The Walden Ecosystem:
“. . . a perennial spring in the midst of pine and oak woods. . . .”[1]
Edmund A. Schofield, Ph.D.
Introduction: Definition, Delineation, and Description of the Walden Ecosystem
The “Walden Ecosystem”[2] is a 2,680-acre (1,000-hectare, or ca. 4-square-mile)[3] tract of woodland, wetland, and other habitats lying east of the Sudbury River in the contiguous towns[4] of Lincoln and Concord, Middlesex County, Massachusetts, approximately fifteen miles west northwest of the State House in Boston. Its geographic coordinates are 42°27' north latitude, 71°20' west longitude. The Lincoln–Concord town line bisects the ecosystem along a southwest–northeast axis. About 1,500 acres lie in
With reference to current place names on the United States Geological Survey’s map of the Maynard quadrangle (1987),[6] the Walden Ecosystem’s approximate boundary can be described as follows[7]:—
from the westernmost point of the 45-meter contour line southeast of that section of Sudbury Road lying between the Sudbury River and State Route 2, northeastward along the same contour line, across Route 2 to the Concord–Carlisle High School; thence through the High School complex and grounds to the junction of Thoreau Street with Walden Street; thence northeastward to the western and northern shores of Fairyland Pond and on to the Cambridge Turnpike; thence east southeasterly, parallel to and north of the Cambridge Turnpike, nearly to the latter’s junction with Route 2; thence northeastward parallel to but west of the Concord–Lincoln town line to, or nearly to, the southern boundary of Minuteman National Historical Park; thence trending southward and south-southwestward into Lincoln, along and then beyond the western flank of Smith’s Hill, southward as far as the northern shore of Sandy Pond; thence southward along the western shore of Sandy Pond to the vicinity of the Pumping Station; thence southward to the junction of Baker Bridge Road with Sandy Pond Road; thence, curving gradually southward and southwestward, to the vicinity of Saint Anne’s Church, near the junction of Codman Road with State Route 126; thence southwestward along the stream that flows south of Mount Misery into Farrar’s Pond, as far as State Route 117; thence westward along Route 117 to the 36-meter contour line; thence northward about 200 meters (600 to 650 feet) to the eastern shore of the Sudbury River, just south of Fairhaven Bay; thence into Concord, in a generally northerly direction, along the eastern shore of the river, including the smaller wetlands and the river meadows, to the point on the 36-meter contour line at which the western flank of Fairhaven Hill comes nearest to the river; thence approximately along the 36-meter contour line to the vicinity of the first-mentioned point; and connecting finally with that point.
Most of the area delineated bears the green overlay indicating woodland, there being large nonwooded tracts in the vicinity of
Most of the Walden Ecosystem lies within the
On the basis of surficial geology,[10] the Walden Ecosystem consists of two units, or components—a larger and geologically fairly homogeneous “Walden Pond Unit,” in Concord and Lincoln (the “Walden Sand Plain”), and a related but geologically more diverse “Sandy Pond Unit,” which lies entirely within the Town of Lincoln. The
The Walden Pond Unit of the ecosystem is essentially synonymous with the “sand plain” of the early geomorphologists[11] and later ecologists.[12] About three quarters of the Walden Pond Unit (1,182 acres) lie in
The Sandy Pond Unit of the Walden Ecosystem (about 1,025 acres, in
The Walden Pond Unit—i.e., the sand plain, or kame delta complex—is dominated by a hydrological regime centered on or in the vicinity of Walden Pond: groundwater flows radially away from
These two physical environmental factors, physiography (surficial geology) and hydrology,[17] originally determined and continue to control the character of the Walden Ecosystem.
Approach to Determining the Boundaries of the Walden Ecosystem
Despite marked fluctuations in its borders due to logging and shifting socioeconomic pressures, the Walden Ecosystem (Walden Woods) has retained its ecological integrity and identity virtually from Colonial times. Its principal biotic community is
The boundaries of Walden Woods differ somewhat from map to map, in most cases only slightly, depending upon the decade in which the map was made. A great variety of literary references and legal records contribute to defining the full and proper boundaries of Walden Woods. All of these more traditional ways of defining geographic boundaries can be brought into sharper focus through a study of the unique ecosystem known as Walden Woods. Such a study provides insights into and explanations for those geographic boundaries. The literary, legal, and other records demonstrate that indeed there has been an entity known as Walden Woods for the past three centuries or more; the ecosystem approach—in addition to providing a rational, logical, and scientifically based method for precisely delimiting that ecological entity—reveals how and why that entity has endured in the face of vigorous long-term settlement and widespread agriculture. Even at the height of agriculture in
Determining the “full and proper” boundaries of Walden Woods presents some challenges. For example, since nearly all of
The great plant geographer A. W. Küchler distinguishes these changes by establishing several categories of vegetation, based on the extent to which human beings have affected vegetation.[18] Küchler distinguishes “actual,” “original,” “natural,” and “cultural” vegetation from each other. “Actual vegetation” he defines as “that vegetation which actually exists [on a site] at the time of observation, regardless of the character, condition, and stability of its component communities.” He distinguishes “original vegetation” from “natural vegetation.” The former, he says, exists in a landscape before man significantly affects it, but, “As much of the surface of the earth has been populated for a long time, the original vegetation is often chiefly of historical interest.”
“Natural vegetation” is the vegetation that exists in the landscape unaffected by man. “It is,” Küchler says, “in balance with the abiotic and biotic forces of its site. The biotic forces include man, as long as his activities do not alter the vegetation basically. As of when such a change is basic can be determined only in an arbitrary way or by agreement.”
In some parts of the world (e.g., high-altitude areas and high-latitude areas) the original natural vegetation and the actual natural vegetation coincide, implying that man has played no significant role there.
In a crucial passage, Küchler establishes yet another category, the “potential natural vegetation”:
Usually, man has become very active, destroying natural plant communities, changing them or replacing them with others. Hence we can speak only of the potential natural vegetation. This, however, is most important, and in order to obtain it, two assumptions are necessary: (1) that man be removed from the scene, and (2) that the resulting succession of plant communities be telescoped into a single moment in order to exclude the effects of climatic changes. This, then, is the potential natural vegetation of today. In it, man’s past activities may remain a factor. It is essentially the same as the climax vegetation. . . .
Frank E. Egler[19] says that a plant community “is a spatial phenomenon, a relative continuity between relative discontinuities (or ‘ecotones’), in whatever terms the community is defined. As a spatial phenomenon, the community has borders, edges, or margins.” The “most desirable” kind of border, “from the standpoint of a tidy Vegetation science,” he continues, “is one that is an abrupt and sudden change in predominant species. . . .” In the case of Walden Woods, “abrupt and sudden change in predominant species” along certain of its borders—and, indeed, within Walden Woods itself—is due to centuries of human intervention and is not a reflection of natural (i.e., nonhuman) influences.
It is tempting, in trying to delineate the full and proper boundaries of Walden Woods, to use abrupt spatial changes in vegetation (from, say, woodland to farmland) as the criterion; but the long history of human—especially European—influence on Walden Woods and the fluctuation of such abrupt changes from decade to decade make this approach less than desirable. What Egler calls “A Site Border,” however, serves our present purpose very well. With respect to this type of plant-community border Egler says (page 93):
There are times when the Vegetation itself forms no obvious and distinct [and, we might add, with respect to Walden Woods, no permanent or stable] borders, but the site itself does. This site border may be in terms of soil, or rock substratum, of water table, or of some other feature of the environment. For example, a sterile acid sand may lie sharply demarcated from a heavy limestone-derived soil. In such instances it may be reasonable and just to demarcate the community in terms of the environment. If the present Vegetation does not show a distinction, it would be reasonably certain that the history of the area had been different, and that the potentialities for such as timber or forage would be different [emphases added].
Egler defines and discusses[20] another kind of border that applies to Walden Woods, the “Anthropic” border—i.e., a border due to, and reflecting, the uses to which the land has been put by human beings. As examples of anthropic borders Egler mentions fence lines, highways, and powerline rights-of-way. “Even in newly settled
Clearly, differences in the species composition of various parts of Walden Woods reflect anthropic factors, given the three and one-half centuries of European influence on the land and the several millennia of previous Indian influence[21]; similarly, anthropic factors must be included in any attempt to determine the borders of Walden Woods. With respect to Walden Woods, however, it is abundantly clear that the anthropic factors have been strongly influenced, or controlled, by site factors: that is, surficial geology and hydrologic regime have had an overriding influence on the uses to which people have been able to put the land (farming versus forestry, for the most part). Thus, while the borders of Walden Woods must be established largely with respect to fluctuating or ephemeral anthropic factors, the anthropic factors in turn must be interpreted strictly in reference to such permanent site factors (which they reflect) as surficial geology, soil properties, and depth to groundwater.
Thus, the mere presence or absence of trees at any one site at any particular time is probably the least reliable criterion for establishing the exact boundaries of Historic Walden Woods. Ecological relationships, which are perennial and for all intents and purposes permanent, and which transcend the caprices of economic trends, are far more useful for that task: surficial geology, hydrological relationships, and certain soil characteristics are stable environmental factors.
Cartographic Evidence
Walden Woods appears as wooded terrain on maps drafted or published over the past two centuries or more[22], although it is named on only one of the maps. It is a perennial and persistent feature of such maps, although its borders fluctuate with the ebb and flow of socioeconomic forces. On no map on which woodland is designated is Walden Woods absent; on the contrary, it is a conspicuous feature of all known maps that depict vegetative cover or the presence or absence of woodland.
In his history of Lincoln,[23] John C. MacLean indicates (map, page 55) that there were woodlots along what is now the Lincoln–Concord town line, between Fairhaven Bay and Walden Pond, in the seventeenth century. He states (page 155) that “the west part of
Shattuck[24] states (page 9) that the settlers established their farm lots “extending back from the road across the Great Fields and Great Meadows, and in front across the meadows on Mill Brook . . . because it contained land of easy tillage . . . ,” while (page 15) “The uplands, which the first planters selected for cultivation, proved to be of a poor quality. . .” [emphasis added].
Ecological Evidence
Walden Woods consists primarily of mixed deciduous–coniferous woodland. It includes also smaller “peripheral” and “included,” contingent habitats such as ponds, wetlands, and watercourses. Its configuration and characteristics are determined in the first instance by local and regional hydrological relationships, which are in turn determined primarily by surficial geology. Historic land-use patterns in the Walden Ecosystem have reflected the same controlling environmental influences, especially the hydrological relationships.
By definition, Walden Woods lies east of the
Walden Woods is best described, understood, and treated as a single, self-contained ecosystem. Its origins as an artifact of the retreating continental glacier, outward-flowing groundwater regime, and deep water table all confer unity and ecological coherence on it. Its internal integrity is reflected in the limited, woodland-dependent uses to which the Walden Ecosystem has been put since European settlement. Its distinctiveness is brought out sharply when its land-use history is compared with that of surrounding areas, especially the area to its north, in
The environmental factor that ultimately controls the character of the Walden Ecosystem is the vertical distance from the surface of the ground to the water table, which is well over ten feet in most parts of the ecosystem (excluding, of course, the ponds, streams, and wetlands and the zones immediately surrounding them). This great depth to groundwater is due, in its turn, to topographic relationships and, especially, to the highly permeable nature of the glaciolacustrine (glacial-lake) and glaciofluvial (glacial-stream) ice-contact deposits (kames, deltas, eskers, etc.) on which the Walden Ecosystem has persisted despite three and one-half centuries of intensive farming in Lincoln and (especially) Concord. The deep water table and highly permeable substrate create growing conditions that are inimical to farming.
By the same token, the deep water table and highly permeable soils of the Walden Sand Plain supported a distinct biotic community—the Northern Pine–
Biotic Communities
The biotic “community” is a key concept in modern ecology. “Everyone recognizes the differences between forests and fields,” states Golley,
and those who depend upon these natural systems, such as hunter–gatherers, foresters or range managers, recognize a variety of types of each. These types are termed communities and they are characterized as the complex of plants, animals, and microorganisms living together at a defined time and place.
Two fundamental problems of community ecology relate to studies of ecological succession. First, ecologists have asked if communities are distinct, real entities in nature or are they mental constructs? . . .
The second problem grows out of the first. If communities are real, how are they related to other natural systems?
Odum distinguishes two kinds of biotic communities, “major communities” and minor communities.”[26] Major communities
are those which are of sufficient size and completeness of organization that they are relatively independent; that is, they need only to receive sun energy from the outside and are relatively independent of inputs and outputs from adjacent communities. Minor communities are those which are more or less dependent on neighboring aggregations.
This distinction can readily be applied to Walden Woods: the major community is the wooded part of the ecosystem (the oak and pine woods—formally designated the “Walden Northern Pine–Oak Forest”), which occurs on the higher and drier terrain, while the minor communities (plural) are the ponds, pools, streams, and wetlands that are interspersed within and around the woodland; they are functions, even “accidents,” of topography (occurring—in the case of the ponds, pools, and wetlands—in depressions or other low areas, where the water table approaches or intersects the surface of the ground), and which depend “more or less” upon the encompassing or adjacent woodland for, e.g., their metabolic energy in the form of organic detritus. In this report, these minor communities might be referred to as “contingent ecosystems” because they derive their existence and identities from the same geomorphological and hydrological factors as the woodland, and obtain nutrients and energy from the woodland itself.
Odum (1983) distinguishes the term “biotic community” from the term “ecosystem” as follows:
. . . [C]ommunity, in the ecological sense (sometimes designated as “biotic community”), includes all the populations occupying a given area. The community and the nonliving environment function together as an ecological system or ecosystem.[27]
A biotic community is the integrated expression or manifestation of a few fundamental controlling environmental factors: of climate (the availability of water over the course of a year, annual temperature regime, etc.); of geology (composition, texture, and pH of substrate; etc.); and so on. The distribution of plants and animals is anything but random; on the contrary, it is intimately related to and strongly determined by the physical environment; nor is the overall combination of organisms at a site—plants, animals, microorganisms, etc.—random or arbitrary. Certain animals (herbivores) and parasites feed only on certain plants (primary producers), some on only one or a few species of plants, others on many species; certain animals (primary carnivores) and parasites feed only on certain animals (again, some on only one or a few, others on many); and certain other animals (secondary and tertiary carnivores, or tertiary and quaternary herbivores) feed only on certain primary carnivores (yet again, some on only one or a few, others on many).
