Geoscience Reference
In-Depth Information
INTRODUCTION
The study of biogeography - the soils, vegetation
and wildlife of Earth - is a more recent branch of
physical geography than geomorphology and cli-
matology. Although eighteenth and nineteenth
century explorers like the German biogeographer
Alexander von Humboldt (1769-1859) compiled
descriptions of climate, vegetation and animal life
in their world travels, and brought back specimens
for the botanical gardens and zoos of Europe and
North America, it was not until the mid twentieth
century that biogeography developed into a sci-
ence that dealt with more than distributions of
organisms. In the period 1920-1960 the science of
ecology expanded rapidly on two fronts: as a pure
science under the inspiration of Sir Charles Elton
and Sir Arthur Tansley; and as an applied science
under W.H. Pearsall, Derek Ratcliffe and Sir
Ghillean Prance. The main application, of course,
was in the emerging field of species and habitat
conservation. The study of soils was a Cinderella
part of physical geography until the 1960s when
Geography departments in many British univer-
sities set up laboratories for soil investigations.
The motive in these early days, as still in many of
today's soil studies, was an applied interest in
increasing the productivity of soil resources for
food production in both Developed and Less
Developed Countries.
The soil resource is examined in
Chapters 18
and 19.
Chapter 18
concentrates on the processes
which form soils from solid rocks or unconsoli-
dated raw parent materials like glacial deposits.
The processes involve the movement of materials
within the soil profile, producing the distinctive
layering or horizons of the soil body. These
processes are discussed in temperate, subtropi-
cal and tropical environments. The resulting types
of soil have unique sequences of horizons which
are illustrated. Like any science, soil science has
its own taxonomy, or rather taxonomies, for nam-
ing soils. An international system from the United
Nations Educational, Scientific and Cultural
Organisation - Food and Agriculture Organisation
(UNESCO-FAO) is discussed, as are the classifi-
cations of the Soil Surveys of England and Wales
(SSEW) and of Scotland (SSofS). The distribution
of soils along transects of topography in the land-
scape are analysed in the section on slope
sequences or catenas.
Chapter 19
studies the
physical, chemical and biological characteristics
of soils. This knowledge forms the basis of under-
standing how soils can be managed sustainably.
The soil scientist needs to present sound, objec-
tive and relevant data as a vital prerequisite to
decisions on land use and soil management,
whether for agriculture, forestry or other uses.
Some of the challenges for soil science such as
soil fertility, land reclamation, soil erosion, and
organic and biodynamic farming systems are dis-
cussed.
Different aspects of ecosystems are discussed
in
Chapters 20,
21
and
22.
Chapter 20
introduces
basic terminology, energy flows, productivity, and
the theory of gradients, niches and successions.
As with soils, knowledge of basic theory and facts
is necessary for an understanding for land-use
policies and land management, as, for example,
in the growing field of nature conservation and
wilderness management.
Chapter 21
examines
nutrient cycling in ecosystems. The importance of
the carbon cycle has been known for a long time,
but only recently have the roles of carbon sources
and carbon sinks at the global scale been appre-
ciated. The dependence of natural ecosystems and
human land usage on the efficient and reliable pro-
vision of essential plant nutrients is paramount.
Major cycles of nitrogen and phosphorus are dis-
cussed, as are the cycles of metallic ions and
micro-nutrients. Part Four ends with a discussion
of ecosystem biodiversity in
Chapter 22.
This field
has sprung to prominence in the past 15 years due
to interest from politicians and in the media. The
measurement and controls of biodiversity are
described, and the global latitudinal gradient is
discussed. The second half of the chapter exam-
ines the on-going, complex debate on the inter-
connections between ecosystem biodiversity on
the one hand, and ecological stability and fragility
on the other.
