Tree ancestors : a glimpse into the past

Contents

MT. Methods of preservation of fossil plants... ........ ene. esas 10 IV. Geological time and methods of reckoning.................... 14

ILLUSTRATIONS

The giant bald cypress of Santa Maria del Tule................ Frontispiece

Chapter I Introduction

St. Bernard said: ‘‘Trees and rocks will teach what thou canst not hear from a master,’ and Tennyson has expressed the same thought, of the mystery and romance of biology wedded to geology, more sonorously in the following lines:

There rolls the deep where grew the tree.

O earth what changes hast thou seen!

There where the long street roars, hath been The stillness of the central sea.

The hills are shadows, and they flow From form to form and nothing stands; They melt like mists, the solid lands,

Like clouds they shape themselves and go.

These two verses compress into cinema-like rapidity what went on at a slow rate over a period of millions of years, and it is these glimpses into the long ago that stimulate the student of geology like new wine, and make him wonder why all the world does not forsake the trivial affairs of life and spend their time in making bricks for the temple of science and the master builder.

The sketches which follow are an attempt to interest the general public in the marvellous history of some of our trees. Although we, as a nation, probably because of our seeming limitless natural resources, have been somewhat slow in awakening to the necessity of scientific forestry, there has always been a large public interested in our forest trees, as witness our numerous tree books. In none of the latter, however, will the reader get any idea that the various tree stocks are many thousands of years old, or that their abundance and geographical distribution have not always been much as we find them today.

The selection of forms in the following pages may seem arbitrary and many will look for some special favorite to find it omitted, since I have chosen forms whose history was better known, but not worn threadbare, and omitted others where the evidence was incomplete or conflicting, as in the case of the pines, spruce, and their allies.

The reader need know no geology or botany as all unnecessary technicalities have been avoided. One cannot, however, discuss history without some sort of a chronology, and I have therefore given a simplified geological time table in Chapter II which will be sufficient after it has been understood to render clear such references as appear in the following pages.

The main theme then will be the geological or distribution in time, and the geographical or distribution in space, of the trees. Although I will not refrain from mentioning the usefulness of the trees to us humans, it should be remembered that a tree is no longer a tree when it has become timber, and it is only in deference to a practical people and to a forestry which regards our woodlands as so many potential board feet that utility may be considered as a possible avenue to a more general appreciation of the wonders of their present state and the grandeurs of their past history.

- CHAPTER II GEOLOGICAL PRINCIPLES

When we visit the Garden of the Gods and learn the history of the beautiful and weird shaped masses of red sandstone to which the locality owes its romantic name—how they were deposited originally as loose sands in horizontal beds, were subsequently solidified and bent by the forces that built the Rocky Mountains so that the original horizontal bedding became perpendicular, and were subsequently carved to their present proportions from solid sheets of rock by the slow action of rain, wind and frost, it may readily be believed that strange and unknown forces of great magnitude were operative in past times. The same feeling is aroused by the grandeur of the Grand Canon of the Colorado or by the columnar lava of Fingalls Cave and the Giants Causeway, or even by the majestic lava sheet that forms the Palisades of the Hudson. And if we have ever seen the overturned folds of rock common in most mountain regions or especially the great double fold in the Glarner Alps south of Lake Zurich, we may feel justified in concluding that very different and titanic physical forces were operative on the earth before the advent of man, just as we know gigantic animals flourished in past geologic times and just as the plants allied to our modern lowly club mosses and mares tails were tall trees during the coal period.

This is exactly what the earlier students of the earth thought. When they found the remains of marine shells in the rocks of the mountain tops they concluded that vast caverns in the earth’s crust had swallowed the waters of the primeval universal ocean. When knowledge had progressed so that men knew that the traces of former life in each succeeding layer of rocks differed from all others both earlier and later they concluded that mighty cataclysms or revolutions of nature had repeatedly swept the life off of the face of the earth and that each time this had happened it had been subsequently renewed by special divine creations.