In this way, “food webs” are established among the plants, animals, and organisms of a biotic community, whose presence in the community was in turn determined by a few overriding environmental factors of climate, geology, hydrology, etc. Each stage, or node, of a food web is called a “trophic level,” “trophic” being derived from the Greek words trofe (“food”) and trofein (“to feed”). The plants “feed,” of course, on sunlight (solar energy), while the “decomposers”—bacteria, fungi, etc.—break down the organic matter excreted by or created upon the death of the producers and consumers.
In modern ecosystems science, this transfer of food from trophic level to trophic level is seen to consist of two linked phenomena: the flow of energy into, through, and out of an ecosystem (“energy flow”) and the cycling of matter (minerals, water, etc.) within an ecosystem (“nutrient cycling”). This conceptual framework guides ecologists in measuring the energy flow and nutrient cycling of ecosystems and thus permits them to understand how ecosystems function. The framework is derived from the infra-ecosystemic links among the organisms that compose the ecosystem; it also contributes to the realization that an ecosystem, which is composed of both biotic (living) and abiotic (nonliving) components, is a functional unity, not a disparate, random agglomeration of isolated, unconnected, or randomly juxtaposed components. Even in the face of prolonged perturbation by human beings, as in the case of the present Walden Ecosystem, the functional unity is perceivable in the form of the classic indicator species that occur there. Developmental community ecology tells us that were human interference to cease or moderate, a mature Northern Pine–Oak Forest would again occupy the Walden Sand Plain after the lapse of a few decades. If fires could be prevented altogether, the
Concept of the ecosystem
Bates and Jackson define an ecosystem as
An ecologic system, composed of organisms and their environment. It is the result of interaction between biological, geochemical, and geophysical systems.[28]
Odum states that
Any unit (a biosystem) that include all the organisms that function together (the biotic community) in a given area interacting with the physical environment so that a flow of energy leads to clearly defined biotic structures and cycling of materials between living and nonliving parts is an ecological system or ecosystem.
The ecosystem is the basic functional unit in ecology, since it includes both organisms and abiotic environment, each influencing the properties of the other and both necessary for the maintenance of life as we have it on earth. . . .[29]
Smith (1970) states, with respect to the emerging science of ecosystem analysis, that
Conceptually the ecosystem is viewed as a functional unit with recognizable boundaries and an internal homogeneity. Operationally, we first recognize that boundaries are arbitrary and that functional unity may exist like beauty only in the eye of the beholder. We have, therefore, defined the ecosystem as everything that exists and happens within a precisely bounded region. Two sets of criteria are used for the location of the boundary. For many purposes the region must be large enough to contain a full set of ecosystem processes and their interactions; secondly, the boundary should be placed where inputs and outputs across it are most easily measured.
Once an ecosystem is defined by the location of its boundary (perimeter, roof, and floor), the next stage is to identify all its significant components. The air, land, and water can be subdivided into a number of components, and the plants and animals can be broken down to their species or to major species and groups of minor species. By lumping or splitting in various ways, the total number of components in an idealized ecosystem can vary from 5 to 50,000, the only restriction being that they must always add up to the whole ecosystem. . . . Hopefully, the total number of components needed to account for the significant ecosystem processes will not be more than several hundred.
The four major groups of components are the producers, the consumers, the decomposers, and the abiotic environment.[30]
A “natural resource ecosystem” is
an integrated ecological system, one element of which is a product of direct or indirect use to man. The product may be biological as in the case of forests, ranges, agricultural products, fish, and wildlife; physical as in the case of water, air, and soil; or both. In all cases, the distinguishing facet of a natural resource ecosystem is that man has a direct involvement in the complex set of ecological interactions.
Management is defined as the manipulation of the ecosystem by man. Beneficial management involves manipulation to maximize the returns to man, while exploitation is management that results in the reduction of the productivity of the ecosystem to mankind over a period of time. The ecological principles of natural resource ecosystems are generally applicable regardless of the particular natural commodity. So, too, are the tools of management and the basic rules governing their application. The principles of ecosystem management apply equally to wilderness and to the urban environment, but they are most clearly understood today with regard to the wildland resources of forest, range, wildlife, and the like.[31]
Spurr (page 6) traces a major branch of the science of ecology, “synecology,” “directly back” to eighteenth and nineteenth century naturalists, citing specifically only Thoreau and his work on the succession of forest trees, and Charles Darwin, both of whom lived worked during the nineteenth century. Synecology, Spurr notes, has developed along two major lines during the twentieth century: (1) along the lines of the American plant-succession school and (2) along the lines of the European plant-sociological school.
Odum[32] states that “Because outdoor ecosystems are complex, hard to delineate, and often difficult to study by traditional means of ‘experiment and control,’ many ecologists are turning to laboratory and field microecosystems which can have discrete boundaries and can be manipulated and replicated at will.” He discusses several “outdoor ecosystems”: an open-water pond, a watershed unit, and a meadow or old-field. With respect to the watershed unit, Odum says, among other things, that
it is the whole drainage basin, not just the body of water, that must be considered as the minimum ecosystem unit when it comes to man’s interests [italics in original]. The ecosystem unit for practical management must then include for every square meter or acre of water at least 20 times an area of terrestrial watershed. . . . The entire drainage or catchment basin must be considered as the management unit. . . .[33]
The Walden Ecosystem
The Walden Ecosystem is analogous to a watershed unit (catchment, or drainage, basin), except that (1) it is topographically convex (an upland plain), not concave, and (2) water (groundwater) flows radially outward from its center (Walden Pond), like spokes from a hub, rather than into its center as does water in the drainage basins of ordinary ponds or streams. Because of its tight links to the local topography and surficial geology, the Walden Ecosystem is nearly as discrete, homogeneous, and easily delineated as is a lake or pond.
Harold F. Hemond, a hydrologist who was affiliated with the Department of Civil Engineering at the Massachusetts Institute of Technology, applied such principles to his study of Thoreau’s Bog, or Gowing’s Swamp, in
Referring to Koteff’s map of the surficial geology of the
Hydrologically the ecosystems differ as well, since the groundwater is near or above the surface in the bog ecosystem but very deep in the Walden Ecosystem. Nonetheless, both ecosystems are describable and definable by reference to the same general phenomena or environmental factors, and by means of the same terminology. With respect to hydrology, for example, the bog is permanently wet, while Walden Woods is permanently dry, wetness and dryness being aspects of the same environmental factor. Hydrological relationships, which are modulated by surficial and bedrock geology, determine whether a site will be wet or dry. The wetness or dryness of a site, or habitat, along with other environmental factors, determines which plants and animals will be able to survive on the site.
Hemond notes that the “bog itself is part of a larger wetland complex, the bulk of which may best characterized as red maple swamp.” Hence, in the terminology established in the present report, Thoreau’s Bog is an included ecosystem of the larger Red Maple Swamp ecosystem. Hemond notes, for example (page 524), that
the adjoining hummocky red maple swamp may contribute in a small but important way to the water balance of the bog, since it [the swamp] provides a catchment area which is physically separated from the upland and the mineral soil groundwater regime. This catchment becomes uncovered, and thus increases water input to the bog, during the driest months of the year. Although difficult to quantify precisely, the contribution of this catchment could effect a significant increase in surface and subsurface runoff, and thus have an impact on bog geochemistry. In turn, the surface runoff, being strongly stage dependent, acts as a regulation mechanism in maintaining mean annual bog stage (and perhaps, as a result, a constant growth rate of Sphagnum moss).
The 2,680-acre Walden Ecosystem consists of two linked “units,” or subunits, viz.: (1) the “Walden Pond Unit” of 1,660 acres and (2) the “Sandy Pond Unit” of 1,020 acres. Except for its till-covered portions (Fairhaven Hill, Emerson’s Cliff, Mount Misery, etc.), the Walden Pond Unit consists of sands and gravels deposited in Glacial Lake Sudbury along the edge of the receding glacier, the Sandy Pond Unit (except for its till-covered portions—Pine Hill and Bear Hill) of coarse sands and gravels deposited by torrents of glacial meltwater flowing into Glacial Lake Sudbury during the lake’s very last stages. The till-covered portions were islands or peninsulas in Glacial Lake Sudbury and therefore were not covered by the sands and gravels carried in the glacial meltwater.[35]
An important link between the two units of the Walden Ecosystem is Pine Hill in
While it is ecologically integrated, the Walden Pond Unit is not homogeneous, even in its non-wetland portions. It does exhibit some degree of gradation (though not disjunction) along axes fanning outward (primarily southward) from the receding ice-contact source of glacial meltwater, the gradation being primarily in the particle-size distribution of the sand and gravel deposits (as is typical of deltas and other ice-contact, glacial-lake features), heavier particles of gravel and sand having been deposited closer to the edge of the ice than the lighter particles. This may explain why historically there have been a few enclaves of farming in the southern part of this unit (Baker Farm, etc.). Another reason may be that groundwater flowing southward from Walden Pond and southwestward from Sandy Pond and into Fairhaven Bay is forced nearer the surface of the ground by bedrock highs or topographic lows (the Sudbury River Aquifer, one of Lincoln’s principal aquifers, lies beneath those farming enclaves).
An ecosystem consists of both (1) abiotic and (2) biotic elements, by definition. The Walden Pond Unit of the Walden Ecosystem thus consists of (1) the Walden Sand Plain (plus the related geological elements of the Sandy Pond Unit) and (2) the
The Sandy Pond Unit of the Walden Ecosystem, while related to the Walden Pond Unit through its common geological origins and hydrological regime, is not a “sand plain,” or kame delta complex. (Koteff’s map of the surficial geology of the
Soils of the Walden Ecosystem[37]
Although climate is largely responsible for the nature of the plant cover in a given area, soils and topographic relief are important also. For example, the effectiveness of rainfall may be offset by a very porous soil, or by marked relief that leads to rapid runoff. Ravines or river bottomlands may offer situations that are cooler and damper than all the surrounding region. Steep and rocky hillsides, coarse gravels, rocky outcrops, permanently wet depressions, subsoils exposed by erosion—all may inhibit local development of a vegetation that is widespread in the general vicinity. Plants need four essential services to become established in a particular soil: anchorage, a supply of water, mineral nutrients, and aeration of roots. Species of plants differ in the degree to which they require these “services.” From this perspective, a soil has four major components: (1) mineral material derived from the parent rock; (2) organic substances added by plants and animals; (3) water; and (4) soil air. These components vary in amount and proportion from place to place, and the variation may be a significant factor in determining the occurrence of species and vegetation types.
Soils consist of (1) an inorganic, mineral component—the “matrix material,” or “parent material”—and (2) an organic component consisting of still-living, dead, and partially decomposed organisms (plants, animals, and microorganisms). Under the influence of such climatic factors as temperature and precipitation and such local and site-specific factors as drainage and topography, soils develop on newly exposed matrix material, whether it be lava, water-laid sediments, or, as in the case of Walden Woods, glacial deposits.
Soil, the Dictionary of Geological Terms declares, is merely “The natural medium for the growth of land plants.”[38] The Soil Conservation Service of the United States Department of Agriculture defines soil more expansively, as “A natural, three-dimensional body at the earth’s surface . . . capable of supporting plants and [having] properties resulting from the integrated effect of climate and living matter [i.e., organisms] acting on earthy parent material, as conditioned by relief [topography] over periods of time.”[39] From an ecological point-of-view the second is the more meaningful and sophisticated definition, but it appears to contradict the cause-and-effect relationship between soils and plants described by Griscom. In fact, however, it does not, for soils and plants (“vegetation”) have reciprocal cause-and-effect relationships, and both are influenced by climate (and topographic relief): soil and vegetation strongly affect, and even control the character of, each other, but local climate and topography modulate the way in which and the degree to which they do so. Topography affects vegetation indirectly by modifying other environmental factors, but it nevertheless has a significant influence upon all plant communities. The greatest differences in vegetation associated with local variations in topography can usually be correlated with moisture, either in respect to an excess or to a deficiency.[40]
Soil scientists distinguish two kinds of soils, zonal soils and intrazonal, or azonal, soils. Zonal soils occur over wide, more or less continuous areas of the so-called “general upland,” while intrazonal, or zonal, soils occur on special or unusual sites—so-called “abnormal” areas. Climate, which varies with latitude and longitude, includes the important factors in soil formation, especially temperature and rainfall. Within a climatic area, differences in parent material and topographic position often are reflected in soil variations, which may be chemical or physical. Such variations are most pronounced where parent rock is newly exposed or where soil materials have weathered but slightly, as below a receding glacier. After longer exposure the developing soils become much more alike, and the longer the time involved, the less noticeable will be differences related to local conditions. Evidence is sufficient to indicate that, within a climatic area, soil development progresses toward a a particular kind of soil and profile regardless of the origin or nature of the materials; likewise, that the ultimate soil group for similar climatic regions of the world will be similar to each other.
Since climatic conditions determine the activities and kinds of organisms of a region, it is not surprising that vegetation types and soil types are closely related. The development of a soil is paralleled by vegetational changes, the vegetation contributing to soil maturation an the soil controlling a progression of plant communities. Ultimately, the majority of the soils in a region and the communities they support attain a state of equilibrium with each other under the existing climate. The soils will then have similar mature profiles and the vegetation will be in climax condition. Likewise, the general area in which mature soil profiles are similar will coincide with the general range of a climax vegetation type.
Egler notes that there are striking correlations between the major physiognomic Vegetation regions [of
Podzolization occurs typically in humid, cold temperate regions where rainfall exceeds evaporation and where vegetation produces acid humus. The acid decomposition products from the litter increase the solvent power of the plentiful percolating water so that soluble materials and colloids are almost completely removed from the surface soil, which is therefore, of single-grain structure at maturity. Although podzolization occurs under hardwood and pine forests, its strongest development takes place where spruce, fir, or hemlock are dominant. The process is partly the product of the vegetation, for the content of bases in the needles of these trees is notably low, and decomposition products of the litter they produce always give an acid reaction. Podzolization occurs in cool, moist temperate regions; it is typical of infertile acid soils with an upper gray silica layer and a lower layer rich in aluminum and iron.[42]
Laterization is characteristic of tropical conditions with high temperatures and abundant rainfall. It is essentially the leaching of silica from the surface soil. The low acidity produced by decomposition of tropical litter promotes the solution of silica as well as of alkaline materials. After laterization, the surface soil is high in iron and aluminum, which are not removed by the process. True laterites are red throughout. Laterization occurs in warm, moist regions, where the silica in the parent material is lost from the surface layers by leaching, and where the iron and aluminum accumulate above.[43] There are many American classifications of soils. One of the most commonly used is a binomial system that reflects both genetic and textural characteristics. For example, “
There are close parallels between the concepts soil scientists have devised for describing and understanding soil development and those for the development of ecological communities. Soil scientists speak in terms of “mature” soils at steady state, for example, while ecologists recognize the “climax” communities that grow on and live in these same soils. (A climax community, the final stage in ecological succession, is stable, self-replacing, and in dynamic equilibrium with its environment.) These two components of the ecosystem—soils and vegetation—are intricately interrelated and interdependent; each strongly influences the other. Except in forests and rain forests (in which there is a north–south, temperature-dependent gradation from podzols to lateritic forest soils), there is usually a one-to-one correspondence between types of vegetation and soils.
