ECOSYSTEMS

STRUCTURE OF AN ECOSYSTEM:

The components of an ecosystem are categorised as either BIOTIC or ABIOTIC

• BIOTIC - means the living environment e.g. vegetation (living & decomposing) & mammals (insects, birds & microorganisms)
• ABIOTIC - the non-living chemical & physical components of the ecosystem e.g. climate, soil characteristics, underlying parent rock, relief of land, drainage characteristics

The physical environment (abiotic) provides the energy, nutrients & living space that plants & animals (biotic) need to survive.

Ecosystems are known as OPEN SYSTEMS, as energy & living matter can both enter & leave the system

Like any system, they have inputs, outputs, stores & flows

•  INPUTS - most important input is energy from sun, drives photosynthesis enabling plants to grow. Other inputs include animals from elsewhere, and water (by rain or rivers)
• OUTPUTS - nutrients are transferred out of the system in a number of ways - animals can physically move, water by rivers & evapotranspiration, throughflow & groundwater flow
• STORES - 3 main stores of nutrients are in vegetation, plant litter & soils
• FLOWS - within an ecosystem nutrients can be transferred from one store to another e.g. from soil to the vegetation through capillary uptake by plant roots

Within all ecosystems, nutrients are required for plant growth & are recycled from one store to another - e.g. leaves fall from a tree and decompose, returning nutrients to soil

The commonly accepted way of demonstrating the cycling of nutrients within the stores of a biome is by a Gersmehl diagram

• Inputs include nutrients such as carbon & nitrogen dissolved in precipitation & minerals from weathered parent rock
• Outputs include loss of nutrients from the soil by leaching & by surface run off
• Flows & transfers include leaf fall from the biomass to the litter, decomposition of little transferring nutrients to the soil, and uptake of nutrients from the soil by trees/plants

Trophic level: a feeding level within a food chain

• first level - primary producers

Succession & Climatic Climax

The composition of vegetation depends on the interaction between all the components that make up the environment (the plants habitat) - these include natural factors such as climate, relief & soils, and human influence through clearance, fires & livestock grazing

Plants will survive under suitable conditions, depending on environmental factors & competition. Plant populations vary from one area to another & become more complex over time - this change in plant community is known as a 'succession'

If allowed to contine undisturbed, succession will reach its 'climatic climax'

• Primary succession - occurs on surfaces that have had no previous vegetation e.g. lava flows, bare rock, sand dunes. 2 main types:
  • Xeroseres - formed on dry land (Lithoseres - bare rock Psammosere - sand dunes)
  •  Hyrdoseres - formed in water (Haloseres - salt water Hydroseres - fresh water)
• Secondary succession - follows the destruction or modification of an existing plant community - can occur naturally e.g. after a landslide, or through human activity e.g. deforestation

As a succession develops it passes through stages called 'sere's

Here the process of invasion, colonisation, competition, dominance & decline operate to influence the composition of the vegetation

• When plants first invade bare ground, groups of particular species become established
• These pioneer species are extremely hardy plants - adapted to survive in harsh conditions e.g. long rooted salt-tolerant marram grass on sand dunes
• Pioneers compete for available space, water, nutrients & light - and as they die, help to modify the habitat, adding organic matter to the developing soil
• can affect the microclimate of the area (wind speed at ground level, shelter, temp & humidity) and the soil conditions (organic content, nutrient recycling, acidity and water retention)
• the roots of pioneer plants help to break up and weather the surface - aiding soil formation

• as ground is improved by the creation of an immature soil - other plants able to colonise & change existing balance of species
• each stage of colonisation provides better conditions for plant growth than the previous one - so an increasing number of species is found
• addition of organic matter into soil (from decaying vegetation) improves its structure & water retention
• allows the growth of taller/more aggresive plants that are more demanding of water, nutrients & anchorage
• taller plants also provide shelter from the sun/wind - allows other plants to establish below
• at each stage there is a dominant species - these are the tallest plants & cover most ground

Overtime - period of relative stability is reached in which vegetation has reached its climatic climax, with dominants excluding rivals less suited to the current environmental conditions. Once the major dominants are in place, the number of species begin to decline

Community becomes 'closed' - saturation point has been reached. known as the 'Climatic Climax Community' - the natural vegetation having reached a stable balance with the climate & soils of the area

Some biogeographers believe that within one climate, local factors such as drainage, geology & relief can create variations in the Climatic Climax Community - known as 'Polyclimax Theory'

The temperate deciduous woodland is an example of a high-energy biome, with high productivity in relation to other global vegetation zones.

