Popular Science Monthly/Volume 67/September 1905/The Ancestors of the Big Trees
| THE ANCESTORS OF THE BIG TREES. |
By EDWARD W. BERRY,
PASSAIC, N. J.
THE big trees, or sequoias, have furnished a theme for song and story and have been a Mecca for the tourist for so long a time that any remarks regarding the size or longevity of the far-famed trees of Mariposa and Calaveras would seem trite. Their present isolation—for they are but few in number and do not seem to be holding their own in the struggle with the surrounding vegetation or with the cupidity of civilization—but adds to their majestic grandeur.
To the traveler who journeys to California and for the first time stands in their mighty presence many questions may suggest themselves. How long has it taken these giants of the forest to reach up some four hundred feet above mother earth? Were they created thus? Were they just entering upon a career before the red man's fire or the pale-face's ax checked them, or are they the survivors of a long existing line, struggling to maintain themselves in their last stronghold?
The records of their descent are locked up in the rocks and clays of the world, bits of twigs, cones, and occasionally large pieces of trunks that floated down to the ancient seas and were entombed in the sand and mud, to become preserved as fossils for the edification of later ages. Exploration has unearthed a part of this record. Sequoia remains have been found at almost every locality where Mesozoic fossil plants have been discovered; the cones, especially, because of their hard woody structure, being admirably adapted for preservation. In fact the fossil cones were described away back in the first quarter of the nineteenth century, even before the big trees of California had been described.
So we learn that death has played sad havoc in their noble line. Some have been dead, say, seven million years, with thousands of feet of rock lying vertically over their graves. Fig. 1 gives a diagrammatical summary of sequoia evolution, with the accompanying changes in geological, climatic and floral conditions. The left-hand column shows an ideal geological section, with the ages and periods, and their probable durations expressed roughly in years. In the middle column the procession of changing physical conditions are shown, together with the accompanying changes in climate and flora. The right-hand column is devoted exclusively to events in the genealogy of the sequoia.
The earliest known species is represented by well-defined cones which have been found in the Upper Jurassic of France. When we say that sequoias flourished in the Upper Jurassic we have a dim idea that they are a pretty old type and that, although compared to the most ancient known rocks the Jurassic rocks are mere infants, still the Jurassic age came to a close several million years ago. But we can form no more of a concept of the duration of several million years than
we do of astronomical distances, and it is only by glancing at the progress of life on the globe during all those years that we can get any sort of an idea of the remoteness of the period.
Fig. 4 is designed to show this progress of life in a general way, in the animal kingdom, which has been chosen rather than the vegetable kingdom because the changes in the former are more striking and much more apparent to the casual observer. The plants have undergone a like evolution, which has been, however, more of structure than of external appearance. Could imagination transport us to Jurassic times and set us down near the mouth of the Hudson River,
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we should find little that was familiar in either the fauna or the flora. The sediments which now exist as the red sandstones of the Connecticut valley and New Jersey had already been deposited. Volcanic activity
had been considerable and vast quantities of molten rock had been forced through the crust, forming, among others, the Orange Mountains of New Jersey and the noble line of Palisades along the Hudson. However, it is quite probable that one would have been as little disturbed
Fig. 4. Section showing Progress of Animal Life during which Sequoias have Flourished, upper space shows compatible sections of a trunk of a modern tree.
These restorations which are after Chas. R. Knight's drawings are used with the kind permission of Professor Henry Fairfield Osborn of the American Museum of Natural History.
by earthquakes eight million years ago as are the inhabitants of New Jersey at the present time by the sinking of their eastern coast. Events moved with inconceivable slowness then as now, though, of course, progress was quickened now and then. Our Jurassic sojourner would find everything strange. In the marshes flourished great ferns with undivided evergreen fronds (Marattiaceæ), and numerous representatives of our modern royal and cinnamon ferns (Osmundaceæ). Close by, ancient tree-ferns (Cyatheaceæ) vied with an amazing variety of forms known as cycads—curious plants of which the commonly cultivated sago palm is a familiar example. In the dryer spots flourished the numerous ancestors of the ginkgo, the maiden-hair tree, that curious relic of bygone days, which has been saved from extinction in modern times by the loving care of the priests about the temples of China and Japan.