Through the process of ecological succession a mature biotic community develops on a site in response to regional climatic and local geological factors. The community continues to occupy the site until some natural or manmade force (e.g., fire, lumbering) intervenes. Similarly, the soil of a particular site develops in response to the plants that grow in it for centuries or millennia. Thus, the soil reflects its original natural vegetative cover, even after the vegetation has been removed, and it continues to do so for many decades or centuries. (Only the most severe catastrophe could obliterate altogether the vegetation’s impact on the soil.) For this reason, perennial ecological factors and relationships, not the chance presence or absence of trees at the time a particular survey, map, or photograph was made, must be used to arrive at a full and accurate delineation of Walden Woods.
Even when ditched and drained, for example, a wetland soil is identifiable as a wetland soil. The thick layer of partially decomposed organic matter laid down over millennia in the wetland imparts certain diagnostic characteristics to the wetland’s soil and remains after it has been exposed to the air, oxidizing gradually. By the same token, a soil developed in an arid site is recognizable as such long after it has been artificially flooded. It takes decades for a layer of organic matter to accumulate in the new wetland, just as it will take decades for that in the natural wetland to disappear through oxidation; even then a soil scientist probably could distinguish the developing soil from a natural wetland soil.
The same principle applies to farmed woodland soils: even after decades of farming, a woodland soil is identifiable as a woodland soil. Furthermore, one can even make reasonable inferences about the types of trees—deciduous versus evergreen, for example, or a mixture of both—that grew in a woodland soil before it was cleared for farming. Only after decades or centuries under the new environmental conditions do the original “telltale imprints” fade from a soil as the new conditions impose a different profile upon it. The soil profile is as much a record of a site’s ecological or land-use history as are the written records that human beings habitually store in libraries and courthouses. One needs only to understand the “language” in which that record was set down—the meaning, for example, of a thick layer of partially decomposed organic matter, as in a wetland, of salinity, or of high acidity, as in other types of soils. Three and one-half centuries of use by Europeans have scarcely smudged the “ink” in which most such records were “written” on the earth’s surface by vegetation and climatic factors.
The surficial geology of
In the millennia that followed the glacier’s retreat, first tundra plants and then forests reclothed the newly exposed landscape. The forest had returned within two thousand years of the ice’s retreat, and have covered most of New England in one form or another ever since. They underwent a series of changes as a result of climatic shifts, the immigration of species, natural catastrophes, and (especially since the arrival of Europeans three hundred and fifty years ago) human impact. Beneath the forests, the processes of soil formation (“pedogenesis”) created podzols, characteristic northern forest soils.[47]
This forest and the climate that supports it have worked together to produce a certain type of soil from the underlying material. These soils are classified as spodosols. Spodosols are formed by a combination of coarse, acidic parent materials, a moist, cool climate, and forest vegetation. They have very little stored fertility. They may support magnificent forests, but the system cycles nutrients slowly and stores little surplus. Thus, spodosols are quickly exhausted when put into crops unless they are very skillfully maintained (actually transformed) by soil-building practices.
The till in the Walden Woods area probably averages 15 feet thick, less in areas of abundant bedrock outcrops, although locally there are accumulations of till as much as 30 feet thick.[48] Kame deltas were built in contact with ice on one or more sides; many are connected with eskers or ice-channel fillings that acted as “feeders” to the kame deltas.[49] The esker in the Laurel Glen section of Walden Woods is an excellent example of such an esker.
In a highly formalized system of nomenclature, names denoting what are called soil “types,” have been assigned to soils. Each type of soil has a unique combination of salient, distinguishing, and edaphically significant characteristics. These characteristics are not selected arbitrarily by soils scientists, but according to the information they provide about a soil’s origins, environmental relationships, and—significantly in the present context—potential uses. A name efficiently conveys large blocks of information about the soil or soils of any one particular site. Thus, pH, chemical composition, amount of organic matter, color, water-holding capacity, cation exchange capacity, and other measurable or describable characteristics are employed to define a soil type; conversely, as a corollary, one immediately knows a good deal about a sample of soil to which one of the formal names has been applied: its approximate pH, for example, its organic-matter content, and its color. One also can make reasonable predictions about its uses by human beings: whether it is suitable for agriculture and, if it is, for what specific kinds of agriculture.
There is a certain amount of tautological reasoning in soil science. Soil science has been supported over most of the past century or two largely to serve agriculture. In recent decades engineering considerations have been taken increasingly into account. Hence, some (but not all) of the characteristics that routinely are used to characterize and distinguish among soil types are selected because of their relation to agriculture or engineering. Many of the characteristics have ecological significance in their own rights, however; that is to say, they have as much significance for the ecologist as they do for the agriculturist or building contractor. With respect to agriculture this may amount to a distinction without a difference, since agriculture deals principally with plants, and plants are arguably the most important components of ecosystems. Thus, it is neither surprising nor inappropriate that ecologically significant factors should have value as well for agriculture, nor that agriculturally significant factors should be of use or interest to ecological science.
The soil map of the Walden Woods area[50] can be simplified somewhat, or generalized, as a means of interpreting and understanding the land-use history of the Walden Ecosystem. Generalization of this kind is an accepted procedure for interpreting the soils and constructing soil maps of an area.
There are two types of generalization, “cartographic generalization” and “categorical generalization.” “Cartographic generalization” is
the practice of omitting lines between soil bodies as shown on detailed soil maps to reduce the detail on the map—or between different taxonomic units if taxa of levels higher than the soil series are used to define and describe the basic map units. That is, it results in a lowering of the number of soil delineations. . . ,
whereas “categorical generalization” is
the identification and description of soil map units in terms of taxa[51] at levels of abstraction higher than the soil series. That is, it involves use of taxonomic units from the family through the order levels to designate the mapping unit name and thus reduce the classification or taxonomic detail.[52]
Spodosols, occurring both on till and outwash, make up at least three-fourths of the soils of
Peats form where accumulations of dead plant material gradually fill up ponds, developing into bogs. Such sites are usually kettleholes, or depressions, in outwash plains or kame delta complexes left by the melting of stranded pieces of ice. Mucks form where drainage is so slow that wetness impedes the full breakdown of organic matter. In their natural state, neither of these soils is very fertile because nutrients are locked in the coarser organic matter. When the swamps and meadows are drained, however, the organic matter oxidizes and decomposes, releasing nutrients, particularly nitrogen, and making these soils potentially the richest to be found in the area.[53]
The Soil Conservation Service describes
The many different kinds of soil in
The many different kinds of soil in a community occupy the landscape in natural recurring groups that are called “soil associations.” Because soils occur on the landscape in such groups, it is possible to make a general soil map that delineates broad areas having the same kinds and combinations of soils. These areas are called “general soil areas.”
A general soil area is made up of a few dominant soils and several other soils of lesser extent. Each general soil area is named for the dominant or the more prevalent kinds of soils it contains. The soils within a general soil area may be similar to one another, or may have widely differing properties. Commonly, however, the properties of the dominant soils within a general soil area have about the same degree of limitation for a particular use. For example, a general soil may contain two dominant soils that occur primarily on 0 to 8 percent slopes. One of the soils is well drained and has formed in deep sand deposits; the other soil is excessively drained and has formed in deep gravelly deposits. These soils are similar to one another as both of them have a rapidly permeable substratum, and the seasonal high water table is many feet below the surface.
Each general soil area may contain secondary, less extensive soils that constitute 10 to 30 percent of the area. These secondary soils may have properties and limitations either alike or greatly different from the dominant soils in the general soil area. It is the dominant soils that determine the overall suitability of the general soil area for a particular use, even though there are tracts of land containing secondary soils that have a completely different suitability for that use.[55]
The Windsor–Hinckley–Deerfield Association occupies about half of
Droughty
Most of this general soil area has slight limitations for agricultural use, although supplemental irrigation is needed during most growing seasons to insure satisfactory crop yields.
Merrimac soils are well drained to somewhat droughty soils formed in sandy material underlain by layers of sand and gravel at a depth of about 2 feet. In places, the surface soil and the subsoil contain some gravel, but they do not contain stones or boulders. These soils are loose and porous, especially in the substratum. Surface soils and subsoils have moderately rapid or rapid permeability, and the underlying sand and gravel layers have rapid permeability. Water tables in these soils are generally more than 10 feet from the surface.
The soils of
Correlation between Geology and Vegetation
Walden Woods lies along the junction of the Fells Upland and
The bedrock of the
In his book on the birds of Concord, Ludlow Griscom, an ornithologist who was affiliated with Harvard University’s Museum of Comparative Zoology, states matter-of-factly (but correctly) that
The geology and climate [of an area] come first. The underlying rocks and soils condition the flora. The climate also controls the length of the vegetative season, and therefore the composition of the flora.[59]
Professor John C. Kricher, an ecologist who teaches at
a plant cannot escape an unsuitable area by merely running, hopping, or flying away. Therefore, plant distribution is tightly linked to climate and soil type, both of which vary considerably across
Kricher points out that geology and soil—the substrate—have a very strong influence on biological communities. The pH, texture, and drainage of soils are ecologically important characteristics. “Geological characteristics and soil type vary throughout eastern
and combine with climate in affecting forests. . . . For example, some species . . . are common only on soils rich in limestone. Other species . . . prosper only on sandy soils too poor for many other species. A forest may be xeric . . . because it is located in a hot, dry climate or because it sits on sandy, highly drained soils that cannot retain moisture. Though not as important a determinant as climate, soil and geological characteristics cannot be neglected in interpreting forest types.[61]
Thoreau was acutely aware of the correlation between soils and vegetation. For example, in his Journal entry for October 17, 1860, he states
It is an interesting inquiry what determines which species of these [trees—viz., white pine, pitch pine, oaks, white birch, and red maple] grow on a given tract. It is evident that the soil determines this to some extent, as of the oaks only the swamp white stands in our meadows, and, so far as these seven trees are concerned, swamps will be composed only of red maples, swamp white oaks, white birch, and white pine. By removing to upland we get rid of the swamp white oak and red maples in masses, and are reduced to white and pitch pine, oaks, and white birches only, i.e., of those that are abundant and important.
Even as early as 1837, when he was only twenty, Thoreau was well aware of the correlation between plants and soils:
Every part of nature teaches that the passing away of one life is the making room for another. The oak dies down to the ground, leaving within its rind a rich virgin mould, which will impart a vigorous life to an infant forest —— The pine leaves a sandy and sterile soil—the harder woods a stronger and fruitful mould ——
So this constant abrasion and decay makes the soil of my future growth. As I live now so shall I reap. If I grow pines and birches, my virgin mould will not sustain the oak, but pines and birches, or, perchance, weeds and brambles, will constitute my second growth. ——[62]
Glacial
In a long passage in the “Spring” chapter of Walden Thoreau describes leaf-like patterns created by the oozing of “sand of every degree of fineness and of various rich colors, commonly mixed with a little clay,” from the Deep Cut, a twenty- to forty-foot high bank created a year or two before Thoreau went to live in Walden Woods, when the Fitchburg Railroad was being built. This passage, probably the artistic and philosophical climax of the entire book, owes its existence to the water-laid deposits of Glacial Lake Sudbury.
The hydraulic gradient is the direction in which groundwater flows under the force of gravity.[63] It is determined by the amount of precipitation, the precipitation regime (or seasonality of precipitation), surficial geology, porosity of the substrate or mantle material, and depth to bedrock.
The Walden Ecosystem is unified by virtue of the fact that groundwater flows outward from the System on all sides except the eastern (because of the presence of Pine Hill, off of which groundwater flows in a westerly direction into
Eugene H. Walker’s article, “Walden’s Way Revealed,”[64] Anthony Maevsky’s report on groundwater levels in Massachusetts from 1936 to 1974[65], and Henry Thoreau’s comments in his Journal and Walden[66] all describe and discuss the hydrological relationships of Walden Pond and the other ponds on the Walden Woods kame delta complex, including the central role of the system’s fluctuating water table.
Thoreau’s comments in his Journal and in Walden reflect his awareness of the hydrological unity of the Walden Ecosystem. “I have said that Walden has no visible inlet or outlet,” he writes in his Journal,
but it is on the one hand distantly and indirectly related to Flint’s [i.e., Sandy] Pond, which is more elevated [for example, 70.5 meters above sea level in 1987, as opposed to Walden’s 48.5 meters], by a chain of small ponds coming from that quarter [Goose Pond, Little Goose Pond, and the smaller nearby kettle ponds], and on the other hand directly and manifestly related to Concord [i.e., Sudbury] River, which is lower [circa 35 meters above sea level], by a similar chain of ponds [the Andromeda Ponds], through which in some other geological period it may have flowed thither [into Fairhaven Bay, an embayment of the Sudbury River], and by a little digging, which God forbid, could probably be made to flow thither again.[67]
In Walden, Thoreau states:
The pond [i.e.,
As for the inlet or outlet of Walden, I have not discovered any but rain and snow and evaporation, though perhaps, with a thermometer and a line, such places may be found, for where the water flows into the pond it will probably be coldest in summer and warmest in winter. . . .[68]
A temporal ecocline, or a change in community composition in time, both by changes in the relative importance of component populations and by extinction of old species and invasion of new ones, is termed a succession. Primary succession . . . is the development of communities from bare rock; secondary successions are changes that take place after destruction of the natural vegetation of an area with soil. . . . The composition of the avifauna and bird species diversity also change drastically with these successional changes in the vegetation and are part of the community succession. Plants in each stage modify the environment, presumably making it more suitable for other species in following stages . Typically, shade tolerance increases as succession proceeds. The entire process of secondary succession may take many years. . . . Only the oak–hickory forest is a stable community in a dynamic equilibrium that replaces itself; such a final stage in succession is termed its climax. In deserts, where the open vegetation alters microclimate very little and soil formation is virtually nonexistent, the first plants to invade are usually the climax species, and the succession, if one calls it such, is short. Earth’s biomes represent the climax communities that prevail at different localities. Disturbances, both man-made and natural (lightning, fires, droughts, hurricanes, floods), are often frequent enough that extensive areas have not had time enough to reach their own climax state. An equilibrium is reached whereby the proportion of a habitat supporting early successional stages is determined by the frequency of disturbance. Largely undisturbed areas may be primarily in the climax state. During the course of succession, annual production exceeds annual respiration, and organic materials accumulate to form soils and, generally, an increasingly larger biomass of plants and animals. At climax, production equals respiration, and organic materials cease to accumulate.
