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Secondary Succession
Primary Succession

The Heathland Project area at the Woodland Education Centre. Cleared in 1993.

Secondary succession is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat. Examples include areas which have been cleared of existing vegetation (such as after tree-felling in a woodland) and destructive events such as fires.

Secondary succession is usually much quicker than primary succession for the following reasons:

  • There is already an existing seed bank of suitable plants in the soil.

  • Root systems undisturbed in the soil, stumps and other plant parts from previously existing plants can rapidly regenerate.

  • The fertility and structure of the soil has also already been substantially modified by previous organisms to make it more suitable for growth and colonization.

 

The Heathland Project site at the Woodland Education Centre provides a good example of secondary succession in action. The area was cleared of mixed woodland, with an understorey of rhododendron,  in 1993 (picture above). It was then treated with Roundup, a biodegradable herbicide, to clear the site of all existing vegetation.

The site has since been divided into nine different strips and it has been allowed to regenerate naturally.  Different management methods are used on the strips, with the aim of determining which is the best method for regenerating heathland.

One of the strips has been left untouched to act as a control strip. It is this strip which provides an excellent example of secondary succession.

Initially (1996), the control strip was dominated by grasses such as Yorkshire Fog (Holcus lanatus) and Common Bent (Agrostis capillaris). Heather (Calluna vulgaris) was present in small quantities, together with European Gorse (Ulex europaeus) and tree seedlings, such as Birch (Betula spp).

Heathland Restoration Project. Control Strip, 1998.

By May 1998, two years later, the gorse had grown to over 1 metre high, shading out most of the grass and Heather.
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Heathland Project Area. Control Strip, 2002. By 2002, the Gorse had reached heights of well over 2.5 metres. The shading effect was almost complete and all grasses and herbaceous plants had been eliminated beneath it. Only a few extremely shade tolerant moss species remained.

Brambles intertwined through the Gorse and tree saplings of birch (Betula spp.), Hazel (Corylus avellana), Sycamore (Acer pseudoplanatus) and willow (Salix spp.) had grown up extensively amongst the Gorse.

Rhododendron (Rhododendron ponticum) was also among the regenerating plants.

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By 2004, the Gorse and tree species were well over 3m tall.

The lower branches of the tall Gorse had died and it had become very sparse underneath. However, the ground was still heavily shaded and mostly devoid of plant cover.

Brambles climbed through the upper reaches of the strip.

 

Eventually, the Gorse will be shaded out by the developing trees. In time, the strip will become a miniature wood. However, this will not be the climax stage in the succession.

The Rhododendron will form an understorey under the mature trees. The extreme shading effect of the Rhododendron will prevent anything from growing underneath. When the mature trees eventually die, there will be no tree seedlings or pioneer species able to replace them and the Rhododendron will take over completely.

Without intervention, the climax stage in the succession will be Rhododendron. This non-native species causes extensive ecological damage to native habitats.

 

  Continue to

Summary of Succession

 

 

The Heathland Project

 

Succession Contents

 

 

 

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