Probably the best global study: Mt Tamalpais Declaration  World Rainforest Movement Challenges the validity of carbon tree farm plantations used for VCM - Voluntary Carbon Marketplace credits for the CDM - Clean Development Mechanisim of the Kyoto Accord... sold as carbon offset credits to polluting industrialized countries thereby reducing developing countries international debt to the Wolrd Bank which funds deforestation and fossil fuel burning projects world wide concurrently and the IMF... Offsets provide no responsible accounting of ecological and societal nightmares.