According to John C. Kricher,
The pines appear ‘scrubby’ and often grow in dense single-species stands. Oaks may grow both upright or shrublike and often make a thick spreading shrub layer beneath the pines. Huckleberries are usually abundant, along with other heaths, and add to the dense shrub layer. Evidence of fire is usually apparent. In older, fire-protected tracts, Red, Black, and White oaks gradually replace the pines. Atlantic White-cedar Swamps . . . occur on mesic (moist) sites. . . .
[Its range is] Coastal New England from Massachusetts (including all of Cape Cod, Nantucket, and Martha’s Vineyard) south through Long Island, New Jersey, and eastern North Carolina. . . .
. . . Sometimes called the ‘
[T]he Northern Pine–
Several ‘scrubby’ oak species are abundant in this forest type. Bear Oak [Quercus ilicifolia—Thoreau’s shrub oak] rarely grows higher than 20 ft. and can develop into a very thick ‘shrub’ layer. Blackjack Oaks [not found in
In A Description of New England, published in 1616, Captain John Smith said of the region’s forests that “Oke [Oak] is the chief wood; of which there is great difference in regard of soyle [soil] where it groweth.” He dismissed
Pine barrens, or pinelands, occur not only on Cape Cod, but in
Despite their many assets, the New Jersey Pine Barrens [read “Walden Woods”] have not been densely settled and today are a comparative wilderness in the heavily populated stretch from
In more recent years, entrepreneurs subdivided parts of the land into homesites and small farms.
Ecologists have identified six major vegetation types in the
Sand Plains
Egler[76] discusses “a type of landscape, sufficiently distinctive for Vegetation[77] to become an entity in thinking and research, called sand-plains and sand-hills.” “Because the Vegetation [of sand plains and sand hills] is often sparse or stunted, or dominated by pine in the northern hemisphere,” he continues, “the terms sand barrens and pine barrens are frequent.” Egler’s discussion of sand plains has much that is applicable to Walden Woods:
Sand-plains are extensive flat sandy areas. Physiographically, they may be old flood-plain terraces, sometimes related to Pleistocene glaciation. They may develop on the sandy bottoms of drained lakes [emphasis added]. . . .
As a habitat for Vegetation, sand-plains form a distinctive Total Environment. The soil is loose, porous and well-leached. Nutrients are low in quantity, and the reaction is generally acid. These conditions, from the viewpoint of agriculture and forestry, are considered relatively undesirable. Upper surfaces of the soil become exceedingly dry in a season of low precipitation (when heavier soils would not become as dry [emphasis added]. The vegetation also becomes dry. Fires are started readily, and because of the flat land, sweep for vast distances. Since the entire ecosystem is related to geomorphic conditions, sand-plains may be very ancient. Endemic species are frequently found, tho[ugh] these are rarely of vegetational importance. The plant-communities tend to be open and scrubby, of slow growth. Sometimes growth may be so extremely slow as to give rise to a dwarf Vegetation of species which grow much taller on other sites. Developmental trends are toward a more closed and mesic Vegetation, but which may have remained as trends for millennia.
Neil Jorgensen describes and discusses the sand-plain communities of
The sand plain community is distinctive more for its soils and its botanical characteristics than for its topography. The hilly land on parts of
By the 1890s geomorphologists had become interested in the so-called “sand plains” of Glacial Lake Sudbury. In 1891, for example, Warren Upham reported on the Walden Sand Plain before the Boston Society of Natural History[80]. In 1892 and 1898, George Hunt Barton, a geologist who taught at MIT and Boston University and who had worked on the State Topographic Survey, photographed and studied the Walden Sand Plain.[81] In 1905, James Walter Goldthwait, a Harvard doctoral candidate, reported on “The Sand Plains of Glacial Lake Sudbury” in the Bulletin of Harvard’s
Upham began his report by stating that
The lakes and ponds here considered are bounded wholly or in large part by modified drift, that is, beds of gravel and sand, or rarely of fine silt or clay, which were supplied directly from the melting and receding ice-sheet, in which these materials had been held and from which they were brought and deposited in their present position by streams flowing down from the ice-surface.
Goldthwait describes
The lake is wholly enclosed by beds of coarse gravel and sand, which in some places have an uneven contour of irregular knolls and hollows, but mostly are nearly level to distances varying from an eighth to three-quarters of a mile from the lake, with their surface approximately 200 feet above the sea. On the south and west these plains abut upon hills of rock; but northward, in which direction they extend farthest, their boundary is a sudden descent of about 60 feet to the fertile farming land near [the village of] Concord [emphasis added]. The modified drift enclosing Lake Walden is thus indented by a hollow [i.e., a glacial kettle] a half mile long from east to west and a fourth of a mile wide, which now sinks about 150 feet and originally may have been considerably deeper. Obviously the strong currents bringing the gravel must have [i.e., would have] filled the basin [the kettle] if it had been empty when the plain was deposited.
Goldthwait (pages 269 and 270) discusses the origins of Glacial Lake Sudbury’s “sand deltas,” or “sand plains,” defines and describes them, and distinguishes them from ordinary deltas. It is worth presenting Goldthwait’s discussion in extenso:
Sand plains are delta-like deposits of sand and gravel, built out from the ice into standing water at its front. . . . In their broader features of form and structure, sand plains resemble deltas built under ordinary conditions, by streams entering a body of standing water. Like normal deltas, they have a nearly flat, gently sloping surface, the ‘top slope,’ and an outer or free border, the ‘front slope,’ which slants more decidedly and is lobate in form; in composition, the material becomes noticeably finer towards the free border; in structure, the sand plains show inclined beds below with horizontal beds of coarser material above. Yet while sand plains are delta-like in these respects, the peculiar conditions under which they are built give them certain very definite characteristics not common to ordinary deltas. Instead of being fan-shaped deposits built out from lake-shores by single streams, sand plains are more often semi-elliptical in outline, as if built out continuously from the ice for some distance along its front by many streams. In fact, they are most irregular in plan.
The headward border of a sand plain, moreover, is not the lake-shore border of a common delta, but an ‘ice-contact’ or ‘back slope,’ which marks the position of the ice-front against which the gravels were laid down. Inasmuch as the back slope shows exactly where the ice-front was when the sand plain was built, it is a great help in determining the ice boundary of the ice-front lake at that time [emphasis added]. In linear extent the back slope is straight or irregular, according as the ice-front was straight or irregular. In surface form it may be a simple straight slope of from 30 to 45 degrees,—the natural slope or ‘angle of repose’ assumed by the gravels when their ice support was removed by melting. It is frequently broken, however, by hollows or kettle-holes [e.g., originally, near the summit of Brister’s Hill], where isolated blocks of ice were enclosed in the gravel, and occasionally the ice margin of a plain is wholly a belt of knobs and kettles, indicating an irregular ice-front where deposition took place among ice-blocks or upon a thin irregular ice-margin [Thoreau, in Walden, writes of just such a “belt of knobs and kettles” when he mentions his having spent time reading “by a spring which was the source of a swamp and of a brook, oozing from under Brister’s Hill {i.e., groundwater oozing from the ice-contact, or back slope, of the Walden Sand Plain} half a mile from my field,” and whose approach was “through a succession of descending grassy hollows {kettles}, full of young pitch pines, into a larger wood about the swamp.”]. . . .
The top slope is often so flat as to appear like a level plain; but usually there is a perceptible slope, 3 to 5 degrees, from the ice-border towards the free border [i.e., from north to south—in the case of the Walden Sand Plain, from, e.g., the Brister’s Hill–Laurel Glen area to the Emerson’s Cliff–Baker Bridge–Mount Misery area]. Near the back [i.e., northern edge] of the plain, kettle-holes are common, forming depressions [Thoreau’s “hollows”] in the top slope; near its front the plain is flattest, often unbroken save for shallow depressions which lead down to interlobate hollows, and which seem to indicate partial scouring, subsequent to the building of the plain. Cross-sections through the body of the plain [north to south in the case of the Walden Sand Plain] generally show a decrease in size of material towards the front, with also a decrease in thickness of the topset beds. . . . Associated with these ice-bound delta deposits are usually ridges of gravel, eskers, which mark the courses of streams that fed the deltas. . . .
Jorgensen[84] describes the differences between lake-bottom deposits and ice-contact or lake-shore deposits. “If the [extinct glacial] lakes lasted for any time,” he notes,
the accumulation of fine sediments gradually smoothed out the irregularities on the lake bottoms, producing a very flat area [e.g., much of
Some of these extinct lakes show a complex history. Many have existed at several different levels [e.g., Glacial Lake Sudbury and Glacial Lake Concord], becoming progressively lower as first one spillway [e.g., with respect to Glacial Lake Sudbury, the Cherry Brook spillway] and then another [the Hobbs Brook spillway] became ice free. These levels are often marked by elevated beaches and terraces that sometimes run for several miles along the valley sides.
Meltwater streams flowing into these glacial lakes formed deltas along their shores [that] often superficially resemble kame terraces; both are usually steep sided and often nearly flat on top. Where a gravel pit has been dug into the side of a delta, however, the difference is usually easy to see. The gravel layers in deltas are usually diagonal while these same layers in kame terraces are often jumbled where they collapsed as the ice melted from beside them. . . .
. . . In
John C. MacLean, in his recent history of
The local landscape acquired much of its character from the uplifting and faulting of its bedrock. . . .
Later glacial action also had a major impact upon the landscape. Till from the advancing glaciers settled on the far side of outcroppings to create drumlins. As the glaciers retreated, water and till ran through cracks in the ice. Heavy till remained in the cracks and eventually settled to the ground as eskers. Finer till and silt washed out of the cracks and were deposited as delta-shaped outwash. (The coarsest materials settled near the mouth of the crack and finer silt and sand near the outskirts of the delta. Much of
It is primarily this gradual north-to-south diminution of particle size that accounts for the greater water-holding capacity of soils in the southern sections of the Walden Sand Plain. Nonetheless, the kame and delta complex a single geological feature, Goldthwait’s “sand plain.”
Thomson discusses the sand plains of New England, concentrating on one particularly dry one (much drier than the Walden Sand Plain) in
[T]he soil [of the North Haven sand plain], like so much of
When at last the ice was entirely gone and plants could return to the valley, the old lake floor was left as a wide terrace standing high and dry above the little river. There was plenty of rain, but it trickled away so fast through the loose sand that the earth became dry again soon after every storm or shower. Only highly drought-resistant plants could grow in such a place; and for ages the sand plains were covered entirely with grass.
The Northern
Several systems are used to classify the vegetation of the
Eaton states that
The dominant forest element in Concord for at least the past three millennia has been the so-called oak–chestnut–hickory association[90] with a lingering and perhaps an increasing (since 1000 a.d.) of species characteristic of the cooler upland forests of western and northern New England: hemlock, yellow and white birch, beech, striped maple (rare), sugar-maple (rare). Before the land was cleared by the colonists for general farming, one may visualize a mature forest, broken only by river meadows, swamps, ponds and Indian clearings. Its understory must have been relatively free of shrubs and herbs, except in openings caused by blow-downs, fire, lightning and so on.[91]
The principal biotic component of the Walden Ecosystem, however, is
Bromley states that
Some of the higher over-drained gravelly plains were . . . destitute of large trees from the earliest times. The difficulties of the early settlers at
According to Jorgensen,[96] “The sand plain community is distinctive more for its soils and its botanical characteristics than for its topography. . . . The hilly land on parts of
The
The rest of the Walden Ecosystem is divided among several other types of biotic community: wetland, stream, pond, and
The presence of the Walden Ecosystem and its persistence as a landscape unit during the three and one-half centuries since European settlement are due directly to the area’s distinctive surficial geology, which itself is a product of the Pleistocene glaciation. The surficial geology led to the development of an “island” of
Even before the advent of the Europeans in
Indicator Species of the Northern
The edaphic climax, or potential natural vegetation of the Walden Ecosystem (or, at the very least, of its sand-plain component—the so-called “Walden Pond Unit”) is “
Kricher lists what he calls “indicator species” for the
He notes (page 11) that
When we recognize a species as being an indicator of a certain habitat, what we are saying is that this species is biologically adapted to survive under the conditions imposed upon it in that area. Each species has certain tolerance limits beyond which it cannot persist. . . .
