon in permafrost.

在热带雨林中，高太阳输入驱动高蒸散和快速养分循环。土壤常常风化深度大但贫瘠，因为养分储存在植被中而非土壤中。相比之下，苔原分解缓慢，并在永久冻土中储存大量碳。

Feature	Tropical Rainforest	Tundra
Temperature	25–28°C all year	-40°C to 10°C
Precipitation	2000–4000 mm/year	150–350 mm/year
Vegetation	Layered broadleaf evergreen trees	Mosses, lichens, dwarf shrubs
Soil	Deep, heavily leached (oxisols)	Thin, poorly developed (gelisols)

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10. Exam Tips and Conclusion | 考试要点与总结

When answering biome distribution questions, always mention the interplay of climatic, edaphic, biotic, and human factors. Use named examples, and draw comparative tables to demonstrate depth. Avoid simply listing biomes; explain the mechanism behind each boundary.

在回答生物群系分布问题时，务必提及气候、土壤、生物和人类因素的相互作用。使用具体命名实例，并通过比较表格展示深度。避免只罗列生物群系；要解释每个边界背后的机制。

Remember the key exam phrase: ‘Climate controls where, soil modifies what, vegetation reflects both, and humans alter everything.’ Succinct comparisons and clear causal chains earn high marks.

记住关键考试语句：“气候决定在哪里，土壤改变什么，植被反映两者，人类改变一切。”简洁的比较和清晰的因果链可以赢得高分。

In summary, biome distribution is a balance between energy and water, further modified by disturbances and human activity. Master the major biomes, their climatic fingerprints, and the reasons local factors deviate from the global pattern.

总之，生物群系分布是能量与水之间的平衡，并受到干扰和人类活动的进一步改变。掌握主要生物群系、它们的气候特征指纹，以及局部因素偏离全球格局的原因。

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