Skip to main content
It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.

A-level Geography - Ecosystems: Change and Challenge: Ecosystem issues on a local scale

The impact of urbanisation on ecosystems

Urbanisation means an increase in the proportion of people living in towns and cities compared to rural areas. Urban areas now house well over half of the world's population/ As a result, ecosystems in these built-up areas are rapidly changing in response to human activities and changes to local climates, water supply and air quality.

Within an ecosystem all living organisms occupy a niche. Their niche is the place where they live (their habitat) and how they interact with other species (their role in the ecosystem). Changes in local ecosystem resulting from ubanisation create a variety of urban niches.  

Living in an urban ecosystem can provide challenges for wildlife. Here are just some of the problems which might have to be overcome

  • Large areas of soil are covered by impermeable materials which interrupts the flow of water through the ecosystem.
  • Pollution levels may be high.
  • Plant roots often encounter physical barriers.
  • There are changes in microclimate e.g. increased temperature and changes in light.
  • Sites might be temporary. There is often a high degree of disturbance of the soil and surface plants.
  • Alien species (ones which wouldn't naturally be found in Britain) are often introduced. Similarly others like stinging nettles (not liked by some humans) may be removed.
  • Many habitats are isolated and small. This may make it difficult for species to colonise new sites or to complete their breeding cycle. 

Changes in ecosystems resulting from urbanisation

Tower Hamlets Cemetery Park , London
(Source: www.panoramio.com)

By the mid 1960s many public cemetries in UK were effectively abandoned due to the lack of money for long term maintenance. However, these sites are of great importance not only for their historical and social interest but as a very important contribution to the green space in urban areas. Many offer a wide variety of wildlife habitats and have a high biodiversity. They can provide important sites for education about the environment and recreation.

Using Tower Hamlets Cemetery Park as an example, it was badly neglect in 1960s, but today it is one of the largest areas of woodland in east London and become a valuable community asset.

How is the cemetery managed today?

  • The amount of sycamore has been reduced, woodland clearings created and a variety of native trees and shrubs planted. This all helps to increase biodiversity.
  • For example, the population of speckled wood butterflies has risen in response to an increase in light on the woodland floor.
  • Public access has been encouraged by restoring pathways, installing benches and putting in wheelchair access. 
  • An informal education programme (e.g. guided nature walks and woodland craft days) help to promote local interest.
  • The education centre (the Soanes Centre) provides more formal education facilities for local schools.


(Source: www.field-studies-council.org)

Secondary succession in an abandoned car park

Stage 1 - pioneers

This open habitat is exposed to extremes of weather conditions, such as large fluctuations in temperature, exposure to drought and strong sunlight. Soil is present between the stony material but is hard and compacted. The first community to colonise the aggregate therefore contains plants and other organisms typical of a pioneer community like mosses.

Of particular interest is the presence of the blue green alga Nostoc. This species shows all the characteristics of a pioneer coloniser and can also fix atmospheric nitrogen. 

Stage 2 - grasses and flowering plants arrive

Mosses have increased in abundance. Their presence helps to retain water in the substrate and trap plant debris. More food is now present for consumers and decomposers so that the rate of soil formation is speeded up. Already a few grasses and seedlings of other flowering plants can be seen.

Stage 3 - grasses and flowering plants dominate

Grasses and other flowering plants are now dominating the site and shading out the pioneer moss species. Large perennials (plants which live for several years), like the thistles, are beginning to colonise the site.

Stage 4 - perennial plants dominate

Large clumps of perennial grasses which persist from year to year now cover the site and other perennials like the thistles are also common. The moss community is now made up of species adapted to living beneath the grass sward where, although there is less light, conditions are more humid and climatic conditions in general are less extreme.

Stage 5 - woody plants invade

Brambles have begun to invade the site from neighbouring disused areas. Their long arching shoots develop roots and form new plants wherever they touch the ground.

Stage 6 - trees

Bramble is likely to become the dominant plant on the site in the near future. If the site is left undeveloped for long enough trees (such as sycamore trees) may eventually colonise.

Ponds, ditches and wetlands are valuable, and often rich habitats supporting a wide range of wildlife including invertebrates, amphibians, plants and many birds and animals. Throughout the UK ponds have declined due to pollution, drainage, infilling of farm ponds, and development and industrialisation of areas that were once open countryside.

