Primary succession starts on land that has never had soil or a community before. Examples include bare rock left by a volcanic eruption or a retreating glacier, and newly formed sand dunes.Pioneer species colonise first. On bare rock these are often lichens, and on sand dunes marram grass. Pioneers have adaptations to hostile conditions, such as:
• producing large numbers of seeds or spores that are easily dispersed by wind;
• rapid germination and growth;
• tolerance of extreme conditions, such as drought, high light or high salt;
• the ability to photosynthesise, so they do not depend on other organisms for food;
• in some species, the ability to fix nitrogen, since the ground is poor in nitrates.Lichens slowly break down the rock surface. When pioneers die, saprobionts decompose them, and the organic matter mixes with rock particles to form a thin soil. Soil holds water and mineral ions, so conditions become less hostile.Mosses, then grasses and small flowering plants, can now grow. They die and decompose too, so the soil becomes deeper and richer. This supports larger plants such as shrubs, and eventually trees, which shade out many smaller plants. Animals arrive as their food plants and shelter become available.Example: a sand dune
Marram grass has long roots and leaves that roll to reduce water loss. It traps sand and stabilises the dune. As it decomposes, it adds humus, allowing other grasses, then shrubs such as sea buckthorn, and finally trees to grow further inland.
• producing large numbers of seeds or spores that are easily dispersed by wind;
• rapid germination and growth;
• tolerance of extreme conditions, such as drought, high light or high salt;
• the ability to photosynthesise, so they do not depend on other organisms for food;
• in some species, the ability to fix nitrogen, since the ground is poor in nitrates.Lichens slowly break down the rock surface. When pioneers die, saprobionts decompose them, and the organic matter mixes with rock particles to form a thin soil. Soil holds water and mineral ions, so conditions become less hostile.Mosses, then grasses and small flowering plants, can now grow. They die and decompose too, so the soil becomes deeper and richer. This supports larger plants such as shrubs, and eventually trees, which shade out many smaller plants. Animals arrive as their food plants and shelter become available.Example: a sand dune
Marram grass has long roots and leaves that roll to reduce water loss. It traps sand and stabilises the dune. As it decomposes, it adds humus, allowing other grasses, then shrubs such as sea buckthorn, and finally trees to grow further inland.