When a tree grows, it captures carbon. If after N years it is cut, in most cases that carbon is NOT going to go back to the atmosphere. Most CO2 emissions come from fossil fuels (oil, etc), NOT from voluntary wood burning.
Wood burning is not the only way to release that CO2 back into the atmosphere. Just cutting a tree and letting it decompose also releases the same carbon. You need to store it in wood form, or bury it deep.