All ponds silt up over time and this can reduce the amount of open water available and allow the pond to dry up. By having lots of overhanging vegetation at the pond, leaf fall can add to the rate of siltation as would the deposition of grass cuttings within a 6m distance from the water. If the pond area is not managed it will, over time, naturally dry up due to vegetation build up and silting. To maintain as great a diversity of habitats as possible it is recommended this area be managed to prevent succession to a dry woodland area.

Click toexplore wildlife in different wetland centres in UK!

 

Visit Arundel

Arundel
West Sussex

 

Visit Caerlaverock

Caerlaverock
Dumfriesshire

 

Visit Castle Espie

Castle Espie
County Down

Visit Llanelli

Llanelli
Carmarthenshire

Visit London

London
barnes

Visit Martin Mere

Martin Mere
Lancashire

Visit Slimbridge

Slimbridge
Gloucestershire

Visit Washington

Washington
Tyne & Wear

Visit Welney

Welney
Norfolk


(Source of images: www.field-studies-council.org)

Wasteland habitat is unmanaged land characterised by vegetation in the early stages of succession, from a thin covering of pioneer plant species through to dense swards of tall herbs with the occasional shrub or small tree.

Wasteland is particularly associated with inner city areas, though it is found in all but the most affluent parts of a town, and includes unused or vacant land such as areas of former industrial or mining land; abandoned factories and other large building areas such as demolished houses; and former railway land such as sidings and disused trackways. 

This kind of wasteland often represents a temporary land use since many such areas are scheduled to be re-developed for other uses. Where there is no change in land use wasteland will often develop through succession into other habitat types, e.g. grassland, scrub and woodland.

Wasteland can also include corridor habitat such as cuttings and embankments associated with railway tracks and some urban roadsides.

Wasteland sites have an intrinsic value to local and regional biodiversity and conservation, and with low levels of care many could be turned into sites of importance for local communities.

Watch the following video to see how a derelict site of Union Street was transformed into an imaginative pop-up community garden.

Click play button to start. Click bottom right for captions. Click link below to view in full size.

(Source: www.bbc.com)

A private garden can provide a wide range of habitats for plants and animals. Gardens occupy a significant amount of space in the average British city (e.g. 20% of London). It is important to help people understand how gardening can be linked not only directly to wild life and its conservation but to many other environmental issues (e.g. reduction in water, noise and air pollution). Private gardens will play a key role in helping to maintain the richness of wildlife (biodiversity) in the urban ecosystem.

To attract wildlife the garden has to provide food, water, shelter and breeding sites. Some general guidelines:

  • Don't be too tidy otherwise you might remove places for animals to shelter in and potential food resources
  • Make sure that there are a large number of native species providing good nectar sources and food in other forms e.g. berries throughout the year
  • Even if there is not space for a pond a washing up bowl sunk into the ground can provide a source of water
  • Make sure you do not disturb potential breeding sites e.g. by cutting hedges at the wrong time of year
  • Avoid using chemicals. As in any habitat there are complex feeding relationships between the animals and plants in a garden. 

Isight into a unique 2 acre nature reserve in the heart of London.

On the disused car park the habitat is initially unsuitable for most of the flowering plants. These need a soil which their roots can penetrate to obtain water and mineral salts. The first stage in the succession is therefore dominated by mosses and algae, very similar to the pioneer community which is found in a primary succession. On the allotment soil conditions are ideal for the flowering plants and the sites are rapidly dominated by them.

Stage 1 - invasion by annual weeds 

unweeded beetroot bed

This beetroot crop has not been weeded for about 10 months.

Annuals (plants which complete their life cycle within a year) such as the common field-speedwell (Veronica persica) and cleavers (Galium aparine) have rapidly spread over a site competing with the beetroot plants for space, light and mineral nutrients.

Such successful weeds typically produce large numbers of seeds and have efficient seed dispersal mechanisms. Their seeds are also able to survive in the soil for long periods of time.

common field-speedwell

A successful annual weed: the common field-speedwell (Veronica persica).

Two generations of plants may be produced in a year and a large plant can produce up to 7000 seeds. Some seeds may survive in the soil for up to 20 years. This plant can also grow from stem fragments left after weeding. 

