Jump to ContentJump to Main Navigation
People and the Land through TimeLinking Ecology and History, Second Edition$

Emily W. B. Russell Southgate

Print publication date: 2019

Print ISBN-13: 9780300225808

Published to Yale Scholarship Online: January 2020

DOI: 10.12987/yale/9780300225808.001.0001

Show Summary Details
Page of

PRINTED FROM YALE SCHOLARSHIP ONLINE (www.yale.universitypressscholarship.com). (c) Copyright Yale University Press, 2022. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in YSO for personal use. Subscriber: null; date: 16 May 2022

Patterns of Human Settlement and Industrialization

Patterns of Human Settlement and Industrialization

Chapter:
(p.150) 9 Patterns of Human Settlement and Industrialization
Source:
People and the Land through Time
Author(s):

Emily W. B. Russell Southgate

Publisher:
Yale University Press
DOI:10.12987/yale/9780300225808.003.0009

Abstract and Keywords

This chapter treats a variety of human interactions with the land that trace their origins more to political and commercial drivers rather than directly to geology, topography, soils and local biota. Examples of land subdivisions are taken mostly from the United States, which illustrates a variety of land-use patterns that result from property surveys. Land hunger and government policies have also contributed to wars, which have altered landscapes. These have characterized the history of most parts of the world, having major repercussions on the environment as well as on people. Examples range over time and space. Industrialization increased the ability of people to travel and thus trade quickly over long distances thus intensifying and extending the impact of humans on the land, especially as industrialization further separated local land use from resource protection. Cities have flourished, often along trade routes, perhaps even before the development of agriculture Some all but disappeared, but all have had both local and regional effects on the land. Examples are discussed of effects both within cities today and resulting from cities that no longer exist.

Keywords:   settlement, industrialization, land-use patterns, war, industrialization, trade, cities

As agricultural productivity allowed a greater proportion of the population to become less reliant on the natural world, patterns of human settlements became ever more divorced from natural landscape features. Political boundaries bisected such biomes as the tropical rain forest of Southeast Asia, the temperate deciduous forest of western Europe, and the grassland of North America. Each of these great complexes of vegetation extends across several nations or states, each with its own history of land divisions, legal systems, and population agglomerations. Although the lands within one biome, for example, grassland or deciduous forest, may have similar susceptibility to fire and invasion by exotic species, similar suitability for exploitation of natural resources and agriculture, the expression of these characteristics have differed after millennia or even centuries of domination by different political systems and the different impacts that go along with them. Extensive trade has also allowed those living in one part of the world to appropriate the natural resources of another.

The Judeo-Christian tradition in the West emphasized that the deity had put natural resources on the earth for the (wise) use of and perfection by humanity. If people were not making appropriate use of their land, they did not deserve it, so that those who would put it to better use were fully justified in acquiring it, by force if needed.

(p.151) In North America, historian William Cronon has argued that the major factor distinguishing land use by the Amerindians from use by European settlers was a shift from treating land as territory that did not belong to any one person or group of persons and was not thus an item of trade to treating it as a commodity.1 Furthermore, although Native Americans derived their livelihood from the land, they apparently did not perceive that they had any responsibility to change it. Right to land was not tied to some manipulative use of it. This difference in the conception of the human relation to the environment allowed the European settlers both to justify appropriating native territory and to alter it for their own use. Unchanged land represented unfinished business.

Dividing Up the Land

In much of the world, political and urban systems have developed over millennia, and the reasons for current patterns of land subdivision are well buried in the past, some even beneath mature forests. In other areas, such as the Americas and Australia, recent human invaders have imposed new systems of land allocation with little or no regard for entrenched indigenous customs. The consequences are dramatic and often bizarre, bearing little or no relation to topography. In South Australia, for example, it has been suggested that the “survey was the first, the greatest, and probably the most enduring imprint of man on the land.”2 Where people have settled and how communities have grown, interacted, and waned have left indelible impacts on landscapes. Tracing changes in the landscape brought about by land subdivision and urbanization adds a temporal dimension to landscape analysis that may help explain anomalous characteristics in the resulting ecosystems. Many edges that separate landscape features are the result of human activity, and as such have been determined by regional and local culture through time.3

These patterns are often discernible, however, without reference to history; the history of the patterns adds depth to the analysis. First, it can tell us something of the age of the pattern, which affects the amount of influence the pattern exerts on current ecosystem structure and processes. Second, the rationale for dividing properties may produce long-lasting and often perplexing landscape patterns. Why, for example, are so many woodlots in North America square? How did some forest stands escape the axe? What led to the current patterns of native plants in deserts and prairies?

