Two picturesque pine stumps stood for years in the edge of a grove
near my cabin. They looked as old as the hills. Although they had
wasted a little through weathering, they showed no sign of decay.
Probably they were the ruins of yellow pine trees that before my day
had perished in a forest fire. The heat of the fire that had caused
their death had boiled the pores of these stumps full of pitch. They
were thus preserved, and would endure a long, long time.
I often wondered how old they were. A chance to get this information
came one morning when a number of old pines that grew around these
stumps were blown over. Among those that went down were three large
and ancient yellow pines and several smaller lodge-pole pines. These I
dissected and studied, with the idea that their annual wood rings,
together with the scars and embossments, might give information
concerning the death of the old brown-gray stumps.
Two of the yellow pines showed two hundred and fifty-six annual rings;
the other showed two hundred and fifty-five. All carried fire scars,
received in the year 1781. Apparently, then, the stumps had been dead
and weathering since 1781. The annual rings in the overthrown
lodge-poles showed that they started to grow in 1782. Lodge-pole pines
commonly spring up immediately after a fire; these had apparently
taken possession of the ground as soon as it was laid bare by the fire
that had killed and partly consumed the two yellow pines and injured
the three scarred ones. Since the lodge-poles were free from fire
scars, since the yellow pine showed no scar after 1781, and since all
these trees had stood close about the stumps, it was plain that the
stumps were the remnants of trees that perished in a forest fire in
1781.
Later, a number of trees elsewhere in the grove were called upon to
testify, and these told a story that agreed with that of the trees
that had stood close to the stumps. These stumps are now the
newel-posts in a rustic stairway.
[Illustration: A WESTERN YELLOW PINE]
Near my home on the slope of Long's Peak are the records of an
extraordinary succession of forest fires. During the last two hundred
and fifty years eight large fires and numerous small ones have
occurred. Each left a black, fire-engraved date-mark. The dates of
some of these fires are 1675, 1707, 1753, 1781, 1842, 1864, 1878,
1885, and 1900. Each fire burned over from a few hundred to a few
thousand acres. In part, nature promptly reforested after each fire;
consequently some of the later fires swept over areas that had been
burned over by the earlier ones. Here and there a fire-scarred tree,
escaping with its life, lived on to preserve in its rings the date of
the conflagration. In one old pine I found seven widely separated
scars that told of seven different fires. In addition to the records
in isolated trees, there were records also in many injured trees in
groves that had survived and in ragged forest-edges where forest fires
had stopped. An excellent check on the evidence given by the annual
rings of fire-scarred trees was found in the age of the new
tree-growth that came up in the fire-swept territory in which, or on
the borders of which, were the telltale fire-injured trees.
Some fires swept so clean that they left behind no date of their
ravages, but here and there the character of the forest and of the
soil in which it stood made me feel certain that the growth had arisen
from the ashes of a fire, and that I could tell the extent of the
fire. In most localities the fire-killed forest is at once restored by
nature. That ever enthusiastic sower, the wind, reseeds most burned
areas within a year. Burns on the Western mountains commonly are
covered with young lodge-pole or aspen within three years. There are a
few dry wind-swept slopes or places left rocky for which years or even
centuries may be required to re-earth and reforest.
Some members of the Pine Family endure fire much better than others.
The "big tree," the redwood, and the yellow and sugar pines will
survive far hotter fires than their relatives, for their vitals are
protected by a thick sheath of slow-burning bark. The Western yellow
pine is one of the best fire-fighters in the forest world. Its vitals
appear able to endure unusual heat without death, and it will survive
fires that kill neighboring trees of other kinds. In old trees the
trunk and large limbs are thickly covered with heat-and-fire-resisting
bark. In examining a number of these old fellows that were at last
laid low by snow or landslide or the axe, I found that some had
triumphantly survived a number of fiery ordeals and two or three
lightning-strokes. One pine of eight centuries carried the scars of
four thunderbolts and seven wounds that were received from fires
decades apart.
The deciduous, or broad-leaf, trees resist fires better than the
coniferous, or evergreen, trees. Pines and spruces take fire much more
readily than oaks and maples, because of the resinous sap that
circulates through them; moreover, the pines and spruces when heated
give off an inflammable gas which, rising in front of a forest fire,
adds to the heat and destructiveness, and the eagerness of the blaze.
Considered in relation to a fire, the coniferous forest is a poor
risk because it is more inflammable than a deciduous one.
Another advantage possessed by broad-leaf trees lies in the rapid
growth of their seedlings. Surface fires annihilate most tiny trees.