Stage 2 - colonisation by perennials

nettles

Longer living plants (biennials and perennials) like the bristly oxtongue (Picris echiodes ) and broad-leaved dock (Rumex obtusifolius) do not usually flower in the first year but grow rapidly their underground parts surviving through the winter.

By the second year they will usually be shading out both the crop and the first annual colonisers. Many of the perennials are also able to spread rapidly by means of creeping underground shoots (rhizomes). 

Stage 3 - establishment of woody trees and shrubs

blackthorn spreading

Bramble is often an early shrubby coloniser, spreading in from surrounding areas by means of its arching shoots which root wherever they touch the ground. Blackthorn can be seen spreading by means of underground suckers from the hedge.

Slower growing woody shrubs and trees will eventually become established. Although soil conditions would have allowed these woody species to colonise early in the succession the timing of their arrival is dependent on the availability of seed and the ability of seedlings to compete with already established perennials.

 

Tree plantings in streets, parks and royal parks are the core part of urban forestry programs. They are used not only for aesthetic and environmental reasons but also to provide health benefits to urban and suburban communities. The public health benefits of trees are direct and indirect. Direct benefits include clean air, clean water, protection form harmful UV rays, and the positive psychological effects associated with the proximity of natural environments. Indirect benefits include a more active lifestyle linked to increased outdoor activity. The 5,000 acres of historic royal parks provide unparalleled opportunities for enjoyment, exploration and healthy living in the heart of the capital. 

However, trees are constantly under threat due to urbanisation. Large areas of trees may be lost when land is developed or roads are widened, while individual trees can be harmed in many ways such as high levels of air pollution, excessive use of salt on roads, over-pruning, low nutrient levels due to the removal of dead leaves, etc..

When making decisions about whether to protect or plant trees urban planners need to make sure that the benefits outweigh the disadvantageous costs. Different kinds of trees also vary in their characteristics and this must be taken into account in when choosing species and deciding where to plant them.

Changes in the rural-urban fringe

Land-use changes in the rural-urban fringe have both negative and positive effects on ecosystems. Urban sprawl destroys natural habitats (woodland, meadows, ponds, etc.) with concomitant losses of wildlife. Planning strategies such as green belt have failed to stop urban sprawl. According to the Council for the Protection of Rural England roughly 110 km2 of green belt land has been lost each year since 1997. Other threats to wildlife in the rural-urban fringe include dog walking, wind turbines, landfill sites and vandalism.

Developments can damage the ecosystems and quality of farming land in many ways. Impermeable surfaces increase run off leading to the creating of bogs in low lying areas and compaction of the soil reduces the growth of plant roots and capacity for water to infiltrate through the soil. Acidation of the soil from pollutants during construction also reduces the nutrients available.

Positively, many local authorities and other organisations have created conservation areas in the rural-urban fringe. Old mine workings have been reclaimed and re vegetated in former coalfields; gravel pits and sewage beds have been converted to wetland habitats; country parks have been established; and nature reserves set up, managed by wildlife trusts, local authorities and other conservation bodies. In Moors valley, south east England, government scheme has created a wildlife corridor and recreational space that attracts tourists, important to the local economy.

Ecological conservation in urban areas

Ecological onnservation areas are locations which receive protection because of their recognised natural, ecological and/or cultural values. The aim of ecological conservation areas is to protect and restore nature ecosystems. In protecting species and their habitats, ecological conservation areas support the biodiversity of an area. The management of these areas involves sutainable development and the use of natural and human resources. For example, conservation areas will often include recreation spaces and many provide routeways such as cycle paths. Other reasons for development ecological conservation areas include:

  • improving the appearance of an area
  • stimilating investment to encourage tourism or the return of industry
  • providing educational functions such as nature walks or wildlife gardening
  • providing multi-purpose spaces 
  • managing flood risk, for example, reducing the impact of reviver bank erosion by afforestation
  • maintaining rich biodiversity bt protecting native species

Conservation areas tend to have very limited budgets and are typically viewed as a low-cost management solution. Their success depends on engaging local communities and making use of volunteers

Ecological conservation Singapore case study - Labrador Nature Reserve

(Original source: www.nparks.gov.sg)

Labrador Nature Reserve is located in the southern part of the main island of Singapore. It contains the only rocky sea-cliff on the mainland that is accessible to the public. Since Jan 2002, 10 hectares of coastal secondary vegetation and its rocky shore have been gazetted as a nature reserve.

