Geoscience Reference
In-Depth Information
circumstances the birch grew very poorly, and the ground flora remained dominated
by acidic moorland species such as wavy hair grass
Deschampsia flexuosa
and bil-
berry
Vaccinium myrtilus.
This site was probably too deficient in calcium for most
earthworms, unlike the Scottish situation where calcium was evidently sufficient to
support low densities in the open moorland, and worms were thus able to spread and
multiply as the birch litter increased.
In upland areas where less wet and cold climates have, with the aid of subsidies,
justified agricultural improvement, 'reclamation' of moorland to grassland has been
a prominent land use change. On Exmoor, in southwest England, E. Maltby followed
the effects on soil microbial populations that resulted from such reclamation of Peaty
Gley and Peaty Podzol soils. Cultivation and fertilizer applications caused an imme-
diate upsurge in bacterial numbers of about a hundredfold as compared with those
in unchanged moorland soils. In the early years after reclamation, bacteria remained
dominant among microorganisms, but actinomycetes increased relatively in soils re-
claimed for longer periods. They seemed to react more slowly to changed environ-
ments. The physical, chemical and biological effects of conversion to grassland pro-
duced mull humus surface horizons like those seen in typical Brown Earths on sim-
ilar parent materials at lower altitudes. Beneath the zone modified by cultivation, the
lower horizons remained as relic features persisting from the initial Podzol and Gley
profiles.
If intensive management ceases in such sites, so that lime is no longer being ap-
plied, the vegetation gradually reverts towards moorland grass and heath communit-
ies. The acid mor humus of these characteristic moorland soils may then gradually
redevelop. Biologically, the relative numbers of bacteria and actinomycetes can be
used to assess the degree to which reversion has proceeded from intensively managed
grassland towards moor.
Chapter 10
describes the way the balance of microorganisms
is likewise affected during land reclamation.
Moving to hill areas with higher rainfall, we can look at some contrasts on the
Snowdon National Nature Reserve in North Wales. As described earlier from Bedford
Purlieus, there are sharply different parent materials here which are reflected in very
distinct soils.
At one geological extreme, hard, acidic volcanic lavas and ashes (rhyolites),
have remained as outcrops virtually unweathered in the 10,000 or so years since ice
finally retreated from its last strongholds in the region. In the montane climate of high
rainfall and low temperatures, shallow Peat Ranker soils have formed on exposed sur-
faces by the accumulation of organic matter. Initially, lichens and small mosses col-
onize depressions in the rock surface, but, as organic matter builds up, species such as