Colonial land allocation in New Jersey illustrates the diversity of systems and some possible impacts on the resulting ecosystems. In the seventeenth century, (p.152) political maneuvering split what was to become New Jersey into two parts, East and West Jersey. The dividing line separating these grants was redrawn several times, on rather poorly surveyed maps (fig. 9.1). This led to major problems in settling both the boundary between New Jersey and New York to the north and that between East and West Jersey. In addition, magnetite in the bedrock of northern New Jersey led to erroneous compass readings in lines surveyed on the ground.4 Boundary disputes resulted in uncertain titles to land. Absentee landownership also led to illegal clearing and timber cutting where the demand for land was low and there was a high cost to getting a clear title.5

Actual settlement patterns under this confused regulatory nonsystem were quite varied. Proprietors encouraged settlers to establish villages by advertising with detailed plans of settlements consisting of carefully arranged house and farm plots, with no vacant land left between them. Such farm lots often included rights to essentially unsurveyed woodlots in distant swamps or mountains.6 Farther from these aggregations of surveyed lots, however, the arrangement of farms was much more casual. Farmers cleared and fenced fertile, level land with or without legal title, usually leaving no woodlots on the better soils. These properties had highly irregular boundaries and usually excluded poorer, steep areas, which were used for common grazing and as sources of wood.7 Both pressure on woodlots for grazing, timber, charcoal, and other products and soil or microclimate characteristics varied with time and system of settlement and have continued to vary. Land disputes made some areas less attractive for settlement. These factors have influenced both the composition and structure of remnant and reforested stands. The trees in woodlots left on farmland, used for casual grazing and for wood products for a farm, may be more similar to precolonial forests than those in more extensive forest land cut over repeatedly for charcoal, for example, even though they are more fragmented and smaller.8

The actual patterns of the subdivisions were thus related to both natural features and to culture. In areas of North America originally settled by the French, for example, parts of Quebec, northern Wisconsin, and New Orleans, very long, thin lots prevailed (fig. 9.2).9 Areas settled by the Dutch were also divided into long lots, but these were very large and usually subdivided into smaller farms. The lines dividing these lots, surveyed in the eighteenth century, still formed farm boundaries in the twentieth century (fig. 9.3).

An unusual and well-studied land survey system is the United States General Land Office Survey (GLOS), which made a neat checkerboard of even highly dissected land surfaces (fig. 9.4). After the American Revolution, states ceded most of their extensive, unsettled western territory to the new federal (p.153)

Patterns of Human Settlement and Industrialization

Figure 9.1. Provincial boundary lines of New Jersey. Lack of agreement on these lines contributed to very irregular patterns of settlement.

(Wacker, Peter. Land and People. New Brunswick: Rutgers University Press, 1975.)

(p.154)

Patterns of Human Settlement and Industrialization

Figure 9.2. Farm lots in Assumption Parish, Louisiana. Note that some lots are bordered by long, thin strips of forest and that buildings are concentrated along the bayou to the east, not the road. Complex drainage characterizes the swamp on the left of the photograph, beyond the straight drainage canal into which the farm lots are drained. You can also see some diagonal lines of ancient natural drainage channels.

(Google Earth image, copied 2017.)

government. The federal Ordinance of 1785 imposed a “rational,” rectilinear surveying system on this land in keeping with the philosophy of the Enlightenment. The basic unit was the section, of 640 acres (256 hectares), or 1 square mile (2.6 square kilometers), which was often divided into four quarters for sale. The system also required marking up to four “bearing trees” at each section corner, which, along with qualitative descriptions of land cover, has provided information for reconstructing vegetation at the time of a survey. This system transformed an unknown wilderness into a rational, familiar geometry, ignoring water rights, location of forests, topography, or any other natural features of the land.10 Land was treated even more clearly as a commodity to be traded than it had been under colonial rule.

