THE VARIETY OF SOILS IN BRITAIN - The Soil - page 27

adapt to different environments means that they can occur widely under differing soil
types or land uses. Chapter 10 , for example, describes the recurrence of the red worm
Lumbricus rubellus on a variety of industrial spoil materials and landfill as well as
in natural grassland. Other species have specific controls imposed on them by soil
properties, singly or in combination. Such interactions between soils and their fauna
are particularly clear under semi-natural plant communities. Some examples are con-
sidered in chapter 7 .
S OIL-FORMING FACTORS
The key environmental controls on soil formation are those of climate, parent ma-
terial, landform (i.e. relief or physiography), biological factors (plants, animals and
man); and time over which these factors operate. Of course, the different factors act
simultaneously, and their individual importance varies in different situations.
The broad geographic division of Britain into regional soil zones results from
the wide climatic range across the country. The significance of climate is also domin-
ant on continental and world scales, and was the key to the distribution of major soil
zones that was recognized in Russia by Dokuchaev and his fellow scientists. Rainfall
and temperature combine to influence the speed and type of weathering of rocks; the
directions and rates of transfer of plant nutrients and other mobile chemical constitu-
ents through the soil; the form in which organic matter accumulates; the natural flora
and fauna; and the options for land use.
In this broad geographic zonation, a cooler and wetter 'highland' zone in the
west and north contrasts with the warmer, drier 'lowland' zone of the south and east.
These zonal terms reflect a general environmental idea, rather than implying a simple
boundary at a particular altitude. The dominant rain-bearing winds in Britain are from
the south-west. Steep increases in rainfall take place from the western seaboards to
the central highland spines of Scotland, northern England and Wales. Lower rainfalls
occur at similar altitudes in the rain-shadow areas to the east, compared to the ex-
posed west. In North Wales, for example, annual average rainfall is about 950 milli-
metres at sea level at Bangor on the coast. It rapidly reaches 1500 millimetres 5 kilo-
metres inland at 150 metres altitude, and is 3000 millimetres or more at around 1000
metres altitude (3281 feet), only some 12 kilometres to the southeast on the Snowdo-
nia peaks. In the rain-shadow area to the east of these peaks, 1500 millimetres annual
rainfall is hardly reached on the highest parts of the Denbigh Moors at around 500
metres altitude.