During the last fifty years repeated fires have swept through Western
forests and destroyed vast quantities of timber. As a result of these
fires, most species of trees in the West have lost large areas of
their territory. There is one species of tree, however, that has, by
the very means of these fires, enormously extended its holdings and
gained much of the area lost by the others. This species is the
lodge-pole pine.
My introduction to this intrepid tree took place in the mountains of
Colorado. One day, while watching a forest fire, I paused in the midst
of the new desolation to watch the behavior of the flames. Only a few
hours before, the fire had stripped and killed the half-blackened
trees around me. All the twigs were burned off the tree beneath which
I stood, but the larger limbs remained; and to each of these a score
or more of blackened cones stuck closely. Knowing but little of trees
and being interested in the fire, I paid no attention to these cones
until a number of thin, brownish bits, like insects' wings, came
fluttering and eddying easily down from the treetop.
The ashes and the earth around me were still warm, and the air was
misty with smoke. Near by, a tall snag and some fallen logs smoked and
blazed by turns. Again, a number of these tissue bits came fluttering
and whirling lightly down out of the fire-killed treetop. Watching
carefully, I saw brown tissue bits, one after another, silently climb
out of a blackened cone and make a merry one-winged flight for the
earth. An examination of these brown bits showed that they were the
fertile seeds of the lodge-pole pine. With heroic and inspiring
pioneer spirit, this indomitable tree was sowing seeds, beginning the
work of reconstruction while its fire-ruined empire still smoked.
It is the first tree to be up and doing after destructive flames sweep
by. Hoarded seeds by the million are often set free by fire, and most
of these reach the earth within a few hours or a few days after the
fiery whirlwind has passed by. Being winged and exceedingly light,
thousands are sometimes blown for miles. It would thus appear that the
millions of lodge-pole seeds released by fire begin under most
favorable conditions. Falling as they do, upon earth cleaned for their
reception, there is little or no competition and but few enemies. The
fire has banished most of the injurious animals, consumed competitors
and their seeds, and prepared an ashen, mineralized seed-bed; not a
leaf shades it, and altogether it is an ideal place for the lodge-pole
seed and seedlings.
It seems extraordinary that fire, the archenemy of the lodge-pole
pine, should so largely contribute to the forest extension of this
tree. It is not only one of the most inflammable of trees but it is
easily killed by fire. Despite these weaknesses, such are the
remarkable characteristics of this species that an increase in the
number of forest fires in the West will enable this tree to extend its
holdings; on the other hand, a complete cessation of fires would, in
time, almost eliminate it from the forest!
The lodge-pole pine (_Pinus contorta_, var. _Murrayana_) lives an
adventurous frontier life, and of the six hundred kinds of North
American trees no other has so many pioneer characteristics. This
species strikingly exhibits some of the necessary requisites in trees
that extend or maintain the forest-frontier. The characteristics which
so largely contribute to its success and enable it to succeed through
the agency of fire are its seed-hoarding habit and the ability of its
seedling to thrive best in recently fire-cleaned earth, in the full
glare of the sun. Most coniferous seedlings cannot stand full
sunlight, but must have either completely or partly shaded places for
the first few years of their lives.
Trees grow from seed, sprouts, or cuttings. Hence, in order to grow or
to bring back a forest, it is necessary to get seeds, sprouts, or
cuttings upon the ground. The pitch pine of New Jersey and the redwood
of California, whether felled by fire or by axe, will sprout from root
or stump. So, too, will the aspen, chestnut, cherry, cottonwood, elm,
most of the oaks, and many other kinds of trees. The extensive areas
in New Brunswick and Maine that were cleared by the fires of 1825 were
in large part at once regrown with aspen, most of which sprouted from
the roots of burned aspens. Willow is easily propagated from a short
section of the root, trunk, or limb. These sections may be broken from
the tree by accident, be carried miles down-stream, lodge on shore or
shoal, and there take root and grow. Beaver dams made of willow poles
are commonly overgrown in a short time with willow. Several years ago
a tornado wrecked hundreds of willows along a Kansas stream. Each
willow was broken into scores of pieces, which were carried and
dropped along the track of the tornado. Countless numbers of them were
stuck into the earth. Several thousand willow trees were thus
successfully planted by this violent wind.
Seeds are the chief means by which the forest is extended or produced.
They are sown by wind and gravity, by water, by birds and beasts. I
have dwelt at length upon the romance of seed-scattering in "The Spell
of the Rockies," in the chapter concerning "The Fate of a Tree Seed."
Each species of tree has its own way of scattering its seeds. Once
upon the earth, they and the seedlings that may spring from them have
peculiar limitations and special advantages. In some cases--as, for
instance, with most willows and poplars--these seeds must in an
extremely short time find a place and germinate or they perish; the
seeds of few trees will stand exposure for two years and still be
fertile.
