It just isn't feasible. But maybe this is my ecological background speaking. Because, sure, if I'd look at different branches of science, it might be doable and also useful. But if you look at ecology (and making a map of every tree is ecology) then this just isn't useful enough for a task that is basically impossible to achieve. That's why in ecological research there are some standard sampling methods, like plots, transects, etc. Within these, you could do a map of all the trees if necessary. But these will be only a fraction of the whole system you look at.