• found in the mid-latitudes, where there is adequate moisture
  • not found in the interiors of continents where patters of climate are more extreme
• In the British isle's, oak was orginally the dominant species in the lowlands - although as was common in some areas

Climate:

• average winter temp 2-7 C, summer 13-17 C
• total ppt 500-2000 mm y-1 throughout the year
• on-shore westerly winds dominate, moderating temps & bringing moist air
• low pressure weather systems dominate

Vegetation:

• Broadleaved deciduous trees - e.g. oak, ash, beech, birch. Oak dominates
• trees develop large crowns, broad but thin leaves
• shed their leaves in winter - reduces transpiration when less water is avaible
• as soil temps fall, tree roots can only absorb small amounts of water - growth is not fully developed/halts
• heat loss reduces transpiration & the demand for water in cooler months
• below canopy is shrub layer - smaller trees e.g. holly, hazel, hawthorn
• just above forest floor is herb layer - can be dense if enough light filters through shrub layer - made up of grasses, bracke, ferns & some flowing plants e.g. bluebell 
• epiphytes e.g. lichens & mosses grow on trunks/branches of trees

Soils:

• brown earth, fertile zonal soil aprox 1.5m deep dominates
• leaf litter accumulates in autumn - quickly decomposed following year by soil organisms
• soil well mixed by eathworms & other soil organisms - layers are indistinct
• Mild leaching occurs - particularly during autumn & winter when ppt exceeds evaporation

Plant succession can be stopped from reaching the climatic climax, or deflected towards a different climax, by human interference.

Resulting vegetation is known as a 'Plagioclimax'. Human activity that create plagioclimaxes could be:

• deforestation or afforestation
• animal grazing or trampling
• fire clearance

Example of Plagioclimax: sheep grazing on a moorland, preventing it from devloping into a woodland

Secondary Succession - one that develops on land that has been previously vegetated e.g. an area may have been cleared for farming but later abandoned - this land then becomes colonised in secondary succession

• the stages of secondary succession may be more rapid than primary succession as organic matter is already present in the soil - climatic climax will be reached sooner
• Secondary succession can also follow natural events such as change in climate, disease, a mud flow or volcanic eruption

An example of a Plagioclimax in the UK is a Heather Moorland. Many of the uplands in Britain were once covered by a climax vegetation of deciduous woodland, particularly oak forest

• Heather would have featured but only in small amounts
• Gradually the forest was removed for a variety of purposes
• As the soils deteriorated with the deciduous vegetation, hardy plants such as heather came to dominate the uplands.
• Sheep grazing became the major form of agriculture & sheep prevented the regeneration of climax woodland by destroying any young saplings of oak

Many of these uplands have been controlled by managed burning to encourage new heather shoots - burning has eliminated the less fire-resistant species, leading to the dominance of heather

• One of aims of burning heather is to ensure that as much as possible of the available nutrients is conservered in the ecosystem
• In many areas, heather is burnt on average every 15 yrs - if time gap is too long, their will be too much woody tissue, the fires will burn to hot & nutrients will be lost in the smoke
• If the burning does not contine, the heather moorland would degenerate, eventually allowing the growth of trees and a succession to woodland

In the tropical rainforest biome, due to constant high temperatures and rainfall, the vegetation grows more quickly than anywhere else

This produces the greatest amount of organic matter - referred to as 'Net Primary Productivity' (NPP)

Tropical rainforests are high energy biomes.

The greatest biodiversity exists within tropical rainforests which are believed to contain half the world's gene pool.