These conclusions were all rational enough in their day, especially when the belief was well nigh universal that the earth was only about 6000 years old as estimated from the biblical chronicles. When, however, it was finally realized that nature had almost limitless time at her disposal students began to perceive that the apparently insignificant forces which we still find at work—the action of air and water and vulcanism, and the slow changes wrought by evolution, were the agencies that had accomplished such tremendous results in past times.

This belief in the uniformity of factors and the interpretation of the past in terms of nature’s forces that we find acting today was christened uniformitarianism and the late Sir Charles Lyell (1797— 1875) may be regarded as the high priest of this belief. It is quite possible that the forces of nature may have apparently accomplished more rapid results at certain times in the history of the earth but it is very doubtful if, during the time when the ancestors of our forest trees have flourished physical or organic history moved any faster or by any different means than it moves today.

This is one of the great principles of geology—that we may legitimately utilize present conditions in the interpretation of the past, or in what Huxley called retrospective prophecy. We may rest assured that boreal or temperate forests did not flourish in proximity to tropical marine waters, and that insolation, humidity, rainfall, and all the other factors of environment had effects on the trees of past ages similar to their effects on the forests of today. It is as unscientific to assume that trees did not react to their environment during the Eocene as they do at present as it would be to assume that the carrying power of water was not conditioned by its velocity during Eocene time.

A second principle the enunciation of which will be helpful throughout the subsequent discussions relates to climate. The human race since its reached the stage of written traditions has lived under climatic conditions which in general are like those of the present, with the familiar transition from torrid through temperate to polar climates in passing from the equator to the poles. It is most difficult to think of past climates as in any way different

GEOLOGICAL PRINCIPLES 5 from those that we have known since childhood. Hence when we hear of the remains of bread fruit and camphor-trees in latitude 73° north, or coal seams formed by the accumulation of plant remains in both the Arctic and the Antarctic regions it might seem as though the poles must have been somewhere else at the time when Greenland was the land of verdure that its name would seem to indicate. There have been students who subscribed to the theory of wandering poles but it can not be said to have many adherents at the present time and physicists assure us that it is impossible. The truth seems to be that geological climates in general were much more uniform than they are today—milder in the polar regions and less torrid in the equatorial regions. This may seem to be an exception to the principle of uniformity just enunciated, but this is only apparent. Through a combination of causes such as extension and elevation of the land surface of the earth and a consequent restriction of the oceanic areas, and other causes not yet satisfactorily formulated there have been, at widely separated intervals, periods of glaciation which have interrupted the normal more uniform climates that were the rule. One has been recognized in the pre-Paleozoic, another is thought to have occurred in the early Paleozoic but this may be confused with the earlier one just mentioned. A third was ushered in many millions of years later near or at the close of the Paleozoic, and the fourth and most widely known glaciation is the one which after the lapse of many more millions of years immediately preceded the historic period and witnessed the radiation of the men of the Old Stone Age in Europe. Men of this Old Stone Age were witnesses of the great Rhone glacier and of the ice sheet that covered Britain, Scandinavia and the north German plain.

This last great glacial period of which the ice cap of Greenland is probably a surviving remnant continued for many thousands of years and was marked by at least four periods of prevalent ice sheets and mountain glaciers and by intervening interglacial periods of long duration during which the climate was no more severe than it is at present. These were much longer than the time that has elapsed since the last ice sheet dammed the valley of the St. Lawrence, and many students believe that we are today living in a fourth interglacial period. This would account for the present climate with which man is familiar, a climate anomalous when compared with that of the Tertiary or the Cretaceous, since the glacial periods partially due to the extension of land masses and elevation are the result of the consequent changes in the atmospheric and oceanic circulation.

Thus a second principle may be set forth, namely, that throughout the bulk of geologic time climates were more uniform than they are at present. The truth of this statement will be abundantly shown when the former distribution of our forest types is passed in review, although the actual amount of change has usually been overestimated.

