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.