Why does draining a waterlogged carbon-rich soil for oil palm or pasture release more greenhouse gas per hectare than clearing the rainforest that grew on top of it?

Draining a hectare of tropical peatland for oil palm can release more greenhouse gas per year than the one-time carbon pulse of clearing the rainforest above it — because the peat holds roughly twice as much carbon as the forest, and drainage keeps it leaking for decades.