Let me take up your points in reverse order, while recognizing that the most important point of all may be the one we both agree on--that it is likely that present prices undervalue forests and other natural resources, and cause their overexploitation.
Your argument that we have no obligation to protect forests to improve the lot of future generations rests on your unproven assumption that future generations will be better off than the present. I was trying to point out that, over any very long period of time, this is an unproven assumption, even for the United States. Even if average income defined as mean income increases over a given period of time, it might not increase for most people, if income disparities increase. Real welfare might decrease even if total real production increased--putting a half-billion dollars in Bill Gates' pocket while at the same time 1 million working families lose $400 annually impoverishes the population, even though total economic production has increased. And present economic measurements undeniably fail to measure the lost economic value of depleted natural resources, a phenomenon so serious in countries like Costa Rica that what appears on national income reports as growth is almost certainly a decline in per capita income.
If we don't know that future generations will be richer--and I don't think we do--then it is perfectly consistent to argue on an equity basis that we shouldn't reduce the value of the natural estate that they inherit. We are particularly likely to do this if our pricing system causes us to systematically undervalue natural resources and values, the point on which we seem to agree.
So the distinction between the two logics for protecting wild forests is not as clear-cut as you suggest. Now as to the likely future values of future generations, accepting your assumption of greater wealth, we need to look at relative values, not absolute values. The historical trends in this country seem very well established. As we have increased our wealth, we have valued wild places and wild experiences more highly relative to industrial or agricultural commodities. We now invest, by choice, an all-time-high percentage of our total national wealth on trying to protect wilderness, clean air, and clean water. That suggests strongly that the future is likely to value these things even more highly.
Of course, this is not certain. My great-grandchildren might prefer an entirely tame planet devoid of predators and entirely controlled by climate-managing machinery, like the dome societies of science fiction. If they do, alas, they will have the technical capability to move in that direction. That option remains open. If, as I suspect, they will not prefer that outcome, and we wipe out wildness in this generation, my great-grandchildren will not have the technical capability to bring back the salmon or the redwoods. So in the unavoidable presence of some uncertainty, I suggest that we preserve wildness for a third reason--it is the prudent, conservative, option-preserving course of action, and we can afford it.