On what timescale? I.e. trees take time to grow and accumulate carbon. As I understand it, the climate clock is ticking - there's a threshold beyond which some runaway effects kick in.
Growing is the only time they collect carbon. We could plant enough trees to zero out carbon usage (for now).
> trees take time to grow and accumulate carbon
They also burn down or are harvested quite regularly.
Harvesting can be good because it provides space for more trees to grow and store yet more carbon. As long the timber is used for long-term purposes such as housing, then the carbon in the timber kept stored. It's not 100% efficient because when felled the roots and leaves rot and return carbon back to the atmosphere, but AFAIK it's better than not harvesting.