Colonisation of wasteland

Explain the processes by which wasteland can be colonised by vegetation.

Areas of wasteland in both urban and rural areas such as brownfield sites and derelict buildings can be colonised by vegetation. The first stage of this colonisation is where pioneer species such as mosses and lichens develop. These species can live where there is a very limited moisture and nutrient supply so are always first to colonise an area. 

When the mosses dies, they decay and leave a very simple soil and humus layer. As this process repeats a protosoil is formed and allows seeds from other plants to settle and develop. Dust and more soil builds and stage two begins. This is where species such as Oxford ragwort sow their seeds and germinate in the cracks of walls, pavements and other shaded niches available on the wasteland. As moisture begins to be retained and soil levels increase, larger and much more ruderal and taller plants such as Buddleia also known as the 'butterfly bush' self-sow and begin to develop as the new dominant species.

 

As soils deepen and nutrients from decayed plants increase the soil's fertility, stage three species such as Rosebay Willowherb colonise the wasteland when taller Ragwort and Buddleia die off. This plant spreads via rhizomes which are like horizontal roots and so easily becomes dominant. 

Stage four species such as grasses then colonise as soil enrichment continues and replace the smaller meadow grasses. The are will then take on the appearance of grassland at this stage. In addition, some invasive species such as Japanese Knotweed may be introduced at this time since the nutrient and moisture retention levels are sufficient enough for the species to grow. Should the area be redeveloped in the future, this invasive alien species may cause serious problems. The land has not been previously managed by this stage and so will have enabled the Knotweed to thrive.

The final stage of colonisation is where woody shrubs and trees such as Willow, Laburnum and Bramble replace the previously dominant plants. These stage five species compete effectively and can grow roots into deeper crevices in rock. Thickets of bramble will develop and the previous wasteland will take on less of a derelict appearance. 

pictures sourced from ::

gloucestershirewildlifetrust.co.uk

ipm.ucdavis.edu

languard.co.uk