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Urban ecosystems
Brussels sprouts

Secondary succession in an abandoned allotment plot

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 describes a case-study of secondary succession on a previously vegetated surface - an abandoned allotment plot. See the case study of Secondary succession in an abandoned car park to explore how secondary succession proceeds on an artificial surface.

To produce a good crop of Brussels sprouts as shown in the photograph, a plot needs constant care and attention. A cultivated allotment plot or vegetable garden will have been managed to improve the soil for the growth of crops and to reduce damage caused by weeds and pests. The soil on a cultivated site will normally have a good texture and an ample supply of mineral nutrients.

compost

Soil

The basic soil on this allotment site is a heavy clay. Most of the gardeners regularly improve the texture and mineral nutrient content of the soil by adding compost made from waste vegetable material produced on the allotment itself, or materials such as spent mushroom compost.

poppy

Weeds

Weeds (any plants which the gardener doesn't want) will regularly be removed either by hand weeding or hoeing or by the use of weed killers (herbicides).

Remember that even attractive plants such as poppies may be classed as weeds if they are growing in the wrong place.

Pests

Damage by pests such as insect larvae may be controlled in a variety of ways (e.g. by chemical pesticides). Netting is often used to protect crops from larger herbivores (e.g. rabbits and pigeons).

Stages of succession

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 (in the seed bank) 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

nettles

Stage 2 - colonisation by perennials

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. Some, like the docks, have deep tap roots while many of the grasses form dense tussocks. Such plants can survive cutting by regenerating from the base of the plant and are difficult to remove.

Many of the perennials are also able to spread rapidly by means of creeping underground shoots (rhizomes). The common nettle (Urtica dioica) and the white dead-nettle (Lamium album) which dominate the plot shown in fig 6 both spread by this means. Other examples of rapidly spreading plants on cultivated ground are couch grass (Elytrigia repens), field bindweed (Convolvulus arvensis), ground-elder (Aegopodium podagraria) and creeping thistle (Cirsium arvense).

blackthorn spreading

Stage 3 - establishment of woody trees and shrubs

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

On the site shown here, which has not been cultivated for about 10 years, blackthorn (Prunus spinosa) can be seen spreading by means of underground suckers from the hedge which surrounds the allotment plots.

If the site continues to be left, 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.

Comparison with the case study of an abandoned car park

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.


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