The major concern of the government was to get the land into private hands. The system it adopted led to widespread speculation, in which individuals gained title to large numbers of sections that they hoped to sell for a profit. Squatters often cleared land, acquiring title only later, so that there was a disjunction between the surveys and actual settlement.11 Nevertheless, as these areas developed, farmsteads were usually to be found near the boundaries of the sections or quarters, frequently with a woodlot (often square) left in the center of the quarter. The locations of the woodlots were (p.155)

Patterns of Human Settlement and Industrialization

Figure 9.3. Farm landscape, Saratoga County, New York, 1948. Arrows indicate the location of boundaries between large lots as surveyed in 1750. Farm divisions within the large lots can also be traced back to the eighteenth century.

(Photo courtesy of Saratoga National Historical Park.)

determined not by the quality of the soil or steepness of the terrain, but by the distance from the farmstead, with cultivated land closer to the house. In other areas, woodlots were left near homesteads or planted there to afford convenient access to wood products and to serve as a windbreak. It is often difficult to determine today the history of such woodlots, whether they are relics of the preclearance forest or second growth on cleared land. In either case, farmers would have relied heavily on them for wood products, but their composition and dynamics may differ. Planting, for example, for maple sugar production, affected the structure of many woodlots. In the prairie, where there were few trees, the entire parcel was usually cultivated, creating heavy pressure on the few trees that grew along watercourses, although there were incentives for planting trees as windbreaks. (p.156)

Patterns of Human Settlement and Industrialization

Figure 9.4. Satellite image near Spokane, Washington. The straight lines mark GLOS boundaries and bear no relation to topography and the irregular pattern of vegetation and physiography.

(Google Earth image, copied 2018.)

In each township, the government reserved four half-section lots for public purposes, such as to support a school or minister. None was reserved to preserve native natural resources. Many of these lots were unused, but they contributed to a highly dispersed arrangement of undeveloped lands in many townships, and often remain as the sole remnants of native vegetation. Other lots were granted to railroads as sources of timber for fuel and ties, and these too had a different history from the nearby lots in private hands.12

This subdivision of the land on paper, with no attention to the nature of the landscape, thus led to a pattern of settlement that bore little resemblance to what would develop by the natural spread of cultivation across the land. In 1882, F. B. Hough noted the inappropriateness of a rectilinear survey in mountainous lands, where lots could well contain land on both sides of a mountain range, so that one side of the ridge would be cleared and used but the other not cleared because of the difficulty of access. Straight lines separating sections have often also separated different kinds of land management, such as row cropping and pasture, and also separated cultivated from uncultivated land. If these lots are later abandoned, their future will depend on which side of the line they were located as well as on natural features, especially if soil erosion was more severe on one side than the other. In forested regions, straight boundary lines that have become buried in forest regrowth are clues to these past uses and to probable lingering effects, both of the past (p.157)

Patterns of Human Settlement and Industrialization

Figure 9.5. Farming landscape in Clinton County, Indiana. The irregular dimpled pattern on the right is caused by soil moisture differences, with very little topographic relief. This contrasts with the straight lines of the property and field lines, many woodlots, and roads. Some irregularly shaped gallery forests persist along streams.

(Google Earth image, copied 2017.)

uses and of the consequences of straight as compared with uneven, more natural boundaries.13

In a level landscape subject to the GLOS, almost all woodlots are square or rectangular and fairly evenly distributed across the landscape (fig. 9.5). Hedgerows are rare. In a level area first settled in the 1730s, on the other hand, forest patches tend to have curved edges and few right angles (fig. 9.6), more similar to property lines in other parts of the world. Hedgerows connect many of the woodlots. Although field and woodland patterns resulting from such surveys or other methods of land allocation often remain visible for centuries, their impact on natural resources is more subtle. Narrow, elongated fields with hedgerows may have led to better seed and animal dispersal than more isodiametric fields, for example; sinuous woodland edges may provide more habitat for edge-dwelling species than straight edges, thereby increasing the chance of these species moving from edge to interior of the forest. These field edges have persisted in many areas into the twenty-first century.14

Regulating Land Use

In addition to laying out the land and encouraging or directing settlement, governments have exerted control by regulating what people could do (p.158)

Patterns of Human Settlement and Industrialization

Figure 9.6. Loudoun County, Virginia, farming landscape. Field edges are generally straight, though the angles are irregular. Many woodlots have very irregular boundaries and are concentrated along water courses. Some have grown out from field boundaries or replaced abandoned farm fields.