Not all species serve as indicators of habitats. Red Maple occurs in virtually every forest type in the East and is therefore rarely a suitable indicator of any particular habitat (the exception being Red Maple Swamp Forests of the Northeast). White Oak is another species that is too widely distributed to be a good indicator, though it is a prominent member of the
Kricher lists as indicator species of the
trees
pitch pine (Pinus rigida)***, [102]
bear (or shrub) oak (Quercus ilicifolia)***
blackjack oak (Quercus marilandica)§
chinkapin, yellow, or chestnut, oak (Quercus muehlenbergii)¶
scarlet oak (Quercus coccinea)**
post oak (Quercus stellata)†
black oak (Quercus velutina)***, [103]
eastern red cedar (Juniperus virginiana)*
shrubs
bearberry (Arctostaphylos uva–ursi)*, [104]
huckleberries (Gaylussacia spp.)*
inkberry (Ilex glabra)†
broom crowberry (Corema conradii)†
low-bush blueberry (Vaccinium angustifolium)**/***
sheep laurel (or lambkill) (Kalmia angustifolia)***
wild raisin (Viburnum cassinoides)***, [105]
herbaceous species and vines
blazing star (Chamælirium luteum)
butterfly weed (Asclepias tuberosa)*
pinesap (Monotropa hypopithys)*, [106]
poverty grass (Aristida dichotoma)*
rough hawkweed (Hieracium scabrum)*
wild lupine (Lupinus perennis)*
“wintergreen”*, [107]
little bluestem (Andropogon scoparius, or Schizachyrium scoparium)*
birds[108]
pine warbler (Dendroica pinus)*
prairie warbler (Dendroica discolor)***, [109], ∞
rufous-sided towhee (Pipilo erythrophthalamus)**, ∞
chipping sparrow (Spizella passerina)***
common flicker (Colaptes auratus)***, [110]
brown thrasher (Toxostoma rufum)*, ∞
northern bobwhite (Colinus virginianus)*, [111], ∞
whip-poor-will (Caprimulgus vociferus)**, [112]
great horned owl (Bubo virginianus)*
mourning dove (Zenaida macroura)**, [113]
eastern bluebird (Siala sialis) (uncommon)*, [114]
mammals
gray squirrel (Sciurus carolinensis) (abundant)[115]
eastern chipmunk (Tamias striatus) (abundant)
The pitch pine (Pinus rigida) and the bear, or scrub, oak (Quercus ilicifolia) are primarily successional trees; that is, they occur during the early stages of ecological succession (e.g., in old fields) in areas protected from fires.[116]
Quercus ilicifolia “is most abundant in rather barren, sandy regions along the Atlantic coast. It is characteristic of that part of
In Thoreau’s time, the area between Fairhaven Bay and Fairhaven Hill was called “Shrub Oak Plain”[120]—in reference both to the area’s dominant vegetation, the scrub, shrub, or bear, oak (Quercus ilicifolia),[121] which, according to Kricher, is an indicator species of the Northern Pine–Oak Forest, and to its geomorphology, a sand plain, or “kame delta,” as indicated at precisely this spot by the letters “kd” on Koteff’s map (1964) of the surficial geology of the Concord quadrangle.[122]
Thoreau spent the afternoon of July 13, 1851, on Shrub Oak Plain. His account of the afternoon mentions several indicator species of the
. . . . Looking across the [
William Brewster, the renowned ornithologist, describes a walk he made in Walden Woods in October 1892, from Staples’ Camp on
At 2 p.m. we started through the woods for Walden [Pond]. It was a walk to be long remembered. I think I have never before seen oak woods so richly colored as these—painted woods—wine-red the dominant tint. The scarlet oaks[126] were steeped with this color and the undergrowth of huckleberry[127] bushes seemed to reflect it, as the scarlet of the maples along the river was reflected by the water a week or more ago. Of course these huckleberry bushes were really of the same color as the oaks. In places they formed a rich unbroken carpet which covered the ground as far as the eye could reach under the trees. . . [emphasis added].
In his Wonder-working
. . . [W]ith much difficulties travelling through unknowne woods, and watery swamps . . . they[128] at the end of this meete with a scorching plaine, yet not so plaine, but that the ragged bushes scratch their legs fouly . . . , [a]nd in time of summer, the sun casts such a reflecting heate from the sweet ferne [Comptonia peregrina—not actually a fern but a low shrub with fragrant foliage, a member of the Myricaceæ, or wax-myrtle family, found in “open sterile woodlands, clearings,”[129] “sterile soil, open oak scrub, gravel banks, etc.”[130]—i.e, in terrain exactly like that of Walden Woods, especially during the early stages of secondary succession], whose scent is very strong, that some herewith have beene very nere fainting. . . .
Thus this poore people populate this howling desert, marching manfully on (the Lord assisting) through the greatest difficulties, and sorest labors that any with such weak means have done.
Some modern authorities have dismissed this passage as erroneous or hyperbolic. For example, Townsend Scudder says, “Certainly the families of
The “hurtleberry,” or whortleberry, is the huckleberry—Gaylussacia spp.—an indicator species of the
Huckleberries (Gaylussacia spp.) were important to Henry Thoreau. At his death he left the draft of an essay, “Huckleberries,” which was not published until 1970.[137] It derives its character from the nature of huckleberries and therefore from the ecosystems and plant communities of which they were a part. The following quotation shows that Thoreau was aware of their role in ecological succession:
If you look closely you will find blueberry and huckleberry bushes under your feet, though they may be feeble and barren, throughout all our woods, the most persevering Native Americans, ready to shoot up into place and power at the next election among plants, ready to reclothe the hills when man has laid them bare and feed all kinds of pensioners. What though the woods be cut down; it appears that this emergency was long ago anticipated and provided for by Nature, and the interregnum is not allowed to be a barren one. She not only begins instantly to heal that scar, but she compensates us for the loss and refreshes us with fruits such as the forest did not produce. As the sandal wood is said to diffuse a perfume around the woodman who cuts it—so in this case Nature rewards with unexpected fruits the hand that lays her waste.
I have only to remember each year where the woods have been cut just long enough to know where to look for them. It is to refresh us thus once in a century that they bide their time on the forest floor. If the farmer mows and burns over his overgrown pasture for the benefit of the grass, or to keep the children out, the huckleberries spring up there more vigorous than ever. . . . All our hills are, or have been, huckleberry hills, the three hills of
In short all the whortleberry bushes in the
Compare this passage with a statement from Kricher’s discussion of the
Huckleberries are usually abundant [in the
In terms that have an uncanny resemblance to Edward Johnson’s “thickets,” “ragged bushes,” and “scorching plaine,” Jorgensen describes the effects of forest fires:
In the initial stages of regeneration following fire, the sprouting stumps[139] often produce impenetrable thickets. These sprout thickets are especially dense in areas where the previous forest itself was immature and thick following some earlier disturbance. . . .
A number of shrubs are also favored by fire. Lowbush blueberry, Vaccinium spp., Gaylussacia baccata [a species of huckleberry], sweet fern, Comptonia peregrina, and sheep laurel, Kalmia angustifolia [an indicator species of the Northern Pine–Oak Forest],[140] all quickly appear in burned-over areas, adding further competition in the regenerating forest. In areas with a history of forest fires, these shrubs often form a continuous layer.[141]
Jorgensen proceeds to discuss the pitch pine’s ecological role in such fire-prone areas:
Among the conifers of the region, only pitch pine, Pinus rigida, is thoroughly adapted to periodic burning. If all its foliage is burned away, needles will grow again on the branches. If the terminal shoot is killed, a new one will develop. If the trunk is killed, a new one will sprout from the base. On some trees the cones will remain closed for several years, in many cases until the heat of a fire opens them. Trees with this characteristic have evolved in areas with the worst forest fire history.[142]
In Walden Thoreau states that “There were scores of pitch-pines around my house, from one to four inches in diameter. . . .”[143] In his Journal he speculates on the place of the pitch pine in ecological succession:[144]
. . . Though the pitch pines are the prevailing trees at the south end [of Hubbard’s Wood, a part of Walden Woods], I see no young pitch pines under them.
Perhaps this is the way that a natural succession takes place. Perhaps oak seedlings do not so readily spring up and thrive within a mixed white pine and oak woods as pines do,—in the more open parts,—and thus, as the oaks decay, they are replaced by pines rather than by oaks.
But where did the pitch pines stand originally? Who cleared the land for its seedlings to spring up in? It is commonly referred to very poor and sandy soil, yet I find it growing on the best land also. The expression “a pitch pine plain” is but another name for a poor and sandy level. It grows on both the sand and [in] the swamp, and the fact that it grows on the sand chiefly is not so much evidence that it prefers it as that other trees have excluded it from better soil. If you cut down the pines on the pitch pine plain, oaks will come up there too. Who knows but the fires or clearings of the Indians may have to do with the presence of these trees there? They regularly cleared extensive tracts for cultivation, and these were always level tracts where the soil was light—such as they could turn over with their rude hoes. Such was the land which they are known to have cultivated extensively in this town, as the Great Fields and the rear of Mr. Dennis’s,—sandy plains. It is in such places chiefly that you find their relics in any part of the county. They did not cultivate such soil as our maple swamps occupy, or such a succession of hills and dales as this oak wood covers. Other trees will grow where the pitch pine does, but the former will maintain its ground there the best. I know of no tree so likely to spread rapidly over such areas when abandoned by the aborigines as the pitch pine—and next birches and white pines.
In his Birds of Concord Ludlow Griscom discusses the role of fire on natural ecosystems and gives as a telling example the history of Walden Woods that corroborates Kricher’s statements about the Northern Pine–Oak Forest. Griscom first assesses the impact of fires in general:
Whether or not fires are regarded as destructive is largely a matter of human interest, and popularly they are so considered; but biologically they are neutral, as the destruction of one type of habitat and the local decrease of one set of birds are followed by the creation of a new habitat and the arrival of a new set of birds previously locally unknown or rare. Under absolutely natural conditions the area affected reverts to the primeval forest, but under modern civilized conditions this never happens and becomes theoretical. In certain cases where an area has been constantly (and unnaturally) fire-swept, the humus and the top soil have been completely destroyed and leached out, and foresters debate as to how long, if ever, it will take for original conditions to return.[145]
As a case in point, he describes the effects of fire on Walden Woods:
An excellent example [of fire’s effect on bird populations] is furnished by the Walden Woods between
As noted above, all three of the birds that Griscom mentions in his discussion of the role of fire in the history of Walden Woods—viz., the chewink (i.e., the rufous-sided towhee), the field sparrow, and the brown thrasher—as well as the prairie warbler, are “indicator birds” of the Northern Pine–Oak Forest of Kricher’s system. Thoreau mentions three of them in Walden.
Brewster, in his book Concord River, reports seeing two of the indicator birds of the Northern Pine–Oak Forest—the brown thrasher and the rufous-sided towhee—in large numbers on Fairhaven Hill, a part of Walden Woods: “Brown Thrashers and Towhees numerous on Fairhaven Hill and in full song.”[152]
Richard Walton[153] and Sandy Mallett[154] report that the prairie warbler is still found in the
Thoreau mentioned a number of the other indicator species of the
Thoreau mentions the whip-poor-will, another indicator bird of the
Regularly at half-past seven, in one part of the summer, after the evening train had gone by, the whip-poor-wills chanted their vespers for half an hour, sitting on a stump by my door, or upon the ridge-pole of the house. They would begin to sing almost with as much precision as a clock, within five minutes of a particular time, referred to the setting of the sun, every evening. I had a rare opportunity to become acquainted with their habits. Sometimes I heard four or five at once in different parts of the wood, by accident one a bar behind the other, and so near that I distinguished not only the cluck after each note, but often that singular buzzing sound like a fly in a spider’s web, only proportionally louder. Sometimes one would circle round and round me in the woods a few feet distant as if tethered by a string, when probably I was near its eggs. They sang at intervals throughout the night, and were again as musical as ever just before and about dawn.[160]
The great horned owl[161], another indicator species of the Northern Pine–Oak Forest, makes at least two long appearances in Walden—evidence that it indeed is an indicator species for Walden Woods (and, therefore, that Walden Woods can be characterized as a Northern Pine–Oak Forest). “I was also serenaded by a hooting owl,” he says in the chapter “Sounds.”[162] “. . . It reminded me of ghouls and idiots and insane howlings. But now one answers from far woods in a strain made really melancholy by distance.—Hoo hoo hoo, hoorer hoo; and indeed for the most part it suggested only pleasing associations, whether by day or night, summer or winter.
“I rejoice that there are owls,” he writes. “Let them do the idiotic and maniacal hooting for me. . . .”
“For sounds in winter nights,” Thoreau writes later, in the “Winter Animals” chapter of Walden,[163]
I heard the forlorn but melodious note of the hooting owl indefinitely far; such a sound as the frozen earth would yield if struck with a suitable plectrum, the very lingua vernacula of Walden Wood, and quite familiar to me at last, though I never saw the bird while it was making it. I seldom opened my door in a winter evening without hearing it; Hoo hoo hoo, hoorer hoo,[164] sounded sonorously, and the first three syllables accented somewhat like how der do; or sometimes hoo hoo only[165]. One night in the beginning of winter, before the pond froze over, about nine o’clock, I was startled by the loud honking of a goose, and, stepping to the door, heard the sound of their wings like a tempest in the woods as they flew over my house. They passed over the pond toward Fair Haven, seemingly deterred from settling by my light, their commodore honking all the while with a regular beat. Suddenly an unmistakable cat owl[166] from very near me, with the most harsh and tremendous voice I ever heard from any inhabitant of the woods, responded at regular intervals to the goose, as if determined to expose and disgrace this intruder from Hudson’s Bay by exhibiting a greater compass and volume of voice in a native, and boo-hoo him out of Concord horizon. What do you mean by alarming the citadel at this time of night consecrated to me? Do you think I am ever caught napping at such an hour, and that I have not got lungs and a larynx as well as yourself? Boo-hoo, boo-hoo, boo-hoo! It was one of the most thrilling discords I ever heard. And yet, if you had a discriminating ear, there were in it the elements of a concord such as these plains never saw or heard.
In October Farm, William Brewster, who often encountered great horned owls near his farm in the northeastern part of Concord, describes an encounter with one on the Fairhaven Bay side of Walden Woods some forty-five years after Thoreau lived in the Woods.[167] Brewster and the naturalist Frank Bolles were paddling down the
It was very dark when we reached Fairhaven Cliff and Bolles began hooting like a Barred Owl. I followed with a feeble imitation of the Great-horned Owl which, after a few minutes and to my infinite surprise, was answered by Bubo himself from the tall pines on the west bank of the river. We stopped paddling, of course, and I continued the conversation in the best Owl language that I could command. Bubo was prompt in his responses and presently appeared directly over our heads—a great shadowy bird with broad wings and big head, flapping at first, then sailing as majestically as an Eagle, finally descending in a series of undulations to the low trees on the shore of the Cliff landing. More Owl talk and Bubo soon on his way back to the pines, evidently sorely puzzled and speedily impelled to repeat the flight which he made three times each way, in all, passing over us each time.
Later that evening, at eight o’clock, after the rising moon had flooded
Francis Allen states (page 183, note), with reference to the great horned owl, that “There appear to have been two pairs of these birds regularly in Concord in Thoreau’s time,—one in the Walden woods and one in the Ministerial Swamp[[169]] in the southwestern part of town.” His observation is consistent with Walton’s statement that “The Great Horned Owl’s relatively large territorial requirements . . . limit the number of pairs in [the Sudbury River valley]” and with the fact that both the Walden Woods and Ministerial Swamp–Dugan Desert owls occupied virtually identical, “sibling” geological features formed in Glacial Lake Sudbury.