Labrador has representatives of several major intertidal ecosystems: natural rocky shore, seagrass areas, coral rubble and coral reefs. A path built on the edge of the secondary forest provides a prime view of the cliff side vegetation coupled with a panoramic view of the sea. It is not uncommon to hear songs of a variety of bird species, including the oriental magpie-robin and black-naped oriole. While you are taking a leisurely stroll along one of the nature trails, you can spot squirrels scurrying up trees.

Flora and Fauna
Labrador Nature Reserve has a rich variety of flora and fauna that will delight nature lovers. More than 70 kinds of birds, including the blue-crowned hanging parrot, the rufous woodpecker and Abbott's babbler, have been seen here. Tree species like symplocos adenophyllasyzygium grande (Sea Apple), rhodamnia cinerea (Silverback),Ixonanthes reticulate can also be seen.

Some 60 bird species, 19 fish species and 14 true mangrove plant species have been recorded here. Some 11 species of butterflies have also been recorded. Birds, spiders and thousands of insects, some too small to be seen, all have their functions in keeping the rich forest a self-perpetuating habitat.

War Relics
The Reserve is also famous for its many historical sites of WWII bunkers and other relics. The history trail with lots of informative signs captures the history of the fort and the war where visitors can view a casemate (war bunker) and tunnels in the Reserve. 

Being the last mainland rocky shore and reef with rich biodiversity and history heritage, Labrador shore is often studied by students of all ages.

Urban niches: colonisation of wasteland

When a building is demolished in an urban area, the land is quickly colonised by plants and animals. In any habitat, including urban habitats, a successful plant or animal needs to to be able to go through two stages:

Stage 1: Dispersal 

Although plants are not obviously mobile, they are still able to spread to new sites. They can do this EITHER by spreading their seeds and spores OR by vegetative reproduction. Seeds and spores can be self dispersed or use the help of animals, wind and occasionally water.

Stage 2: Getting established on site

Once plants and animals have arrived, they need to become established on site. Both plants and animals must avoid being eaten and compete for resources. Competition in plants will be mainly for space, light, water and minerals whilst animals will be competing with other species for food, shelter and nest sites.

The first species to colonise are pioneer species which are tolerant of low moisture availability and lack of nutrients. These include lichens and mosses which live in cracks where moisture is more available and live of nutrients from the bare surface and through photosynthesis. This colonisation usually takes 1-3 years. The next stage which occurs over 3-6 years is the introduction of Oxford ragwort by seeds carried on the wind or invasion form a close-by site. The level of nutrients has increased allowing more such species to colonise however vegetation still grows in crack to offer protection and moisture. 

The next stage between 8-10 years pioneer species starts to become shaded out by taller species of grasses. This creates a nutrient layer of humus allowing more complex plants to colonise such as rose bay willow herb. As competition increases plants colonise through windblown seeds and rhizomes under the soil which can grow up to 1m per year. As nutrients increase worms are introduced and taller species replace smaller ones. Grasses weeds and bracken start to appear including Japanese knotweed. If left for enough time birch, willow and alder trees may become established which are able to survive on poor soil conditions, as well as rowan, hawthorn and sycamore.

Urban niches: the planned and unplanned introduction of new species

g

 

The planned introduction of new species 

Result from introduction to a garden for example urban areas have a vastly higher numbers of exotic plants than rural areas. For example some species that have been introduced are the Canadian golden rod, sycamore, laburnum and wormwood from Europe and Japanese knotweed – now Britain’s most invasive species. The London plane tree has also been introduced in London to create a less urban feeling environment. 

The unplanned introduction of new species 

Unplanned introduction of species has come from seed dispersal by the wind as well as animal’s birds and transport. Oxford ragwort was one of the examples:


Benefits and negatives

The positive effects are that some species may benefit local wildlife becoming an alternate source of food allowing particular species to flourish; they may not be competitive with native species such as corn and tomato. However, species such as Japanese knotweed form Japan has become Britain’s most invasive species and its presence is growing, causing problems especially in conservation areas such as Troopers Hill where habitats are very sensitive. The introduction of species can also be detrimental to local wildlife, as has been suggested by Oxford ragwort which in large quantities could cause damage to horse’s health.

