It isn't; they take decades to grow to their full size and gather / sequester CO2 (about 15-25 kilos per year? Some sources say as much anyway; I don't know how that compares to emissions), but they will release most of that again if they die and are left to rot. Burying them is an option, but it would have to be in an anaerobic and/or sealed environment so it doesn't break down.

For the opposite effect, the permafrost is melting, allowing thousands of years of sequestered and frozen plant material to defrost and finally start rotting. That's adding a lot of CO2 and methane to the atmosphere, and it adds to the cascading global warming. Just that makes me think we've past the point of no return a while ago.