Bare rock can become a forest. What grows first, and how does each stage make way for the next?

What you'll discover

• Tough pioneer species such as lichens and mosses are the first to grow on bare rock.
• Each community changes the soil, shade and moisture, which helps the next group of plants move in.
• Succession is much faster after a fire or on an abandoned field, because the soil is already there.

The science in plain words

Ecological succession is the gradual change in the species living in a place over time. Primary succession begins where there is no soil at all, such as fresh lava, rock left behind by a retreating glacier or a new sand dune.

The first colonists are pioneer species, usually lichens and mosses, which can cling to bare rock and survive drought and harsh sunlight. Lichens release acids that slowly break down the rock surface, and as they die their remains add organic matter. Wind-blown dust collects around them, and a thin soil begins to form. Small plants such as grasses and hardy flowers can then take root. Their roots break the rock further and their decay deepens the soil, letting larger shrubs grow. Eventually trees arrive, and their shade crowds out many of the sun-loving plants that came before. Animals change too, as each new stage offers different food and shelter.

Over a long time, often centuries, a fairly stable community develops, called a climax community, such as a forest in many wet climates. Secondary succession happens where soil remains after a disturbance, for example after a forest fire or when farmland is left alone. Because the soil and seeds are already there, it moves much faster.

Where it fits

• India, NCERT: Ecological succession goes beyond the NCERT syllabus for classes 6 to 10; it builds on Class 8 How Nature Works in Harmony.
• United States: Grades 6 to 12
• Next Generation Science Standards: MS-LS2-4, HS-LS2-6

Common questions

What is ecological succession?

Ecological succession is the slow, step-by-step change in the plants and animals living in an area over time. Simple pioneer species arrive first and change the conditions, which lets other species move in and replace them, until a fairly stable community develops.

What are pioneer species?

Pioneer species are the first living things to colonise bare or damaged ground. Lichens and mosses are typical pioneers on rock. They are tough, spread easily and start to make soil, which makes the place suitable for other plants to follow.

How long does it take for bare rock to become a forest?

It usually takes hundreds of years or longer, because soil forms very slowly from bare rock. The speed depends on the climate, the type of rock and which seeds can reach the area. Recovery after a fire is much faster because the soil survives.

Related labs

• Biodiversity Index: How do ecologists measure how varied a meadow is? Throw some quadrats and count.
• Volcanic Eruption: Why do some volcanoes pour out rivers of lava, and others explode?
• Erosion: Pour water on a slope of sand: where does the sand go?

See all biology labs or every Taz science lab.

Try it yourself

The Ecological Succession lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.

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