I hope this is not your usual standard of thinking or argument. At what CO2 level in the atmosphere would land-based vegetation go extinct? should one take thi

I hope this is not your usual standard of thinking or argument. At what CO2 level in the atmosphere would land-based vegetation go extinct? should one take this into account when designing or advocating massive mechanisms to remove CO2 from the atmosphere? once you've admitted that some CO2 level is good for the planet, why and how do you determine an ideal/target level?