Afforestation in CONUS has potential to sequester about 3% of annual US carbon emissions, per study discussed here:
A paper from a few years back listed the global potential as an additional 0.9 billion hectares (an increase of 25%) storing a total of ~200 gigatonnes at maturity. But people threw a shitstorm about the authors’ math/assumptions and I haven’t dug into it since then. They did end up publishing an erratum.