Geoscience Reference
In-Depth Information
NATURAL HABITATS
is based on the idea that one can recognize links and relationships between different
soil classes resulting from the interaction of consistent soil-forming factors. Mature
profiles, typical of these different soil classes, only develop when natural trends oper-
ate over a sufficient length of time without significant human interference. Completely
natural situations that provide these conditions are rare in Britain, especially in lowland
regions. Most uncultivated sites, even in what appear to be natural habitats, are more
correctly thought of as semi-natural because of their past cultivation or other land use
influences. Even such semi-natural soils are quite uncommon in the parts of Britain
dominated by intensive agriculture. Everywhere, however, they are important 'bench-
mark' soils which justify protection, as we said in
chapter 2
, as they are part of the
natural environment that cannot be re-created. By displaying the least modified expres-
sion of natural soil development appropriate to a particular site, these type examples
give a foundation for soil classification. They also help us to understand the processes
of soil development and the modifications produced by cultivation.
Contrasts between soil profiles of cultivated and uncultivated variants of the same
class are most conspicuous in their upper organic horizons. Surface horizons are, of
course, those most disturbed by cultivations, and they are also the hub of biological
activity. Their character is produced by the differing trends and rates at which soil or-
ganisms return plant litter to the nutrient and energy bank of the soil. The way these
trends are expressed is largely determined by the physical and chemical properties of
the underlying mineral soil, but it is also affected by the vegetation cover. Natural or
imposed vegetation changes influence soil development directly, and also indirectly
through the soil fauna, as illustrated below. This is a two-way interaction, with soil
characteristics controlling, and being the consequence of, biological activities. In some
soil classes, e.g. Brown Earths, organic matter becomes intimately mixed with the min-
eral soil as described in
chapter 2
, while in others, e.g. Podzols, organic horizons re-
main sharply distinct.
This interacting 'world of the soil' has in the past been approached more often as
if it were two parallel but separate worlds rather than as a single entity; usually, the pe-
dological and biological approaches have made only glancing contact with each other.
One can readily understand this situation since specialists in these two fields have gen-
erally come from quite different scientific backgrounds. There are also intrinsic diffi-
