eg, Younger forests are not as productive as older forests when it comes to carbon sequestration.
Is canopy reasonable enough after a certain percent increase (say, 5% increase)? We are talking about percentages of the Earth's dry land, so nontrivial certainly.
Does not seem like an impossible task, I see two preliminary ways at least to attack the problem, but probably both will be wrong and is not my job to measure this without resources in any case
Ah, I misunderstood. I thought perhaps you had some insight here based on your insistence that canopy is a bad metric.
So canopy is definitely measurable at low-ish cost via satellite monitoring. I would presume it wouldn't be hard to add reasonable time-series based assumptions on new growth and make calibration adjustments that take into account the evolution.
Going into a forest and sampling, everywhere, is going to be cost inefficient relative to a model that can be based on canopy and calibrated on sub-samples of forest sampling, both historical and recent expeditions.
At least, that's how folks who would do this kind of job would likely approach it, based on my experience in similar domains. When it comes to funding, academia is a brutal place where resources are slim. Obvious adjustments are the next-best low hanging fruit to original development -- so a direct canopy measure would next likely be iterated to account for new-ness of forest and carbon sequestration calibration.