Douglas fir is not the only Western tree which usually grows in even-aged stands. Lodgepole pine has the same habit, often supplanting yellow pine after fire or logging. Western white pine is perhaps more tolerant than Douglas fir, hence more likely to hold its own without artificial aid, but is also more certain to compete successfully if it has such aid. The same is true of tamarack. NATURE AS A MODEL We thus see that if economic reasons suggest it, we may use the selection system as a basis for artificially managing the shade bearing species such as hemlock, white fir, cedar, spruce, and even Western yellow pine. We may cut the largest and oldest trees and still have a well started second crop. If there is not much young growth to leave, even a little is valuable. It may be decidedly best to leave medium sized trees, which otherwise we would cut, because they are still growing rapidly. On the other hand, we see that this method would not be of any advantage at all in insuring a second crop of Douglas fir, for there is no young growth of this species to protect. The small and medium sized trees, instead of being immature, are merely stunted specimens of the same age as their larger brothers and unlikely to gain in size if left. Selection cutting here would save for future use only such understory of shade-bearing species as may exist. Unless this is an object, the best plan is to cut clean and get all we can. If we leave any fir at all it is for the purpose of reseeding, not to secure better utilization of the trees themselves, and whether we do so depends, theoretically at least, upon whether it is better than artificial seeding or planting. In short, selection cutting harvests the ripest trees of a perpetual forest, while clean cutting destroys the forest in order to start an entirely new and more rapid growing one. Clean cutting is therefore necessary as well as natural in dealing with intolerant trees. But it does not follow that the selection system, although natural to tolerant species, is the only one adaptable to them. While the one class demands light, the other does not demand shade. It is merely capable of enduring it. Indeed, except for the greater susceptibility of some species to extreme heat and dryness when very young, as a rule shade bearing trees grow much better if they do have ample light supply. Consequently clean cutting may be the best system for these also under certain economic conditions.