Primary succession
- Starts from bare rock or water.
- Occurs in an environment that is devoid of vegetation, organisms and soil (such as a lava flow or area left from retreated glacier).
- Basically, it’s the gradual growth of an ecosystem over time.
- Quite unusual in the world today.
- Sand dunes are one of the few places where it takes place.
- Volcanic islands (e.g Surtsey, Iceland)
•Pioneer species are the first species to colonise an area, and tend to be lichen
•They are opportunistic species which are able to rapidly exploit a sudden new opening in ground plant cover.
•They are able to withstand desiccation, extremes of temperature and low levels of nutrients.
•They must be able to grow quickly, but are usually short lived.
•The pioneer species penetrate and break up the rock.
•As they die and decompose, humus builds up.
•This allows other simple plants such as mosses and ferns to now grow.
•Mosses and ferns cast shade to stop further growth of lichens
•Their roots are longer and so further break up the rock.
•The organic matter gradually increases as these bigger plants die. More water is retained by this, so grasses, small flowering plants and shrubs can grow.
•Growth of larger plants and the animals which inhabit them will cause further changes in soil and light conditions.
•The shading effect of the larger plants kills some of the smaller ones.
•Eventually the area is colonised by dominant plant species and a climax community is reached.
•This would usually be oak woodland in the UK, but as we’re in Australia, a good example would be a rainforest.
The plants present at each seral stage modify the environment making it more favourable for other plant species to colonise and out compete the current plants (e.g. the growth, death and decay of lichens produces organic matter which allows the growth of mosses which could not grow before the lichens).
↓Bare rock
↓Pioneers
↓Grasses/herbaceous plants
↓Perennial herbs
↓Shrubs/scrub
↓Small trees
Deciduous woodland – the climax community
Pioneer species are effective colonisers because of some specific features:
- ability to fixate nitrogen
- tolerance to extreme conditions
- rapid germination of seeds
- ability to photosynthesise