Geologists in dealing with the rocks of the earth’s crust and their succession in time divide them into geological formations which are thus the units of geological history and each formation may be considered as a page of earth history or a phase of geological time. From the remains of animals and plants that were preserved in the rocks of a geological formation, i.e., its fossil content, and from the nature of the enclosing rock that constitutes the matrix of the fossils, i.e., their physical and mineralogical character, and from their relations to adjacent rocks, it is possible to in a measure restore the environment which existed at the time that they were deposited, namely the topography, temperature, rainfall, forestation, etc.

These stratigraphic units or formations representing phases of time are grouped together in larger units known as stages (étages) representing what are called ages of time and these in turn are grouped into units of still larger magnitude known as epochs of time or series of stages, as for example the Eocene, Oligocene and Miocene series of stages or epochs of time. These series or epochs are further grouped into systems of series (rocks) or periods of time, as for example, the Carboniferous system or coal period, the Cretaceous system or chalk period, and so on. The Eocene, Oligocene, Miocene and Pliocene series collectively constitute the Tertiary period during which both the Mammals or warm blooded non-avian animals and the Angiosperms or flowering plants under-

GEOLOGICAL PRINCIPLES 7 went their most obvious differentiation and distribution over the face of the earth.

These systems of rocks representing the history of periods of time are themselves gathered together into groups that represent what are called eras of time, thus the Triassic, Jurassic and Cretaceous periods constitute the Mesozoic group of periods or the Mesozoic era of time—the era of gymnosperms (more familiarly conifers) among plants and the era of reptiles among animals.

All this may seem complicated and abtruse to the non-geological reader, but it must be obvious that we cannot discuss the noble races of trees that have passed across the face of nature in past ages without a definite chronology and nomenclature, any more than we could live our daily lives and transact its affairs comfortably and effectively without time pieces and calendars. Nor can we compare the contents of the rocks of different countries and determine the place of origin or the subsequent history of the migrations and extinctions of plants or animals without a carefully worked out chronology. Without such our situation might be compared to that in civil life before standard time was adopted.

The following somewhat abbreviated table will furnish the reader with the geological divisions that it will be necessary to use in trying to picture the history of the ancestors of our trees. It also gives a few of the facts of earth history and organic history that will serve to emphasize and fix the former in mind.

To those who notice the fate of the leaves each autumn it may seem that for any adequate geological record of bygone vegetation the conditions for the successful preservation or fossilization of parts of plants must have been very different in the past from what they are at the present time. Except for the fact that the continental masses are somewhat larger now than was the case for the greater part of geological time this is not so. The facilities for fossilization in inland and upland regions have always been limited to lake and flood-plain (river overflow) deposits. Mountain lakes have frequently preserved marvellous records of the contemporaneous life as that of the Miocene lake of Florissant in the heart of the Colorado Rockies or the even more celebrated Miocene

Time of the Ice age and the ancestors of man. Extinction of many large animals and trees. Evolution of herbs. Elevation and extension of the continents.

Quaternary | Pleistocene period epoch

Pliocene Cosmopolitan forest types.

CENOZOIC ERA epoch Elevation of the Andes.

Mammals and Miocene | Zenith of development of forests.

PGES epoch Elevation of the Swiss Alps. plants Tertiary Olicoc Culmination of Eocene types. Warm period a — climate with some aridity. 2s Elevation of the Pyrenees.

Forests in the polar regions.

Eocene et : ; oe Beginning of elevation of Cordilleras.

P Community of Holarctica.

Earliest known palms. Beginnings of the modern Cretaceous : : - 4 forests flora mixed with survivals from the fern, i cycad and conifer flora of the older Mesozoic. Widespread warm seas, marine faunas and terres- MESOZOIC ERA] Jurassic trial floras.

Reptiles, Cycads period Origin of the dicotyledons. and conifers Beginning of the Sierra Nevadas. Shallow seas and lagoons. Widespread red con- Triassic tinental deposits. Igneous activity and mounperiod tain making.

Land extension.

Appalachian revolution,

Fishes, ferns and fern-like plants.

