Ecology of the Northern Lowland Bogs and Conifer Forests PDF
Preview Ecology of the Northern Lowland Bogs and Conifer Forests
Ecology of the Northern Lowland Bogs and Conifer Forests James A. Larsen University-Industry Research Program University of Wisconsin Madison, Wisconsin ACADEMIC PRESS A Subsidiary of Harcourt Brace Jovanovich, Publishers New York London Paris San Diego San Francisco Sâo Paulo Sydney Tokyo Toronto COPYRIGHT © 1982, BY ACADEMIC PRESS, INC. ALL RIGHTS RESERVED. NO PART OF THIS PUBLICATION MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM OR BY ANY MEANS, ELECTRONIC OR MECHANICAL, INCLUDING PHOTOCOPY, RECORDING, OR ANY INFORMATION STORAGE AND RETRIEVAL SYSTEM, WITHOUT PERMISSION IN WRITING FROM THE PUBLISHER. ACADEMIC PRESS, INC. Ill Fifth Avenue, New York, New York 10003 United Kingdom Edition published by ACADEMIC PRESS, INC. (LONDON) LTD. 24/28 Oval Road, London NW1 7DX Library of Congress Cataloging ia Publication Data Larsen, James Arthur. Ecology of the northern lowland bogs and conifer forests. Includes bibliographical references and index. 1. Bog ecology—United States. 2. Bog ecology—Canada. 3. Forest ecology—United States. U. Forest ecology— Canada. 5. Conifers—United St at e s-«—Ecology. 6. Conifers —Canada—Ecology. I. Title. QKL0U.L3U 1982 58ΐ.5,2β325 82-11368 ISBN 0-12-U36860-3 PRINTED IN THE UNITED STATES OF AMERICA 82 83 84 85 9 8 7 6 5 4 3 2 1 Preface It is a warm afternoon and the bright sun is setting in a cloudless sky. The few resident ducks sit quietly on a pond just visible in the distance. A marsh hawk has drifted past over sedges emergent in a shallow slough, the water rippling in the gentle breezes. The peace is so absolute it is almost unimaginable. One is inclined to feel, against better judgment, that this placid scene will be perpetuated forever. It will, however, be broken in a day or a week by harsher winds and flights of migrant ducks. Wedges of geese will sweep in from the north. The idyllic Elysium will turn boisterous, the tamaracks will shade into brilliant gold. The spruces will be a black onyx set into the backdrop of higher hills beyond the bog. Both bog and adjacent marsh will be covered with a drifting of fallen leaves over dried sedges. This is a book on the ecology of bogs and conifer swamps and, to some extent, the marshlands. An appreciation of bog and marshland ecology is as much an esthetic experience as is the perception of bog sights and sounds during the seasons of the year. To a scientist, there is an esthetics of science, just as to a com poser there is a science of musicology. Often, sensuous appreciation of nature precedes intellectual maturing and fascination with the sciences. The chapters that follow are, for the most part, a review of what is known about the northern bogs and lowland forests, written in the terminology of science in the hope, as well as the expectation, that such knowledge will be of value to those who appreciate the beauty of bogs and marshlands, to ecologists and other biological scientists, naturalists, wildlife conservationists, hunters, trappers, construction engineers, as well as to others whose vocations or avoca tions take them afield. The discussion is devoted, at least primarily, to the ecology of one kind of wetland—the lowland bogs and conifer forests—and treats only in passing the marshlands and other kinds of vegetational communities that are also classified as wetlands. In general, the former can be distinguished from the latter by the presence in lowland bogs and conifer forests of the Sphagnum mosses and by ac cumulations of peat. The bogs and conifer forests are, therefore, known also as peatlands, but the distinction between the two kinds of communities—peatlands and marshes — is not always clear to the unpracticed eye. A quick view of the northern landscape will, moreover, usually reveal that marshes, lowland bogs, and conifer forests are intermingled, and that these com munities all grade into one another so that it is difficult to decide where one begins and another ends. We are concerned, however, with the lowland peat bogs and forests, particularly those that have developed to a point where their identity ix X Preface is indisputable for the simple reason that no other review of accumulated knowl edge on these vegetational communities is presently available. Many books, arti cles, and research papers have been written on the marshlands, much fewer on the lowland bogs and conifer forests. This is perhaps because the marshlands are of value to hunters and trappers and all who are interested in wildlife. The marshes, too, are in most cases more accessible—a person can travel to them or through them easily by boat. The bogs and conifer swamps, on the other hand, are hard to get to, and even more difficult to get through—one must walk, and the walking is not easy, since feet sink into wet moss and peat at every step and the sense that one is mired is unsettling to say the least. Hence, the bogs and conifer forests have not been studied very much. By now, however, the importance of bogs and coni fer swamps, in regions where they are found, is becoming more deeply appre ciated, and research has expanded