Succession
Succession is the sequential changes in a plant community as it moves to a seral climax.
Sere: a stage of a succession sequence. Each sere is named after the dominant plant in the species.
Seral Progression: progressive development of a vegetation community.
Pioneer Community: the first sere which is characterised by the first plants that develop and colonise.
Climatic Climax Vegetation: the vegetation that is in equilibrium with the environment (therefore only changes if the environment does).
However, conditions rarely persist long enough for a climax community to develop; caused by:
· Physical – tectonic activity, erosion and deposition may alter drainage.
· Human – de/af-forestation, ploughing, burning, drainage and flooding.
Human interference can lead to a Plagioclimax Community (prevention of succession where by one sere is maintained). An example of this is Heather Moorland. Natural interruptions preventing the environment reaching the climatic climax are called ‘Interrupted Succession’.
Succession that begins in new habitats, uninfluenced by pre-existing communities is called Primary Succession, whereas succession that follows disruption of a pre-existing community is called Secondary Succession.
There are two types of primary succession (otherwise known as Prisere):
· Xerosere: occurring in dry conditions; for example Psammoseres (on sand dunes)
· Hydrosere: occurring in wet conditions; for example Hydroseres (in fresh water)
Case Study - Hydrosere
Hydrosere is the primary succession sequence which develops in aquatic environments such as lakes and ponds. It represents a conversion of water body and its community into a land community. For example an oxbow lake or a kettle lake. Over time, an area of open freshwater will naturally dry out. Ultimately, it will become woodland, after going through several different stages.
Sere: a stage of a succession sequence. Each sere is named after the dominant plant in the species.
Seral Progression: progressive development of a vegetation community.
Pioneer Community: the first sere which is characterised by the first plants that develop and colonise.
Climatic Climax Vegetation: the vegetation that is in equilibrium with the environment (therefore only changes if the environment does).
However, conditions rarely persist long enough for a climax community to develop; caused by:
· Physical – tectonic activity, erosion and deposition may alter drainage.
· Human – de/af-forestation, ploughing, burning, drainage and flooding.
Human interference can lead to a Plagioclimax Community (prevention of succession where by one sere is maintained). An example of this is Heather Moorland. Natural interruptions preventing the environment reaching the climatic climax are called ‘Interrupted Succession’.
Succession that begins in new habitats, uninfluenced by pre-existing communities is called Primary Succession, whereas succession that follows disruption of a pre-existing community is called Secondary Succession.
There are two types of primary succession (otherwise known as Prisere):
· Xerosere: occurring in dry conditions; for example Psammoseres (on sand dunes)
· Hydrosere: occurring in wet conditions; for example Hydroseres (in fresh water)
Case Study - Hydrosere
Hydrosere is the primary succession sequence which develops in aquatic environments such as lakes and ponds. It represents a conversion of water body and its community into a land community. For example an oxbow lake or a kettle lake. Over time, an area of open freshwater will naturally dry out. Ultimately, it will become woodland, after going through several different stages.
Phytoplankton Stage:
Algae (unicellular floating plants) are the pioneer species of a bare water body, such as a pond. Their spores are carried by air to the pond. The algae are followed by zooplankton (small animals that consume algae). After death, both settle to the bottom of the pond, and decay into humus that mixes with silt and clay particles brought into the water body by run-off water and wave action to form soil. As soil builds up, the pond becomes shallower.
Submerged Stage:
As the water body becomes shallower, more submerged (under the surface) rooted species are able to become established due to the increasing depth that light can penetrate to in the shallower water. This is suitable for growth of rooted submerged species such as Elodea and Hydrilla. Once submerged species colonize, the successional changes are more rapid. Sediment is still entering the water body and is trapped more quickly by the net of plant roots growing on the pond floor.
Floating Stage:
The water body becomes sufficiently shallow (2–5 feet) for floating species and therefore less suitable for rooted submerged plants. These include species like Nymphaea and Nelumbo. The large and broad leaves of floating plants shade the water surface and conditions become unsuitable for growth of submerged species which start disappearing. The plants decay to form organic mud which makes the pond yet more shallow (1–3 feet).
Algae (unicellular floating plants) are the pioneer species of a bare water body, such as a pond. Their spores are carried by air to the pond. The algae are followed by zooplankton (small animals that consume algae). After death, both settle to the bottom of the pond, and decay into humus that mixes with silt and clay particles brought into the water body by run-off water and wave action to form soil. As soil builds up, the pond becomes shallower.