Two-year-old chestnuts, maples, and, in fact, many of the broad-leaf
youngsters, are three or more feet high, and are able to survive a
severe fire; but two-year-old white pine, Engelmann spruce, or
long-leaf pine are barely two inches high,--just fuzzy-topped matches
stuck in the earth that perish in a flash from a single breath of
flame.
The ability to send up sprouts, which most deciduous trees possess, is
also a very great advantage in the fight against fire. A fire may
destroy a deciduous forest and all its seeds without injuring the
potent roots beneath the surface. The year following the fire, most of
these roots send up sprouts that swiftly grow to replace the fallen
forest. Among the so-called Pine Family, the ability to send up
sprouts or shoots is limited to a few kinds, most prominent of which
is the redwood.
Repeated forest fires have injured enormously the Southern hardwood
forests; they have damaged millions of trees so that they have become
hollow or punky-hearted. These fires have burned off limbs or burned
into the trunks or the roots and made openings through which many
kinds of fungi have entered the hearts of the trees, to doom them to
rot and decay.
Forest fires have been common through the ages. Charcoal has been
found in fossil. This has a possible age of a million years. Charred
logs have been found, in Dakota and elsewhere, several hundred feet
beneath the surface. The big trees of California have fire scars that
are two thousand years old.
The most remarkable forest fire records that I ever saw were found in
a giant California redwood. This tree was felled a few years ago. Its
trunk was cut to pieces and studied by scientific men, who from the
number of its annual rings found the year of its birth, and also
deciphered the dates of the various experiences the tree had had with
fire.
This patriarch had stood three hundred feet high, was sound to the
core, and had lived through two thousand one hundred and seventy-one
years. Its existence began in the year 271 B.C. After more than five
centuries of life, in A.D. 245 it was in the pathway of a forest fire
from which it received a bad burn on the lower trunk. It was one
hundred and five years before this burn was fully covered with tissue
and bark.
Following this fire came the peaceful procession of twelve centuries.
Eleven hundred and ninety-six times the golden poppies came to glorify
the green hills of spring, while the songs of mating birds filled
woods and meadows. More than a thousand times the aspens ripened and
scattered their golden leaves, while this serene evergreen grew and
towered more and more noble through the centuries.
Elsewhere the forests were dim with smoke, and on the Sierra during
these centuries the heroic "big trees" received many a scar from fire.
But not until 1441 did fire again try this veteran. Soon after this
burn was healed there came a third fire. This was less injurious than
the preceding ones, for the wound that it inflicted healed in half a
century.
Higher and more stately the tree grew, and in 1729 it attained the age
of two thousand years. At the age of two thousand and eighty-eight
years the fourth fire attacked it. This fire burned an eighteen-foot
scar upon the trunk of the old tree. In 1900, after the lapse of
almost a century, only a small part of this wound was overgrown. This
year, 1900, came the reaper, the axeman, who laid low this aged and
monumental tree!
What starts forest fires? Some are started by lightning; others are
kindled by meteors that are flung from the sky, or by fire that is
hurled or poured from a volcano; a few are caused by spontaneous
combustion; and many are set by man. Down through the ages primitive
and civilized men have frequently set fire to the forest. These fires
are set sometimes accidentally, sometimes intentionally. The forest
has been fired to drive out game, to improve pasturage, to bewilder
the enemy during war, and to clear the land for the plow.
During one of my Colorado camping-trips a high October wind brought me
the information that spruce wood was burning near by. While I was
searching for the fire in the thick needle carpet of the forest floor,
a spark from above settled before me. A fire was sputtering and
starting in a tree top about thirty feet above the earth. This fire
was starting where a dead leaning tree-trunk was rasping and rubbing
against an upright one. The bark of the standing tree was powdered and
tufted with wood-dust which had been ground by friction from the
trunks as they swayed and rotated in the wind. This inflammable
wood-dust, together with accumulated bark-bits and needles, had been
set on fire from the heat generated by these two big sticks rubbing
together. Plainly this was a friction fire. The incessant swaying of
treetops in the tireless wind occasionally causes a smoke from
friction at points where overlapping limbs or entangled trees are
rubbing. Within a few minutes after my discovery, this fire was
roaring eagerly through the treetops.
Friction fires are rare, but my old notebooks tell of numerous fires
that were set by lightning. Before this fire, which was in the Sangre
de Cristo Mountains, had died out, a lightning-set fire in the
mountains of central Colorado had attracted my attention with massive,
magnificent smoke-clouds, which were two or three thousand feet above
the mountain-tops. Though thirty miles distant, these clouds
occasionally took on the bossy white splendor of big cumuli assembling
for summer rain. I resolved to see the fire at close range.
