The Hidden Forest

Soil, fungi, water and the processes beneath the surface

Some of the most important parts of a forest are also the easiest to overlook.

We notice the trees because they rise above us. We hear birds and insects because they move and call around us. But beneath every step lies another biological system that is essential to everything growing above it.

Forest soil is alive.

It contains bacteria, fungi, microscopic organisms, insects, worms and many other invertebrates living among roots, minerals, water, air and decomposing organic material. Their combined activity influences nutrient availability, soil structure and the conditions in which plants are able to grow.

Much of this begins with decomposition.

A leaf that falls from a tree still contains carbon, nitrogen and many other elements that were once part of living tissue. On the forest floor, decomposers gradually process this material. Fungi and microorganisms break down complex organic compounds, while small animals fragment leaves and wood into smaller pieces.

Over time, materials that belonged to one organism become available to others.

The process is continuous.

Leaves grow, fall and decompose. Trees die and become habitat. Animals produce waste or die themselves. Nutrients move through organisms and eventually return to soil, vegetation and new life.

The forest is therefore constantly recycling its own biological material.

Plant roots are deeply involved in this underground system.

Rather than simply absorbing water and minerals from an inert substrate, roots exist within an active biological environment. Many plants form associations with mycorrhizal fungi, whose fine fungal structures can extend through soil beyond the immediate reach of the roots.

Through these relationships, fungi can help plants access nutrients and water, while the plant supplies carbon compounds produced through photosynthesis.

The exact relationships vary among species and environments, and scientists continue to investigate their complexity. What is clear is that below-ground biology plays an important role in forest function.

Water connects these underground processes with the atmosphere above.

When rain reaches a forest, not all of it immediately reaches the soil. Leaves and branches intercept part of the rainfall. Some evaporates back into the atmosphere, while some moves down trunks or drips through the canopy.

Once water reaches the ground, vegetation, roots, organic material and soil structure influence what happens next.

Healthy forest soils can allow water to infiltrate rather than immediately flowing across the surface. Some is retained within the soil, some travels deeper underground and some is absorbed by plants.

Trees then return water to the atmosphere through transpiration.

Water taken up by roots moves through the plant and eventually leaves through microscopic openings in the leaves. Across large forested landscapes, the combined effect of this process can become an important component of regional water cycles.

Forests therefore do not simply receive rain.

They participate in the movement of water between soil, vegetation and atmosphere.

These processes also connect forests with climate. Vegetation exchanges water, carbon and energy with the atmosphere, while forests store substantial quantities of carbon in living biomass and soils.

The exact role of a forest depends on its location, structure, climate and ecological condition, but the larger principle remains the same: forests are active components of Earth's environmental systems.

Much of this activity happens without attracting our attention.

A fungus decomposing wood.

A root absorbing water.

A microorganism processing organic matter.

A leaf releasing water vapour.

Individually, these processes seem small.

Together, repeated across millions of organisms and enormous areas of vegetation, they help maintain the conditions of the forest itself.

The visible forest depends upon this hidden one.