Trees do replace themselves!
We have ash and sycamore in our field boundaries and they are bent on world domination. I pull up hundreds of seedlings every year but the ones I miss grow at the speed of light (or seem to).
Trees can be managed by coppicing or pollarding and regenerate very quickly. I notice that in the part of France where we have a share in a holiday home, all the trees are managed like this for a supply of firewood.
So, if properly managed they can supply oxygen and fuel.
I do realise that trees wouldn't be sufficient to supply fuel to a whole country but they can contribute a renewable source to cut the use of non renewable fossil fuels.
Yes, we have a clean burn woodburner.
It's a beautiful clear night tonight here, with a nearly full moon. A bit cold, though...