First 454 words of the document:
Plagioclimax- the plant community that exists when human interaction
prevents the climatic climax vegetation being reached.
Climatic climax vegetation- the vegetation that evolves in a climate region
if the seral progression is uninterrupted by human activity, tectonic
processes, etc. The climatic climax vegetation for the UK is Oak and Ash
Heather moorland is one of the major components of the British Isles,
especially in the upland areas, but it was never a major part of the
primary succession that followed the retreat of the ice at the end of the
last ice age, about 20,000 years ago. It owes its present extent to human
interference and the clearance of the upland forests.
This means that the Heather moorland is a plagioclimax. A plagioclimax is
when humans stop the climatic climax vegetation being reached.
The woodland was first cleared out to allow crops to be grown and to
provide space for grazing, but once the trees were removed there were
no deep roots to bring the nutrients to the surface and renew the soil
fertility. Instead the heavy rainfall, which would have been intercepted by
the trees, was able to leach the nutrients out of the soils. So the upland
areas were often colonised by bracken, grasses, scrub woodland and
As long as the moorlands were grazed heavily this mixed moorland
vegetation was maintained. Sheep often grazed these areas as they are
indiscriminate eaters, which means they would eat anything.
In many areas, such as the North York Moors, parts of the Pennines and
large parts of the Eastern Scottish Highlands, there is a deliberate
management policy to maintain the land as Heather moorland. This is
because the young shoots of the heather provide ideal food for red
grouse, which are used as the basis for the very lucrative shooting
industries which are present in these areas.
To encourage the growth of new shoots, the old, woody heather plants
are burnt off every three or four years. Estate managers burn off sections
of their moor in rotation, so that at any time the moor has a variety of
different habitats, with some areas of new Heather providing food supplies
and areas of older Heather providing good cover for the grouse.
If burning and grazing stops the Heather will grow old and woody. It would
then be possible for scrub and woodland to invade. Overgrazing can lead
to destruction of the young Heather shoots and invasion by the bracken
or by mat grasses.