(Google Earth image, copied 2018.)

with their land. The motives for regulation have varied, from maximizing profit to caring about resource depletion. The first consideration in regulating land use, whether by custom or by law, is the perception of whether there is an adequate supply of land for subsistence. Wherever population became too dense to supply enough suitable land by moving around, in the tropics of Central America, the chilly, temperate climates of western Europe and China, or the deserts of Africa and Asia, farmers have had to learn how to maintain soil fertility in one place for generations. Terracing to hold soil and water, irrigating to distribute water, draining wetlands, fertilizing with organic wastes from humans and domestic livestock, collecting forest twigs, and other techniques have maintained agriculture in one place in a wide variety of habitats. Planting trees, coppicing, and other methods of growing timber have conserved the supply of wood. Governments have regulated many of these practices, even though knowledge of the best methods has often been lacking, and even when the knowledge was there, enforcement has been problematic. The consequences of changing regulations are superimposed on each other, producing complex patterns that may continue to influence ecosystems and landscape patterns for centuries, if not millennia. Until the twentieth century, these regulations were usually designed to protect a specific resource, such as wood for the navy or agricultural productivity, not rare species or habitats.

(p.159) The French ordinance for waters and forests of 1669 ensured that there were big trees available for the navy by regulating the rotation of cutting and the maintenance of standards (large trees) in coppices in the royal forests.15 This ordinance embodied most of the characteristics of laws governing the use of natural resources and thus affecting the structure of the ecosystems. It had a direct relation to the resource that was needed, for example, the directive to leave standards in the coppices and cut them at certain intervals, and it affected only lands that had not yet been alienated from public control. The kind of forest this system created could be understood only by reference to the kind of management that was imposed on it, which may have lapsed a century or more ago.

In England, one of the most controversial sets of regulations affecting large parcels of land was the enclosure movement in the eighteenth and nineteenth centuries. The stated aim of these enclosures was to ensure that land was used in the way best suited to its soil and climate. Villages had been enclosing common lands at least since the fifteenth century, but the pace accelerated in the eighteenth, especially in the Midlands, where enclosure was mandated by act of Parliament. Large open fields were divided into smaller fields with various uses. The effects on the landscape were dramatic, as hedgerows and stone walls separating individual holdings broke up wide open spaces. Whereas the earlier enclosures had produced small fields with irregular boundaries, the later ones, reflecting the ideals of the Enlightenment, produced somewhat larger fields with straight borders. This proliferation of hedges, stone walls, and smaller fields, with arable land being converted to pasture and vice versa depending on the conditions, changed the potential for vegetational development in unplanted pastures at the same time that it created new, unanticipated habitats in the hedges and walls. In the late twentieth century, heavy machinery and other incentives led to the grubbing out of old hedges, again changing the landscape pattern. The ages of these patterns, and therefore their effects on the ecology of the landscape, thus vary greatly depending on the local history of enclosure by regulation or local practice.16

Differences across national borders highlight the importance of historical land use and regulation on current vegetation patterns. Until the 1890s, the border between Mexico and the United States was unfenced. The photographs of monuments erected as part of the border survey in the 1890s document a landscape apparently denuded by overgrazing and/or drought, although the presence of construction crews erecting the monuments in all likelihood exaggerated the devastation of the vegetation as seen in the photographs. In 1976, a survey of vegetation on both sides of the border at twelve boundary monuments found 2.8 percent more grass cover on the U.S. side than (p.160) the Mexican and 30 percent less barren ground. One may hypothesize that contrasting government regulations since the 1890s, superimposed on the conditions when the border was fenced, account for these differences. The United States Forest Service regulates grazing on the U.S. side by limiting stocking. In Mexico, however, the emphasis was on maximum stocking, which may have contributed to overgrazing. Tree density in 1976 was the same on both sides of the line, however, perhaps because of the lack of demand on the wood products on the U.S. side and the prohibition on cutting green wood on the Mexican side.17 To test these hypotheses would require integration of the history of regulation, specific impacts and grazing intensities, and other features of the local environments and landscape patterns.

