How does the deforestation of the amazon rainforest contribute to global warming?

Mature forests are not net absorbers of CO2. In the growing season they absorb CO2, but in the dormant season the leaves drop and rot, releasing their CO2. This is the reason carbon credits are being used to finance the destruction of the rain forest. Fast growing bio-fuel crops are being grown instead. This vast acreage of monoculture requires many tonnes of fertiliser and pesticide to keep it going which contaminates the few bits of natural forest left, and kills off the many endangered species that live there.