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
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
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
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).
||By May 1998, two years later, the gorse had grown to
over 1 metre high, shading out most of the grass and Heather.
||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
had grown up extensively amongst the Gorse.
ponticum) was also among the regenerating plants.
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
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.