3.1.6.4 ecosystems in the British isles

• Succession

  A series of changes that take place in a plant community over time
• Seral stage

  Individual stages of succession, temporary stages that develop over time
• Autogenic factors

  Changes that occur in an environment due to internal factors, the environmental changes due to the plant community
• Arresting factors

  Natural or human events that interfere with succession, leading to a subclimax community, the vegetation that dominates when arresting factors interfere and stop the succession towards climatic climax vegetation
• Allogenic factors

  External factors that effect succession i.e human activity
• Climatic climax vegetation

  The final plant stage, dynamic equilibrium with plants + env, can take thousands of years

  
• Pond or lake fill in


  Due to sediment accumulation and from sides because of gradually spreading vegetation
• Plagioclimax


  The plant community that exists when human interference prevents climatic climax community being reached, i.e deforestation, ploughing + burning. Permanently influenced the final community
• Primary succession


  1. On land that is newly formed/exposed

  2. Abiotic conditions are harsh, seeds + spores blown in by wind

  3. 1st species = pioneer species, specialised to cope with harsh conditions

  4. Pioneer species alter microclimate, autogenic, die + decompose = basic soil, retain water, more organisms die + decompose = larger plants i.e shrubs grow in deeper soil

  
• Secondary succession


  1. Happens on land that's been cleared of all plants, only soil remains ie fires

  2. Secondary succession happens at a later seral stage, pinoeer species are larger plants

  3. At each stage different plants and animals are better adapted for improved conditions arrive, outcompete plants + animals that are already there > become dominant species

  
• As succession goes on

  Ecosystem = more complex, new species + more species diversity, more species richness and more species diversity = increase
• Climax community


  Final seral stage, ecosystem supports largest + most complex community = dynamic equilibrium = balance + stable + resilient
• Lithosere succession


  1. Pioneers = lichen + mosses

  2. Mosses grow on top symbiotic relationship

  3. Species are small + slow growing, they are tolerant to extreme conditions

  4. Start to weather rock by secreting acids + form thin soils

  5. Biological weathering allows the rock to retain more water as face is uneven

  6. Mooses + Lichen die = organic matter + added to thin soils

  7. Early colonisers = grasses + herbs + flowering plants + nettles

  8. Larger leaf area + outcompete the pioneer

  9. Larger roots = more weathering of rock = deeper soil + more decomposition = humus

  10. Shrubs + herbs

  11. Larger animal dispersed seeds

  12. Grow faster + taller, outcompeting smaller herbs

  13. Reduce wind, increase nitrogen content + more photosynthesis

  14. Trees, ash + oak

  15. Finally trees grow slowly but eventually shade and outcompete the shrubs

  16. Replaces by shade tolerant floor species

  17. Complex layered community + many trophic levels + interactions

  
• Hydrosere


  1. Pelagic zone : Pioneer species = algae + duckweed

  2. Die + sink to bottom = accumulate silt

  3. Emergent zone - rooted plant species = elodea + starwort + grasses

  4. Water = shallower due to increase in sediments + accumulation

  5. Rooted in lake bed + trap + hold more sediment

  6. Fringing = swamp + marsh plants = reed + rushes + pond weeds

  7. Very shallow

  8. Reeds + rushes = lots of leaf litter = forms wet soil

  9. Fringing = ferns, willow + alder

  10. Plants decease soil moisture by transpiration, until soil is no longer water logged

  11. Soil deepens and becomes drier as larger plants die and decompose

  12. Provides suitable conditions for large climatic climax trees, i.e oak, ash and beech

  
• Temperate deciduous woodland, the characteristics of the climatic climax
• Theoretical climax communities in Britain

  • Woodland
  • Soils
• Used to be 100% deciduous woodland now the largest % of ancient woodland in a county is up to approx 10%, with the majority of counties having 0%
• Functioning of deciduous woodlands

  • Lose their leaves in autumn reduces water loss from leaves
  • The canopy layer made up of trees oak elm beech dominant species in the winter months
  • Canopy layer
  • Mnb layer
  • Herb layer
  • Spring
  • Net primary productivity 1200,91m year
• Plagioclimax communities


  • Are those determined by human activity – they are stopped from reaching their full climatic climax by being deflected towards a different climax community. Arresting factors that stop the climatic climax community developing and deflect the succession towards a plagioclimax include:
  • Cutting down existing vegetation
  • Burning to clear forest
  • Planting new trees or crops
  • Grazing and trampling by domestic animals
  • Harvesting
• Heather Moorland in the UK

  1. The uplands of northern Britain were once covered by deciduous oak woodland. Some heather would have been present, but in relatively small amounts.

  2. The forests were removed during the early Middle Ages (4000-2000 years ago) for timber and fuel and to create space for agriculture.

  3. The soils deteriorated as a result and heather came to dominant the plant community, usually up to 600m.

  4. Sheep grazing, which was the main agricultural activity prevented, re-growth of woodland by destroying any new saplings.

  5. The heather is a hardy shrub, so was able to survive the poor soil conditions and flourished because there was less competition from other species.

  6. In more recent times the process of muirburn (also known as swaling) has been taking place. This involves the controlled rotational burning of any heather at cool temperatures, which does not kill the heather and allows new shoots to grow from the existing rootstock below the surface.

  7. The burning process 'shocks' the heather seed lying in the ground into germinating quickly.

  8. Heather cannot be burned between 15 April and 31 August so it does not get out of control in the summer heat. In any 1km2 area about 6 patches of 1 hectare (0.01km2) are burnt resulting in a patchwork of heather at various stages of development.

  9. Heather is usually burnt after every 15 years, once its life cycle has become mature and eventually senile. If longer was left between burning the vegetation is too woody so the fires become too hot and nutrients are lost in the smoke. The ash from burning adds to the soil fertility and the new growth provides sheep with a more nutritious diet.

  10. Also, some areas practice muirburn to keep the heather short which is a better habitat for grouse. This is not the case in Somerset, however, as there are no grouse there. The burning maintains this plagioclimax. Also, the heather chokes out any other species that may try to become established, eg gorse, bilberry, and remains the dominant species.

  11. 60% of the heather moorlands in England and Wales have been designated as Sites of Special Scientific Interest, Special Protection Areas or Special Areas of Conservation.
• Heather nutrient cycle


  Heather Cycle

  
• Economic reasons for maintaining the heather plagioclimax
• Why is heather so well adapted to grow in moorland environments?


  • Heather is comprised of small evergreen leaves which contain resin. This helps reduce water loss from evapotranspiration. They are also adapted to grow in low nutrient soils by having symbiotic fungi in their roots which help break down organic matter and minerals for absorption.
• Moorlands, also known as moors, heaths, or peatlands, are important ecosystems for several reasons:
• Reasons moorlands are important ecosystems

  • Biodiversity Conservation
  • Carbon Sequestration
  • Water Regulation
  • Cultural and Recreational Value
  • Unique Plant Adaptations
  • Habitat for Specialized Fauna
  • Flood Prevention
  • Peat Formation and Soil Fertility