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Urban ecosystems
car park in use

Secondary succession in an abandoned car park

Human disturbance is constantly creating habitats. Over time, the plants and animals that live in the habitat will change and develop. This process is known as succession. When disturbance has not resulted in the loss of soil or even all species a secondary succession will take place. On a disturbed urban site e.g. waste land where buildings have been removed, it may well be possible for both primary and secondary succession to be observed. See the Disturbance and succession section for more general information about the ecological process of succession.

This page looks at a case study of secondary succession on an artificial surface; in this case, the compacted aggregate surface of a car park which is no longer in use. See the case study of Secondary succession in an abandoned allotment plot to explore how secondary succession proceeds in a previously cultivated area.

A change of use in business premises has led to a decrease in the number of vehicles so that parts of the car park are no longer used and succession is beginning to take place. Succession is a continuous process but the main stages are described below.

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 (find out about the characteristics of pioneer species).

car park surface moss growing between stones
Car park surface when still in use Car park surface after it has been abandoned. Moss is growing between the stones
Nostoc

Of particular interest is the presence of the blue green alga Nostoc (see photograph left). Its filaments (chains of cells) are enclosed in a thin membrane. When it is wet they form the large brown jelly-like masses which can be seen here. This species shows all the characteristics of a pioneer coloniser and can also fix atmospheric nitrogen. This not only makes it less dependent on nitrogen in the substrate but may improve soil nutrient conditions for other species.

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.

Nostoc Common whitlow-grass
Increased coverage of mosses The common whitlow-grass Erophila verna growing amongst the mosses. This is a tiny annual plant which flowers and produces fruits in early spring

Already a few grasses and seedlings of other flowering plants can be seen (see here to find out why soil is important to many of the plants like flowering plants which have a vascular system).

Most flowering plants colonising such sites in the early stages of a succession will be small species which do not require much soil. Many are also annuals which can complete their life cycle and set seed before the onset of the hot dry conditions that may occur in the summer months. Their roots will help to loosen and break up the original compacted soil.

Common whitlow grass

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.

grasses

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. The photograph left shows a grass dominated area of the car park. Both young thistle plants (1) and the remains of the previous year's plants (2) can be seen.

brambles

Stage 5 - woody plants invade

Brambles (Rubus fruticosus agg.) 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 (see here for more information about bramble and its success as a coloniser).

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 may eventually colonise.

sycamore fruits sycamore flowers
fruits of the sycamore tree sycamore tree - leaves and flowers

The first colonisers are likely to be species like the sycamore Acer pseudoplatanus. It is tolerant of a wide range of soil conditions and urban pollution. Its winged fruits are spread widely by wind and germinate and grow rapidly.


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