Borders that split environmentally similar landforms provide a special chance to compare the importance of local drivers of ecosystem change. For example, in an area of Switzerland near Zurich, changes in land cover from 1930 to 2000 were driven by urbanization as mediated by conditions and regulations in individual cantons. The differences would not have been easily explicable with reference only to natural environmental factors.18

In some places the role of past government policies on vegetation has been much more subtle. In central New Jersey, an area of more than one hundred hectares of Virginia pine (Pinus virginiana) constitutes the northernmost stand of this species in this area, many kilometers disjunct from another Virginia pine stand. Ecologists began noticing it in the 1970s when an interstate highway cut through its edge. Because of its irregular shape and the varied sizes of the trees, they assumed that it was a naturally occurring stand on highly eroded red shale. On searching the history of the stand, however, I found that it had been planted in the 1930s as part of the government’s efforts to revegetate badly eroded soils. The trees had thrived and even begun seeding into recently abandoned fields along with local red cedar. This potential range extension of the species in this state can be understood only with reference to the combination of farming, erosion, and government policy. Analysis of the current conditions under which it is growing would not explain its presence there.

Conflict: Wars

Land hunger and government policies have also contributed to armed conflicts, which have altered landscapes. The internecine struggles that have characterized the history of most parts of the world have had major repercussions not just on the people involved in the conflicts but on the environment as a whole. Battles require weapons and the massing of people and beasts of (p.161) burden. Weapons, until recently, were fashioned mainly from products of the forest. Siege apparatus required tremendous amounts of wood, including huge old trees used as battering rams. During the Thirty Years’ War in the early seventeenth century, Germany used its forests as a source of wood for canon carriages, fortifications, and campfires, for tannins needed to prepare leather for the cavalry, and later for rebuilding burned buildings. Forests that regenerated after this onslaught included more alders, birches, and aspens than the more long-lived oaks and beeches. Depopulation from the depredations of the war meant that there were fewer animals grazing in the forests and fewer loggers cutting down trees than before. The impetus for experimental forestry and silviculture languished as the attention of the government turned elsewhere. Forests regenerated under very different conditions than they had before the war, when major efforts had been made to plant and manage new plantations.19

In New Jersey, George Washington’s troops leveled local forests for fuel and building supplies in the late eighteenth century. Some of these denuded forests were later turned into farmland, but many of them were left to regenerate where the soil was poor and rocky and the slopes steep. This kind of deforestation associated with wars continued at least into the twentieth century. For example, during the First World War, in Israel, the last of the Tabor oak forest was cut to supply fuel for the railroad and wood for defense works.20 In other words, war led to the cutting of wood on land that might not have otherwise been cleared. The ecology of these recently cleared lands may differ from that of lands cleared longer ago, in part because of the varying lengths of time since they have been cleared and diverse postclearing management.

Some battlefield structures and alterations may remain for centuries or even longer, altering drainage locally and providing microsites for a variety of locally rare or unusual species. For example, foxholes dug during the First World War persist in the forest of Fontainebleau near Paris, and old soil structures can be seen at many Revolutionary War sites in the United States. Tanks moving across the land in western France in the Second World War cut across ancient hedgerows, breaking the continuity of habitat.

Bombs and chemicals have wreaked havoc during the last century in ways that will also persist for many centuries. Plants characteristic of bombed-out sites have even received common names commemorating that habitat preference, for example, blitz-weed, a common name for Chamerion angustifolium in England. Defoliation of large areas of mangrove forests on the Mekong Delta in Indochina during the Vietnam War left saturated soils and barren areas that have been colonized by the palm Phoenix paludosa and the fern Acrostichum aureum. Forests have been slow to recover without planting.21

(p.162) Battles and wars have had indirect effects, too. Overharvest of mammals for food in Mozambique during civil war there from 1977 to 1992 decimated their populations, leading to a significant increase in tree cover. An ecological consequence was to find that regardless of fire, grazing alone could reduce tree cover, or at least its absence could foster tree growth.22

Reallocation of land after war can also change land-use patterns. After the American Civil War of the mid-nineteenth century, the rate of forest clearing in the southeastern United States decreased because landowners, deprived of slave labor, had to pay laborers for their work. In three counties in north-central North Carolina, for example, the amount of woodland on farms increased after 1870. The proliferation of small tenant farms may also have led to increased soil erosion, as farmers concentrated on the labor-intensive but soil-destructive crop tobacco. Analysis of these historical data, however, is complicated because data collected by the Census Bureau in the decades immediately after the war are not easily comparable to those before due to changes in tenancy and landownership.23

