IIRC it does not help because the trees will decay into CO2 after they die. So you'd basically have to bury the dead treas if you want to prevent the carbon from entering the atmosphere again.
Only if you let them rot. If you were to burn the trees then you'd have a useful energy sourse and a significant amount (50% for an open fire, up to 90% in a specially designed burner) of the carbon would be turned in to charcoal which doesn't rot down to CO2 and be returned to the ground as fertiliser for the next round of trees.
Seriously, this is like, fossil fuels 101 people.