Until burned territory was reached, I followed along sky-line ridges
through changing conditions of clear sky, smoke, and falling ashes,
ready for swift retreat down a slope in case the fire advanced under
smoke cover and surprised me. The burn was entered at the first edge I
reached. Millions of seared and blackened trees were standing
steadfastly where they had died at their post. All twigs and leafage
were burned away, but the majority of the trees still carried their
larger limbs and patches of bark. In places only the tree-trunk, a
fire-carved totem pole, remained. Whirlwinds of flame had moved, and
in places every burnable thing on the surface was consumed, and even
tree-roots were burned out two and three feet beneath the surface.
Though weirdly interesting, these ashen fields of desolation were not
wholly lifeless. Here, as elsewhere, feasters came to banquet, and
good fortune brought favorites to the scene of panic and death. Flocks
of gorged magpies were about, and unwontedly bold coyotes, both filled
and foraging, were frequently met with. At one place a half-dozen
beaver were portaging round a tumble of charred tree-trunks that
obstructed the brook-channel. Fire had destroyed the food-supply, and
the beaver were seeking home and harvest in other scenes. A grizzly
bear was wading their pond and feasting on the dead trout that floated
on the surface. Two black bears, despite terrible threats from the
grizzly, claimed all the fish that came within reach of the shore.
They discreetly kept out of the pond.
Two fawns and their mother lay dead at the foot of a cliff. Either
blinded or terrorized by fire or smoke, they apparently had leaped or
fallen to death. As I gained the top in climbing to investigate, an
eagle swooped angrily at me from a topless trunk. Her mate with
scorched feathers lay on the rocks near by. On returning a few days
later I found her still watching the lifeless one from the same perch
in the dead tree.
In the heart of the burned tract was a thirty-or-forty-acre tract of
forest that had escaped the fire. It was surrounded with wide though
broken barriers of rock ledges. In this green oasis were numerous
wild-folk refugees. Chipmunks, rats, woodchucks, and birds were
startlingly abundant, but no big game. Apparently the home people had
welcomed the refugees, or had received them indifferently. The only
fight noticed was between mountain rats. However, this crowding and
overrunning of territory when the exciting fire was over, probably
made many terrible pages of animal history, before exodus and death
brought a normal readjustment of life to the territory.
Wandering on across the burn toward the fire-line, I came to the
place where a ragged-edged and beautiful glacier meadow had reposed, a
poetic park among the spruces dark and tall. Commonly these meadows
are sufficiently saturated to defy fire, but this one was burning,
though slowly and with but little blaze or smoke. The fire was working
toward the centre from the edges and eating downward from one to three
feet. This kind of meadow usually carries a covering stratum of a kind
of peat or turf which is composed almost entirely of matted grass or
sedge roots that are almost free from earthy or mineral matter. These
meadows lack warmth or soil sufficient to germinate tree seeds or to
grow trees. Often they remain beautiful treeless gardens for
generations, while wind and wash slowly bring sediment, or until a
flood or landslip brings soil. The deep burning of the surface and the
consequent deposit of ash on the new surface probably offered an
abiding-place to the next adventurous tree seeds. Glacier meadows
occasionally have this kind of ending.
Two prospectors were found at work in a spruce forest near which the
fire started but which it did not reach for a week. These men said
that, an hour or so after a thunder-shower of a few days before, one
of the brown beetle-killed pines had sent up a smoke-column.
Apparently lightning had struck this tree. The following day a small
fire was burning near it. This expanded into the forest fire. Commonly
it is a standing dead tree that is set on fire by the lightning, but
the bolt sometimes fires accumulated trash around the roots where it
enters the earth.
Within this extensive burn the trees had stood from thirty to one
hundred and forty feet high and from two hundred to three thousand to
the acre, and they were from thirty to four hundred and fifty years
old. A majority were about two centuries old. The predominating kinds
were yellow pine, Douglas spruce, Engelmann spruce, and aspen.
Different altitudes, forest fires, and a variety of slope-exposures,
along with the peculiar characteristics of each species, had
distributed these in almost pure stands, an area of each kind to
itself. There was some overlapping and mixing, but lodge-pole pine
noticeably stood by itself.