Tropical rainforests have been stable ecosystems for up to 100mill yrs

In their undisturbed state, they have continued to gain new species

The tropical rainforest biome circles the earth, mainly between latitudes 10 N and 10 S of the equator - occurs in the Amazon basin in S.America, the Democratic Republic of Congo & the Guinea coast of Africa, parts of southeast Asia, Indonesia & northern Australia

Climate:

• little seasonal variation - low pressure dominates throughout the year
• mean monthly temps of 25-28 C
• humidity remains high throughout the year
• annual ppt often over 2000mm - evenly distributed
• convection rain occurs most afternoons
• both day & night are roughly 12 hours long throughout the year

Vegetation:

• evergreen appearance due to year-long growing season
• forest has a 5-layer structure
• tallest tree's called emergents are up to 45m tall, above canopy
• upper canopy layer absorbs most of light & intercepts most ppt
• trees in constant competition for light, when a tree dies and falls, brings down others creating a small gap - trees take advantage and grow quickly to reach light
• trunks branchless under canopy - too dark for photosynthesis, saving energy for top of tree
• leaves are waxy, have drip-tips to help shed rain
• plants such as liana's grow on trees as there is insufficient light on forest floor
• tree roots spread out horizontally near or on the surface as nutrients are in top layers of soil only
• tallest trees developed buttress roots to support their great height - anchorage/stability

Soils:

• Latosoils or ferralitic soils dominate - red coloured, nutrient poor soils
• soils up to 40m deep - resulting from rapid chemical weathering due to hot weather climate
• leaching/eluviation occur due to moisture surplus; evapotranspiration exceeds ppt
• red colour from the accumulation of iron & aluminium oxides
• nutrient poor, thin humus layer despite rapid decomposition of litter due to equally rapid uptake of nutrients from soil by vegetation

Biodiversity:

• most diverse/productive biome on earth
• up to 300 species of tree per square km - including mahogany, teak, rosewood and brazil nut
• amazon rainforest has nearly 600 species of mammal, nearly 2000 species of birds, more than 1500 species of amphibians & fish
• scientists believe that some species are yet to be discovered
• threatened species include gorilla, chimpanzee & orang-utan, jaguar, parrot & toucan

Impact of human activity on Tropical Rainforest: Deforestation

Major issue. In some NICs tropical rainforests e.g. those in the Amazon basin in S. America are being destroyed at an alarming rate - claims that half of the worlds original rainforests have already been cleare (an area the size of the UK destroyed every year)

Climatic climax vegetation has been destroyed, resulting in both secondary succession & plagioclimax - the vegetation that eventually grows to replace the original rainforest tends to be smaller in height/less diverse; with reduction in overall biomass

Causes:

• increasing demand for hardwood for building/furniture,
• many developing countries rely on export earnings from timber;
• to provide land for rubber plantations, cattle ranches, soya plantations, roads & railways
• mining - vast resources of aluminium & iron under rainforests
• population pressure - rainforests located in developing world, increasing pop. - need room

Impacts of Deforestation on the Tropical Rainforest:

Can be physical, economic, social & cultural. Impacts mainly occur on local scale, but some can be global:

• plant species become endangered, food chain disrupted - some animals threatened by extinction e.g. tigers
• vegetation protects the latosoil from heavy rainfall - topsoil is left open to erosion & to leaching of nutrients/minerals
  • run off also causes the large amount of sediment to block river channels & increase flooding
• Microclimate of the forest is disturbed - daily water cycle of rapid evapotranspiration followed by afternoon ppt cannot occur as there is less cloud cover, so a greater temp. range
• Burning associated with forest clearance leads to local air pollution & contributes to climate change

Deforestation can have huge economic benefits in terms of income from mining, farming and exports. HOWEVER - the culture of indigenous people is destroyed & may be forced to move from their land

Urban areas contain a wide variety of habitats, including:

• industrial sites, derelict land, residential gardens/allotments, parks & other open green areas, transport routes (canals, roadsides, verges, railway embankments), waste disposal areas, urban forests & water bodies

This variety means its difficult to make generalisations about urban ecology - all these habitats contain different mixes of flora & fauna (Human impact also makes urban habitats unstable)

URBAN NICHES: - a small scale area or microhabitat within a area/town/city, providing a specialised environment for certain species. e.g mosses taking root & growing undisturbed on top of high walls/ledges 

Secondary succession will develop on any wasteland surface: e.g. concrete/brick will provide the initial surface for a lithosere (bare rock succession) & disued canals will allow development of a hydrosere

