Urban Wasteland Ecosystems (AQA A Level Geography)

• An urban wasteland is defined as:

An area of previously built-on and used land, that is now abandoned and left for nature to take over - also known as a brownfield site

• Urban wastelands include abandoned factories or routeways (e.g. railway lines), industrial waste dump sites, building demolition sites and old quarries
• Each wasteland provides different micro-habitats due to:  
  • The variety of surfaces (e.g. bare soil and rubble)
  • Topography (e.g. mounds, holes and wide open spaces) 
•  Succession is rapid, successful and highly adaptive, despite conditions of the land 
  • Soil depth can be minimal or non existent
  • Contaminated ground - past industrial use or spills

Image showing generalised plant succession of an urban wasteland 

• This is a form of secondary succession, similar to the pattern of lithosere succession where one plant community replaces another over time and is influenced by changes in the environment
• In this instance, the change would be the abandonment of a building/site or a reduction in ground maintenance around the building

• There are a number of climatic factors that influence which plants can colonise a wasteland:
  • Buildings and debris
    • These create subtle variations in microclimates that encourage different types of colonisation
    • Concrete surfaces provide stable environment for initial colonisation 
  • Shade
    • If the area too shady, only shade tolerant plants will be able to colonise easily
    • Sheltered sun traps attracts buddleia and attract butterflies
  • Moisture levels 
    • Mosses in damp areas
    • Spiders in drier areas
  • Space
    • The larger the area, the greater the number of species of any group
  • Wind
    • Exposed areas can receive seeds from elsewhere
    • Sheltered areas rely on bird dispersal of seeds inwards and outwards
  • Previous use
    • If heavy metals present, initial colonisers need to be pollution tolerant
  • Topography 
    • Cracks, crevices, uneven ground, soil and rubble mounds - all of these provide micro-climate habitats for niche colonisation

• Soil
  • Absent - soil will be mostly absent, thin and/or infertile, perfect for pioneer species such as mosses and lichens
  • Slope - debris accumulates on horizontal surfaces and slopes, helping to develop soil
  • Porosity - the more porous the surface, the easier it is colonised
  • Surface - the surface needs to be rough enough for plants to grip onto
    • Cracks and hollows provide a depth of soil that allows deeper-rooted plants and trees to flourish 
    • Impermeable surfaces make root penetration difficult 
  • Pollution levels - previous land use depends on whether there are chemicals which may be toxic to colonisation
  • Compacted subsoil - low oxygen levels, low porosity and difficult for root penetration
  • Soil pH - soil pH determines nutrient solubility and availability to plants
• Soil water budget 
  • Wastelands low levels of soil, results in poor moisture retention
  • Potential evaporation exceeds precipitation
  • Therefore, a negative soil water budget results
  • Plants adapt through shallow root systems, allowing quick absorption of any precipitation
  • In areas where precipitation exceeds runoff, water loving plants succeed such as ferns, ragwort and brambles
  • Slower drainage areas allows for greater diversity of flora and fauna

• Different urban wasteland produces a variety of animals and birds that have adapting to their particular surroundings
  • Each type of wasteland has differentiated fauna and flora, specific to their habitats
    • E.g. the London Underground mosquito is a distinct subspecies that is found only within the underground system.
    • These mosquitos are believed to have achieved 'reproductive isolation', or barriers to reproduction with different species, in the underground tunnels
    • Making them unique to that specific type of habitat around the world - underground railways
• Adaptation in urban wastelands is faster as new mutations are needed to give a species the ability to survive in that 'extreme' environment
  • The 'hawk's beard' plant produces 2 types of seeds, one large and the other small
  • The smaller seed has 'parachutes' to drift on wind currents, but there is no guarantee the seed will land on soil and germinate 
  • The larger and heavier seeds, fall to the floor and germinates at the foot of the parent plant
• Urban wastelands bring challenges to animals and birds that are not found in the wild
  • Crows tend to drop seeds and nuts from height to break open the tough casing
  • However, some crows in urban areas, place walnuts under the tyres of cars to crack open the nut, this habit has spread and other urban birds have followed the solution to nut cracking
• Nesting opportunities
  • New food, resources and nesting opportunities all have to be overcome 
  • Wild animals are shy, but urban animals are opportunistic and have a keen sense of finding food, shelter and adapting their surroundings for nesting/sleeping
    • City blackbirds have shorter beaks, do not migrate anymore, breed much earlier in the year due to the urban heat island effect, respond differently to stressors and sing at a different pitch to their rural counterparts
• Overall, flora and fauna in the urban wasteland have to adapt quickly to their dynamic environment 
• One adaptation does not cover all the situation or conditions found there, just as cities are different, so too are their urban wastelands