greatly and has begun to catch up with work on marshes in recent years. Wetlands were once valued only as wildlife habitats or as areas of potential value for agriculture, highways, or buildings. The high intrinsic value of natural, undisturbed wetlands for ground water replenishment, flood control, as well as wildlife habitat has led both federal and state conservation agencies to enact pro tective legislation and to acquire wetlands for wildlife sanctuaries and for storage basins that insure continued supplies of water for lakes, rivers, and wells. The result has often pitted private gain against public good, but growing official con cern and public awareness has given wetland conservation an impetus lacking in early days. Even so, the Great Lakes Basin Commission estimated that 20,000 acres of Great Lakes Basin wetlands are drained or filled each year. No exact figures are available on the proportion of original native wetlands that now have been con verted for other purposes, but nationally the figure is thought to range between 30 and 40 percent. In Wisconsin, figures exist to show that only about 25 percent of the original wetlands now remain in what might be considered an undisturbed condition, although some disturbance has, of course, occurred in all of them dur ing the past century. The lowland bogs and conifer swamps, which together form the peatlands, are usually adjacent to, or at least near, marshes and sloughs that provide food, shelter, and breeding ground for waterfowl, mink, and muskrats, as well as for other mammals such as raccoons and white-tailed deer. The peatlands store water that maintains adequate levels in the spawning grounds of walleye and northern pike, muskellunge, trout, perch, and other fish species. The lowland bogs are probably the only native plant community that is cropped extensively, and this for cranberries, of which Wisconsin and Michigan are the nation's top producers. This use does not seriously conflict with some of the other useful functions of bogs, such as water storage and control of sediment carried by runoff from sur rounding uplands. Much commercially valuable timber is also found in the low land forests—tree species such as northern white cedar and black spruce. Preface xi Regional economists have said that it is difficult to put an accurate price tag on any of the values that wetlands possess, but it is now clear that the preservation of the remaining wetlands may well prove vital to the environmental and economic well-being of the Great Lakes region as well as to areas where the lowland bogs and conifer forests may be found, among which are the Pacific Northwest, British Columbia, Alaska, central Canada, New England, and the Maritime Provinces. It is my hope that the environmental and economic value of the northern lowland bogs and conifer forests, as well as an appreciation of the esthetic and scientific values of the research conducted there, will be communicated to those who read this book. James A. Larsen 1 Lowland Bog and Conifer Forest Ecology: Historical Perspective Looking back over the history of ecology in the United States—not in any systematic way but as revealed in a casual reading of a few issues of old botanical journals—the sur prising thing is not that the material seems so old, but that it seems so new. There have been no great revolutions in ecological thought. There have been refinements, more detailed observations, and now, recently, mathematical treatment of data and principles, but on the whole the basic foundations of ecology laid down as long as a century ago still stand. It is significant that this should be the case. The same is true of all fundamental sciences—chemistry and physics, for example—in which underlying foundations established in the eighteenth and nineteenth centuries remain largely intact. This is only applicable, of course, to events at the level scientists were capable of studying at the time: events that can be made to occur in flasks and test tubes or that can be observed in nature, not the subatomic phenomena more recently studied with the use of an array of powerful instruments avail able to modern scientists. The same cannot be said about the so-called soft sciences. The views held today about the nature of reality in psychology, sociology, behavior—if these can be called sciences in the true sense—are in many ways modified substantially from what they were at the turn of the century. The point is that ecology does, indeed, seem more closely allied to basic sciences than to social sciences at least in these respects, although much ecological research employs stat istical methods used in social sciences, such as factor analy sis and principal component analysis, which rarely find use in basic sciences. All of this is prelude to what, to me, are some surprising ly modern statements made in the early botanical papers deal ing with the forests of the Upper Midwest—the western Great Lakes region—found in journals dating to the late years of the nineteenth and the early years of the twentieth century. 