Ecosystems - Succession and Key Terms

ECOSYSTEMS – a summary so far.... Key definitions / Concepts: 1. Definition of Ecosystems 2. Structure of Ecosystems: Biomass – above and below ground variations DOM (Dead Organic Matter) 3. Functioning of Ecosystems (2 main flows – Energy and Nutrients) a. Energy Flows Photosynthesis GPP and NPP Plant Productivity Trophic Levels Food Chains and Food Webs b. Nutrient Cycle Gersmehls model Nutrient Recycling Alteration of the Nutrient Cycle

Amount of energy produced – energy needed for respiration 6CO + 6H 2 O + light energy = Glucose and Oxygen The rate of energy fixation – i.e. rate of production of new tissue – highest where there is an abundance of light, warmth, moisture and where key nutrients are made available e.g. TRF The total mass of living organisms in a plant community at any one moment (expressed as a dry weight per unit area or kg/m 2 The loss by plants of water from the soil via the plant to the atmosphere Sequence of energy transfer in the from of food, from one tropic level to another These consist of living organisms and their physical and chemical (non-living) environments which are interdependent and interacting. Total amount of energy fixed / absorbed by green plants BIOMASS PHOTOSYNTHESIS FOOD CHAIN ECOSYSTEM NPP (Net Primary Production) PRODUCTIVITY TRANSPIRATION GPP (Gross Primary Production) HOW WELL DO YOU KNOW YOUR KEY DEFINITIONS…. Which go with which? BACK

4. EVOLUTION OF AN ECOSYSTEM Plant Succession Pioneer Species (Characteristics of….) Why does Plant Succession Occur? Internal and External Factors Sub-climax Climax Theories Regressive Climax Examples of Primary Succession: Hydrosere – Sweetmere ** Lithosere - Krakatoa / Suertsey ** (also see sheet on Isle of Arran) also read notes on psammosere / halosere (from AS) Plagioclimax Communities : Case Study - Heather Moorlands Key Terms – Plant Succession

Characteristics of Pioneer Species These are the first species to appear during succession (often herbs / grasses) – early invaders Quickly colonise on exposed / newly created surfaces where free of competition from others Well adapted / Hardy (tolerate extremes / harsh environments) Example – Marram grass – xerophytic – features include folded stem, shiny surface, long deep tap roots etc. Others may have root nodes containing nitrogen-fixing bacteria etc. Often short lived – then replaced by others that outcompete them as conditions improve Index Back

PLANT SUCCESSION Plant succession = long term change in a plant community as it develops from a bare surface to a climax community The evolution of a plant community takes place in stages – starting with the initial colonisation of a pioneer community through to the full climax vegetation. This whole series of stages / changes in plant communites is called a sere. At each stage in a succession (known as a seral stage ) there is a distinct community of plants which gradually change over time in response to changing environmental conditions. As each stage continues there are distinct changes: Structurally more complex – stratified Has more biomass Has greater number of species (biologically more complex) Greater NPP (Net Primary Productivity) Nutrient / energy flows increase Back Next

Intial colonisation of Bare rock (or area cleared by fire, flood, volcanic eruption, man) by pioneer species (e.g. weeds (garden) marram grass (dunes) algae (shallow ponds)) which will take up water and minerals. These are free of competition but do not last long. (what are the characteristics of pioneer species?) Decaying plant vegetation – creates humus from dead lichens and mosses. This creates more stability as a soil develops allowing greater humus and water retention. More minerals are now available e.g. nitrogen, potassium etc. Increased nutrients – means more competition between perennials and annuals – small shrubs and trees Climax vegetation – a stable community where annual growth and decay rates (biomass) are balanced and is in equilibrium with its environment Stages of Plant Succession Next…

A simple example of Primary Succession: Source: Greg O’Hare p.66 Soils, Vegetation and Environment Back to Index

Why does Plant Succession Occur? INTERNAL FACTORS: (also known as autogenic factors – changes in the environment bought about by the plant community itself – resulting in primary succession ) Initial colonisation – root action binds soil, prises away rock More plants prevent soil and wind erosion of the soil More vegetation adds organic matter – this holds water and nutrients – alters the conditions of the site and allows new species to colonise EXTERNAL FACTORS: (also known as allogenic factors – usually causes a change to the primary succession that has occurred naturally, resulting in a secondary succession ) Flooding, fire, volcanic activity Human factors e.g. grazing, deforestation, ploughing Back to Index

