Down to Earth

We often identify habitats by the animals we see—a buzzard soaring over a field or a Dartford Warbler darting through the gorse. However, these animals are just the top layer of a complex system that begins beneath our feet.

The Habitat Pyramid: Animal, Vegetable, Mineral

Every habitat can be classified by three interconnected layers:

1. The Mineral Layer (Soil): Ground-up rock that provides the chemical foundation.

2. The Vegetable Matter: Plants that feed on the mineral layer and nutrients.

3. The Animal Layer: Creatures that feed on the vegetation or each other.

The Simplified Food Chain:

• Buzzards eat rabbits > Rabbits eat grass > Grass grows in soil.

• Blue Tits eat caterpillars > Caterpillars eat leaves on trees >  Trees grow in soil.

• Humans eat beef > Cows eat pasture > Pasture grows in soil.

Key takeaway: Without soil, there would be no vegetation; without vegetation, there would be no animals. Soil is the basis of all life on Earth.

What is Soil Made Of?

Soil is a living "home" for seeds, spores, fungi, bacteria, and mammals like the mole. It is composed of four primary ingredients:

• Ground-up fragments of rock (from sand down to microscopic clay).

• Humus (decaying organic matter).

• Water.

• Air

Understanding Soil Composition

The behaviour of soil—and what can grow in it—is determined by the size of its rock particles. Interestingly, a grain of coarse sand is at least a thousand times bigger than a grain of clay.

Particle Type Diameter Size Characteristics

Sand 2mm to 0.06mm Large gaps for air and roots, but drains water very quickly.

Silt 0.06mm to 0.002mm Retains moisture but allows drainage; ideal for most crops (Loam).

Clay Less than 0.002mm Tiny particles that bind together; can become easily waterlogged.

The Influence of Soil Chemistry (pH)

The type of rock the soil comes from dictates its chemistry. This is measured as a pH value, typically ranging from pH 4 to pH 8 in Britain.

• Alkaline/Calcareous: Formed from chalk or limestone. Example: Traveller’s Joy (wild clematis) only grows here.

• Acidic: Formed from certain sandstones. Example: Heathers thrive here but will not tolerate lime.

• Neutral: Balanced soil that is neither strongly acidic nor alkaline.

Habitat Snapshots: Soil Dominance

The dominant grain size in an area creates specific challenges for plants, leading to different common habitats:

1. Sandy Habitats (Inhospitable)

Because sand is loose and dries out fast, plants struggle to find a "foothold". Only plants with deep, complex root systems can survive here.

2. Clay Habitats (Dense)

Clay is so compact that roots find it difficult to penetrate. Plants with shallow root systems often have the advantage here, though they must survive frequent waterlogging.

3. Silt/Loam Habitats (The Battlefield)

Gardeners love "loam" (silt-dominant soil) because it is ideal for growth. However, because conditions are so good, the competition for space is immense; only the strongest, most vigorous plants usually win.