Succession Syllabus

1. Succession Syllabus • 2.3.5 – Describe the concept and processes of succession in a named habitat. • 2.3.6 – Explain the changes in energy flows, gross and net productivity, diversity and mineral cycling in different stages of succession. • 2.3.7 – Describe factors affecting the nature of climax communities.

2. Ecological succession • The gradual process by which the species population of a community changes is called ecological succession. • A forest following a disturbance such as a fire. • Succession takes places as a result of complex interactions of biotic and abiotic factors. • Early communities modify the physical environment causing it to change. • This in turn alters the biotic community which further alters the physical environment and so on.

3. Succession – What happens? • Each successive community makes the environment more favourable for the establishment of new species. • A succession (or sere) proceeds in seral stages, until the formation of a climax community is reached.

4. Primary Succession • Refers to colonization of regions where there is no pre-existing community. • Can you think of examples where this would occur?

5. Primary Succession • Community changes on a glacial moraines • After a volcanic eruption

6. Questions – Glacial Moraines • During succession there is a change in species composition of a community. There are also changes in species diversity, stability of the ecosystem, and in gross and net production until a climax community is reached. • Explain what is meant by a climax community. • Explain each of the following changes which occur during succession: • Species diversity increases • Gross production increases • Stability of the ecosystem increases • Give two reasons why farmland in the UK does not reach a climax community.

7. Primary and Secondary Succession • Primary Succession – occurs on newly formed habitats that have not previously supported a community. • Examples? • Secondary Succession – occurs on sites that have been disturbed. • Examples?

8. Primary Succession – Bare Rock Mosses, Grasses and small shrubs Lichens, bryophytes and annual herbs Bare Rock After 100-200 years Fast growing trees e.g. Ash Slower growing broadleaf species e.g. oak Complex Community Example for a Northern Hemisphere lithosere: a succession on bare rock

9. In Summary - the 1st Invaders! • These are usually fast growing plants that photosynthesize well in full sunlight. • We call these pioneer species making up the pioneer community • Examples = lichens, grasses, herbs • As these species begin to grow well, they produce shade. Their own seedlings grow more poorly than shade-adapted plants. • Plants that grow well under full sun are replaced by plants that germinate and grow better in deeper shade.

10. Secondary Succession • This type of succession takes place after a land clearance (e.g. from fire or landslide). • These events do not involve loss of the soil. • Secondary succession therefore occurs more rapidly than primary succession. • Humans may deflect the natural course of succession in these circumstances (e.g. by mowing or farming). • This leads to the development of a different climax community than would otherwise develop naturally.

11. Secondary Succession – Cleared Land Open pioneer community (annual grasses) Primary Bare Earth Grasses and low growing perennials Time to develop: Years 1-2 3-5 Young broad leaved woodland Scrub: shrubs and small trees 16-30 31-150 Mature woodland: mainly oak 150+ = climax community

12. Succession Continues • As the plant community changes, the soil will also undergo changes (abiotic factors will change). • Decomposers will join the community as well as animal species. • Animal species have a profound affect on the plant species occurring within a habitat. • Changing conditions in the present community allows for new species to become established (the future community). • Succession continues until the climax community is reached.

13. Wetland Succession • Wetland areas present a special case of ecological succession. • Wetlands are constantly changing: Open water Plant invasion Siltation and Infilling • Wetland ecosystem may develop in a variety of ways:

14. Wetland Succession • In well drained areas, pasture or heath may develop as a result of succession from fresh water to dry land. • In non-acidic, poorly drained areas, a swamp will eventually develop into a fen. • In special circumstances, a an acid peat bog may develop. (may take 5000+ years).

15. Productivity • Think back to the work on food webs/chains • It is often useful to know how much energy is passing through a trophic level over a period of time. • This is called productivity • Productivity is a measure of the amount of energy incorporated into the organisms in a trophic level, in an area, over a certain period of time.

16. Productivity • The area is normally one square metre and the time is usually one year. • It is therefore measured in units of kilojoules per square metre per year (kJ m-2 year-1) • The rate at which producers convert light energy into chemical energy is called primary productivity.

17. Gross Productivity • Gross Productivity (GP) – is the total gain in energy or biomass per unit time. • This is sometimes shown as GPP – Gross Primary Productivity • It is related to the total amount of chemical energy incorporated into the producers. • The producers use some of this energy during respiration and energy needs which is eventually lost to the environment as heat. • The remaining energy is available to the herbivores and is known as net primary productivity (NPP)

18. Remember • NPP = GPP – R • Net Primary Productivity = Gross Primary Productivity - Respiration

19. NPP and GPP in Succession • The NPP and GPP of any ecosystem is going to fluctuate. This is especially the case during each seral stage. • As ecosystems become more diverse, the overall GPP is also going to increase. • This is because climax communities are better adapted to an efficient rate of utilisation of their resources.

20. The Early Stages • Gross Productivity = Low • This is due to the initial conditions and the relatively low density of producers. • Net Productivity = High • This is due to low respiration rates of the initial producers and therefore a lot of energy available to be passed on. • This allows the system to grow and biomass to accumulate.

21. The Later Stages • Gross Productivity = High • This is due to an increase in the consumer community who can synthesise a lot of energy from the food they eat. • Net Productivity = Low • Increased rates of respiration and other energy sapping activities by consumers means that NP will begin approaching zero.

22. Climax community • The P:R ratio approaches zero. • The productivity : respiration ratio approaches zero • Think about it: • NPP = GPP – R • “0” = high value – high value

23. The Climax • Succession comes to an end with the establishment of a mature, relatively stable community – the climax • Climax communities are more stable that the seral stages that preceded them. • Ultimately, the climate will be responsible for affecting the nature of the climax community unless human or other factors maintain an equilibrium at a sub-climax community.

24. Climax Communities • The major factor affecting the formation of the climax community is the climate: temperature and humidity. • Edaphic Factors, such as components of the soil or the presence of toxic substances also affect the formation of the climax community.