Biome Components and Local Distribution Factors

Local differences within a global biome

A biome is a very large ecosystem characterised by its climate, vegetation and animal life. Climate explains the broad global pattern, but places within the same climatic region do not necessarily support identical vegetation. A mountain slope, a shallow rocky soil and a waterlogged hollow offer different growing conditions.

Four important local factors are altitude, rock type, soil type and drainage. They affect which plants can grow, how densely they grow and, consequently, the food and habitats available to animals.

Altitude changes growing conditions

Altitude means height above sea level. As altitude increases, temperature generally falls. Colder conditions limit plant growth, so vegetation can change as you climb a mountain even though its latitude stays the same.

On Mount Kilimanjaro in Tanzania, forest on lower slopes gives way to scrub and increasingly sparse vegetation higher up. This illustrates how altitude can interrupt the broad vegetation pattern expected in a tropical region. Higher slopes can also have thinner soils, further restricting dense forest growth.

The important connection is not simply that mountains are colder: lower temperatures change which plants can survive, altering the local distribution of vegetation.

Rock and soil influence what can grow

Rock is the underlying material from which many soil particles and minerals come. Weathering, the breakdown of rock, supplies fragments that help form soil. Different rocks therefore influence the soil's mineral content and its acidity or alkalinity, measured by pH. Plant species differ in the soil conditions they tolerate, so a change in underlying rock can produce a change in vegetation.

Rock also affects water movement. Permeable rock allows water to pass through it; impermeable rock does not readily allow this. These differences help determine whether the ground is well drained or becomes waterlogged.

Soil contains mineral particles, organic material, water and air. Its nutrient content, depth, pH and ability to hold water all influence plant growth. Nutrient-rich soil can support more vegetation, while shallow soil gives plants less space for roots and fewer stores of water and nutrients.

For a concrete contrast, sandy soil drains quickly, so plants growing there may need to tolerate dry conditions. Clay soil drains more slowly and can retain nutrients, but may become waterlogged. Neither soil is automatically best for every plant: different species suit different combinations of moisture, nutrients and pH.

Drainage creates local contrasts

Drainage controls how quickly water leaves an area or moves through its soil and rock. Rapid drainage can leave too little moisture for some plants. Poor drainage can keep the ground saturated and prevent many tree species from growing.

A frequently waterlogged patch may therefore support marsh vegetation, including adapted plants such as bulrushes, rather than the trees found nearby. This is a local change in vegetation caused by ground conditions, not necessarily a change in the wider regional climate.

These factors work together. For example, impermeable rock can contribute to poor drainage, which changes soil moisture and then the vegetation able to survive.

Living and non-living components form a connected system

The biotic components of a biome are its living organisms: flora means plants, and fauna means animals. Decomposers are living components too. The abiotic components are non-living parts, including soils, rock, water and the atmosphere.

These components are interdependent: they affect and depend on one another. Plants need water, nutrients from soil, carbon dioxide from the atmosphere and sunlight for growth. Through photosynthesis, they take in carbon dioxide and release oxygen. Plants provide food and habitats for animals, while some animals feed on other animals.

When organisms die, decomposers break down their remains and return nutrients to the soil. Dead leaves and other organic material, together with particles from weathered rock, help soil develop. The soil then supports further plant growth: living things do not merely use their surroundings; they also change them.

A change can spread through the biome

Removing vegetation shows why these links matter. Fewer plants mean less food and fewer habitats for animals. Less dead plant material reaches the ground, reducing the nutrients returned through decomposition. The exposed soil also loses protection from rain, increasing the risk of erosion.

One change to a biotic component can therefore affect both other living organisms and abiotic conditions. Those changed soil conditions can, in turn, make future plant growth more difficult.

Four local controls

• Altitude: higher land is generally colder, restricting plant growth and changing vegetation.
• Rock type: influences soil minerals, pH and permeability.
• Soil type: nutrient content, depth, pH and water retention affect which plants grow.
• Drainage: rapid drainage can cause dry conditions; poor drainage can cause waterlogging and favour marsh vegetation over trees.

Local factors modify vegetation within the broad climate-controlled biome pattern.

Components and connections

Biotic: flora, fauna and decomposers.
Abiotic: soils, rock, water and atmosphere.

• Weathered rock + dead organic material → soil formation.
• Soil nutrients + water + sunlight + atmospheric carbon dioxide → plant growth.
• Plants → food and habitats for animals.
• Dead organisms → decomposition → nutrients returned to soil.

Interdependence

Vegetation removal → less food and habitat, less nutrient return and greater soil erosion → effects on animals, soil and future plant growth.