The only representatives of those flowering plants which are dominant in the vegetation of the world to-day, the Angiosperms. were the little-known and curious (probably) semi-aquatic plants with netted veined leaves, which have been named pro-angiosperms. Ancient lungfishes, gar pikes and crocodiles haunt the rivers; out at sea are swarms of sharks and ganoid fishes. Bat-like flying reptiles are the common denizens of the air, the primitive toothed birds with long reptilian tails being in the minority. Sea-inhabiting reptiles of gigantic size, long-necked plesiosaurs and dolphin-like ichthyosaurs, land-inhabiting dinosaurs (the name means terrible lizard), of immense size and bizarre form, are the dominant creatures, while the noble class of mammals with man at their summit is still but a promise and, so far as the fossils indicate, represented by only a few forms of mouse-like size. The continents had not yet assumed their modern dimensions. Such great mountain chains as the Alps. Himalayas and Rockies had not been elevated; and yet the sequoia flourished and its cones were not very different from those found in California at the present time.
The next succeeding geological period, the Cretaceous, continued to be the age of gigantic reptiles, some of which are shown in Fig. 4. The two left-hand monsters figured were between twenty and forty feet long, and were ancient Jerseyites, the spoonbill, a herbivorous, and the leaper, a carnivorous, species. Occasional bones and teeth of these and other related creatures are found in the marl beds that were deposited in the sea off the eastern coast of those days. The Mississippi valley was part of a great gulf that extended northward from the present Gulf of Mexico almost to the Arctic circle, and was a veritable summer sea, peopled with gigantic sea-lizards (mosasaurs), and with a host of other strange forms. Flying reptiles with a spread of fifteen to twenty feet circled overhead.
The vegetation, however, particularly in the Upper Cretaceous, begins to assume a more modern aspect and we find along with the ancient types of ferns (Cladophlebis, Thyrsopteris), broad-leaved conifers (Nageiopsis), and juniper-like evergreens (Moriconia), numerous leaves of oaks, willows, figs, magnolias, sassafras and laurel. The earliest known palms are found at this time. The Cretaceous clays which skirt Raritan Bay in New Jersey abound with these layers of leaves, as do also the Dakota sandstones of the middle west. The magnificent specimen of sequoia with the large cone and the needle-like curved leaves shown in Fig. 2 is from the clays near Cliffwood, N. J., where the twigs are among the most abundant fossils, looking like elegant lithographs against the background of dove-colored clay. This species had cones almost exactly like those of the living Californian tree and the foliage was also very similar. It was a very wide ranging form, and is considered to have been the source (in part at least) of the amber which is so common in the coastal plain Cretaceous at certain points.
Fig. 3 shows a flat-leaved form and attached cone of a species more like the modern redwood, in fact it was probably one of its ancestors, which first appeared during the Cretaceous and which became widely distributed, and continued through the Miocene. During the three to five million years of Cretaceous time the sequoias flourished and became widespread. They saw many changes going on all about them. Beneath their shade new races were springing up; the plants of a modern type which were to replace all others in the struggle for existence had obtained their start; animals gamboled about their trunks or climbed in their branches[1] that were destined to replace the unintelligent and clumsy reptiles, and by and by to give rise to the horses, dogs and cats of a later day, and finally to produce that animal which was to attain universal distribution, and to be the destructor of countless other species—man.
Remains of sequoias from the lower beds of the Cretaceous have been found in western Europe, in Spitzbergen, in Texas and in the eastern United States. In slightly more recent deposits we find them in Greenland, Canada, in the Black Hills and in Montana. By the middle of the Cretaceous we find over a dozen different species spread over the United States, with still others in Greenland and in central and western Europe. Their remains are often extremely common, whole branches bearing numerous cones, and innumerable twigs, often beautifully preserved, being common fossils. The warm humid climate of the period seems to have been very favorable for their development, and the elevation of the land, by which natural bridges, such as those closing Bering Straits and the English Channel, enabled them to spread all over the northern hemisphere and even into the southern, for in the next age, the Eocene, we find their remains in far-off Australia and New Zealand,[2] while others occur in Alaska, stragglers from the migration into Asia.
