Environmental Engineering Reference
In-Depth Information
Plate 21.3
Early stages of a lithosere on limestone pavement
in northern England. In the gryke there is more shelter, more
soil and protection from grazing for the higher plants which
are colonizing.
Photo: Ken Atkinson.
water-holding soil increases. The
third
-
stage community
consists of hardy grasses (e.g.
sheep's fescue,
Festuca ovina
) and annual herbs. The
fourth
-
stage community
will
consist of shrubs such as bramble (
Rubus fruticosus
) and dog rose (
Rosa canina
). Soil is
thickening continually, and the water content and nutrient content increase in step with
the increase in soil colloids; clay minerals are synthesized from the products of rock
weathering, and organic colloids are formed from humification. The
late successional
community
would witness the arrival of the first tree seedlings such as birch (
Betula
spp.),
rowan (
Sorbus aucuparia
) and ash (
Fraxinus excelsior
). Eventually deeper-rooting trees
of the
climax vegetation
(e.g. oak,
Quercus
spp.) will be able to colonize.
As the weathering of hard consolidated rock proceeds slowly, the lithosere takes
hundreds of years to reach a climax condition. The key variables are, first, the
