Nature on our doorsteps: Lichens, Nature’s living soil-makers

Rosaleen Dwyer is the County Heritage Officer at South Dublin County Council – every week she gives us an insight into the natural heritage around us and the beautiful biodiversity of the plants and creatures.

ROCKS are worn down over many thousands of years by weather and by the eroding effects of water and ice.

As the bare rock is worn away, tiny rock fragments and grains of minerals are released, and these are the basic building blocks of soil.

When organic matter from rotting plants is added to this foundation, fertile soils may be formed.

Another way that rocks can be broken down is by the effect of one of nature’s highly specialised living organisms, the lichens.

Lichens grow even in the harshest of environments, and they are often the first growing things we see appearing on bare rocks, block walls, tree bark, and wooden fences.

Polished marble, however, or shiny, smooth, metals perhaps pose a real challenge for them.

A wide variety of shapes and colours of lichen species can grow in woodland habitats

Lichens are an example of a symbiotic relationship in nature, where both partners in the relationship benefits.

The partners in this case are a fungus and a single celled organism known as an alga.

Algae can make their own food by converting energy from the sun to make sugars.

Being single-celled, however, they are limited in how much they can grow and spread.

Fungi, on the other hand, do not make their own sugars but they have a living structure which allows them to grow in many different locations.

Combining their efforts, the fungus provides the physical structure (or scaffolding) within which the more delicate alga cells can safely live.

In return, the alga provides sugars to the fungus for its growth, and both partners benefit.

As the lichens gain a foothold on the bare surface, they begin to slowly break down the rock or wood into basic minerals to help it grow and spread.

When the lichen eventually dies and disintegrates, it leaves organic matter and broken-down minerals available as the beginnings of soil for other mosses and plant seeds to grow.

In this way, lichens are not only champion colonisers of harsh environments, but they also support the development of soil and the growth of other plants.