The great frozen north of to-day had not yet been hinted at, a warm, if not subtropical, climate prevailed even in the far north, and Greenland was the garden spot that its name implies. On its western coast many plant-beds have been discovered, containing the remains of tree-ferns, cycads, incense cedars, figs, camphor trees, magnolias, eucalypts and other natives of warm climes. This northern region with numerous land connections to lower latitudes was probably the original home of our modern floras and faunas, which spread southward in successive waves of migration. We know that the Mid-Cretaceous witnessed the apparently sudden appearance of a host of new and higher plant types, and the basal Eocene witnessed, a like sudden appearance of mammalian types. It is to the frozen north of to-day that we look, hopeful that it will shed light on ancestral forms that flourished there in the far distant past.
With the ushering in of the Eocene period the gigantic reptiles are entirely replaced by higher types; small mammals, some races of which soon attained great size, uncouth beasts long since passed away, besides the remote and generalized ancestors of some of our modern animals. It is in the rocks of this period that we find the dainty little four-toed ancestor of the horse. The Eocene, together with the next period, the Oligocene, represents a couple of million years, during which the sequoias were almost as abundant and widespread as are the pines in our existing flora. In Fig. 4 are shown some of the characteristic animals of these periods, and in Fig. 1 we get some idea of the geological and floral conditions. In the far west this was a time of plains, rivers and lakes, the verdant surroundings of the latter rivaling the Louisiana country of the present day.
Along with the sequoias were many hardwood trees—oaks and maples, hickory and ash; alligators pushed their way through the sedges; the cypress and palmetto grew in Montana, Colorado and Greenland. Stately palms furnished shade for primitive rhinoceroses, tapirs and camels. Monkeys swung from branch to branch and gathered the fruits, where to-day there is nothing but the barren wastes of the alkali 'bad-lands.'
The next period, the Miocene, witnessed the zenith of sequoia development. Contemporaneous with the tapirs, rhinoceroses, horses and saber-toothed tigers, the sequoias are found from Tasmania to Iceland and Spitzbergen, and from Ireland to Japan. Their remains are everywhere—in France, Italy, Greece, Bohemia, Greenland, America—they had even found their way down along the South American coast as far as Chili.
In the Yellowstone region whole forests have been changed to stone by the mineral waters, or buried in the showers of ashes from the active volcanoes in the vicinity. The remains of the trunks are still from six to ten feet in diameter, and the erect butts are often thirty feet or more in height, standing just as they grew, a veritable Aladdin's forest turned to stone. From a microscopic study of the wood we find that these Yellowstone trees are scarcely to be distinguished from the Californian redwood and it seems a reasonable inference that they represent its direct ancestor, particularly as other petrified woods from western Canada are likewise closely related to the redwood. The Miocene, like the Eocene and Oligocene periods, was characterized to a large extent by vast continental fresh-water deposits laid down chiefly by streams, small lakes and drifting sand. To the westward ran a low range of hills, the embryonic Rocky Mountains, where the ancient crystalline strata were slowly pushing their way upward through the overlying Mesozoic and Tertiary rocks. Around the water courses grew swamp maples and alders, gum trees and mulberries; figs still flourished in the latitude of Puget Sound; saber-toothed tigers hunted the hornless rhinoceroses; and the primitive mastodons with four tusks, two in each jaw, vied with the great horned rhinoceroses for possession of the soil.
The volcanic eruptions, which first became a prominent feature during the Cretaceous, culminated during the Miocene, as the immense number of extinct cones in the western half of North America give abundant evidence. The interval between the close of the Miocene and the modern sequoias is imperfectly known. Climates were becoming cooler and the sequoias were on the wane. But few fossils are found and it is presumed that the elevation of mountain ranges, shutting off the vernal breezes, and the consequent alterations in humidity, as well as the vast changes attendant upon the coming of the ice fields of the glacial period, were sufficient to all but extinguish the noble sequoia family.