Edward Howe Forbush, State Ornithologist, describes hearing a great horned owl just after dark one evening when he was staying at one of Brewster’s cabins on the
Allen (pages 183 to 189) quotes Journal entries on the great horned owls in Walden Woods for February 3, 1852; May 1, 1852; December 9, 1856; December 15, 1856; December 19, 1856; May 20, 1856; and June 18, 1858. The other quotations on those pages refer to the owls near
In the passage for May 20, 1858, Thoreau records seeing
in the street a young cat owl, one of two which Skinner killed in Walden Woods yesterday. . . . I visited the nest. It was in a large white pine close on the north side of the path, some ten rods west of the old Stratton cellar in the woods. . . . There were many white droppings about and large rejected pellets containing the vertebræ and hair of a skunk. As I stood there, I heard the crows making a great noise some thirty or forty rods off, and immediately suspected that they were pestering one of the old owls, which Skinner had not seen. It proved so. . . .
In his Journal entry for June 18, 1858, Thoreau writes
A boy climbs to the cat owl’s nest and casts down what is left of it,—a few short sticks and some earthy almost turfy foundation, as if it were the accumulation of years. Beside much black and white skunk-hair, there are many fishes’ scales (!) intimately mixed with its substance, and some skunk’s bones [emphasis added].
According to Forbush and May (pages 266 and 267) “Great Horned Owls kill and eat many skunks, and seem to care little for the disagreeable consequences of attacking these pungent animals. Many of the owls that I [i.e., E. H. Forbush] have handled give olfactory evidence of this habit.” They report that the owl also eats fish, as well as many other animals, and that great horned owls are continually harassed by crows, as does William Brewster, who also reported “an unmistakable but not very strong smell of Skunk mingled with the more offensive odors” emanating from the pellets and excrement of great horned owls he found in Lawrence’s Woods in Concord, but he “failed to find any skunk hair or other remains.”[171]
In the last paragraph of “Sounds” Thoreau recapitulates, mentioning again several of the indicator species (as well as non-indicator species) of the
. . . . I kept neither dog, cat, cow, pig, nor hens, so that you would have said there was a deficiency of domestic sounds; . . . An old-fashioned man would have lost his senses or died of ennui before this. Not even rats in the wall, for they were starved out, or rather were never baited in,—only squirrels on the roof and under the floor, a whip-poor-will on the ridge-pole, a blue jay screaming beneath the window, a hare or woodchuck under the house, a screech owl or a cat owl behind it, a flock of wild geese or a laughing loon on the pond, and a fox to bark in the night. Not even a lark or an oriole, those mild plantation birds, ever visited my clearing. . . . A young forest growing up under your windows, and wild sumachs and blackberry vines breaking through into your cellar; sturdy pitch pines rubbing and creaking against the shingles for want of room, their roots reaching quite under the house. Instead of a scuttle or a blind blown off in the gale,—a pine tree snapped off or torn up by the roots behind your house for fuel. . .[172]
At the end of the “Spring” chapter of Walden is a paragraph remarkable for the wealth of ecological insights it supplies about the composition of Walden Woods, its plants and animals. In light of modern ecological knowledge of biotic communities, Thoreau’s words, while those of a consummate artist and not designed to fit the constraints of scientific nomenclature, reflect accurately the natural world he saw around his house in Walden Woods. In this paragraph, Thoreau mentions no fewer than five indicator species of the
In the next to the last paragraph of “Spring” Thoreau says:[173]
Early in May, the oaks, hickories, maples, and other trees, just putting out amidst the pine woods around the pond, imparted a brightness like sunshine to the landscape, especially in cloudy days, as if the sun were breaking through mists and shining faintly on the hillside here and there. On the third or fourth of May I saw a loon in the pond, and during the first week of the month I heard the whip-poor-will, the brown thrasher, the veery, the wood pewee, the chewink, and other birds. I had heard the wood thrush long before. The phœbe had already come once more and looked in at my door and window, to see if my house was cavern-like enough for her, sustaining herself on humming wings with clinched talons, as if she held by the air, while she surveyed the premises. The sulphur-like pollen of the pitch pine soon covered the pond and the stones and rotten wood along the shore, so that you could have collected a barrelful. . . .
In this single paragraph of Walden Thoreau explicitly mentions four indicator species of the
This analysis shows beyond any reasonable doubt that virtually all of the indicator species of the Northern Pine–Oak Forest whose ranges extend far enough east, north, or inland to encompass the Concord area occur in Walden Woods—or, to be more exact, on the Walden Sand Plain (i.e., the Walden Pond Unit of the Walden Ecosystem). At the very least one can say that Walden Woods is an inland northeastern variant of the type. Individually, none of these species would warrant special attention. Individually, no one of them makes Walden Woods a recognizable
Because this “island” of
History of the Walden Ecosystem
By applying modern ecological knowledge to the fragmentary and disparate accounts of
Woodlands were plentiful in
The first European settlers of
Some of Walden Woods’ soils theoretically were suitable for agriculture (that is, were not stony, shallow, steep, water-logged, etc.), but they were excessively drained and “droughty” and could have been farmed profitably only with the aid of irrigation. Given, first, the presence of much better agricultural soils nearby in Concord, second, the expense of irrigation, third, the primitiveness or even absence of irrigation technology during the first two or three centuries of European occupation, and, fourth, the general exodus of farmers from New England to the Midwest beginning in the mid-nineteenth century, it would have been unnecessary, exorbitantly expensive, foolhardy, or even impossible to squander one’s meagre resources irrigating the dry soils of the Walden Sand Plain. Those soils were best left in woodland that could be tapped for fuel wood and timber as needed. The evidence presented graphically on maps dating from before 1820 to the present day—namely, the presence of virtually continuous woodland on the Walden Sand Plain—reflects these ecological and economic realities. Any exceptions to the general rule (and there have been a few exceptions) have been sporadic and short-lived.
As early as the 1830s, Lemuel Shattuck, the historian of
The uneven soil at the north and northeastern, and the south and southwestern parts of the town [i.e., kames, deltas, etc., laid down in glacial lakes Concord and Sudbury], appears to be of a primary formation, and is composed chiefly of a thin, gravelly loam, mixed with various combinations of sand, clay, decayed vegetable matter, and rocks. Though not uniformly well calculated for agricultural purposes, it contains some highly productive farms [emphasis added].[180]
Socioeconomic Pressures on the Walden Ecosystem
The woodlands of
In an historical survey of
The use of wood for fuel has been one of the greatest drains upon the forests [of
By means of a graph, Harper chronicles (page 447) a precipitous decline in the percentage of forest cover in Massachusetts between 1620 and 1910, the low point coming during the 1850s and 1860s. The fluctuating borders of Walden Woods as shown on the several maps (Hales, Walling, Wood, Appalachian Mountain Club, etc., to the present day) reflect the socioeconomic forces at work on Walden Woods.
During the 1830s much of Walden Woods between Walden Pond and Sandy Pond in
. . . about thirty acres of WOOD standing on a lot in Lincoln, near Flint’s [Sandy] Pond . . . sold by the cord or by the lot.
Cyrus Stow of
ALL the WOOD and TIMBER standing on eighteen acres of land—near to Flint’s Pond in Lincoln.
MacLean notes that
Joel Britton of
. . . all the wood and timber cut by me during the past Winter together with all the wood standing on several lots of Land in said Lincoln being the same wood and timber purchased by me of Major Weston and Cyrus Stow also all the wood and timber owned by me and now lying near Bakers Bridge in said Lincoln ready for transportation on the Fitchburg Rail Road.[186]
The cutting of firewood had always been an essential part of the farmer’s life in
The present fine sleighing and the continued high price of fuel in Boston, keeps our farmers quite busy—so much so, that it is with difficulty that we can get a stick of wood into our market, notwithstanding it goes quick at $4.00 a cord. We learn that one of our driving farmers, with no other assistance than his usual farm help, took $83 last week in
In 1841, four years before the Fitchburg Railroad was built, George B. Emerson, author of several works on the trees and forests of
After 1844, the Fitchburg Railroad would transport many cords of wood from Walden Woods and elsewhere to
During the early 1850s Thoreau witnessed with anxiety and sadness the accelerating destruction of Walden Woods, mourning their destruction. He describes in Walden “timber like long battering-rams going twenty miles an hour against the city’s walls.” In 1853, he complained, “You can walk in the woods in no direction but you hear the sound of the axe.”[191]
Expressing alienation at the loss, he records in his Journal (entry for January 24, 1852):
I see in the woods [in Walden Woods] the woodman’s embers, which have melted a circular hole in the snow, where he warms his coffee at noon. . . .
These woods! Why do I not feel their being cut more sorely? Does it not affect me nearly? The axe can deprive me of much.
Although the virgin forests of New England have been reduced from 95 percent of the landscape to 5 percent, enough time has elapsed since the last widespread lumbering operations took place that the forests have begun to regain a semblance of their original primeval character, especially in protected areas. The recovering species are primarily birch, a few white pines, red pines, and red oaks.[193]
Significance of the Walden Ecosystem
Had Walden Woods not existed, or had its character been different from what it is, the book Walden would have been a very different book—had it been written at all. The Walden Sand Plain provided habitat for a distinct biotic community, the
To be sure, as a master artist he might have used other features of landscape to achieve the same or a similar end, but Walden would have been quite a different book had he been forced to do so. And, of course, had Walden Woods not been a
From both the literary and the scientific perspective Walden Woods occupies a strategically important position in the development of American culture, particularly in those aspects of American culture dealing with man’s attitudes toward and relationship to the natural world. Because of the Walden Sand Plain’s distinctive characteristics, Henry Thoreau had a pond and a surrounding forest to which he could resort for his literary and scientific pursuits. The pond and the forest have become symbols of wildness in American culture.
Were the preglacial geology, the Pleistocene geology, and the land-use history of the Concord–Lincoln area not what they are, Thoreau would never have been able to write a book like Walden or discover the principles of ecological succession, because the Walden Woods area would not have remained largely in woodland but would have been cleared and exploited for annual crops like those raised in the surrounding parts of Lincoln and (especially) Concord. There is a direct cause-and-effect link between the surficial geology of the Walden Woods area and both the substance and character of Thoreau’s writings—his Journal, Walden, and “The Succession of Forest Trees,” in particular. There is a similar cause-and-effect link between surficial geology and the character of the
The history of
Clearly, the very substance and character of Walden are linked inextricably, in a cause-and-effect manner, to the characteristics of the Walden Ecosystem. To the humble scenery and unremarkable denizens of this living ecosystem we owe, in large measure, one of the masterpieces of American literature.
Printed on
[1]Henry D. Thoreau. Walden (Princeton, New Jersey, 1971), page 175.
[2]The terms “Walden Ecosystem,” “Historic Walden Woods,” and “Walden Woods” are employed as approximate synonyms in this report, the term used in any instance depending upon the requirements of the immediate context and purpose of discussion. All three of the terms refer to exactly the same geographic area, or “landscape unit,” but from different conceptual perspectives. Two similar, related terms, “Walden Northern Pine–Oak Forest” and “Walden Sand Plain Community,” are not synonymous with the others because the sand plain (or kame–delta complex) on which the forest community has developed does not encompass the entire ecosystem as defined herein; it forms only one (albeit the larger) part of it.
For all intents and purposes the latter two terms are synonymous with the “Walden Pond Unit” of the Walden Ecosystem (see below). Even within the sand-plain sector, however, there are smaller “islands” of different habitats, or biotic communities: a different type of forest on till-covered hills (e.g., Fairhaven Hill), for example; streams; wetlands and ponds in depressions, etc. These distinct habitat types should still be considered parts of the overall Walden Ecosystem, however, because they are due to interaction among the same set of basic natural elements (surficial geology, hydrology, etc.) that give rise to the other habitats and biotic communities. Thus, the various habitats of the Walden Ecosystems may be thought of as “variations on a common theme.”
[3]The areas of the Walden Ecosystem and its subunits were determined from Carl Koteff’s map of the surficial geology of the
[4]In New England land-survey usage, the word “town” is roughly equivalent to the term “township” as it is used in most other regions of the
[5]The usage “Bear Hill” is taken from Thoreau’s Journal. It applies to a hill near the southwestern corner of Sandy Pond that usually is called “Ridge Hill” or “Great Ridge Hill” (see, for example, Kerry Glass and Elizabeth A. Little. Lincoln, County of Middlesex, in His Majesty’s Province of Massachusetts Bay in New England, 1775 Anno Domini—in the 15th Year of the Reign of King George the Third [Map] [Lincoln, Massachusetts, 1975], where it is called “Great Ridge Hill”).
[6]Geological Survey. Maynard, Massachusetts 42071–D3–TM–025. 7.5 x 15 Minute Series (Topographic). 1:25,000.
[7]Proceeding clockwise from the northwestern corner of the ecosystem, in
[8]Town of
[9]E.g., Town of
[10]Carl Koteff. Surficial Geology of the
[11]E.g., James Walter Goldthwait. The sand plains of glacial
[12]E.g.,
[13]In Robert L. Bates and Julia A. Jackson, editors. Dictionary of Geological Terms, Third edition, (Garden City, New York, 1984), a “kettle” is defined (page 281) as
A depression in glacial drift, esp. in outwash and a kame field, formed by the melting of a detached block of stagnant ice that was buried in the drift. It often contains a lake or swamp; Thoreau’s
Walden is thus a “kettle lake”—possibly the best known kettle lake on earth, considering that Bates and Jackson give it as the single example in their Dictionary of Geological Terms. A “kame field” is “A group of closely spaced kames, interspersed in places with kettles and eskers, and having a characteristic hummocky topography” (ibid., page 279).
[14]John C. Kricher. A Field Guide to Eastern Forests [of]
[15]These wetlands might be termed “dependent,” or “contingent,” communities if the forests (woodlands) are considered the primary biotic communities of the Walden Ecosystem. Bromley (Ecological Monographs, Volume 5, Number 1 [January 1935], page 164) points out that a physiographic unit “might be described as a physiographically determined habitat-complex: it represents a complex of habitats linked together by physiographic development, and therefore [is] to be regarded as a unit in its relation to the physiographic features of the region in which it occurs.”
[16]W. J. Latimer and M. O. Lanphear. Soil Survey of
[17]As used herein, “hydrology” means “the hydrology of an area or district” (Robert L. Bates and Julia A. Jackson, editors. Dictionary of Geological Terms. Third edition [Garden City, New York, 1984], page 245), as opposed to the broader definition of the term (viz., “The science that deals with global water [both liquid and solid], its properties, circulation, and distribution, on and under the earth’s surface and in the atmosphere, from the moment of its precipitation until it is returned to the atmosphere through evapotranspiration or is discharged into the ocean” [ibid.]); that is, the term is used here in the narrower, site-specific sense.
