Environmental Engineering Reference
In-Depth Information
convenient scale for fieldwork. Biologists also work at various levels of study, and there
is an overlap between the subject matter of the biologist and that of the geographer. Table
20.2 shows the views of the American ecologist Odum on similar levels of study in
biology.
THE CONCEPT OF THE ECOSYSTEM
The previous section introduced a real distinction between 'vegetation' and 'ecosystem'
which must now be explained. The term ecosystem was first used by Arthur Tansley in
1935, when writing about British vegetation. For him, the ecosystem is 'the whole
system, including not only the organism-complex but also the whole complex of physical
factors forming what we call the environment'. The terms
landscape
,
environment
,
terrain
and
ecosystem
are often used interchangeably by ecologists to mean a specific
land system or land area whose interrelated parts are rocks, landforms, soils, topoclimate
and organisms. What emerges is that it is impracticable to understand the dynamics of
any vegetation communities without a parallel examination of geology, topography, soils,
hydrology and microclimate which together make up the habitat of plant life. The value
of the ecosystem concept is that, by focusing on living organisms and physical
environment together, it broadens understanding of what is functionally and structurally
important in the landscape. The ecosystem is a geographical unit of air, earth and water
that encompasses all living organisms, whether flora or fauna; it forms a layered structure
of interactive parts at Earth's surface. Since Tansley's first definition there have been
many others, as more understanding of ecosystems has come about. Many stress the role
of energy in ecosystems (see p. 442); thus Billings defines an ecosystem as 'an energy-
driven complex of community and environment'. However, the key properties are the
relationships between organisms (both plants and animals), and between organisms and
their physical environment. Thus a useful definition of an ecosystem would be 'the
biological and non-biological components of the landscape which exist as an adjusted
system whose parts are interrelated'.
Over the years scientists have traditionally studied the 'environment' through their
own specialized fields or disciplines. Scientific knowledge has advanced by reduction, by
subdividing systems into subsystems. The ecosystem approach is strikingly different. It
tries to conceptualize and study 'environment' in an integrated, holistic manner. The
study of specialized fields or disciplines can be justified only by reference to the
wholeness of the environment and the hierarchy of its functional wholes (see Chapter 1).
ENVIRONMENTAL FACTORS
The growth of plants places demands upon the plant's environmental resources. For
successful growth the plant
