III
DISTRIBUTION OF AMERICAN FORESTS
THE geographical distribution of trees has been referred to occasionally in the preceding chapters. This distribution, gradually accomplished during the progress of ages, has not been accidental; on the contrary, it has been due to natural causes, and arises out of the special needs and adaptations of each species. The geology of a region, which determines in many respects the character of the physical forces of both the earth and the air, is no small factor in the development of the forest. The character of the climate, the nature of the soil, the degree of moisture in the soil and in the atmosphere, the amount and intensity of the sunlight—in short, the various elements and natural forces that constitute the environment of a tree—are the all-important conditions of its life. On these it depends, and according to its own peculiar nature and its special needs, selects its natural home.
Yet the manner in which this selection is accomplished, though simple in theory, is complicated by many circumstances. Frost, fire, insects, and floods, by destroying the trees or their seeds, may retard the progress of the species. The wind may be unfavorable. The seeds hang upon the trees ready and ripe for germination, but a breeze comes along and carries them to a place where the conditions are ill adapted to their peculiar nature. The following year the wind is propitious and the little trees soon start into life. But presently the seeds of another tree, whose growth is by nature faster, are conveyed to the same spot, and the intruders outstrip the others in rapidity of growth and spread a canopy of foliage that screens the smaller trees from the life-giving sun and dooms them to destruction. Thus only a few of the numberless seeds that are produced each year live, and fewer still are able to maintain or extend the boundaries of the parent tree. Sometimes, too, the frugality or hardiness of a species may be the reason for its exclusive occupation of a certain locality, since other trees may find it impossible to live at high altitudes and on rocky ridges or to subsist upon rough, poor soil. Consequently we shall find some kinds of trees exclusive, gregarious only among themselves, while others mingle freely in the general concourse.
Through the persistency, therefore, of the vital forces of nature, through a suitable climate or situation, through the power of adaptation and the delicate adjustment of many details, the vast armies of trees, like migratory races, have at last accomplished their purpose and found their several homes; and to us the varied aspect of the forests, as we traverse the extended territory of our country, is in a manner explained. There are stretches of land over which the tree growth is dense and uniform; where the forest is given over, it may be, almost entirely to a single kind of tree. In other places the trees may join in varied luxuriance, young and old, familiar and strange, on some fertile, protected plain or well watered mountain side. In still other places they may be seen struggling up the steep slopes and maintaining a precarious existence on bleak, rocky ridges.
While the eastern portion of the United States is, generally speaking, the home of the broadleaf species, and the northern and western portions are similarly occupied by the coniferous forests, these areas may readily be subdivided into specified regions of distinct forest growth. The latter, however, cannot be accurately delimited, since the regions naturally penetrate into one another and overlap, on account of the manner in which forests have extended their bounds.
In the basin of the Great Lakes, where the glaciers of a recent geological age have prepared a light, loose, gravelly or sandy soil, the white pine belt extends through the States of Minnesota, Wisconsin, and Michigan, and penetrates into portions of Pennsylvania, New York, and New England. Once covered with dense tall forests of white pine, interspersed in places with other northern conifers, or broken by smaller areas of broadleaf forests, the white pine belt has now yielded to us its richest treasures. The exacting demands of our modern artificial civilization have drawn ceaselessly upon these resources, and the assiduous ax and the fire that follows in its train have invaded even the most secluded regions. The resulting barren spaces, where they have not become cultivated land, have either reverted to the young white pine itself or have been transformed into oak barrens and open forests of broadleaf trees. Thus the aspect of the region has been altered, though many a limited spot may be found in which the tall majesty of the primeval forest still finds its full expression.
Extending from southern New England along the entire range of the Appalachians, sloping toward the Atlantic, and spreading far westward to the Mississippi and beyond, the region of the eastern broadleaf forests covers a vast territory. Not that the conifers are here entirely absent, for several of these, including the white pine itself, follow the mountain ranges and scatter throughout the hills and plains; but their number dwindles in the proportion of the whole.
Beyond this region to the southward, in the States that border the Gulf east of the Mississippi, in Georgia, and stretching along the coast northward, a region of pines is once more encountered. This section of our forests, though it has already yielded generous supplies, is among the richest in the country. From the pineries of the South is obtained much of our construction timber; and thence, too, we derive our pitch, tar, and turpentine from the sap of the trees.
Finally, within the eastern forests a restricted region at the southern end of Florida, including the Keys, may properly be separated from the rest. For here is found a distinctively tropical vegetation, differing entirely in character from the forest flora to the north. Many trees indigenous to the West India Islands have established themselves upon this small area, on which the number of species exceeds that of any region of equal extent within the United States, not excepting even the varied forest growth of the Mexican border line, to which alone it might be worthily compared.
Separating the forest floras of the western and eastern United States, lies the broad region of prairies and plains. Though trees are found for the greater part only along the banks of streams, this region has a curious interest for the forester. It is believed by many that this wide country, now waving in grain and grass and covered with extensive farms, was at one time enriched with scattered forests; but that these have disappeared under the ravages of repeated fires, kindled, it is supposed, chiefly by the Indians. At present our own race is perseveringly reclothing these prairie lands with groves and avenues of trees, and is planting belts of them about farms and orchards for protection from hot or frosty winds. Thus the fringed borders of the streams are widening. The outcome of this activity is a development that stands in marked contrast with the hurried consumption of our other forests.
Then, lastly, there lies beyond this region the vast territory of the Rockies and the ranges of the Pacific coast. Extending over so great a part of our country, the forests of this region exhibit many transitions that reveal the intimate relations between trees and their natural environment; yet here we cannot but notice the enormous preponderance of the coniferous over the broadleaf trees. Indeed, it amounts almost to an exclusion of the latter; for, while some of the poplars and willows and several species of oaks and a few maples are indigenous to this part of the country, the last two in particular to portions of California, other broadleaf trees are mere stragglers in the land.
The forests of the West retain much more of the flavor of wildness than do those of the East, though they likewise show many evidences of the hand of man. It is true that paths and roads lead from many familiar resorts into these mountain forests, that there are signs of the lumber industry and of fires, and that there are large barren areas where sheep have been continuously driven for pasture. Extensive as this interference with original conditions has been, however, the changed aspect of the forest has not always remained permanent, because nature, where it is possible, comes back patiently to restore life and beauty to the wasted places. Over lofty ranges and in inaccessible places we may still find the original forest bequeathed to us from early days; but not in such places only: for if we look closely we shall also recognize the old character and expression in the harvested forests that have long since been deserted and forgotten and at last returned, like lost children, to the fostering care of their mother.
The forests of the West may be fitly separated into two parts. The greater part embraces the Rocky Mountain ranges, while the other extends from the crests of the Sierra Nevada to the sea. In the former the forests are sometimes open in character and separated by parks or grassy plains, or they constitute a scattered tree growth on the high altitudes of the rougher ridges. This open character is sometimes due to devastation by fires, but generally it is the result of climatic conditions. And yet there are wide tracts and spaces within this region that bear dense forests, notwithstanding the barren soil and the austere climate; forests that have been but little or in no wise disturbed, and whose expression differs in an unmistakable manner from the opener growth of the broadleaf forests of the East.
Denser than these and more awe-inspiring are the forests of the States bordering the Pacific. Here the moisture from the sea, an equable climate, and a generous soil, have produced the tall and somber red firs, the stately hemlocks and cedars, the redwoods of the coast, and the consummate beauty and magnificence of those opener groves of big trees, sugar pines, and bull pines, that have always commanded the admiration and wonder of visitors to that region.