[18]A. W. Küchler. Vegetation Mapping (New York, 1967), pages 22 to 26.
[19]Frank E. Egler. The Nature of Vegetation, Its Management and Mismanagement: An Introduction to Vegetation Science. Limited edition (Norfolk, Connecticut, 1977), page 93.
[20]Frank E. Egler. The Nature of Vegetation, Its Management and Mismanagement: An Introduction to Vegetation Science. Limited edition (Norfolk, Connecticut, 1977), page 94.
[21]In this respect, however, European influence would differ from that of the Indians because, among other things, Indians did not divide the landscape into individual lots, nor did they engage to any extent in activities that changed topographic relationships; thus, their impact would have been less diverse on a tract of land like Walden Woods than would that of that of Europeans.
[22]Or, in one case, on a map constructed from historical data two centuries after the fact.
[23]John C. MacLean. A Rich Harvest: The History, Buildings, and People of
[24]Lemuel Shattuck. A History of the Town of Concord; Middlesex County, Massachusetts, from Its Earliest Settlement to 1832; and of the Adjoining Towns, Bedford, Acton, Lincoln, and Carlisle; Containing Notices of County and State History Not Heretofore Published (Boston and Concord, 1835), pages 9 and 15.
[25]Richard Jefferson Eaton. A Flora of
[26]Eugene P. Odum. Fundamentals of Ecology. Third edition (Philadelphia, London, and Toronto, 1971), page 140.
[27]Eugene P. Odum. Basic Ecology (Philadelphia, New York, and elsewhere, 1983), page 4.
[28]Robert L. Bates and Julia A. Jackson, editors. Dictionary of Geological Terms. Third edition (Garden City, New York, 1984), page 158.
[29]Eugene P. Odum. Basic Ecology (Philadelphia, New York, and elsewhere, 1983), page 13.
[30]Frederick E. Smith. Analysis of ecosystems. Pages 7 to 18 in: David E. Reichle, editor. Analysis of Temperate
[31]Stephen H. Spurr. The natural resource ecosystem. Pages 3 to 7 in: George M. Van Dyne, editor. The Ecosystem Concept in Natural Resource Management (New York and London, 1969). Page 3.
[32]Eugene P. Odum. Fundamentals of Ecology. Third edition (Philadelphia, London, and Toronto, 1971), page 20.
[33]Eugene P. Odum. Fundamentals of Ecology. Third edition (Philadelphia, London, and Toronto, 1971), page 16.
[34]Harold F. Hemond. Biogeochemistry of Thoreau’s Bog,
[35]Actually, till that was laid down before Glacial Lake Sudbury formed behind the northward-retreating glacier remains, concealed underneath the sands and gravels that were deposited in Glacial Lake Sudbury.
[36]Carl Koteff. Surficial Geology of the
[37]This discussion of soils and their interaction with vegetation derives primarily from Frank E. Egler. The Nature of Vegetation, Its Management and Mismanagement: An Introduction to Vegetation Science. Limited edition (Norfolk, Connecticut, 1977); Henry J. Oosting. The Study of Plant Communities. Second edition (San Francisco and London, 1956); Wilfred T. Neill. The Geography of Life (New York and London, 1969);
[38]Robert L. Bates and Julia A. Jackson, editors. Dictionary of Geological Terms. Third edition (Garden City, New York, 1984), page 275.
[39]Soil Conservation
[40]Henry J. Oosting. The Study of Plant Communities. Second edition (San Francisco and London, 1956), pages 204 and 205.
[41]Egler, Frank E. The Nature of Vegetation, Its Management and Mismanagement: An Introduction to Vegetation Science. Limited edition (Norfolk, Connecticut, 1977), page 275.
[42]Podzols are a “group of zonal soils having an organic mat and a very thin organic–mineral layer overlying a gray, leached A2 horizon and a dark brown, illuvial B horizon enriched in iron oxide, alumina, and organic matter.” They develop “under coniferous or mixed forests or under heath, in a cool to temperate moist climate.”
[43]Latosols are a “great group of zonal soils characterized by deep weathering and abundant hydrous-oxide material. They are developed under forested humid tropical conditions.” A laterite is a “highly weathered red subsoil or material rich in secondary oxides of iron, aluminum, or both, nearly devoid of bases and primary silicates, and commonly with quartz and kaolinate. It develops in a tropical or forested warm to temperate climate, and is a residual product of weathering.”
[44]Carl Koteff. Surficial Geology of the
[45]“Till” is defined as “Unstratified drift, deposited directly by a glacier without reworking by meltwater, and consisting of a mixture of clay, silt, sand, gravel, and boulders ranging widely in size and shape” (Robert L. Bates and Julia A. Jackson, editors. Dictionary of Geological Terms. Third edition [Garden City,
[46]Carl Koteff. Surficial Geology of the
[47]Brian Donahue. The forests and fields of
[48]Carl Koteff. Surficial Geology of the
[49]Carl Koteff. Surficial Geology of the
[50][Soil Conservation Service.] [Soils of Walden Woods and Vicinity,
[51]A “taxon” (plural: “taxa”) is a unit of classification at any level, or rank. Taxonomy is the naming of taxa.
[52]S. W. Buol, F. D. Hole, and R. J. McCracken. Soil Genesis and Classification. (Ames, Iowa, 1973), page 312.
[53]Nyle C. Brady. The Nature and Properties of Soils. Eighth edition (New York, 1974), (quoted in Donahue, pages 17 and 18); Soil Survey Staff. Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys. Agriculture Handbook No. 436 ([Washington, D. C.], 1975), pages .
[54]R. Work and E. L. Francis. Soils and Their Interpretations for Various Land Uses: Town of
[55]Soil Conservation Service. Soils and Their Interpretations for Various Land Uses:
[56]James W. Skehan, S. J. Puddingstone, Drumlins, and Ancient Volcanoes: A Geologic Field Guide along Historic Trails of Greater
[57]Richard J. Eaton. A Flora of
[58]James W. Skehan, S. J. Puddingstone, Drumlins, and Ancient Volcanoes: A Geologic Field Guide along Historic Trails of Greater
[59]
[60]John C. Kricher. A Field Guide to Eastern Forests [of] North America (
[61]John C. Kricher. A Field Guide to Eastern Forests [of] North America (
[62]Entry for October 24, 1837, in: Henry D. Thoreau. Journal. Volume 1: 1837–1844. Edited by E. H. Witherell, W. L. Howarth, R. Sattelmeyer, and T. Blanding (Princeton, New Jersey, 1981), page 5.
[63]In Robert L. Bates and Julia A. Jackson, editors. Dictionary of Geological Terms. Third edition (Garden City, New York, 1984), page 243, “hydraulic gradient is defined as “the rate of change of total head per unit of distance of flow at a given point and in a given direction.”
[64]Eugene H. Walker. Walden’s way revealed. Man and Nature [Massachusets Audubon Society], December 1971, pages 11 to 20.
[65]Henry D. Thoreau. Journal (
[66]Anthony Maevsky. Ground-Water Levels in
[67]Henry D. Thoreau. Journal (
[68]Henry D. Thoreau. Walden (Princeton, New Jersey, 1971), pages 180, 181, 292.
[69]Usually spelled “Chinquapin.”
[70]John C. Kricher. A Field Guide to Eastern Forests [of] North America, (
[71]Quoted in Betty
[72]The
[73]Ann Sutton and Myron Sutton. Eastern Forests (New York, 1985), page 95.
[74]Ann Sutton and Myron Sutton. Eastern Forests (New York, 1985), pages 95 and 96.
[75]Ann Sutton and Myron Sutton. Eastern Forests (New York, 1985), page 96.
[76]Frank E. Egler. The Nature of Vegetation, Its Management and Mismanagement: An Introduction to Vegetation Science. Limited edition (Norfolk, Connecticut, 1977), page 251.
[77]Egler’s idiosyncratic (though not inconsistent) capitalization, spelling, and hyphenation are retained in this and other quotations from his book, The Nature of Vegetation.
[78]Neil Jorgensen. A Sierra Club Naturalist’s Guide to
[79]James Walter Goldthwait. The sand plains of glacial
[80]Warren Upham. Walden, Cochituate, and other lakes enclosed by modified drift. Proceedings of the Boston Society of Natural History, Volume 25, Part 1, pages 228 to 242 (1891).
[81]Diaries of George Hunt Barton, Barton–Bradshaw Room, Goodnow Memorial Library,
[82]James Walter Goldthwait. The sand plains of glacial
[83]Carl Koteff. Glacial lakes near
[84]Neil Jorgensen. A Guide to
[85]Irving B. Crosby states (Groundwater in the pre-glacial buried valleys of
The valleys [of preglacial streams] in the central and western parts of
[86]John C. MacLean. A Rich Harvest: The History, Buildings, and People of
[87]Betty
[88]A. W. Küchler. Natural Vegetation [of the
[89]Wilfred T. Neill. The Geography of Life (New York and London, 1969), page 306.
[90]Or
[91]Richard Jefferson Eaton. A Flora of Concord: An Account of the Flowering Plants, Ferns, and Fern-Allies Known To Have Occurred without Cultivation in Concord, Massachusetts, from Thoreau’s Time to the Present Day (Cambridge, Massachusetts, 1974), pages 7 and 8.
[92]Neil Jorgensen. A Sierra Club Naturalist’s Guide to
[93]George E. Nichols. A working basis for the ecological classification of plant communities. Part II. Ecology, Volume 4, Number 2 (April 1923), page 177.
[94]
[95]
[96]Neil Jorgensen. A Sierra Club Naturalist’s Guide to
[97]“In ecology, [‘climax’ is] the final stage or equilibrium stage of development that a sere, community, species, flora, or fauna attains in a given environment. . .” (Robert L. Bates and Julia A. Jackson, editors. Dictionary of Geological Terms. Third edition [Garden City,
“Succession” (called variously “biotic succession,” “ecological succession,” “ecosystem development,” etc.) is “the developmental series of communities constituting a sere and leading up to a state of relative stability and permanence known as the climax” (Nicholas Polunin. Introduction to Plant Geography [
Thoreau’s essay, “The Succession of Forest Trees,” the result of studies he made largely in Walden Woods, is one of the earliest treatments of this apparently universal ecological phenomenon. Thoreau seems to have been the first person to attempt to explain how and why it occurs. (See, in this regard, inter alii, Leo Stoller. After Walden: Thoreau’s Changing Views on Economic Man [
[98]The eastern part of the ecosystem, the so-called “Sandy Pond Unit” (for a definition of which see the text), while originally forested, apparently was not
[99]John C. Kricher. A Field Guide to Eastern Forests [of] North America (
[100]Jorgensen distinguishes two related communities that closely resemble Kricher’s
[101]In this list and in the text that follows the species listed by Kricher are correlated with references to the species in Thoreau’s writings and in the writings of other authors (William Brewster, Ludlow Griscom, etc.). It becomes abundantly clear that Walden Woods—at least its sand plain component—is a mosaic of various successional stages of the
[102]Boldface type (including, in the case of Latin binomials, bold italic) indicates species explicitly mentioned by Thoreau (in Walden, his Journal, etc.), William Brewster, Ludlow Griscom, or another author as occurring in Walden Woods as Walden Woods is defined in this Report.
The asterisks (*, **, ***) signify that the species is listed in the standard authorities on the biota of the Walden Woods area (Concord, the Concord area, or Middlesex County); Massachusetts; New England; or the eastern United States; viz.: M. L. Fernald, Gray’s Manual of Botany, Eighth (Centennial) edition (New York and elsewhere,1950; reprinted Portland, Oregon,1988); F. C. Seymour, The Flora of New England (Rutland, Vermont, 1969); L. L. Dame and F. S. Collins, Flora of Middlesex County, Massachusetts (Malden, Massachusetts, 1888); R. J. Eaton, A Flora of Concord (Cambridge, Massachusetts, 1974); R. Angelo, Concord Area Shrubs (Cambridge, Massachusetts, 1978); R. L. Angelo, Concord Area Trees ([Cambridge, Massachusetts?], 1976); R. T. Peterson, A Field Guide to the Birds . . . of Eastern and Central North America, Fourth edition (Boston, 1980); E. H. Forbush, Natural History of the Birds of Eastern and Central North America (Boston, 1939); E. H. Forbush, Birds of Massachusetts and Other New England States, three volumes (Norwood, Massachusetts, 1929); L. Griscom, Birds of Concord (Cambridge, Massachusetts, 1949); and R. K. Walton, Birds of the Sudbury River Valley—An Historical Perspective (Lincoln, Massachusetts, 1984).
A single asterisk (*) indicates that a species is present but rare, infrequent, or uncommon in
The symbol § indicates a southern species not found anywhere in New England, the symbol ¶ a species found only in extreme southern or western New England, and the symbol † a strictly coastal species or one found only in the southeastern part of the state—in each case, therefore, almost certainly absent from Walden Woods.
Note that the asterisks indicate only that published sources have a species occurring in the vicinity of Walden Woods, not that there is readily accessible documentation of its presence in the Walden Woods itself. (Boldface type indicates that there is such documentation, above and beyond the various authorities listed above.) Nonetheless, the likelihood is extremely high that a species recorded for the general vicinity of Walden Woods (i.e., for the
[103]See, for example, Journal, Volume 6, page 244 (7 May 1854).
[104]Angelo (Concord Area Shrubs, page 120) “excludes” this species, but Eaton (page 156) cites a specimen of Edward S. Hoar collected in 1858 from The Cliffs in Walden Woods (Fairhaven Hill), “where it still persisted in 1972.” Thoreau (Journal,Volume 11, page 238 [October 22, 1858]) writes of bearberry on Fairhaven Hill. It is rare in
[105]In Trillium Woods (a part of Walden Woods), Thoreau found Viburnum cassinoides, calling it by its synonym, Viburnum nudum var. pyrifolium (Journal, Volume 5, page 256 [15 June 1853]). In the vicinity of The Cliffs (part of Walden Woods) Thoreau saw the same species (“Viburnum nudum”) on September 4, 1853 (Journal, Volume 5, page 419); he saw it again in Walden Woods, also near The Cliffs, on October 22, 1855 (Journal, Volume 7, page 511) and on November 5, 1855 (Journal, Volume 8, page 10). On August 13, 1856, he saw it at the other end of Walden Woods, near Saw Mill Brook (Journal, Volume 8, page 466).
