Factors Affecting Development (AQA A Level Geography)

There are a number of climate factors that influence which plants can colonise a wasteland:

• Buildings and debris create subtle variations in microclimates that encourage different types of colonisation

• If the area is too shady, only shade-tolerant plants will be able to colonise easily

• Sheltered sun traps attracts buddleia and butterflies

• Mosses and ferns prefer damp areas

• Spiders thrive in drier areas

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 to colonise

• 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 

• Pollution levels: previous land use depends on whether there are chemicals which may be toxic to colonisation

Soil water budget 

• Wastelands low levels of soil result 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 such as ferns, ragwort and brambles thrive

• Slower drainage areas allows for greater diversity of flora and fauna

Stage 1: Pioneers

• Mosses and lichens develop first on bare, exposed or sheltered surfaces

• They obtain nutrients by photosynthesis and from the bare concrete beneath them

• The production of acids in the roots slowly weathers the concrete

• As the plants die, they provide a thin mat of organic matter, which, mixed with the weathered mineral matter, produces a form of soil that other plant species can start to root into

Stage 2: Oxford ragwort

• Cracks in the surface provide sheltered places for seeds to germinate

• The cracks also retain moisture and dust, that help with plant rooting

• Wind-blown seeds like the Oxford Ragwort arrive, and due to its long flowering season (May–November), it produces millions of seeds

• Many plants like willow herb, annual meadow-grass and dandelion can tolerate waste, rubbish and debris

• Plant succession is usually rapid at this stage

Stage 3: Tall herbs

• As stage 2 plants die off, they produce thicker and more nutrient-rich soil

• Taller plants can become established

• The most common is rosebay willow herb, which spreads initially by seeds and then rhizomes which can extend up to 1 metre a year

• Other common plants include fennel and daisies

• These plants shade out smaller plants, preventing them from photosynthesising 

Stage 4: Grassland

• As soil depth and nutrients continue to increase, the amount of grass vegetation increases

• Taller species take the place of the smaller grasses

• At this stage, the area takes on the appearance of grassland, containing scattered clumps of tall herbaceous plants

• Invasive species can begin to colonise due to improved soil conditions and smother out most species beneath them

Stage 5: Scrub woodland

• The taller herbaceous plants eventually give way to shrubs and then trees

• The early woody plant are grey willow and birch and have light, windborne seeds

• However, as the herbaceous vegetation thickens, it becomes difficult for these small-seeded plants to establish unless there is further disturbance, such as fire

• Later trees have larger seeds that can enter denser vegetation

• These include the sycamore, laburnum, rowan and hawthorn

• Denser thickets of bramble and other scrubby plants develop in the deeper crevices in the brickwork or concrete

At each stage, plant succession allows the development of fauna, such as as earthworms, as the soil improves

There is also an increase in the number and diversity of insects and mammals

Due to sub-stratum (soil) variations, there can be a number of different successions, all in the same area

This results in variations in the type of surface being colonised for example, the differences between the colonisation of an alkaline surface compared to an acidic one