Don’t you then need to worry about enforcement mechanisms to keep those trees from getting cut down? If they’re all harvested after say n decades, there’s no net effect on climate.
Forests used to be real carbon sinks meaning that trees would just die without decomposing, because life hasn't figured out yet how to decompose it. This is how coal was formed around the globe.
Maybe some better technology to sequester CO2 emerges. But planting trees is a good approach for the start. If we want to slow down climate change, the CO2 sequestration industry will have to become huge within the next decades.
Even if the trees die or are cut down, as long as new ones are allowed to grow, that area will absorb roughly constant amount of CO2.
Now, if we can harvest some trees regularly, and use them to replace plastics or fossil fuels, then that's a win for the environment even if those harvested trees end up releasing their CO2 back to the atmosphere, because we didn't introduce any _more_ CO2, we just recycled what we already have.
If you think it will be over, or at least completely unrecognizable, in 50 years your - in itself valid - concern doesn't matter.
If I imagine people 50 or 100 years ago trying to plan to solve our problems in 2019, knowing what they did then, I don't think they could have accomplished much of anything of substance, even with the best intentions and the commitment of huge resources.