As others have said the carbon is locked into the physical wood. When it rots or burns, that carbon is released back. However, you can hijack the process a lit

As others have said the carbon is locked into the physical wood. When it rots or burns, that carbon is released back. However, you can hijack the process a little and keep the carbon locked away by doing things. You could use the wood as lumber or you could burn the wood in a special way which produces biochar.