On an old industrial site, likely to be many different surfaces e.g. tarmac, concrete, rubble etc. - these differences provide small scale urban niches, and are called substratum variations - where several parallell successions take place

On this type of area, a Lithosere type succession would develop. The types of plants that can initially colonise here are influenced by:

• slope - on horizontal surfaces or gentle slopes, debris accumulates, eventually developing into a soil
• moisture available - on horizontal or gentle slopes, rainwater accumulates; on steep slopes faster runoff creates dry areas
• aspect - south facing slopes are warmer/drier
• porosity (ability to hold water) - surfaces that can hold water colonise quicker
• surface roughness - allowing plants to get a hold; glass/metal too smooth for most plants
• pollution levels - depend on previous use of site; substances that are toxic to plants e.g. lead, may contaminate ground

The succession on an abandoned industrial site for example, would occur as follows:

• Stage 1 The Pioneets - mosses/lichens are first to develop on bare surfaces 
  •  able to exist in areas of little water, obtaining nutrients from photosynthesis & bare concrete. Concrete is slowly weathered by production of acids
  • when plants die, provide a thin mat of organic matter which, mixed with the weathered mineral matter, produces a protosoil for other plants too root into
• Stage 2 Oxford Ragwort - cracks in surface provide sheltered place for seeds to germinate & also retain moisture & dust which helps plants too root
  • most common invaders are plants with windblown seeds e.g. oxford ragwort (long flowing season - produces millions of seeds)
  • known as Ruderal species - able to tolerate waste ground, rubbish & debris
  • plant succession at this stage is rapid
• Stage 3 Tall herbs - as these ruderal species die off, produce thicker/more nutrient rich soil - taller plants can become established/
  • Rosebay Willowherb common - spreads initially by seed then by rhizomes (horizontal underground root systems
  • Others include - Fennel & Goldenrod. These plants gradually shade out smaller plants, stopping them photosynthesising

• Stage 4 Grassland - as soil enrichment continues, amount of grass in vegetation increases
  • smaller meadow grasses of earlier stages are replaced by taller species
  • at this stage, area takes on the appearance of a grassland containing scattered clumps of tall herb
  • one invader includes Japanese Knotweed - can grow up to 3m high, dense canopies shade out most species beneath
• Stage 5 Scrub Woodland - as process of soil enrichment & competition continue, taller herb plants replaced by shrubs & eventually trees
  • early woody plant colonists (e.g. birch, grey willow) all possess light, windborne seeds - but when herb vegetation thickens, becomes difficult for these to establish
  • Later trees have larger seeds that can enter closed vegetation e.g. sycamore, hawthorn
  • dense areas of bramble & other scrubby plants develop - able to compete as can grow roots into deeper crevices in rock/concrete

As the plant succession develops, there are changes in the Fauna. Soil fauna e.g. earthworms, increase in numbers as soil improves. Increase in number/diversity of insect population                              - provides food for small mammals, then allows for the presence of predators such as Kestrel & Fox      - arrival of trees may also bring squirrels , feeding on available nuts/seeds



Routeways are distinctive habitats as exotic species of plants & insects may be brought in by traffic - also provide wildlife corridors for species such as foxes, comparable with hedges in rural areas

Railway lines - windbourne seeds can be sucked along by trains, allowing the establishment of plants such as Oxford Ragwort. As the track is fenced off, a lack of human interference encourages wildlife such as badgers & urban foxes, and bramble-filled areas provide nesting sites for a variety of birds

Roads - act in a similar way. Provide homes on verges & embankments for kestrels & scavenger birds. Nitrogen rich exhaust fumes boost the growth of some wild flowers, and these then increase the presence of insects and animals further up food chain HOWEVER some roadsides are now managed e.g. by mowing/planting trees, shrubs, flowers.

Canals - act like long ponds, providing habitat for a variety of equatic plants (e.g. yellow flag iris), waterfowl (e.g. ducks, kingfishers) & water insects e.g. dragonflies

Routeways have introduced exotic species such as 'Buddleia' into many gardens & have spread to open spaces - Japanese Knotweed has also been spread, but is problematic as its invasive, resistant to pesticides and difficult to get rid of once its started to colonise

Many of the plant & animal species found in urban areas are recently introduced - relatively few native species. Cities are centres for the establishment & spreaf of foreign species.

