Succession in Ecosystems
- Ecosystems develop through distinct successions from a ‘sterile’ area to a climatic climax community
- Vegetation succession can be considered:
The evolution of plant communities at a site over time - from pioneer species to climax vegetation
- At each stage of succession the plant community alters the soil and microclimate, allowing the establishment of another group of species
- One community of plants is therefore replaced by another as the succession develops
- Eventually a climax community is reached where the vegetation is in a state of equilibrium with the environment and there is no further influx of new species
- The process takes hundreds of years and the climax community is dependent on the climate it forms in
Primary succession from bare rock to a climax community over hundreds of years
Seres and climax vegetation
- The developmental stages of a community are known seral stages and the final stage as the climax community
- The entire seral communities that gives the site/area its characteristics is called a sere
- Particular species are associated with each sere, and certain species becoming dominant
Seral succession in a psammosere (sand dunes)
Climax communities
- If natural conditions are not interrupted, then climatic climax is the final stage that seres reach
- Climatic conditions include light, soil pH and moisture determines which plants survive
- This dictates the natural vegetation that should be found in an area
- For most of the UK this would be deciduous woodland, dominated by Beech, Birch, Ash and Oak
Plagioclimax
- This is where the resultant community has been permanently influenced by humans
- For example, by burning or grazing
Sub-climax
- If vegetation does not reach its climax as a result of interruptions by local factors, such as soil changes or differences in parent rock, the interruptions are known as arresting factors
- Not all climax communities are the same, and if physical factors such as altitude or water hinder ecosystem development a sub-climax community may result
Succession
- The route to climatic climax can take place in two ways:
- Primary succession
- Secondary succession
Primary succession
- Found on new, bare, land surface or in water and various seral stages are passed through before climatic climax is reached
- It is an orderly sequence of events where one community is replaced by another
- Biomass is created via decomposition and provides more nutrients to the soil
- Allowing for more and greater variety of plants and animals to exist at each successive seral stage
- There are four types of seres:
- Lithosere - rock
- Psammosere - sand dunes
- Halosere - salt marshes
- Hydrosere - lakes
- The first to arrive are known as pioneer species - the trailblazers - often herbs and lichen
- These early invaders quickly colonise new surfaces as there is no competition from other species
- They begin to adapt to their environment
- However, they are short lived and are then replaced by others that outcompete them as conditions improve
Route to climatic climax can occur on land and water and have a distinct pathway
Secondary succession
- If plant succession is halted before reaching dynamic equilibrium a secondary succession occurs
- Interruptions include fire, disease, climate change and deforestation
- These events can also alter the final climax community that result
- Not all climax communities are the same, and if physical factors such as altitude or water hinder ecosystem development, a sub-climax community may result
Flowchart showing various routes to climatic climax community through secondary succession.
NB. Prisere succession is the primary route
Exam Tip
The difference between plagio and sub climax succession is that if humans are involved then we get a plagiocliamax community where the vegetation is changed, which changes the climax community. If however, a natural event occurs that halts the succession, then this is called a sub-climax and natural succession will resume at a later date.