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A-level Geography - Ecosystems: Change and Challenge: Ecosystems in the British Isles

Succession and climatic climax - definitions


(Paul Andersen describes the process of ecological succession)

Succession 
Succession is the name given to the replacement of a plant species, by another species, or a group of species over time. In simple terms it refers to how plant communities change with distance away from ‘something’ such as bare rock, a water body or a number of other things. There are two main types of succession:

Primary succession is the colonization of new sites by communities of organisms. It often occurs after a devastating event has wiped out the organisms that lived in an area, or with the creation of a new habitat. It starts with no organic matter (no vegetation, no animals, no insects, no seeds, and no soil) but only mineral material (sand, bare rock, gravel from glacial outwash, volcanic ash and lava, etc.).

There are four main types of primary succession based on its original surface:

Secondary succession is succession that begins after an event clears the community but leaves the soil intact. Examples of events that precede secondary succession would be wildfires and deforestation by clearcutting. Secondary succession is usually much quicker than primary succession because there is already an existing seed bank of suitable plants in the soil.

Each stage in succession is called a sere. In biological terms succession all starts with a pioneer species and ends up in with a climax community

Pioneer species: These are the first species to occupy a new habitat, starting new communities. They have rapid reproductive strategies, enabling them to quickly occupy an uninhabited area. Many have an asexual stage to their reproduction.

Climax community: This is the stable community that is reached, beyond which, no further succession occurs.

Succession and climatic climax - examples

Lithosere is a succession that begins life on a newly exposed rock surface. This might have been created by the eruption of a volcano leaving a new, bare lava surface, or by a raised beach. It has the following stages:

a) Crustose - lichen stage

Lichen species like Graphis Rhizocarpon, Rinodina and Lacanora forms the pioneer community in a lithosere, as they can tolerate desiccation. 

b) Moss stage - Accumulation of soil and humus leads to the growth of mosses such as Polytrichum and Grimmia. 

c) Herb stage - Death and decay of mosses produce a mat of organic moss on partially fragmented rock help the germination to seeds of hardy grasses like Eleusin, Aristicla, Poa, etc. 

d) Shrub stage - Further weathering or rocks and death of herbs make the habitat more suitable for the growth of shrubs like Rhus, Caparis, Zizyphus etc. 

e) Forest stages - Many light demanding, stunted and hardy trees invade the area. Vegetation finally becomes mesophytic. A steady state is reached between the environment and the biotic community. 

Trend of succession in Lithosere
Pioneer Community Seral Communities Climax Community
1 2 3 4 5 6

Crustose lichens stage

e.g
Rhizocarpus,
Rinodina,
Lacanora

Foliose lichens stage

e.g
Parmellia,
Dermato carpon

Moss stage

e.g
Polytrichum,
Tarula,
Grimmia

Herbs stage

e.g
Eleusine,
Aristida

Shrub stage

e.g
Rhus,
Phytocarpus

Forest stage

e.g
Mesophytic trees

(Source: www.tutorvista.com)

The following image shows example stages of lithosere in British heather moorland.

Hydrosere is the ecological succession in the newly formed pond or lake. The process commences with accumulations of silt, enabling initial colonization by submerged or floating plants, such as water lilies and pondweeds, depending on the rate of flow and nutrient status of the water. As silting increases and organic debris is deposited, reeds, sedges, and similar plants begin to appear, forming a swamp. Organic matter builds up as peat, and conditions progressively become drier, creating a stage called a fen, dominated by herbaceous species, and then a carr, in which shrubs and small trees predominate. Eventually, the substrate is sufficiently stable to support the larger trees of mature forest species.


(Source: www.s-cool.co.uk)

The following table shows the different stages of hydrosere:

Pioneer Communily

Seral Communities

Climax Community

1 2 3 4 5 6 7
Plankton stage e.g Diatoms, Bacteria, Cyaanabacteria, Green algae Rooted- submerged stage e.g Elodae. Hydrilla, Vallisneria, Ultricularia, Potamogeton Rooted- floating stage e.g Nymphaea Trapa, Azolla, Lemna, Wolffla, Pistia Reed- swamp stage e.g Sagittaria. Phragmites Typha, Scripus Sedge meadow stage e.g Juncus, Cyperus, Eleochcaris, Carex Woodland stage e.g Salix, Poplus. Almus, Cornus Forest stage e.g Temperate Deciduous


The following presentation shows an example of hydrosere in UK - Poynton Pool, Cheshire.