Origin of the seed plants. hea Old folded mountain systems of the world such as the Caledonian, since worn flat.

Radiation of invertebrate phylae, origin and evolution of fishes and amphibians.

lake of Oeningen in Baden near the present Lake Constance. In both of these fossil lakes thousands of delicate insects and the floral and foliar organs of plants, as well as other forms of life were

GEOLOGICAL PRINCIPLES 9 preserved in great variety and perfection. Great numbers of plants were preserved in the continental deposits of our own western Tertiaries and amber or other exudations of the gum of trees has frequently hermetically sealed a variety of delicate and otherwise unknown fossils.

Any one who has noticed the amount of variety of leaves in the bayous and estuaries of our coastal plain, particularly after a wind storm, or the quantities that are buried by fine mud in the spring freshets of the rivers have little difficulty in picturing conditions favorable for fossilization in past times. When it is further realized that the geological record accumulated not through a few but through thousands of years it is seen that this record is not nearly as inadequate as it seemed at first thought.

CHAPTER III METHODS OF PRESERVATION OF FossIL PLANTS The seasons, whether cold and warm or wet and dry, succeed

one another in a never ending series ages long. ‘Trees ripen their fruits and seeds and shed their leaves, some rapidly and some slowly. Winds contribute windfalls or branches to the forest litter. These and allied processes have been happening since plants first came up out of the primitive oceans and covered the dry land. , Inregions remote from water—either rivers, lakes or ocean—there is but slight chance that this forest litter will be preserved. It is attacked by hosts of insects, and lower plants ranging from bacteria to fungi, and the greater portion is finally partially or wholly oxidized. Swamps may preserve logs as lignite, or scraps of vegetation such as the more resistant seeds, or cuticles and pollen grains, but the great bulk of the swamp accumulations become more or less amorphous carbonaceous masses such as those from which coal beds have been formed.

Fruits and seeds are designed for the perpetuation of the species, but. mortality among seeds is on a vast scale. They have to fall or be carried to a suitable situation in order to sprout. All the non-carnivorous higher animals levy upon the products of the forest. It may be bears coming down into the swamps in the fall for the gum berries (Nyssa), the ever present squirrels and their allies busy with the oaks, valnuts and hickories, swine devouring the beech and oak mast, or ‘t may be birds or fruit bats according to species and clime. While man has been on the scene for but a relatively short time he has probably wrought more damage than any other agency. Consequently it might seem that but few relics of the present forests are being fossilized or that we can never - accumulate much evidence regard.ng the bygone forests that clothed the earth.

While in a general way deserts, piairies, open savannas and pampas have always been present in -ertain areas it remains true

METHODS OF PRESERVATION 11 that in a geological sense they were for the most part short lived features and that the bulk of the earth’s surface has been forested until modern times. .

The agents of fossilization have been and are streams, lakes, lagoons and seas. A constant shower of life falls on the bosom of the waters. Trees have their roots undermined by erosion and topple bodily into the streams; leaves, fruits and sticks make up a large percentage of the river drift. This river drift may travel near or far, much of it rots beyond recognition, but always something is saved. Logs and branches are stranded and buried in river bars where some become petrified. Leaves and fruits become water logged and sink in slack waters where they are covered with mud, or the forest litter on bottom lands may be spread with a mantle of alluvial mud during periods of high water and thus be preserved. Anyone who has seen the variety of leaves and fruits that streams are constantly carrying in our own country or the vast amount of vegetable drift in such estuaries as the Guayaquil, the Amazon or the Orinoco cannot doubt that the present is preserving its records for the future or that the past similarly has not failed us. The forests near the coast contribute like things to the bayous, estuaries and lagoons or carry a part out to sea, and the same processes are taking place around all the innumerable lakes and ponds.

