Environmental Engineering Reference
In-Depth Information
(7) and the
deserts and semi-deserts with cold winters
(7a) occur across Eurasia from the
Black Sea to the Himalayas, and in the grassland regions of Canada and the United
States. In the southern hemisphere this zone occurs in the pampas of Argentina, the semi-
desert of Patagonia and the tussock grassland in the South Island of New Zealand.
Cool, wet summers and cold winters lasting more than six months occur in the
Boreal
or
Cold Temperate Zone
(VIII). The
boreal coniferous
zone (8) occurs across northern
parts of North America and Eurasia, but it is absent in the southern hemisphere. The
Arctic Zone
(IX) is characterized by low precipitation distributed over the entire year and
by low temperatures. Summers are short and wet, with twenty-four-hour days, while
winters are very long and cold, with twenty-four-hour nights. The
tundra
zone (9)
encircles the North Pole in the Arctic, and similar vegetation is found in the southern
hemisphere on the southernmost tip of South America and on many small islands in the
southern ocean. Walter's classification of climates and vegetation is a general zonal one.
Variations will occur within zones caused by factors such as proximity to oceans, the
influence of trade winds and monsoons, and the presence of major mountain ranges, as
well as local micro-environmental differences caused by topography and soil types.
Further details on vegetation in different environments are given in the environment
chapters.
CONCLUSION
The British ecologist Tansley revolutionized the study of natural systems of vegetation
and soil in the 1930s when he introduced the concept of the ecosystem. Since then the
Canadian ecologist Rowe and the US ecologist Odum have both placed the ecosystem
within a hierarchy of ecological units. The distribution of plants is governed by a range of
environmental factors. There are also strongly competitive relations between species
(interspecific competition) and between individual plants (intraspecific competition). The
concept of the ecological niche was introduced by the American ecologist Hutchinson to
summarize the sum total of physical and biological controls. The natural regions of the
world are largely climate-determined. The biome is the major large-scale ecological unit.
The scheme proposed by the German biogeographer Walter is a basis for dividing Earth
into twelve major vegetation zones.
FURTHER READING
Archibold, O. W. (1995)
The Ecology of World Vegetation
, London: Chapman & Hall. An up-to-
date textbook on world vegetation regions and their flora. Clearly written and well illustrated.
Huggett, R. J. (1997)
Environmental Change: the evolving ecosphere
, London: Routledge. Chapter
8 on the biosphere and ecosphere combines a classificatory approach with an evolutionary
approach.
Kent, M., and Coker, P. (1992)
Vegetation Description and Analysis: a practical approach
,
London: Belhaven Press. A standard work on the principles of vegetation distributions, and
methods used to study vegetation communities in the field and the computer laboratory.
