Succession and Climax
- Succession – a series of changes that take place in the plant community over time.
- Climatic climax – the final stage of the plant succession, where the vegetation is in balance with the environmental conditions. Providing the environmental conditions remain unchanged there will be no change in the vegetation once the stage is reached.
- If allowed to continue undisturbed, the succession will reach its climatic climax where the plant species live in perfect balance with the current environmental conditions.
- Climate is the major influence of vegetation on a global scale.
- On a local scale-drainage, geology and relief affect plant growth.
There are two basic types of succession:
- Primary succession-occurs on surfaces that have had no previous vegetation.
- There are two main types of primary succession:
- Xeroseres are formed on dry land, this group can be divided into lithoseres on bare rock and psammoseres on sand dunes.
- Hydroseres are formed in water, haloseres in salt water and hydroseres in fresh water.
- Secondary succession occurs on land that was formerly vegetated but has undergone a loss of vegetation such as deforestation.
Development of a Succession
- As the succession develops it passes through a series of stages called seres which are individual stages in the plant succession where the processes of invasion, colonisation, competition, domination and decline operate to influence the composition of the vegetation.
i). Plants first invade bare ground through the processes of dispersal and migration.
ii). Pioneer species are adapted to surviving harsh conditions such as long-rooted salt-tolerant marram grass, they compete for available space, light, water and nutrients, when they die they help modify the environment by adding organic matter.
iii). The addition of organic matter to the developing soil improves its structure and water retention qualities.
iv). A period of relative stability is eventually reached where the vegetation has reached its climax, the climax is dominated by the tallest species.
v). The saturation point has been reached with all potential niches occupied as a climatic climax community, where the natural vegetation has reached a stable balance with the climate and soils of the area.
- Polyclimax theory – the theory that local factors such as drainage, geology, relief and microclimates can create variations in the climatic climax community.
- Plagioclimax – the plant community that exists when human interference prevents the climatic climax being reached.
Lithosere
- Is a succession that begins life on newly exposed rock surface such as the eruption of a volcano.
i). The bare rock is initially colonised by bacteria and algae.
ii). The pioneers begin to colonise, starting with lichens, they begin to break down the rock and assist water retention.
iii). As water retention improves, mosses begin to grow, water retention improves and weathering to produce the beginning of a soil where advanced plants can grow
iv). Ferns, herbs and flowering plants appear and die back, bacteria convert their remains into humus, helps to recycle nutrients and improve soil fertility.
v). Shrubs start to grow.
vi). Pioneer trees become established, normally fast growing including willow and birch.
vii). Slower growing tree species begin to develop such as ash and oak, they are the dominants of the climatic climax community as temperate deciduous woodland.
Hydrosere
- A hydrosere develops as follows:
i). In a freshwater environment, submerged aquatics are the first plants to develop, they help to trap sediment which enables other species to move in.
ii). The next seral stage is the growth of reed beds and swamp conditions.
iii). Colonisation by alder and fern begins, they further modify the environmental conditions, improving drainage and mineral content of the immature soil, allowing the entry of willow and ash.
iv). The climatic climax vegetation of deciduous oak or beech woodland is reached, throughout the succession there are progressive changes to the soil conditions, ground-level microclimate and animal activity.