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What are ecosystems?

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.

Read about current threats to ecosystems:
coastal | forest | grassland | freshwater | agricultural | urban

As printed in World Resources 2000-2001 —
People and Ecosystems: The Fraying Web of Life
Reproduced courtesy of the World Resources Institute.


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