Such species could have been introduced by:

• escapes from gardens
• brought in by collectors or amateur gardeners
• wind-blown seed
• seed carried by animals & transport

Urban areas are attractive for immigrant species due to the variety of habitats, the constant creation of new habitats & the reduced level of competition

Gardens (private/public), allotments, parks, cemeteries, playing fields and school property are all areas where the vegetation is managed.

Species are introduced, many from overseas, and others are removed or controlled by mowing, weeding or the use of pesticides or herbicides. 

•  e.g. sports fields reduce the diversity of plant species by maintaining grass pitches where once there were meadows with a variety of plants

Other reasons for management:

• altruistic motives - giving dull urban landscape more colour, improving asthetic value
• improving visual outlook - hiding eyesores to encourage buisnesses or residents to move in
• schools may produce a diverse environment for educational purposes
• local buisnesses may want a pleasant site to attract customers
• groups such as birdwatchers may wish for a diverse environment to attract new species
• to act as noise & pollution barriers
• to provide shade
• to reduce soil erosion on embankments

The rural-urban fringe is the countryside immediately surrounding towns & cities

• home to a wide range of activities/residents - seen as attractive location for developments e.g. buisness parks, airports, theme parks, and high cost housing
• Other pressures for development include the need for improved transport networks, landfill sites and sewage works
• In S.E England alone, 500,000 new homes are needed over the next 25yrs
• Although the fringe is under pressure from development, many such areas in the UK are designated green belt, with regulations that strictly control new development
• Open countryside in the fringe is often degraded - farmers face problems from fly-tipping, illegal camping, trespass and vandalism
• Secondary succession may begin on untended fields - weeds, thorns, brambles
• Despire lack of investment, land values often high due to speculation regarding future development - there is a belief that derelict, unkept land is more likely to gain planning permission

However - recent government policy is in favour of sustainable development of the rural-urban fringe & the recycling of derelict/degraded lang e.g. through planting of woodland, to improve the local landscape

Many urban areas have seen the introduction of 'country parks' on the fringe - relatively unmanaged, harbour more natural plant communities, providing potential breeding sites for bird species etc

Conservation areas are developed for a variety of reasons. Some include:

• encouraging wildlife back into cities
• making cheap use of a derelict area that would be more expensive to set up as a park
• reducing maintenance cost in an area
• maintaining a diverse species base and reintroducing locally extinct species

Work done in these areas includes planting of trees, planting of native species, dredging ponds & other water bodies & soil improvements

There is a range of attitudes towards conservation of vegetated areas in urban environments -

•  local authorities have planning needs, have to balance desire to make use of derelict land against potential cost to local taxpayers
• Conservation groups want to create environments where traditional species can re-establish
• local people want safe environment for leisure persuits

Issues of conservation include: the management plan for area, the resolution of owenership & cost/satisfaction of the needs of various groups

Dulwich Upper wood is in S.E London. The park is open at all times & has a network of trails

Species in the Wood:

• the wood was developed from abandoned gardens of old victorian houses & a small core of ancient woodland
• trees include sycamore, oak, ash, yew & chesnut
• as most of ground is shaded, few of the garden plants remain
• plants from the ancient woodland have survived including lords & ladies, bluebell and yellow pimpernel
• over 250 different types of fungi - live on dead wood or leaf litter helping to break down the materials & return nutrients to soil
• many mammals such as foxes, bats, mice & hedgehogs, live in the wood
• more than 40 species of birds nest here
• also butterflies, moths & variety of other insects

• conservation of both abandoned Victorian gardens & ancient woodland
• a number of both preserved and re-created habitats including wet areas, herb garden & foxglove area
• the site is both managed & allowed to grow wild in different areas
• there is a range of different habitats
• there is plenty of wildlife on the site
• 'original' habitats have been preserved, enabling native species of plants & animals to survive
• good example of how habitats can be preserved and created, and yet still allow the public access through a network of trails
• the site has an educational value with a posted nature trail

HUMAN ACTIVITY, BIODIVERSITY & SUSTAINABILITY:

Human activity is important because it can modify the natural environment, with both positive & negative impacts

In 2005, the Millennium Ecosystem Assessment