Sub-Climax At any point in the development of an ecosystem succession can be halted either temporarily or permanently by ARRESTING FACTORS. They can occur suddenly or gradually. This results in a sub-climax , where the plant community has been prevented from reaching its climax state (i.e. it is not in equilibrium with the environmental conditions). 1. TOPOCLIMAX – controlled by relief e.g. – landslide / volcanic eruption (e.g. Krakatoa; earthquake etc.) 2. HYDROCLIMAX – controlled by drainage 3. EDAPHIC CLIMAX – controlled by soil change – e.g. neolithic man (middle ages) – cutting down trees – soils become increasingly acidic – also Suertsey – salty wind – affected soil 4. BIOTIC CLIMAX – controlled by animals e.g. grazing goats (Mediterranean) 5. PLAGIOCLIMAX – controlled by man – e.g. grazing sheep on Welsh Mountains (man determining location); burning heather etc. see summary diagram of succession

Case study of Lithosere Succession: KRAKATOA Location: between Java and Sumatra Date: 27 th August 1883 Event: a volcanic eruption destroyed 2/3rds of the island a layer of ash 50m deep was left behind and all animal life was destroyed. BUT – rapid rate of recolonisation / succession Within 3 years – 30 species; 10 years – 64 species (savanna grassland and shrubs) and 25 years – thick forest (equatorial forest) How did species arrive? 60% by sea; 32% air; 8% by birds Why so rapid? High temperatures >28 o C and heavy rainfall (>2500mm p.a) – ideal conditions for plant growth (and decay to provide nutrients from litter for nutrient cycling) Volcanic soils quickly weather under these conditions and release nutrients Presence of nearby islands (for species dispersal) Good example of plant succession – BUT, many of plants arrived by chance (e.g. on driftwood – does NOT have as many vegetation species as climax forest on the mainland Back Surtsey example

Back to Krakatoa Notes Back to Index

Case study of Lithosere Succession: SURTSEY (and sub-climax) Surtsey – 1963 – a new island (climax vegetation = silver birch woodland) Covers an area of 2.5km 2 Slow colonisation – algae / fern and fruit spores (slower due to cooler conditions) Sources of colonisation: 1. Wind 2. Sea 3. Birds (seagull excreta acts as fertiliser) Sub-Climax – succession arrested due to salt spray and strong winds / heavy storms – developed a sub-climax vegetation of heath (moss, sedges, short willow) Back

Climax Theories MONO-CLIMAX THEORY It was in the 1930s that Clements et.al . put forward the belief that plant succession in any one region tended to up with a particular vegetation type – the climax vegetation. This climax vegetation had a fixed and predictable composition directly related to and in balance with the physical environment. It was believed that the climax vegetation of a region was dependent principally on one main factor – the climate (hence climatic climax community ) – this is known as the MONO CLIMAX THEORY POLYCLIMAX THEORY (sub-climax vegetation) Today we still recognised the importance of climate and its role in determining the climax vegetation is clearly true on a large-scale – e.g. tropical rainforest, desert etc. However, it has become increasingly recognised that the nature of a climax vegetation on a local scale will be determined by a lot of other factors (as well as climate) i.e. soil, relief, drainage, nature of parent rock, people / animal influence etc – this is known as the POLY CLIMAX THEORY Where vegetation is prevented from reaching its climatic climax vegetation due to the effect of a local factor, this is called a sub-climax. Back

Case Study: Succession in a Hydrosere (Sweetmere, Shropshire) B irch O ak Index 6 26 Number of Plant Species 18 10 Number of Plant Species 7.3 pH level 4.3 3.7 pH level A lder / Birch Woodland A lders Closed Wooded Fen W illows Open Wooded Fen S edges Marsh or Fen Bull Rushes Reed Swamp Algae & Lillies Open water

Case Study: Succession in a Hydrosere (Sweetmere, Shropshire) This shows the colonisation of freshwater by vegetation How does it change Type of species – Pioneer Species (algae / water lillies – submerged / floating) – then bullrushes rooted in water (flowering part above) then S edges, W illow, A lder, B irch and Alder, B irch, O ak (SWABBO) pH Changes – stars as freshwater – pH7 – becomes increasingly acidic as birch sees ground level rise above water table and an acid / peaty layer develops No of species – initially steady increase (6-26) but then decreases again as oak and birch develop Why does it change? Reason for change in type of species: As reeds develop – greater deposition of silt and clay – organic matter and nutrients increase and more species can develop – as this continues, by stage 5 and the growth of Alder, organic material has formed black mineral soil and earthworms are present (help aerate / mix the soil) (so at each level – more sediment trapped and increased depth of soil and rise in surface level – giving drier conditions) Reason for change in pH : pH changes as vegetation from Birch forms acidic soils Reason for change in species number : Above the water table, the canopy of birch and oak develops – this shades out the ground species therefore there are fewer of them – also fewer species can tolerate the increasingly acidic conditions Back Forward