The actual methods of preservation are divided into two categories—one termed infiltration and the second known as inclusion. In the first the plant tissue of whatever sort from trunk to seed is more or less completely permeated or replaced molecule by molecule by silicic acid, calcium carbonate or other mineral substances such as magnesium, pyrite, marcasite, limonite, etc. According to the completeness of this replacement the internal structure is preserved with more or less fidelity, often to such an extraordinary degree that the histology is completely decipherable, and such delicate objects as the mycelial threads and spores of parasitic fungi or even bacteria are recognizable. Remains preserved as petrifactions are relatively uncommon although characteristic of regions of thermal activity like the Yellowstone Park. Calcified plant tissues characterize certain horizons in the coal measures especially in England, Westphalia and Moravia. Silicified plant tissues have rendered the Permian of St. Etienne and Autun in France famous, and quantities of Mesozoic cycads have been similarly silicified especially around the rim of the Black Hills. Fossil woods are commonly silicified, opalized or jasperized at very many localities and geological horizons, as in the Arizona National Park, where they are of Permian or Triassic age, or in the Yellowstone Park where they are Tertiary inage. Scattered trunks and fragments of petrified wood are abundant in all sandy formations.

The second general method of preservation, by far the most common mode of occurrence of fossil plants, is by simple inclusion in clay, shale, amber or other material, and is often known as incrustation. The bulk of the fossil plants with which the general public is familiar are of this type of preservation which often furnishes the most beautiful impressions of foliage or even flowers —the fimer grained the sediment in which the plant remains were entombed the more perfect the impression. Thus a flocculent calcareous mud or lithographic stone will preserve every detail of form, or a fine mud like that of the fire clays beneath coal beds or the roofing shales above them will be crowded with the delicate remains of the plants that formed the coal, or a fine volcanic dust falling in a lake will preserve most beautiful specimens. Travertines will encrust the vegetable débris of deep ravines in a limestone country as in the case of the celebrated early Eocene travertines of Sézanne in France, or the younger travertines of northern Italy, or stalagmite will preserve the litter of burrows or dens of animals or of men of the Old Stone Age that lived in rockshelters.

Plant remains preserved by inclusion or incrustation may have some of their substance preserved as carbon, it may be replaced by salts of iron or other mineral, or it may be entirely dissipated leaving only the impression or cavity. Lignite beds and coal seams, or the impure peats of buried swamps so common in our Pleistocene deposits, are examples of inclusion (incrustation) of plants en masse. Occasionally such swamp deposits of great age like those of Brandon, Vermont, or of the German lignites, both of

METHODS OF PRESERVATION 13

Tertiary age, will furnish quantities of the fruits and seeds of bygone forests that flourished on their sites. Peat bogs are veritable mines of more recent vegetable history and where their contents are studied intensively as in some of the European countries they record the changes from sphagnum to rushes and the succession of willow, birch, pine and hazel much more certainly decipherable than the early written records of human history. Amber and other gums frequently contain small plant fragments in an exquisite state of preservation but the great bulk of fossil foliage was buried in shallow water muds of flood plains, lakes, bayous and estuaries and lagoons. Occasionally lignified wood may retain its internal structure and by special methods of treatment it may be sectioned and studied microscopically.

The details of the past history of our forest trees will doubtless always remain imperfectly known but this knowledge is increasing rapidly and we can already sketch the broader outlines of the history of a large number of our trees as the present sketches bear witness, and we can leave to the future the filling in of the details of these pictures when we know that these broader outlines are not founded upon fancies or theory, but upon facts.

Chapter IV Geological Time And Methods Of Reckoning

There are a great many ways of estimating the duration of geological time or the age of the earth. This is a fascinating subject that has always invited speculation by physicists and biologists as well as geologists. Most of these methods are dependent on the data furnished by the comparison of past processes with present processes, such as the rate of the formation of peat in bogs, or of stalactites in caverns, or the rates of accumulation of different kinds of sedimentary materials. Other methods take as their basis the rate of cooling of lavas, the amount of salts in solution in the oceans compared with the rate at which rivers are bringing them down to the seas, the effects of tidal stresses in retarding the earth’s rotation, the rate at which the sun is supposed to be losing its heat, and by other less obvious methods, such as the state and rate of change of radium minerals in rocks.