Halosere is the plant succession in salty conditions. The first flowering plants that begin to grow on salt marsh are pioneer species like Salicornia sp (glasswort) or Spartina spp (cord grass). Migration must have occurred for anything at all to be present on the site. If their seeds are sufficiently undisturbed (i.e. if the mud has built up high enough) they will germinate and grow successfully. Small pioneer plants will begin to colonise the surface of the mud. Consequently the muddy shore spends more time emersed (out of the water). Conditions become suitable for more species and they migrate to the area and begin to grow as well. Following the stages of establishment, competition and stabilisation,  halosere may often end, at some distance inland, with a mature deciduous forest - the climatic climax community of the UK.

An example of halosere in UK can be found in Hurst Castle and Keyhaven salt marshes.

  1. Keyhaven marshes are located on the south coast of England, in the western Solent in Southern Hampshire. They have formed behind Hurst Castle Spit, which has formed because of longshore drift from the West.
  2. This spit provided a sheltered place for sediment accumulation and for eel grass to accumulate away from the impact of strong winds and coastal erosion.
  3. The pioneer colonising plant, eel grass, helps to stabilise the area further by trapping more sediment.
  4. Gradually, halophytes (salt tolerant plants) such as glass wort and sea blite colonise the accumulating mudflats.
  5. These plants trap more sediment and contribute organic matter when they die. These processes help the salty marsh to grow.
  6. Eventually the salt marsh will grow further and an even more complex set of plants will colonise the area, until the climax community of alder and ash trees is reached, with a fully developed creek system. 

Succession presentation

Forest Succession Animations

Ecosystem succession activities

Tree with characteristics of deciduous woodland in UK

The following diagram shows the characteristics of deciduous woodland trees in UK.

Management of heather moorland in UK - a video

Effects of human activity on succession - Plagioclimax heather moorland

Plant successions can be stopped from reaching the climatic climax, or deflected towards a different climax, by human interference. The resulting vegetation is known as a plagioclimax. The ecosystem may have been stopped from reaching its full climatic climax or deflected towards a different climax by activities such as:

  •  Cutting down the existing vegetation
  •  Burning as a means of forest clearance
  •  Planting trees or crops
  •  Grazing and trampling by domesticated animals
  •  Harvesting of planted crops

 These activities are known as arresting factors. If the human activity continues, the community will be held in a stable position and further succession will not occur until the human activity ceases.

Location of temperate deciduous forest

Temperate deciduous forests are located between 40° and 60° north and south of the equator. In the northern hemisphere, they can be found in the eastern part of the United States and Canada, most of Europe and parts of China and Japan. In the southern hemisphere, temperate forests can be found on the southern tip of South America and in Eastern Australia.

Temperate deciduous forests are most notable because they go through four seasons. Leaves change color in autumn, fall off in the winter, and grow back in the spring; this adaptation allows plants to survive cold winters.

The climatic climax vegetation in UK is the temperate deciduous forest. UK is at a latitude where one would expect taiga to predominate instead of temperate forest if it weren't for the effect of the Atlantic Conveyor.

Characteristics and climate of temperate deciduous forest

The temperate deciduous forest gets its name because the temperatures are temperate meaning they are not extreme. The average yearly temperature is about 10°C. The summer temperatures average between 20-25°CAlthough the winter typically sees temperatures below freezing, the average temperature remains above 0°CForests higher in the mountains are colder.

Deciduous forests receive from 2 to 5 feet (0.5-1.5 m) of precipitation (both rain and snow) spread fairly evenly throughout the year, Humidity in these forests is high, from 60% to 80%

The term deciduous refers to the plant’s ability to lose it’s leaves when times get tough. Temperate deciduous forests are most notable because they go through four seasons as summer, autumn, winter, and the spring. Leaves change color in autumn, fall off in the winter, and grow back in the spring; this adaptation allows plants to survive cold winters.

Compared to tropical rainforest, trees in temperate deciduous forest are less dense and widely spaced. Only a few types of trees dominant the forest. Most of the trees are broadleaf trees such as oak, maple, beech, hickory and chestnut.

