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We are intimately familiar with ecosystems. They are the woodlands
where we live, hunt, cut timber, or hike; the lakes, streams, and
rivers we fish, boat, transport our goods on, and tap for water; the
rangelands where we graze our cattle; the beaches where we play, and
the marine waters we trawl; the farmlands we till; even the urban
parks and green spaces we stroll. In effect, every centimeter of the
planet is part of an ecosystem.
Ecosystems are:
- They are systems combined of organic and inorganic matter and
natural forces that interact and change.
- They are intricately woven together by food chains and nutrient
cycles.
- They are living sums greater than their parts.
- Their complexity and dynamism contribute to their productivity,
but make them challenging to manage.
When talking about ecosystems, the matter of scale or size is important.
- A small bog, a single sand dune, or a tiny patch of forest may
be viewed as an ecosystem, unique in its mix of species and microclimate — a microenvironment.
- On a much larger scale, an ecosystem may also refer to much
more extensive communities — a 100 or 1,000 square kilometer
forest, or a major river system, each having many such microenvironments.
In World Resources 2000-2001, "ecosystem" refers to an even
larger concept — categories of ecosystems. Coastal,
forest, grassland,
freshwater, and agricultural
ecosystems are addressed, all on a global scale; and each may include
a number of local variations.
For example, forest ecosystems range from
the tropical rainforests of the equatorial latitudes to the extensive
boreal forests of higher latitudes — systems that are quite different
in their details, but similar in basic structure and in the kinds
of benefits they provide. Dividing ecosystems in this way allows us
to examine them on a global scale and think in broad terms about the
challenges of managing them sustainably.
However, the divisions between ecosystems are less important than
the linkages between them. Grasslands
give way to savannas that segue into forests.
Fresh water becomes brackish as it approaches
a coastal area. The systems are tightly
knit into a global continuum of energy and nutrients and organisms — the biosphere in which we live.
We include in our analysis of ecosystems both "managed," such as farms,
pastures, or forest plantations that have been modified to enhance
the yield of certain products, and "natural," such as forests or rangeland
tracts that retain much of their original structure and functioning.
In reality human influence affects all the world's ecosystems to some
extent — even the most isolated. Again using the example of forests,
the spectrum of human influence ranges from relatively undisturbed
old-growth forests, to nondestructive tapping of rubber trees, to
clear-cutting, and even to single-species tree plantations consisting
of only eucalypt or pine trees.
Both "managed" and "natural" ecosystems are living systems capable
of producing an array of benefits, and both are crucial to human survival.
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