It is only a question of a few years until seeds are carried to every
treeless locality. They may journey down-stream or across lakes on a
log, fly with birds across mountain-ranges, ride by easy stages
clinging to the fur of animals, or be blown in storms across deserts;
but these adventurous seeds may find grass in possession of the
locality and so thickly sodded that for a century or longer they may
try in vain to establish a forest.
Commonly wind-blown seeds are first upon the ground and the most
numerous. Though it is of advantage to be the first upon the ground,
it is of immense importance that the seed which falls in an opening
produce a seedling which thrives in the sun-glare,--which grows
without shade. The seedlings of our great oaks and most strong and
long-lived trees cannot thrive unless shielded from the sun, sheltered
from the wind, and protected from the sudden temperature-changes which
so often afflict openings. While these maintain the forest areas, they
extend it but little. Only a small number of trees have the peculiar
frontier characteristics. Young trees which cannot live in the sun are
called tolerant,--they tolerate shade and need it. Species which
conquer sunny territory are called intolerant,--they cannot stand
shade and need sunlight. It will thus be seen that the acquirement of
treeless territory by any species of tree demands not only that the
tree get its seeds upon the earth in that territory, but also that the
seeds, once there, have the ability to survive in the sunlight and
endure the sudden changes of the shelterless opening. Most species of
oaks, elms, firs, and spruces require shade during their first few
years, and though they steadfastly defend possessions, they can do
but little toward winning new territory. On the other hand, aspens,
willows, gray birch, cottonwood, old-field pine, and lodge-pole pine
produce seedlings that glory in the sunlight and seek to gain more
territory,--to push forward the forest-frontier.
Again and again the forest has been swept away by fire; but again and
again a few aggressive species have retaken speedily the lost
territory. In this pioneer reclamation the aspen and the lodge-pole
are leaders. The aspen follows the water-courses, running along the
muddy places, while the lodge-pole occupies the dry and rocky slope of
the burned area. Seen from a distance the aspen groves suggest bright
ribbons and pockets on the sombre cloak with which lodge-pole drapes
the mountain. And even beneath the trees the contrast between the
methods of these two agents of reforestation is marked. The lodge-pole
pine is all for business. Its forest floor is swept clean and remains
uncarpeted. The aspen groves, on the other hand, seem like the haunts
of little women. Here the floor has a carpet of grass gay with
columbines, sweet peas, and wild roses. While the aspens and the
lodge-poles are still young they begin to shelter the less hardy
coniferous seedlings. But sooner or later both the aspens and the
lodge-poles themselves are smothered by their nurslings. They then
surrender their areas to forest trees that will live to be many times
their age.
But that species which is preëminently successful in bringing back the
forest to a burned-over area is the lodge-pole pine. It produces seeds
each year and commonly hoards them for many years. Its seeds are
light, winged, and easily carried by the wind. As they are frequently
released by fire, they are sown at the most opportune time, scattered
in profusion, and, in windy weather, transported long distances.
Commonly lodge-pole pine holds on to, or hoards, a percentage of the
seeds it bears; that is to say, these seeds remain in the cone, and
the cone remains on the tree. In some situations it begins to bear at
eight years of age, and in most localities by the time it is twelve.
Year after year the cones, with their fertile seeds safely enclosed,
are borne and cling to the tree. Some of these cones remain unopened
from three to nine years. A small percentage of them do not open and
distribute their seeds until they have been on the tree from twelve to
twenty years, and many of the cones cling to the tree through life.
Under favorable conditions the lodge-pole is a rapidly growing
conifer. In a forty-five-year growth near my home, the varied light
and soil conditions were so spotted that in a small area marked
differences in growth were shown. A few clusters were vigorous, and
the trees showed an average diameter of six inches and a height of
thirty-four feet. From this the size dropped, and in one group the
individuals were less than one inch in diameter and scarcely tall
enough to be used as a cane; yet all were forty-five years old.
The lodge-pole is not long-lived. The oldest one I ever measured grew
upon the slope of Long's Peak. It was three hundred and forty-six
years of age, measured twenty-nine inches in diameter, and stood
eighty-four feet high. A study of its annual rings showed that at the
age of two hundred it was only eleven inches in diameter, with a
height of sixty-nine feet. Evidently it had lived two centuries in an
overcrowded district. The soil and moisture conditions were good, and
apparently in its two hundred and second year a forest fire brought it
advantages by sweeping away its crowding, retarding competitors. Its
annual ring two hundred and two bore a big fire-scar, and after this
age it grew with a marked increase of rapidity over the rate of
previous years. A mature lodge-pole of average size and age measures
about eighteen inches in diameter and stands sixty feet high, with an
age of between one hundred and twenty-five and one hundred and
seventy-five years.