Structure of temperate deciduous forest

The five layers in the temperate deciduous forest and their main vegetation in UK include the:

  • Tree stratum or tree layer, the tallest layer, 60 -100 feet high, with large oak, maple, birchbeech, pinechestnutmagnoliawillowpoplaraspenshickory, elm, basswood, linden, walnut, holly, rowan, hazel or sweet gum trees.

  • Small tree or sapling layer - short tree species and young trees like dogwoods and redbuds.

  • Shrub layer - shrubs like rhododendrons, azaleas, mountain laurels, and huckleberries.

  • Herb layer - short plants like yearly wildflowers, bluebells, wood anemones, ferns, perennial forbslady slipper, jack-in-the-pulpit and trillium.

  • Ground layer - lichens, clubmosses, and true mosses. Lichens and mosses also grow on the trunks of trees. 

Take a walk in the London's Sydenham Hill Woods to find some specific trees and plants in UK!

Plant adaptation of temperate deciduous forest

Plants in the temperate deciduous forests adjust their growth and activity to the seasons of the year:

  • In SUMMER, their broad green leaves help capture sunlight needed to make food through photosynthesis.

  • As temperatures drop, the tree cuts off the supply of water to the leaves and seals off the area between the leaf stem and the tree trunk. With limited sunlight and water, the leaves are unable to continue producing chlorophyll (green pigment in leaves) causing them to change into the beautiful red, yellow and orange leaf colours of AUTUMN.

  • In WINTER, it is too cold for the trees to protect their leaves from freezing, so they simply loose them and seal up the places where the leaves attach to the branch. Losing their leaves helps trees to conserve water loss through transpiration. (Dried leaves continue to hang on the branches of some deciduous trees until the new leaves come out.)

  • Before the leaves die, some of the food material they contain is drawn back into the twigs and branches where it is stored and used the following spring.

  • The warmer temperatures of SPRING signal to the trees that they can grow new leaves again, and restart the cycle. 

Soil and nutrient cycling of temperate deciduous forest

The soil type is brown earth. Brown earth soils are widespread in Britain, except in highland areas. This is a fertile soil. 

The  major soil horizons: 
O horizon is the topmost layer of most soils. It is composed mainly of plant litter at various levels of decomposition and humus.
1. A horizon, is where biological activity and humus content are at their maximum. It is also the zone that is most affected by the leaching of soluble materials and by the downward eluviation of clay particles.
2. B horizon which is the zone of accumulation or illuviation, where clays or other materials moved down from the A horizons are redeposited. The A and B horizons together make up the true soil.
3. C horizon consists mainly of weathered material (regolith) resting on the bedrock (unaltered underlying geology).


In temperate deciduous forests, most nutrients are abundant and held in loose cycles. Nutrients replenished each year by leaf fall and weathering. This makes the forests suitable for sustainable forestry and agriculture. The following presentation shows the  nutrient cycling of temperate deciduous forest.

Forest in Northern Ireland

Click to explore the temperate deciduous forest in Northern Ireland!

Plagioclimax heather moorland in North Yorkshire, UK

75% of the world's heather moorland is found in Britain. it can be found in many upland areas such the North Yorkshire Moors. The uplands of Northern England were once covered by deciduous woodland. Some heather would have been present, but in relatively small amounts. Gradually the forests were removed during the early Middle Ages for timber and fuel purposes, and to create space for agricultural activities. The soil deteriorated as a result and heather came to dominate the plant community. Sheep grazing was the major form of agriculture in the area at the time and the sheep prevented the re-growth of woodland by destroying any young saplings.

In more recent times the process of controlled burning of the heather has taken place. The heather is burnt after 7 - 15 years of its life cycle before it becomes mature and allows colonization of the area by other plants. The ash adds to the soil fertility and the new growth that results increase the productivity of the ecosystem and provides the sheep with a more nutritious diet than is provided by the elder heather. This controlled burning maintains a plant community which is not the climatic climax of the area, and is therefore a plagioclimax.

The burning management creates an ideal habitat for large populations of red grouse, a game bird which supports a lucrative shooting industry in upland Britain. Firing the heather does a number of things: it eliminates plant species that might compete with heather; it stimulates new heather shoots, the staple food of red grouse; and it encourages the germination of heather seeds. 

Heather moorland is also managed (sometimes illegally) by eliminating potential predators of red grouse and their chicks such as foxes, stoats, crows and raptors. Light grazing by sheep is also encouraged to prune the heather.

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