Succession

Net Primary Productivity (NPP) – The total amount of energy transferred from sunlight to chemical potential energy (biomass) less any used in respiration.

Gross Primary Productivity (GPP) – The total amount of energy transferred from sunlight to chemical potential energy (biomass) by plants.

Ecology – The study of the interactions between the environment and the organisms that inhabit it.

Succession = When changes to the environment causes the plant and animal species to change. Or… Transition in the species composition of a biological community, often following ecological disturbance to the community; the establishment of a biological community in an area virtually barren of life.

Changes at a predictable rate and predictable species.
Primary succession = Bare rock. Need erosion, wind and rain for soil. = No soil, life has to re-establish.
Secondary succession = Disturbance but soil remains. E.g. forest fires. Pioneer organisms come into an area after disturbance. E.g. large pole pines. Climax species = what happens after succession.
Series of steps where life comes back.

Each step of succession is called seral stages/seres:

Pioneers
Intermediate
Climax

Primary = no soil.

Secondary = soil but no plants or animals.

Pioneer species

Dispersion of seeds/spores carried by wind or animals.
Aren’t reliant on native species.
Lots of seeds/spores. They need to be very light.
Good at germinating
Need to be extremophiles – dry, low nutrients, extreme temperatures.
Penetrate rock.
Biological weathering
Decomposition producing humus.
So mosses and ferns can grow.

Intermediate species

Complex plants
Vascular species
Insects
Pollination
Mosses and ferns cast shade. Stop growth of lichens.
Roots break up rock.
More organic matter as plants die.
More water retained by grasses.
Animals move in changing soil and light conditions.
Shading killing smaller plants.

Climax sere

Colonised by dominant species
Less biodiversity
More stable
E.g. oak woodland in the UK
Heathland management – stops succession

Deflected succession

Climax not reached
E.g. due to agriculture – chalk grasslands of the south downs do not develop into woodland because of the grazing of sheep placed there by man.
Used for conservation
Also due to limiting factors. E.g. around lead mines due to lead in soil.
Called plagioclimax.

Factors which increase as succession increases

Time
Plant and animal diversity
Biomass
Complexity of ecosystem
Stability
Productivity
Height of plants
Number of layers of vegetation
Number of habitats
Number of niches
Soil depth
Soil fertility
Soil organic matter
Soil water holding
Complexity of food webs