Where first encountered, this fire was roaring through a thick second
growth of lodge-pole pine. Scattered through this young growth were
hundreds of dead and limbless trees killed by a fire of thirty years
before. The preservative effect of their fiery death had kept these
great pillars sound, though they had become checked and weathered.
They burned slowly, and that night while the fire-front was storming a
ridge, these columns spread sparks and flames from split sides, or as
gigantic candles blazed only at the top. Yellow pines and Douglas
spruces killed in an intensely hot fire are so cooked and preserved
that they will resist weathering or rot for decades. I have seen a few
of these pitchy broken fellows standing erect in the depth of a
century-old second generation of forest with the arms of the living
trees about and above them.
Down a slope a fire moves more slowly and with lower temperature than
upward on the same slope. A fire may rush in a minute up a slope which
it would require a day to creep down. A fire is more all-consuming in
going up, and even after years have passed, the remains left on a
slope will often enable one to determine whether a fire swept up or
crept down. One peculiarity of flames in young growths on steep slopes
is that they sometimes dart up the heights in tongues, leaving narrow
ragged stretches of unburned trees! Usually these fiery tongues sweep
in a straight line up the slope.
The intense heat of a passing fire-front is withering at long
distances. I have known a fire to blister aspen clumps that were seven
or eight hundred feet from the nearest burned trees. The passing
flames may have been pushed much closer than this by slow heavy
air-swells or by the brief blasts of wild wind rushes.
The habits of forest fires are largely determined by
slope-inclination, wind-speed, and the quantity and quality of the
fuel. In places the fire slips quietly along with low whispering, then
suddenly it goes leaping, whirling, and roaring. A fire may travel
less than one mile or farther than one hundred miles in a day. The
ever varying slope and forest conditions in the mountains are
constantly changing the speed and the enthusiasm of a fire. Where all
conditions are favorable, it sweeps level stretches at a mile-a-minute
speed and rolls up slopes with the speed of sound!
One evening I climbed a high ridge that stood about half a mile in
front of a heavily forested peninsula which the fire-front would reach
in a few hours. The fire was advancing across the valley with a front
of about two miles. On arriving at the top of the ridge, I came up
behind a grizzly bear seated on his haunches like a dog, intently
watching the fire below. On discovering me he took a second look
before concentrating his mind on a speedy retreat. Along the ridge
about a quarter of a mile distant, a number of mountain sheep could be
seen through the falling ashes, with heads toward the fire, but
whether they were excited or simply curious could not be determined.
The forested peninsula which extended from between two forested cañons
had a number of meadow openings on the slopes closest to me. Around
these were many brilliant fiery displays. Overheated trees in or
across these openings often became enveloped in robes of invisible gas
far in advance of the flames. This gas flashed and flared up before
the tree blazed, and occasionally it convoyed the flames across
openings one hundred feet or so above the earth. Heated isolated trees
usually went with a gushing flash. At other places this flaming
sometimes lasted several seconds, and, when seen through steamy
curtains or clouds of smoke, appeared like geysers of red fire.
At times there were vast scrolls and whirling spirals of sparks above
and around the torrential, upstreaming flames of the fire-front.
Millions of these sparks were sometimes formed by high outflowing air
streams into splendid and far-reaching milky ways. In moments of
general calm the sky was deeply filled with myriads of excited sparks,
which gradually quieted, then floated beautifully, peacefully up to
vanish in the night.
Meantime the fire-front was pushed by wind-currents and led by ridges.
By the time the fire-line had advanced to the steeper slopes it was
one vast U about three miles long. Its closed end was around the
peninsula toward me. The fire-front rushed upward through the dense
forest of the peninsula steeps more swiftly than the wildest avalanche
could have plunged down. The flames swept across three-hundred-foot
grassy openings as easily as breakers roll in across a beach. Up the
final two thousand feet there were magnificent outbursts and sheets of
flame with accompanying gale and stormy-ocean roars. Terrific were the
rushes of whirled smoke-and-flame clouds of brown, ashen green, and
sooty black. There were lurid and volcanic effects in molten red and
black, while tattered yellow flames rushed, rolled, and tumbled
everywhere.
An uprushing, explosive burst of flames from all sides wrapped and
united on the summit. For a minute a storm of smoke and flame filled
the heavens with riot. The wild, irresistible, cyclonic rush of fiery
wind carried scores of tree-limbs and many blazing treetops hundreds
of feet above the summit. Fire and sparks were hurled explosively
outward, and a number of blazing treetops rushed off in gale-currents.
One of these blazing tops dropped, a destructive torch, in a forest
more than a mile distant from the summit!