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What is the first stage of succession?
A new habitat such as bare soil is populated by pioneer species whose seeds are blown in by the wind
How are pioneers capable of growing on bare soil?
They are adapted to grow in hostile conditions such as high light intensity and fluctuating temperature
How is soil improved by pioneers?
When they are die pioneers are broken down by saprobiotic bacteria increasing the humus and nitrate content of the soil
The roots stabilise the soil
The leaves provide shade
What are the next plants to grow after pioneers and in what conditions are they capable of surviving in?
Herbaceous annual plants
Less hostile environments
What effects do herbaceous plants have on the population of pioneers?
Herbaceous plants out-compete them for light and nutrients
Leads to a decline in the population of pioneers and an improvement in soil quality
What plants are the next to grow after herbaceous plants?
Woody shrubs and bushes appear as the soil deepens, outcompeting the shrubs and improving soil quality
Which plants grow after woody shrubs?
Fast growing trees such as birch
Form a dense forest
What are the last plants to grow in succession and what is this community called?
Slower growing larger trees such as oak
This is called a climax community
Nothing can outcompete these trees
What happens to abiotic factors as succession continues and what effects does this have?
They become less hostile
This causes the number of niches to increase, enabling a greater variety of plant species to be supported
How does the decreasing hostility of abiotic factors allow organism populations to stabilise?
Many different plant species can grow
Consumers have a number of different species to feed on
What is humus?
The organic matter in soil which provides nitrates and other mineral ions
Also retains water in the soil
Give an example of one ecosystem that has come about due to a holt in succession
Moorland would be woodland if it were not for grazing animals, mowing, removing the growing points of woody shrubs and the controlled burning of heather in order to kill saplings
How can succession occur on exposed rock?
Lichens, consisting of fungal and algal cells, grow
Algae produce sugars via photosynthesis and the fungi produce organic acids which break down into mineral ions
Eventually enough dead matter accumulates for mosses to grow, then grasses, then succession continues
AQA BIOL4 Succession