The clinging habit of the cones of the lodge-pole pine in rare cases
causes numbers of them to be caught by the expanding tissues, held,
and finally overgrown and completely buried up in the tree like a
knot. Commonly the first crop of cones is the one caught. These are
usually stuck a few inches apart in two vertical opposite rows along
the slender trunk. Each knob-like cone is held closely against the
trunk by a short, strong stem.
I have a ten-foot plank from the heart of a large tree which shows
twenty-eight imbedded cones. The biography of this tree, which its
scroll of annual rings pictured in the abstract, is of interest. The
imbedded cones grew upon the sapling before it was thirty years old
and when it was less than twenty-five feet high. They appeared upon
the slender trunk before it was an inch in diameter. Twenty-six annual
wood-rings formed around them and covered them from sight as
completely as the seeds the cone-scales clasped and concealed. The
year of this completed covering, as the annual rings showed, was 1790.
Then the tree was sixty-six years of age; it came into existence in
1724, and apparently, from the forest-history of the place, in the
pathway of a fire. This lodge-pole lived on through one hundred and
eighty-two years. In the spring of 1906 a woodsman cut it down. A few
weeks later two-inch planks were sliced from the log of this tree
in a sawmill. The fourth cut split the pith of the tree, and the
startled sawyer beheld a number of imbedded cones stuck along and
around the pith, the heart of this aged pine. These cones and the
numerous seeds which they contained were approximately one hundred and
fifty years old. I planted two dozen of the seeds, and three of these
were fertile and sprouted.
[Illustration: OVERGROWN CONES IN THE HEART OF A LODGE-POLE PINE
(Showing also the cones as borne on the twigs and an early stage of
the overgrowing process)]
Old trees may carry hundreds or even thousands of seed-filled cones.
Once I counted 14,137 of these on the arms of one veteran lodge-pole.
If we allow but twenty seeds to the cone, this tree alone held a good
seed-reserve. Commonly a forest fire does not consume the tree it
kills. With a lodge-pole it usually burns off the twigs and the
foliage, leaving many of the cones unconsumed. The cones are excellent
fire-resisters, and their seeds usually escape injury, even though the
cones be charred. The heat, however, melts the resinous sealing-wax
that holds the cone-scales closed. I have known the heat of a forest
fire to be so intense as to break the seals on cones that were more
than one hundred feet beyond the side line of the fire.
In most cases the seedlings spring up on a burned-over area the year
following the fire. Often they stand as thickly as grain in the field.
Under favorable conditions as many as one hundred and fifty thousand
will appear upon an acre, and a stand of fifty thousand to the acre is
not uncommon. Starting in a close, even growth, they usually suppress
for years all other species of trees and most other plants. Their
growth is mostly upward--about the only direction possible for
expansion--with moderate rapidity. In a few years they are tall but
exceedingly slender, and they become poles in from twenty-five to
fifty years. The trappers named this tree lodge-pole because of its
common use by the Indians for lodge, or tepee, poles.
In overcrowded stands, especially those in which groups or individual
trees have slight advantages over their neighbors, a heavy percentage
of the growth may die annually for the want of nutrition. If equal
opportunities prevail in a crowded tract, all will grow slowly until
some have an advantage; these will then grow more rapidly, and shade
and suppress neighboring competitors.
The lodge-pole does good work in developing places that are
inhospitable to other and longer-lived trees, but it gives way after
preparing for the coming and the triumph of other species. By the time
lodge-poles are sixty years of age their self-thinning has made
openings in their crowded ranks. In these openings the shade-enduring
seedlings of other species make a start. Years go by, and these
seedlings become great trees that overtop the circle of lodge-poles
around them. From this time forward the lodge-pole is suppressed, and
ultimately its fire-acquired territory is completely surrendered to
other species. It holds fire-gained areas from seventy-five to one
hundred and fifty years. It is often supplanted by Douglas or
Engelmann spruce. Let fire sweep these, and back comes the lodge-pole
pine.
Though it distances all competitors in taking possession of
fire-cleared territory, it is less successful than its fellows in
entering a territory already occupied by other trees or by grass,
because its seedlings cannot endure shade, and its seeds will not
germinate or take root except they be brought directly into contact
with clean mineral soil. The lodge-pole, therefore, needs the
assistance of fire both to acquire and to hold territory. Increase the
number of forest fires, and the lodge-pole extends its holdings; if we
could stop fires altogether, the lodge-pole would become almost
extinct.
The lodge-pole has an astonishing altitudinal as well as latitudinal
range. Scattered pretty well over the mountain region of the western
United States, thence northward along the coast over much of the
head-waters of the Yukon in Alaska, it occupies an enormous area. Over
this it adapts itself with marked success to a variety of soil,
moisture, and climatic conditions, and covers ragged tracts from warm
sea-beaches to dry, cold mountain slopes eleven thousand feet above
the sea. In many places it surrenders the traditional pole form of its
race and wins success by becoming thick-barked, stocky, and
limb-covered from top to bottom.