http://www.fao.org/docrep/005/v9878e/v9878e00.HTM
ftp://ftp.fao.org/docrep/fao/006/x3170e/X3170E00.p...
http://www.cepi.org/content/default.asp?PageID=558...
http://www.policy-powertools.org/Tools/Engaging/do...
http://www.conservationgrade.org/
http://www.conservation.org/sites/celb/Documents/C...
http://www.ciria.org/service/
http://www.bmu.de/files/english/pdf/application/pd...
http://www.wri.org/project/ecosystem-services-revi...
http://www.wbcsd.org/web/cev.htm