[106]In Ebby Hubbard’s Woods (a part of Walden Woods), Thoreau found great quantities of pinesap (Journal, Volume 10, page 69 [6 October 1858]). He named the path on which he was walking “Pine-Sap Path.”
[107]Kricher gives only the common name (and a partial one, at that). Perhaps he means Gaultheria procumbens (the checkerberry, or aromatic wintergreen) or Chimaphila spp. (C. umbellata or C. maculata). Thoreau collected Chimaphila maculata near Goose Pond in Walden Woods (Eaton, page 153), and saw that species near Hubbard’s Close in Walden Woods on July 9, 1854 (Journal, Volume 6, page 388).
[108]Bird populations fluctuate far more rapidly and widely than do those of plants, for example; thus, the notations of abundance (*, **, ***) are approximate and tentative. They are intended only to give a general indication of a species’ abundance. Species that seem to have fluctuated most in numbers between Thoreau’s time and the present are indicated by the symbol “∞.”
[109]Reported by Ludlow Griscom, not Thoreau, for Walden Woods. Griscom, writing in 1948, says (pages 291 and 292) that the prairie warbler was “Formerly unknown; a colony in the Walden Woods, 1899 on; then very rare as a transient; a marked increase in recent years. . . . . Now a regular transient, scattered pairs nesting here and there for brief periods of time. Contemporaneous with a great increase over the whole northeast, the bird is now [1948] rapidly occupying wrecked and burned over areas throughout the interior of the state, north into
[110]Thoreau reports seeing a flicker (which he calls “pigeon woodpecker”), as well as a towhee, on Shrub Oak Plain in Walden Woods on July 13, 1851 (Journal, Volume 2, page 304). The shrub oak (Quercus ilicifolia) is an indicator species of the
[111]Formerly a common resident in
Cruickshank (Thoreau on Birds) notes (page 89) that “
[112]Thoreau mentions hearing the whip-poor-will in Walden Woods several times in his Journal entry for June 11, 1851 (Journal, Volume 2, pages 234 to 237). He says, in part (pages 235 and 236): “The whip-poor-will suggests how wide asunder [are] the woods and the town. Its note is very rarely heard by those who live on the street, and then it is thought to be of ill omen. Only the dwellers on the outskirts of the village hear it occasionally. It sometimes comes into their yards. But go to the woods in a warm night at this season, and it is the prevailing sound. I hear now five or six at once. It is no more of ill omen therefore here than the night and the moonlight are. It is a bird not only of the woods, but of the night side of the woods. . . .”
In 1874, William Brewster reported that the whip-poor-will was abundant in the “great woods” around Sandy Pond, Lincoln (Ludlow Griscom. The Birds of
[113]Griscom (The Birds of Concord, page 233) says that the mourning dove was “Well known to Thoreau.” Thoreau mentions the mourning dove and several other indicator species [set in boldface type] of the Northern Pine–Oak Forest in the following passage from the “Brute Neighbors” chapter of Walden:
. . . Commonly I rested an hour or two in the shade at noon, after planting, and ate my lunch, and read a little by a spring [Brister’s Spring] which was the source of a swamp and of a brook, oozing from under Brister’s Hill, half a mile from my field. The approach to this was through a succession of descending grassy hollows, full of young pitch-pines, into a larger wood about the swamp. There, in a very secluded and shaded spot, under a spreading white-pine, there was yet a clean sward to sit on. . . . There too the turtle-doves [i. e., mourning doves] sat over the spring, or fluttered from bough to bough of the soft white-pines over my head; or the red squirrel, coursing down the nearest bough, was particularly familiar and inquisitive.
Brister’s Spring is located in the present
[114]Thoreau mentions hearing bluebirds on Fairhaven Hill in his Journal (Volume 10, page 73 [7 October 1857]).
[115]In the “Winter Animals” chapter of Walden, Thoreau mentions red squirrels (Tamiasciurus hudsonicus) “coursing over the roof and up and down the sides of the house” (Walden [Princeton, New Jersey, 1971], page 273). In a passage in his Journal on which this passage is based, he states that both red and gray engaged in such antics: “Often a red or grey squirrel awaked me in the dawn—coursing over my roof—and up and down the sides of my house. . .” (Journal, Volume 2: 1842–1848 [Princeton, New Jersey, 1984], page 138 [Fall–Winter 1845–1846]).
[116]John C. Kricher. A Field Guide to Eastern Forests [of] North America (
[118]F. Andrew Michaux. The North American Sylva, or a Description of the Forest Trees of the
[119]Howard A. Miller and Samuel H. Lamb. Oaks of
[120]Herbert W. Gleason. Map of
[121]Angelo (in Botanical Index to the Journal of Henry David Thoreau [Salt Lake City, 1984], page 125) assigns the term “shrub oak” as used in Thoreau’s Journal to Quercus ilicifolia, the SCRUB OAK of his (Angelo’s) Index. Another vernacular name of this species is “bear oak.”
[122]Carl Koteff. Surficial Geology of the
[123]The sweet-fern, so-called, is “an aromatic deciduous shrub found in dry sandy soils as well as fertile pastures” (Kricher, page 122). It becomes abundant during succession but eventually is shaded out by larger shrubs and trees.
[124]Henry D. Thoreau. Journal (
[125]William Brewster. October Farm: From the Journals and Diaries of William Brewster (Cambridge, Massachusetts, 1936), page 69.
[126]Quercus coccinea, an indicator tree of the
[127]Gaylussacia spp., indicator shrubs of the
[128]Rather than the settlers themselves, these were scouts under the command of Major Simon Willard, who reconnoitered the
[129]Merritt Lyndon Fernald. Gray’s Manual of Botany, eighth edition (Portland, Oregon, [1987?]), page 525.
[130]Richard Jefferson Eaton. A Flora of
[131]Townsend Scudder.
[132]Ruth R. Wheeler Concord: Climate for Freedom (
[133]The present town of
[134]John C. MacLean. A Rich Harvest: The History, Buildings, and People of
[135]Early Massachusetts Records, Town of
[136]John C. Kricher. A Field Guide to Eastern Forests [of] North America (
[137]Henry D. Thoreau, “Huckleberries,” edited by Leo Stoller ([
[138]John C. Kricher. A Field Guide to Eastern Forests [of] North America (
[139]Jorgensen states (page 105) that “Oaks, hickories, and red maple, all common southern
[140]Kalmia angustifolia is an “indicator shrub” of the
[141]Neil Jorgensen. A Sierra Club Naturalist’s Guide to
[142]Neil Jorgensen. A Sierra Club Naturalist’s Guide to
[143]Henry D. Thoreau. Walden (Princeton, New Jersey, 1971), page 280.
[144]Journal, Volume 14, pages 271 and 272 (26 November 1860).
[145]
[146]Henry D. Thoreau. Journal (
[147]Described in F. B. Sanborn’s account, “Thoreau and the Walden Woods: The Damage by the Recent Fire Not As Great As Was Reported,”
[148]An indicator bird of the
[149]An indicator bird of the
[150]An indicator bird of the
[151]An indicator bird of the
[152]Smith O. Dexter, editor.
[153]Richard K. Walton. Birds of the
[154]Sandy Mallett. A Year with
[155]Edward Howe Forbush and John Bichard May. Natural History of the Birds of Eastern and Central North America (
[156]Francis H. Allen, editor. Notes on
[157]Helen Cruickshank, compiler. Thoreau on Birds (New York, Toronto, and London, 1964).
[158]Henry D. Thoreau. Walden (Princeton, New Jersey, 1971), pages 158 and 319 and pages 302 and 310, respectively.
[159]Henry D. Thoreau. Walden (Princeton, New Jersey, 1971), page 302 (as “striped squirrel”) and page 319 (as “chewink”), respectively.
[160]Henry D. Thoreau. Walden (Princeton, New Jersey, 1971), pages 127 and 128. Thoreau also mentions whip-poor-wills on pages 86, 128, 129, and 319.
[161]According to Walton (page 140), the great horned owl is “An uncommon permanent resident” of the
[162]Henry D. Thoreau. Walden (Princeton, New Jersey, 1971), page 125. Francis H. Allen (page 183) and Helen Cruickshank (page 111) both identify Thoreau’s “hooting owl” as the great horned owl [Bubo virginianus], as did Thoreau himself in his Journal on November 18, 1851 (where he used the alternative name for that species, “cat owl”). Forbush and May (Natural History of the Birds of Eastern and Central North America [Boston, 1939]), page 265) give “cat owl” and “hoot owl” as alternative names for this species. They describe its calls as “a deep-toned hoot, a blood-curdling shriek, and many others.”
[163]Henry D. Thoreau. Walden (Princeton, New Jersey, 1971), pages 171 to 172. Edward Howe Forbush and John Bichard May (Natural History of the Birds of Eastern and Central North America [Boston, 1939], page 265) say that great horned owls “become vocal” in January and February. They are less vocal later in the year, “but now and then, especially in autumn, their hooting may be heard” (page 266). They are nocturnal birds (page 266), “most active in the dark of the evening and on moonlit nights, but . . . may be hooting at times at midnight in the ‘dark of the moon.’”
Thoreau heard the great horned owl “at sundown” on November 18 and 25, 1851; July 5, 1852; and December 9, 1856 (Journal; quoted in Allen, pages 183 to 188). In his Journal (December 19, 1856), Thoreau asks with respect to his “old acquaintance the owl” in Walden Woods, “Do I not oftenest hear it just before sundown?” On January 7, 1854, he noted that he heard it “Oftenest at twilight.” On a moonlit winter evening (February 3, 1852), he heard “[his] owl” at The Cliffs of Fairhaven Hill (quoted in Allen, page 184).
Virtually every detail of Thoreau’s accounts in Walden and his Journal of hearing the “cat owl” or “hooting owl” in Walden Woods or in the Ministerial Swamp–Dugan Desert area is consistent with Allen’s and Cruickshank’s conclusion that Thoreau heard the great horned owl, which is an indicator species of the Northern Pine–Oak Forest as defined by Kricher.
[164]Peterson (Roger Tory Peterson. A Field Guide to the Birds [
[165] In “The Allegash and East Branch” Thoreau records “Ugh, ugh, ugh,—ugh, ugh” as his guide Joseph Polis’ rendering of the call of the great horned owl:
Just below this, a cat-owl flew heavily against the stream, and he [Joseph Polis], asking if I knew what it was, imitated very well the common hoo, hoo, hoo, hoorer, hoo, of our woods; making a hard, gutteral sound, “Ugh, ugh, ugh,—ugh, ugh.”
[166] “Cat owl” is an alternative vernacular name for the great horned owl (Roger Tory Peterson. A Field Guide to the Birds [
[167]William Brewster. October Farm (Cambridge, Massachusetts, 1936), page 23. The same episode is described by Bolles in “A Voyage to Heard’s
[168]See Koteff’s map of the surficial geology of the
[169]The
[170]Forbush and May. Natural History of the Birds of Eastern and Central North America (
[171]Smith O. Dexter, editor.
[172]Henry D. Thoreau. Walden (Princeton, New Jersey, 1971), pages 127 and 128.
[173]Henry D. Thoreau. Walden (Princeton, New Jersey, 1971), pages 318 and 319.
[174]Charles H. Walcott.
[175]Charles H. Walcott.
[176]Barbara Robinson. From Musketaquid to
[177]Howard S. Russell. Indian
[178]Lemuel Shattuck. A History of the Town of
[179]Ecologists have distinguished two types of “climax” community, the “climatic climax” (also called “regional climax”) and the “local climax” (also called “edaphic climax,” from the Greek word for soil). The climatic climax community “is in equilibrium with the general climate of a region,” while more localized, soil-influenced communities “are modified steady states in equilibrium with special local conditions of the substrate [e.g., with the dry, sandy, fire-prone conditions of the Walden sand plain]” (Eugene P. Odum Basic Ecology [Philadelphia, New York, and elsewhere, 1983], page 469).
The concept of successional climax derives from the so-called “American plant-succession school” of plant synecology (the study of relationships between biotic communities and their environments), which originated with the Harvard geomorphologist, William Morris Davis.
The American ecologist Frederick E. Clements applied this line of reasoning to vegetation, theorizing that such a peneplain eventually would be occupied by a climatic climax, a community of organisms best suited to the particular climate that was being held constant. Ecologists eventually realized that climate is not fixed, however. It changes, and its changes affect the animals and plants of an area much more profoundly than does erosion. They came to realize also that fire, browsing, and windthrow are natural phenomena that are to be expected in most parts of the world.
Despite its purely theoretical nature the concept of climatic climax (and of the related term, local climax) reflects ecological realities. It is of great value to the science of ecology, providing a framework within which to understand and study ecological succession and the development, nature, and functioning of ecosystems, including the Walden Ecosystem (Stephen H. Spurr. The natural resource ecosystem. Pages 3 to 7 in: George M. Van Dyne, editor. The Ecosystem Concept in Natural Resource Management [
[180]Lemuel Shattuck. A History of the Town of
[181]Lemuel Shattuck. A History of the Town of
[182]However, Shattuck presents statistics showing a significant reduction (approximately 33 percent) in the area of woodland in
[183]Lloyd C. Irland. Wildlands and Woodlots: The Story of
[184]Roland M. Harper. Changes in the forest area of
[185]John C. MacLean. A Rich Harvest: The History, Buildings, and People of
[186]John C. MacLean. A Rich Harvest: The History, Buildings, and People of
[187]Quoted in John C. MacLean. A Rich Harvest: The History, Buildings, and People of
[188]“Forest Trees of
[189][George B. Emerson.] Report on the Trees and Shrubs Growing Naturally in the Forests of
[190]John H. White, Jr., “Railroads: Wood To Burn,” pages 199 to 201, 215 in: Brooke Hindle, editor, Material Culture in the Wooden Age (Tarrytown, New York, 1981). Quoted in Thomas J. Lyon, editor, This Incomperable Lande: A Book of American Nature Writing (
[191]Henry D. Thoreau. The Journal of Henry D. Thoreau (New York, 1962), Volume 1, page 521 (28 January 1853).
[192]Henry D. Thoreau. The Journal of Henry D. Thoreau (New York, 1962), Volume 1, page 330.
[193]Ann Sutton and Myron Sutton. Eastern Forests (New York, 1985), pages 43 and 45.
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