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Definition:
An exchange of one thing in return for another, especially relinquishment of
one benefit or advantage for another regarded as more desirable.
Source & ©:
Answers.com
Dictionary 
More:
Management choices that intentionally or otherwise change the type, magnitude,
and relative mix of services provided by ecosystems.
Source & ©:
Millennium Ecosystem Assessment
MA Glossary
To read about this term in context: GreenFacts Digest on Ecosystem Change:
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