1 2 Lowland Bog and Conifer Forest Ecology Ecology now encompasses an astonishing breadth of subject matter, with as many narrowly specialized subfields as any other science and so the discussion here must necessarily be narrow and specialized. Since we are dealing with the vege tation of an area in the Upper Midwest, it will concern one field—the ecology of plant life. It will concern one aspect of the plant life of this region—the native vegetation of parts of Michigan, Wisconsin, Minnesota, and Ontario within the Lake Superior watershed or, in some instances, the upper Mississippi River, and specifically the vegetation of the low land bogs and conifer forests. Ecology is concerned with relationships between living things and their environment. For a hint of what this defini tion means in terms of vegetation, we can take an example from an early ecologist who studied the forests of the Great Lakes region. In an essay on the forests of northern Michigan, Whit- ford (1901) wrote that the purpose of his study was to answer some of the questions involved in the development of forests: In other words, the question is, why are there forests on certain physiographic formations and none on those which lies close by? Also within the forest itself there predomin ates now one and now another tree type. In some places the coniferous forest is prominent, in others the maple-beech- hemlock type is the chief feature. Indeed, if enough re gions are studied an indefinite number of combinations may be observed. Thus not only must the presence or absence of trees be explained, but also where trees are present a reas on must be given for the dominance of any particular kind of forest. If these questions can be answered satisfactorily, some light will be thrown on the origin and development of forests. In the answer three sets of factors are involved, climatic, ecological, and historical.* FOREST INFLUENCES Whitford described in more detail than we need be concerned with here the influence of the various environmental factors upon the vegetation that covered the landscape, using familiar phrases that can be found without major modification in mean ing in recent publications on plant ecology: By atmospheric factors are meant those which influence the aerial parts of plants. They include radiant energy in the form of heat and light, and also the influence of wind... * Reprinted by permisssion of The University of Chicago Press. Ecology of the Northern Lowland Bogs and Conifer Forests 3 Once a dense forest is established, all forms of low vegetation, except those species that have special shade adaptations, are driven out... Again, the struggle may be between plant societies, as the forest and heath, or forest and prairie. The line along which two societies meet has been called the tension line. If the other ecological factors remain the same, the tension line does not change... Not only may the struggle be between the forest on the one hand and some other type of plant society on the other, but it may be between different kinds of forests... The three great physical media—soil, air, and water— are all influential in bringing about certain plant societ ies. These, together with the biotic factors, make that variety in the landscape of any region which is shown in the plant societies that are present... Since trees present a greater transpiration surface than other forms of plants they must occupy those positions where there is sufficient water to maintain the transpiration current. This excludes them from regions where the water content of the soil approaches the minimum; a stagnant con dition of soil water is likewise injurious to trees... The physical properties of the soil play an important role, for upon them depends the capacity of the soil to hold water... The greater part of the eastern half of the United States is a potential forest. Here the two great climatic factors, temperature and moisture, are favorable to the development of forest trees... Within this vast forest formation there are prairie, beach, dune, heath, swamp, and other plant societies; also the forest itself may be divided into a number of different forest societies...* As a demonstration of the fact that these same general topics are those that concern ecologists at the present time, here are a few of the topical divisions of a modern ecology textbook (these are subheads within one section of the volume): "Light as an environmental factor," "The distribution of moist ure within vegetation," "Air movement above the ground and with in vegetation," "The soil environment," "Nitrogen supply." One author of a recent volume on physiological plant ecology (Ban nister, 1976) summarizes the contemporary view by stating that "physiological responses to specific environmental variables can provide at least partial explanations of ecological pheno mena. " He adds that the variables together "form a picture of the whole complex of plant-environment relationships which constitutes plant ecology." * Reprinted by permission of The University of Chicago Press. 