 

KEY ALIEN INVADERS

info-graphic           Plants

  • Rhododendron
  • Japanese knotweed
  • Himalayan balsam (pictured)
  • Giant hogweed
  • Floating pennywort

 

Introduction of new species case study - Japanese knotweed

Where has it come from?

Japanese knotweed is a large, herbaceous perennial plant of the family Polygonaceae, native to Eastern Asia in Japan, China and Korea. Introduced in the early 19th century in Europe as a garden plant, Japanese Knotweed was starting to be highlighted as a pest by the beginning of the 20th century.  Now widespread across the whole of Britain, it is rarely absent from the urban environment.

Why is it so invasive?

Japanese knotweed grows extremely quickly. It grows over 6 feet in first couple months of spring, shading out all other species around it. Even when the visible parts of the plant are cut away, the rhizomes sustain it, making it extraordinarily persistent. It can withstand almost all types of soil, light, and drought conditions. Rhizomes will survive to grow plant even if buried 3 feet deep, or under asphalt. It forces out native plants through shade and thick ground cover, damages wildlife habitat by reducing plant biodiversity. It is also expensive to treat, aesthetically​ displeasing and causes damage to sidewalks and pavement. It is listed by the World Conservation Union as one of the world's worst invasive species. The cost to eradicate it in Britain using conventional methods was estimated to be £1.56 billion.

How is it managed?

Thoroughly digging out roots and stems takes years to succeed, if it ever does -- if even a tiny speck of stem remains, the plant will regenerate. It is vital to burn or otherwise properly dispose of the plant scraps -- it can ruin a compost pile. It takes a minimum of three years to get rid of it, either by cutting away to the stems and treating each stem with an herbicide such as Roundup or by covering the ground with black plastic and heating the soil to the point where the rhizome dies. The shoots can be eaten by grazing animals, but this doesn't eradicate the plant, only control it. Types of biological control agents (BCA) are being studied; it is known that there are many insects and fungi which control the plant's spread in its native range, so prospects are hopeful 

Ecological conservation UK case studies

Dulwich Upper Wood is a 2.4 hectare Local Nature Reserve (LNR) south of Dulwich Village adjacent to the Crystal Palace parade on Farquhar Rd. Dulwich Upper Wood is managed by the Trust for Urban Ecology since 1981 as a nature reserve, educational facility, research area and a place of recreation, with grant aid from the London Borough of Southwark. Dulwich Upper Wood is home to a project to conserve the increasingly rare Stag beetle.

The site has some lovely old oaks and other species of trees, some of which are upwards of 350 years old. The wood also has some important species of plants, fungi and insects that give it associations with Ancient Woodland. An interesting locally rare plant is Ivy broomrape (Orobanche hedera) that was found on the site in 1997 and is totally parasitic on Ivy and is only observed when the spike of pinkish/yellow orchid-like flowers appear in summer. Two species of rare fungi were recorded in the autumn of 2010 - Sowerbyella radiculata var. kewensis and Geastrum striatum (a form of earth star) adding to the list of 350+ species recorded on the site. 

In the 1600s, Trooper Hill was part of a large royal hunting forest. In the late 1700s, the tall chimney on top of the hill was used for copper smelting and later, in the 1800s, coal and fireclay were mined from the hill. The square chimney at the foot of the hill is the remains of an engine house used by the coal mine. 

As development spread in Bristol, the steep slopes and tipped quarry waste deterred builders from developing the site and 1956, the council bought the land for the enjoyment of local residents. 

Troopers Hill was declared as a Local Nature Reserve in 1995 in recognition of the wide range of wildlife present on the hill and its importance as a unique habitat in the Bristol area due to the presence of acidic soils.

Troopers Hill Nature Reserve is a local nature reserve in the St George area of east Bristol, and is owned by Bristol Parks. The hill contains a fascinating mix of history, wild plants and animals. With heather and broom, rocky crags, spoil heaps and gullies, stunning views and two listed chimneys, Troopers Hill Nature Reserve is one of the most spectacular wildlife spots in the city. 

Troopers Hill Local Nature Reserve is owned by Bristol City Council and managed by Bristol Parks in partnership with The Friends of Troopers Hill. The Friends of Troopers Hill are a group of local residents interested in protecting and enhancing the nature reserve.