[throwaway41597]

Not that simple. When carbon in the soil rises beyond a certain percentage (a tree falls) it'll convert back to CO2 because of the bugs eating it. But if the percentage starts at zero (in a desert) and an ecosystem settles there, the percentage will rise and stay above zero for as long as the ecosystem survives. Basically the plants generate matter as fast as wildlife eats it.

This sequestration can be long term if things go well or it can be short term if plants die in large numbers (because of climate change, diseases...).