At about the time the Neanderthal skull housed the brain of a cave dweller who fashioned the paleolithic flints, and who dwelt in the fear of the great hairy mammoth, the cave bear, the hyena and the wooly rhinoceros, or shortly thereafter, the sequoias reached their present habitation in California. Could they but hand down to us the record of history embraced in a generation or two, each lasting between two and four thousand years, what a tale they might unfold. Tradition has it that Napoleon encouraged his soldiers before the battle of the pyramids with the picturesque phrase 'forty centuries look down upon you,' and yet the span of a single sequoia about equals what to the biblical chronologies of Napoleon seemed the limit of time. Many of the still vigorous and growing trees sprouted about the time that Christ was born at Bethlehem in Judea. Most of those still standing had commenced to grow at least before the fall of Rome. We can count the annual layers in the wood of those which have been cut down, and calculate with considerable accuracy their age and the varying rapidity of their growth. For instance, the huge section on exhibition at the American Museum of Natural History shows that the climate of California was very propitious about the time that Charlemagne was crowned by Pope Leo on Christmas clay, A.D. 800, as is evinced by the rapid growth of the tree at that time shown by the comparatively thick layer it added to its girth.
It is not strictly correct to speak of these growth layers as 'annual.' They are primarily the result of the varying rapidity of growth of the cells; thus in trees of temperate climes there is a gradual slowing down of vital activity as the summer advances, followed by a prolonged resting period during the winter, and an accelerated resumption of activity in the spring. These varying functions are recorded in the size and nature of the cells formed. For example, in our oak or chestnut the spring wood consists largely of pitted ducts of large size, which are prominent and in marked contrast with the much smaller celled and more solid additions formed by the slower growth later in the season. In cone-bearing trees like the sequoia the differences are almost entirely of size, the transition being abrupt from the very fine wood-cells formed at the close of the season to the much larger cells of the vigorous vernal growth. In the tropics the varying rapidity of growth is not so marked, although here also there is usually a suspension of vital activity during the hot dry season and a vigorous growth during the humid season. This effectually records the alternation of seasons in the rings of growth. It follows that under certain conditions a tree might add more than one ring in a year, but for our purpose, and generally speaking, it is proper to designate these rings as annual. Year after year the sequoias have been adding layer after layer to their girth in ever widening circles. The thousands of tons of bark shed by each tree during its long career, the tens and hundreds of thousands of tons of sap that have coursed through their venerable trunks, and the innumerable progeny of a single tree in the older, more propitious days—a contemplation of these facts assists us in realizing the true proportions of these forest monarchs. Imagination, however, fails in an attempt to picture the exquisite beauty of that virgin forest, standing age after age in all its unsullied glory—a veritable forest primeval.
Some of the Californian trees were still in their youth and others were approaching middle age when the various hordes of barbarians overran Europe. They had almost reached their full growth at the time of the Wars of the Roses and the discovery of America. They had reached their present height and girth and ripe old age before modern science had commenced its renaissance; in fact, every avenue of human endeavor—social, religious, industrial and intellectual—has shown its most marvelous progress during the time that it has taken the sequoias to add but a few feet to their already giant frames. In the topmost space of Fig. 4 the growth of an existing sequoia through the centuries is illustrated by an imaginary series of sections of the trunk, drawn to scale, showing the comparative diameter of the trunk at the time when the corresponding notable historical events occurred.
We can but wonder at the persistence of this type practically unchanged, for eon after eon, while all around were dissolution and evolution. Their early contemporaries are almost without exception cut off, and were we to go still further back to the probable ancestors of the sequoias, the Voltzias of the earlier ages, we could carry the genealogy back several million more years, almost to the coal period.
And yet the vicissitudes of time have not succeeded in wholly obliterating these ancient records preserved in the great book of history whose torn pages are the solid rock, and we are able to decipher a line here and a broken chapter there, gradually piecing together the main facts of the story, the reading of which becomes not only a labor of love, but a task of the most absorbing interest.