s:937:"TI From principles to numbers: approaches in implementing Payments for Environmental Services (PES) in the Philippines 
AU Villamor G B 
AU Pulhin F B 
AU Catacutan D C 
AU Bertomeu M G 
AU Lasco R D 
AB This paper proposes a way to classify PES projects based on how environmental service payments are justified and determined. Using the IPCC1 approach as a model, we recommend the use of the tier system to classify PES projects. The three tiers are summarized below: Tier 1: Payments based on established ecological principles and local knowledge Tier 2: In addition to the above, payments based on simulation modeling and limited site information Tier 3: In addition to above, payments based on site-specific quantitative measurements of environmental services We illustrate this with case studies from existing PES projects in the Philippines. We then presented a decision tree to determine how the tier system can be used. 
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