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Succession is the process by which an ecosystem changes over time. The biotic conditions change as
the abiotic conditions change. There are two types, primary and secondary succession.
This happens on land that's been newly formed or exposed, e.g. where a volcano erupted to form a
new rock surface, or where the sea level has dropped exposing a new area of land. There's no soil or
organic material to start off with. It starts when species colonise a new land surface. It happens in
The abiotic conditions are very hostile and pioneer species colonise, such as lichens, algae and
mosses can grow, as they are specialised to cope with the harsh conditions. These organisms can
penetrate the rock surface, helping to break it down into grains and trapping organic material, which
will break down to form humus. This is the start of a soil.
Conditions are less hostile, so new organisms can move in and grow. They will usually be ferns, as
they can retain water well and the soil is very light so does not retain much water, or nitrogen fixing
plants, as there will not be sufficient nutrients in the soil. This increases the depth and richness of the
As the soil develops, more water and nutrients are retained and become available for plant roots, so
that less hardy species can survive, and gradually larger plants can be supported and biodiversity of
species increases. Every time a new species moves in, they may be better adapted for the improved
conditions, so out-compete the species already there, and become the dominant species in the
The climax community is reached, where the biodiversity and range of species is generally constant.
It is self sustaining, and usually the most productive group of organisms which that environment can
support. It won't change much more; it's in a steady state.
Secondary succession happens on land that has been cleared of all the plants, but where the soil
remains, e.g. after a forest fire, or where a forest has been cut down by humans.
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It happens in the same way to primary succession, but because the soil is already formed, and
contains seed, roots and soil organisms, the numbers of species present right from the beginning are
much higher. The pioneer species are larger plants, like shrubs.
Deflected Succession, / Plagioclimax.
Human activities can prevent succession, or change it's course, as it could make different species the
dominant. This could result in altered soil composition, different herbivores or different