REGRESSIVE CLIMAX This is where a disturbance causes the climatic climax vegetation to revert to a previous phase ( retrogressive succession ) It results therefore in the replacement of a community of plants of higher ecological order with a community of lower ecological order. This means that the community becomes increasingly simplistic with a lower biomass and a fewer species This may occur e.g. due to a change in climate. For example; increased frequency of drought will cause a decrease in plant productivity and diversity – this would be likely to result in the replacement of perennial species by annuals Overgrazing and a change a change in soil stability may also cause this – even if not a cause, soil deterioration tends to follow vegetation deterioration A regressive climax may be temporary although it may be permanent, this will be dependent on the extent of the disturbance. Back

PLAGIOCLIMAX COMMUNITIES PLAGIOCLIMAX COMMUNITIES – are determined by human activity These are where a plant community as either been stopped from reaching its full climatic climax or deflected towards a different climax by activities such as: Cutting down existing vegetation Burning (for forest clearance) Planting trees / crops Grazing / trampling by domesticated animals Harvesting of planted crops However it is bought about, a plagioclimax results in a community which is not that which would normally be expected in that area – if the human activity continues the community will be held in a stable position until the human activity stops. You must learn a case study of a Plagioclimax Community: HEATHER MOORLANDS Back

HEATHER MOORLANDS CASE STUDY (SEE HANDOUT SHEET) BACKGROUND TO THE PLAGIOCLIMAX The uplands of Northern England were once covered by deciduous woodland – removal of forests during the middle ages for timber / fuel / agricuture resulted in a detoriation of soils and heather became dominant – grazing and later muirburn (burning of heather) has kept Heather dominant See diagram of theoretical plagio-climax in post-glacial lowland Britain MANAGEMENT OF HEATHER MOORLANDS Burning Heather (along with heavy grazing has helped prevent regeneration of the forests and allowed the heather communities to remain stable): Sheep, cattle and grouse thrive on heather. The objective of burning is to keep as much heather as possible at its most productive stage (lots of edible green shoots) Burning carried on in small patches ~ 1hectare(often on a 10-15 yr cycle) – results in a patchy landscape Effect of burning – destroys old wood, releases nutrients as ash – can now be taken up by new shoots Burning also stimulates new growth A well managed heather moorland has a nutrient turnover that’s kept at its optimum. See diagram of STAGES OF HEATHER MOORLAND DEVELOPMENT If burning / grazing was to stop – the dominant heather vegetation wood soon be replaced by birch and pine and possible oak trees. Back

Back to Index THE PROCESS OF SUCCESSION Retrogressive succession NEW ORGANIC SURFACE PIONEER COMMUNITY CLIMAX VEGETATION SERE name given to the whole series of communities that develop during succession from the pioneer species through to the climax vegetation PRIMARY SUCCESSION Involving a series of seral stages A series of possible interruptions which may result in sub-climaxes BIOTIC (animals grazing – e.g. Goats) EDAPHIC Soil Change (e.g. neolithic man – feeling trees - change of pH etc.) PLAGIO (Man cutting, grazing, burning) HYDROCLIMAX (impeded drainage) TOPOCLIMAX (changes in relief – e.g. land-slide) REGRESSIVE CLIMAX

KEY TERMS – PLANT SUCCESSION The group of species that is in equilibrium with the climatic conditions The group of species that is best able to exploit the prevailing environmental conditions The long-term evolution of a plant community from initial colonising species to the climax community The group of plant species living together in an ecosystem The group of species that exist in an ecosystem as a result of the influence of human activity Plant succession in a freshwater environment Plant succession on a bare rock surface The group of species found in an ecosystem found in an ecosystem that has not yet reached a state of equilibrium with the environmental conditions or which have been prevented from doing so. Plant Community Climax Community Hydrosere Plant Succession Lithosere Sub-climax community Plagioclimax Community Climatic Climax Community Can you mix and match the key words to the definitions? Back Next set of key words / definitions….

KEY TERMS – PLANT SUCCESSION The name given to the whole series of stages from pioneer species through to climax community Vegetation Community distinct from the one before and after it Changes in the environmental conditions bought about by the plant community itself that results in primary successsion Change in the environmental conditions caused by an external factor (e.g. human activity, fire etc.) – likely to lead to secondary succession Where a climatic climax vegetation reverts to a previous phase This is succession taking place on land that has been vegetated before but has been disturbed back to an earlier state Sere Seral Stage Allogenic Factors Autogenic Factors Secondary Succession Can you mix and match the key words to the definitions? Back Regressive Climax

Nutrient cycle GERSMEHLS MODEL BACK

Soil nutrient release from litter decomposition input from weathered rock uptake by plants loss by leaching Biomass Litter

Biomass plant uptake fall out as tissue dies Litter Soil

Litter fallout as tissue dies input dissolved in rainfall loss in runoff release as litter decomposes Biomass Soil

Nutrient cycle BACK Remember the size of the circles and the arrows are proportional relative to each other. The size of the stores and flows varies with the type of ecosystem – you must know details of the nutrient cycles of a: FOREST BIOME and a GRASSLAND BIOME

Ecosystems - Succession and Key Terms

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