Submerged Stage:
As the water body becomes shallower, more submerged (under the surface) rooted species are able to become established due to the increasing depth that light can penetrate to in the shallower water. This is suitable for growth of rooted submerged species such as Elodea and Hydrilla. Once submerged species colonize, the successional changes are more rapid. Sediment is still entering the water body and is trapped more quickly by the net of plant roots growing on the pond floor.
Floating Stage:
The water body becomes sufficiently shallow (2–5 feet) for floating species and therefore less suitable for rooted submerged plants. These include species like Nymphaea and Nelumbo. The large and broad leaves of floating plants shade the water surface and conditions become unsuitable for growth of submerged species which start disappearing. The plants decay to form organic mud which makes the pond yet more shallow (1–3 feet).
Reed Swamp/Emergent Stage:
The water body is now invaded by emergent plants (those that break the surface) such as Phragmites (reed-grasses), Typha (cattail), and Zizania (wild rice) to form a reed-swamp (in North America, a marsh). These plants produce large quantities of leaf litter. This litter is resistant to decay and reed peat builds up, converting the surface of the pond to water-saturated marshy land.
Sedge-Meadow/Fringing Stage:
Successive decreases in water level help species such as Carex and Juncus to establish themselves. They form a mat of vegetation extending towards the centre of the pond. The leaves that break the surface transpire water to lower the water level further and add additional leaf litter to the soil. Eventually, sedge peat accumulates above the water level and soil is no longer totally waterlogged. The habitat becomes suitable for invasion of herbs such as Iris, and Galium.
Carr Woodland Stage:
The soil now remains drier for most of the year and becomes suitable for development of wet woodland. It is invaded by shrubs and trees such as Willow, Alders and Populars. These plants produce shade, lower the water table still further by transpiration, build up the soil, and lead to the accumulation of humus. This type of wet woodland is also known as Carr Woodland.
Climax Woodland Stage:
Finally, the climax community develops. It may be a forest if the climate is humid, grassland in case of sub-humid environment, or a desert in arid and semi-arid conditions. A forest is characterized by presence of all types of vegetation including herbs, shrubs, mosses, shade-loving plants and trees.
The overall changes taking place during hydrosere succession are shallowing of water, addition of humus and minerals, soil building and aeration of soil. As the water body fills in with sediment, the area of open water decreases and the vegetation types moves inwards as the water becomes shallower. Many of the above mentioned communities can be seen growing together in a water body. The centre is occupied by floating and submerged plants with reeds nearer the shores, followed by sedges and rushes growing at the edges. Further away, shrubs and trees occupying the dry land.
The water body is now invaded by emergent plants (those that break the surface) such as Phragmites (reed-grasses), Typha (cattail), and Zizania (wild rice) to form a reed-swamp (in North America, a marsh). These plants produce large quantities of leaf litter. This litter is resistant to decay and reed peat builds up, converting the surface of the pond to water-saturated marshy land.
Sedge-Meadow/Fringing Stage:
Successive decreases in water level help species such as Carex and Juncus to establish themselves. They form a mat of vegetation extending towards the centre of the pond. The leaves that break the surface transpire water to lower the water level further and add additional leaf litter to the soil. Eventually, sedge peat accumulates above the water level and soil is no longer totally waterlogged. The habitat becomes suitable for invasion of herbs such as Iris, and Galium.
Carr Woodland Stage:
The soil now remains drier for most of the year and becomes suitable for development of wet woodland. It is invaded by shrubs and trees such as Willow, Alders and Populars. These plants produce shade, lower the water table still further by transpiration, build up the soil, and lead to the accumulation of humus. This type of wet woodland is also known as Carr Woodland.
Climax Woodland Stage:
Finally, the climax community develops. It may be a forest if the climate is humid, grassland in case of sub-humid environment, or a desert in arid and semi-arid conditions. A forest is characterized by presence of all types of vegetation including herbs, shrubs, mosses, shade-loving plants and trees.
The overall changes taking place during hydrosere succession are shallowing of water, addition of humus and minerals, soil building and aeration of soil. As the water body fills in with sediment, the area of open water decreases and the vegetation types moves inwards as the water becomes shallower. Many of the above mentioned communities can be seen growing together in a water body. The centre is occupied by floating and submerged plants with reeds nearer the shores, followed by sedges and rushes growing at the edges. Further away, shrubs and trees occupying the dry land.