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It's been calculated that as little as 1/8" of live green stuff on the land of the Earth would completely zero out the additional Co2 from our activities.
But as tvfcov noted it doesn't have to be trees. It's really just us humans that like the trees better than pond scum.
Basically, if something doesn't form coal beds (like, say, peat bogs) then it is carbon neutral. Doesn't matter if it is an old-growth forest or an inch of slime. When things fall to the forest floor, they rot and the carbon is released right back into the atmosphere. And a lot of forests burn regularly which simply speeds make the process more of a step-wise function.
People have a tendancy to think in timeframe terms they are familiar with; a few decades. Trying to map these geological timescale systems to human timeframes is just stupid.
All of the carbon given off by people on a yearly basis + the vastly more given off by completely natural things (like seasonally cyclic decompositions) + all of the oil and coal reserves under the surface of the earth are completely dwarfed just by the amount of carbon disolved in the waters of the ocean.
Then you have to consider that sequestered by animal activity such as all of the karsk deposits (limestone) which is a massive amount (but nothing compared to that disolved in the ocean.) This is probably one of the main reasons that available atmospheric carbon availability is at historic lows in geological timeframes.
The long and the short of it is that the 'footprint' of humans in the whole carbon cycle analysis is completely trivial and meaningless. That is in terms of both geological timerframes AND human timeframes.
Anthropogenic climate change via carbon dioxide is as big a shame as 'covid-19', and is brought to you by the very same people and for the very same reasons: Seeking to legitimize their power-grabs and scapegoating average people as one of the devices used in their efforts. It's ridiculous and it's sick.
When it comes to trees, it's worth note that the same tiny group of oligarchs who own the mineral wealth also own vast forests (e.g., Weyerhauser in my area.) They simply don't want the competition from state and national forests so they get a bunch of eco-simpletons to worship trees. Note that the greenies almost never hassle to large forest corporations anymore. It's almost always in a national forest where they go 'owl spotting' and such-like.