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.

Besides its influence upon the occurrence of species in the forest,
light practically governs the physical form of the individual tree.
If grown in an opening and not artificially pruned, a tree will have
a conical trunk and living branches almost down to the ground. The
denser and consequently darker the forest, the more cylindrical the
trunk, the smaller the crown of branches and the greater the clear
length. The individual tree has no object in assuming a desirable
commercial form and does so only when deprived of side light by
numerous neighbors. Then it sacrifices diameter growth to height
growth in reaching for the top light necessary for its life. At