These various estimates vary through very wide. limits since no method has been discovered that does not involve a variety of unknown factors. ‘There is, however, a certain amount of concordance in them all and it is possible by carefully estimating the total thickness of the sedimentary rocks and comparing the rate of accumulation at the present time of the different kinds of rocks such as limestones, sands and clays to get a rough approximation of the time necessary to account for the deposition of similar materials in past times. That the results are not. accurate is obvious when it is recalled that conditions of erosion, amount of material and all of the other factors of the environment vary greatly so that one limestone may accumulate rapidly and another slowly. Furthermore very little account can be taken of the time that is represented by the numerous intervals in geological history when the rocks were being worn away by erosion and the resulting deposits are beyond our ken, or when the surface of the land was so

GEOLOGICAL TIME 15 nearly flat that but little sediment was being carried into the seas and lakes and being deposited.

It is obvious, however that this method while very inexact is, when carefully done, much better than no estimates, and when the results are expressed in ratios rather than in actual durations of so many years and we say that one geological period was twice as long as another, or that the time that has elapsed since the last glacial period is but one twenty-fifth of the duration of the whole Pleistocene, we are naming results which while gross from the viewpoint of a mathematician, physicist or chemist, are very satisfactory for the coarse scale of geological work.

Geologists have grouped the rocks of the earth’s crust into the following five major divisions, of which the two earlier are omitted in the table given on a preceding: page. These five divisions are in the order of their age: Archeozoic, Proterozoic, Paleozoic, Mesozoic, and Cenozoic.. The stratified rocks that contain any abundant display of the life of their time are embraced in the Paleozoic (rocks with ancient life), Mesozoic (rocks with middle life), and Cenozoic (rocks with modern life). If 5 be taken to represent the duration of the Cenozoic, then the Mesozoic will be represented by 12 and the Paleozoic by 27. Unity is commonly considered as a million years but it may be more—it certainly is not much less.

CHAPTER V THE LATER GEOLOGICAL H1sTtorY OF NoRTH AMERICA

The present flora of North America, while it probably antedates the arrival of man upon this continent, has not remained unchanged for many thousands of years but has been constantly changing and was preceded by other and ancestral floras in which the grouping of genera, the abundance of specific types within these genera, and the range of the latter, was markedly different from what it is today. Glimpses into these floras of the past, extending back several millions of years, are obtained by piecing together the evidence furnished by the fossil remains of leaves, fruits and stems preserved in the rocks of the various geological formations.

The majority of our present forest types, those belonging to the class Dicotyledonae of the Angiosperm phylum (i.e., flowering plants with closed seed vessels) have an ancestry extending well back into the later Mesozoic or Secondary age, as the old geologists called it. The conifers (pines, spruces, hemlocks, etc.) while less numerous in existing genera and species than the hardwood deciduous trees, making up for it in a measure by their individual abundance, are of enormous antiquity, representatives of this group being present in the rocks of the most ancient deposits in which land plants have been found.

The Mesozoic age, mentioned above, was probably the scene of origin of the Angiosperms, which became abundant before its close. It is often referred to as the age of conifers (more properly gymnosperms) because of the abundance and variety of coniferous types at that time. Faunally it is known as the age of reptiles among vertebrates and the age of ammonites among invertebrates. The diagram shown on page 8 serves to graphically portray the various divisions into which geological time has been divided. In this diagram I have given the sub-divisions of the geological periods for the later ones only as those are the ones with which we are especially concerned in discussing the ancestors of our forest trees.

LATER GEOLOGICAL HISTORY OF NORTH AMERICA tz

Continental outlines have changed greatly during the vast lapse of geologic time, but the student of modern floras need not concern himself with the earlier and more profound changes due to the past movements of the strand. Those changes in geography, topography and climate which have gone hand in hand with the development of the present flora of North America may be sketched in a few words and need not be carried back farther than the Mid- Cretaceous.