4 Lowland Bog and Conifer Forest Ecology DISCOVERY OF THE PRINCIPLES The birth of what we now accept as the fundamental princi ples of ecology somehow seems to lack the drama and intensity of purpose that marks the great discoveries of chemistry and physics, but the parturition in each instance must have been preceded by an intuitive insight, and a feeling of profound rightness, on the part of the participants, just as Newton must have had and just as was evidently the case for Einstein with his concept of relativity. This kind of inspired flush of comprehension has been described by Keynes as the product of intuition, and he says of Newton that "his pre-eminence is due to his muscles of intui tion being the strongest and most enduring..." The same must be true, in perhaps lesser degree, of the botanists who saw that plants have not been placed over the face of the earth by some working of divine will, but rather by the influence of the en vironment. This was not always the accepted view; and the his tory of birth, denunciation, and final acceptance lies deep in the past, as the history of science goes, just as does the his tory of Newton's formulation of the principles that bear his name. In describing these origins, a noted figure in the history of American ecology, Cowles, wrote as follows in 1911: The earliest account which I have discovered that clearly deals with vegetative dynamics is in a short paper in the Philosophical Transactions in 1685, in which William King gives a good account of the origin of bog vegetation from floating mats; many times since, this has been reported as an original discovery. Perhaps the first to have a real glimmer of the doctrine of succession, as understood today, was the great French naturalist Buffon. Although better known for his spendid descriptions of animals, Buffon in his earlier life was much interested in forestry, and 1742 he noted that poplars precede oaks and beeches in the natural development of a forest...Biberg, a student of the great Linnaeus, published his thesis in 1749, and in this he des cribes the gradual development of vegetation on bare rocks; here he observes accurately the pioneer activity of the lichens and mosses, and he notes as well the importance of Sphagnum in the development of bogs. The seeds planted by Buffon and Biberg fell on sterile soil; in France it was observed that Buffon was trespassing on theological grounds, and he was obliged to recant any views which implied that the world was not made in the beginning once for all; in Sweden the influence of Linnaeus was wholly against anything dynamic; he never published anything dynamic himself, and when a student like Biberg set his face in that direction, the master frowned, and said that the student was departing from the true mission Ecology of the Northern Lowland Bogs and Conifer Forests 5 of the botanist. It is not strange, therefore, that there followed a sterile period of three-quarters of a century.* Although Buffon was obviously speaking of succession in his publication on plant communities in 1742, it was not un til 1806 that the term came into use to mean the sequential development of a community through a series of prior stages. In the latter year, a botanist named De Luc wrote: The bottom of every dale is a meadow on a subsoil of peat; this, by gradually advancing into, contracts the original extent of the lakes; and, it was well-known...that many large lakes have been converted into smaller ones, by the peat advancing from the original shores, and in many places now meadows, and only traversed by a stream, had still a lake in them, in the memory of old people...The succession of these different zones, from the border of water towards the original border of sand, represents the succession of changes that have taken place through time in each of the anterior zones... It was Huit, however, who was evidently the first to fully recognize the fundamental importance of successional develop ment in plant communities. He studied the forested land of Blekinge, Finland, and in 1885 traced the succession of each stage, seeing that grassland became heath, that the heath de veloped into forest. The early stages of forest development were dominated by birch, and on dry soil this is followed by pine, on wet soils by spruce. A birch forest can also be re placed by oak forest, which then develops into a beechwood. In swamps, the succession goes from mosses to sedges to a moor vegetation to birch and finally to a spruce forest. These faint beginnings, in the dim distance of a century, still possess some surprisingly modern aspects. So, too, do the works of Humboldt and those also of Warming, who in 1895 published his "Oecology of Plants." In 1898, Schimper pub lished "Plant Geography on a Physiological Basis," translated from German into English in 1903. Cowles published his classic, "The Ecological Relations of the Vegetation on the Sand Dunes of Lake Michigan" in 1899, followed in 1901 by "The Physio graphic Ecology of Chicago and Vicinity." EARLY AMERICANS Cowles has already been mentioned, and he stands today as one of the great hulking figures in early American plant eco logy, standing beside—but slightly apart from—Clements, of whom we speak today in perhaps somewhat awed but not entirely sympathetic terms. Of Cowles there is not much to be said, *Reprinted by permission of The University of Chicago Press.
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