succession – ‘dynamic ecosystems’ ‘succession is the gradual directional change of a...
TRANSCRIPT
Succession – ‘dynamic ecosystems’
‘Succession is the gradual directional change of a community
over time’
There are two types of succession:
Primary successionSecondary succession
Here the starting point is bare ground
Here a community is damaged and the soil is left plants then colonise(e.g. a woodland has been felled).
The END POINT of both types of succession is the climax community
Succession on sand dunes
Nearest the sea, only a few speciescan colonise the sand. Why?•Sand constantly moves
•High salt concentration
• freely draining ‘soil’
• ‘soil’ has a low nutrient status
Succession on sand dunes
Very specialised species live in this area, they are called
PIONEERSThese species are show
xeromorphic & halophytic characteristics
•Sea rocket (Cakile maritima)
•Sea holly (Eryngium maritimum)
Sea holly…………..
……………… pioneer species
Latin name: Eryngium maritimum
………of sand dunes
These PIONEER species give way to other species as you move in
land
Couch grass (Agropyron junceiforme)
This species has widespread roots, this helps in two ways
•Stabilise the substrate
•Absorb all available water
The quality of the substrate improves in two ways as you move
back through the dunes
1. Nutrient levels increase
2.Water retention improves
This is due to: •Death & decay of animals
•Decay of seaweed
•Decay of plant material
A skeletal soil begins to develop
These species further improve the edaphic conditions
This makes the substrate more hospitable, encouraging other
species…….
Marram grass (Ammophila arenaria)
These species are still XEROPHYTIC
Marram grass (Ammophila arenaria)
Large network of roots, leading to dune developement
Marram produces shoots along its stem, ensuring that it is never
covered with sand
This can lead to large sand dune systems
Dunes at this stage are called ‘yellow’ reflecting how little organic matter the substrate
contains
The substrate will turn to ‘grey’ as the levels of dead material
increases
The species to follow next in the succession, are N fixers
Restharrow (Ononis repens)
Bird’s foot trefoil (Lotus corniculatus)
These add N to the soil
As Nitrogen levels increase, other species become more common
A common one is Red Fescue (Festuca rubra)
These species stabilise the substrate further
• http://bcs.whfreeman.com/thelifewire/content/chp55/55020.html
• http://ecoplexity.org/node/219
• www.youtube.com/watch?v=vNHnwHaSolA