Chapter 7
The Big Trees
Part 3
Again, the great trunks of the sequoia last
for centuries after they
fall. I have a specimen block of sequoia wood, cut from a fallen tree,
which is hardly distinguishable from a similar section cut from a
living
tree, although the one cut from the fallen trunk has certainly lain on
the damp forest floor more than 380 years, probably thrice as long. The
time-measure in the case is simply this: When the ponderous trunk to
which the old vestige belonged fell, it sunk itself into the ground,
thus making a long, straight ditch, and in the middle of this ditch a
silver fir four feet in diameter and 380 years old was growing, as I
determined by cutting it half through and counting the rings, thus
demonstrating that the remnant of the trunk that made the ditch has
lain
on the ground more than 380 years. For it is evident that, to
find
the whole time, we must add to the 380 years the time that the vanished
portion of the trunk lay in the ditch before being burned out of the
way, plus the time that passed before the seed from which the
monumental
fir sprang fell into the prepared soil and took root. Now, because
sequoia trunks are never wholly consumed in one forest fire, and those
fires recur only at considerable intervals, and because sequoia ditches
after being cleared are often left unplanted for centuries, it becomes
evident that the trunk-remnant in question may probably have lain a
thousand years or more. And this instance is by no means a late one.
Again, admitting that upon those areas
supposed to have been once
covered with sequoia forests, every tree may have fallen, and every
trunk may have been burned or buried, leaving not a remnant, many of
the
ditches made by the fall of the ponderous trunks, and the bowls made by
their upturning roots, would remain patent for thousands of years after
the last vestige of the trunks that made them had vanished. Much of
this
ditch-writing would no doubt be quickly effaced by the flood-action of
overflowing streams and rain-washing; but no inconsiderable portion
would remain enduringly engraved on ridge-tops beyond such destructive
action; for, where all the conditions are favorable, it is almost
imperishable. Now these historic ditches and root-bowls occur in all
the
present sequoia groves and forests, but, as far as I have observed, not
the faintest vestige of one presents itself outside of them.
We therefore conclude that the area covered
by sequoia has not been
diminished during the last eight or ten thousand years, and probably
not
at all in post-glacial time. Nevertheless, the questions may be asked:
Is the species verging toward extinction? What are its relations to
climate, soil, and associated trees?
All the phenomena bearing on these questions
also throw light, as we
shall endeavor to show, upon the peculiar distribution of the species,
and sustain the conclusion already arrived at as to the question of
former extension. In the northern groups, as we have seen, there are
few young trees or saplings growing up around the old ones to
perpetuate
the race, and inasmuch as those aged sequoias, so nearly childless,
are the only ones commonly known the species, to most observers, seems
doomed to speedy extinction, as being nothing more than an expiring
remnant, vanquished in the so-called struggle for life by pines and
firs
that have driven it into its last strongholds in moist glens where the
climate is supposed to be exceptionally favorable. But the story told
by
the majestic continuous forests of the south creates a very different
impression. No tree in the forest is more enduringly established in
concordance with both climate and soil. It grows heartily
everywhere--on
moraines, rocky ledges, along watercourses, and in the deep, moist
alluvium of meadows with, as we have seen, a multitude of seedlings and
saplings crowding up around the aged, abundantly able to maintain the
forest in prime vigor. So that if all the trees of any section of the
main sequoia forest were ranged together according to age, a very
promising curve would be presented, all the way up from last year's
seedlings to giants, and with the young and middle-aged portion of the
curve many times longer than the old portion. Even as far north as the
Fresno, I counted 536 saplings and seedlings, growing promisingly upon
a landslip not exceeding two acres in area. This soil-bed was about
seven years old, and had been seeded almost simultaneously by pines,
firs, libocedrus, and sequoia, presenting a simple and instructive
illustration of the struggle for life among the rival species; and it
was interesting to note that the conditions thus far affecting them
have
enabled the young sequoias to gain a marked advantage. Toward the south
where the sequoia becomes most exuberant and numerous, the rival trees
become less so; and where they mix with sequoias they grow up beneath
them like slender grasses among stalks of Indian corn. Upon a bed of
sandy floodsoil I counted ninety-four sequoias, from one to twelve feet
high, on a patch of ground once occupied by four large sugar pines
which
lay crumbling beneath them--an instance of conditions which have
enabled
sequoias to crowd out the pines. I also noted eighty-six vigorous
saplings upon a piece of fresh ground prepared for their reception by
fire. Thus fire, the great destroyer of the sequoia, also furnishes the
bare ground required for its growth from the seed. Fresh ground is,
however, furnished in sufficient quantities for the renewal of the
forests without the aid of fire--by the fall of old trees. The soil is
thus upturned and mellowed, and many trees are planted for every one
that falls.
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 the sequoia, leaving its ground to other trees supposed
capable of flourishing in a drier climate. But that the 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 only in well-watered places?" Simply because a growth of sequoias
creates those streams. The thirsty mountaineer knows well that in every
sequoia grove he will find running water, but it is a mistake to
suppose
that the water is the cause of the grove being there; on the contrary,
the grove is the cause of the water being there. Drain off the water
and the trees will remain, but cut off the trees, and the streams will
vanish. Never was cause more completely mistaken for effect than in the
case of these related phenomena of sequoia woods and perennial streams.
When attention is called to the method of
sequoia stream-making, it
will
be apprehended at once. The roots of this immense tree fill the ground,
forming a thick sponge that absorbs and holds back the rain and melting
snow, only allowing it to ooze and flow gently. Indeed, every fallen
leaf and rootlet, as well as long clasping root, and prostrate trunk,
may be regarded as a dam hoarding the bounty of storm-clouds, and
dispensing it as blessings all through the summer, instead of allowing
it to go headlong in short-lived floods.
Since, then, it is a fact that thousands of
sequoias are growing
thriftily on what is termed dry ground, and even clinging like mountain
pines to rifts in granite precipices, and since it has also been shown
that the extra moisture found in connection with the denser growths is
an effect of their presence, instead of a cause of their presence, then
the notions as to the former extension of the species and its near
approach to extinction, based upon its supposed dependence on greater
moisture, are seen to be erroneous.
The decrease in rain and snowfall since the
close of the glacial period
in the Sierra is much less than is commonly guessed. The highest
post-glacial water-marks are well preserved in all the upper river
channels, and they are not greatly higher than the spring flood-marks
of the present; showing conclusively that no extraordinary decrease
has taken place in the volume of the upper tributaries of post-glacial
Sierra streams since they came into existence. But, in the meantime,
eliminating all this complicated question of climatic change, the plain
fact remains that the present rain and snowfall is abundantly
sufficient
for the luxuriant growth of sequoia forests. Indeed, all my
observations
tend to show that in a prolonged drought the sugar pines and firs would
perish before the sequoia, not alone because of the greater longevity
of
individual trees, but because the species can endure more drought, and
make the most of whatever moisture falls.
Again, if the restriction and irregular
distribution of the species be
interpreted as a result of the desiccation of the Range, then instead
of
increasing as it does in individuals toward the south where the
rainfall
is less, it should diminish. If, then, the peculiar distribution of
sequoia has not been governed by superior conditions of soil as to
fertility or moisture, by what has it been governed?
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