Fresh ground is, however,
furnished in sufficient quantities for the constant renewal of the
forests without fire, viz., by the fall of old trees. The soil is thus
upturned and mellowed, and many trees are planted for every one that
falls. Land-slips and floods also give rise to bare virgin ground; and a
tree now and then owes its existence to a burrowing wolf or squirrel,
but the most regular supply of fresh soil is furnished by the fall of
aged trees.
The climatic changes in progress in the Sierra, bearing on the tenure of
tree life, are entirely misapprehended, especially as to the time and
the means employed by Nature in effecting them. It is constantly
asserted in a vague way that the Sierra was vastly wetter than now, and
that the increasing drought will of itself extinguish Sequoia, leaving
its ground to other trees supposed capable of nourishing in a drier
climate. But that Sequoia can and does grow on as dry ground as any of
its present rivals, is manifest in a thousand places. "Why, then," it
will be asked, "are Sequoias always found in greatest abundance in
well-watered places where streams are exceptionally abundant?" Simply
because a growth of Sequoias creates those streams.
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