Trade and Transportation

A more benign contact between groups of people is trade, which has been going on for millennia.24 Transportation obviously moves species around, some on purpose and some by mistake, but it also affects the patterns of settlement, and by itself affects the environment. Earliest transport was obviously by foot and was consequently slow, though the distances could be very great, as in the Paleolithic trade in obsidian between the Mediterranean and the Carpathian Mountains, a distance of about one thousand kilometers.25 The impact on distribution of species and on the land used in the transport routes was, however, probably slight. As beasts of burden came into use, one could go longer distances with more goods. The beasts required forage along the way, and the people who were with them also needed food and water. Livestock being driven long distances from summer to winter pastures grazed heavily along the way, especially coming from winter pastures. This transportation pattern affected the systems of clearing and agriculture in a region, perhaps more than other market or land-use factors.26 Trade also led to the spread of disease in human populations, as discussed in chapter 6.

Long-distance preindustrial transportation was often focused on waterways. Water carried people and products with much less effort than did animals, though the routes were more constrained. Population concentrations grew up near navigable waterways, and transportation allowed areas to specialize in different produce as well as to use products from far away.27 (p.163)

Patterns of Human Settlement and Industrialization

Figure 9.7. Locations of sawmills and river transport corridors in the Adirondack Mountain region of New York, ca. 1810.

(Williams 1989. Cambridge University Press.)

Preindustrial Holland and Flanders, for example, could specialize in dairying and market gardening, while they imported grain and timber from the Baltic states. Transportation thus allowed greater concentration of people in Holland than the land could support and increased the impact of people on the forests of the Baltic states.28 Local population was not a good predictor of the kinds of influences on the land.

The arduousness of inland transport led to a pattern of land use that might be described as “nibbling around the edges.” This was especially true in areas that supplied timber rather than serving as sites of agricultural settlement. In regions as diverse as Tanganyika and northern New York State, timber cutting near navigation routes left the interior more or less forested, while the edges were deforested (fig. 9.7).29 Study of the structure of remaining forests may reveal an imprint of this extensive edge effect.

(p.164) The demand for better shipping, however, led to changes in transportation and access to more land. Early nineteenth-century canal building in North America opened up much of the interior to the logging and mining industries as well as generally opening the region to settlement. Canals also provided a way for fish to migrate beyond their natural boundaries, with the result that alewives and sea lamprey appeared in the lower Great Lakes, for example. The warmer, siltier water caused by erosion following logging further improved conditions for these fish, which flourished in their new habitats. The advent of steam engines made shipping even more attractive by lowering the prices substantially. The cost of shipping three hundred liters of wheat from southern Russia to Britain decreased from 8 shillings, 6 pence in 1872 to 2 shillings, 3 pence in 1900, while the cost of shipping wool from Australia to Britain was halved between 1873 and 1896 because of the increased speed and reliability of steamboats over sailboats. As railroads replaced ox- and horse-drawn wagons, overland shipping became cheaper, too. In Argentina rail freight was one-twelfth the cost of oxcart transport, and in New South Wales, Australia, rail shipment of butter cost one-ninth that of wagon shipment.30 These reduced prices for shipping were strong incentives for further specialization and stimulated specialized and intensive uses of land and water.

The interplay between improved transportation and demand for transportation is complex. In most cases the demand exists before the improved transportation, as in the cases of canals and railroads. However, once the improved transport is in place or a new system of transportation such as steam engines is developed, they can be used to increase demand as well as to satisfy existing demand. The opening of new roads into hitherto inaccessible places by governments that want to be able to tap the resources of the interior of their countries has brought development into areas where the demand did not exist prior to building the road. Decisions were made on the basis of potential profit, either to the individual entrepreneur or to the government, not necessarily on the suitability of the resources and their availability to sustain development. Unlike older systems of transportation, which connected already established settlements, newer systems of transport often opened up previously unreachable areas far from any settlement, thus accelerating the process of change in these remote areas. Much deforestation in the Brazilian Amazon basin, for example, followed transport routes. Analysis of the rates and effects of deforestation should include changes in proximity of the forests to these routes as well as their cumulative effects on fragmenting the forest.31

Railroads required so much wood for the replacement of ties in the United States in the early twentieth century that special congressional committees (p.165) were set up to consider how to deal with the anticipated shortage of wood for ties. At about twenty-nine hundred ties per mile (1.6 kilometers), each with an average life of about six years, the almost 130,000 kilometers of rail lines in the United States in 1877 would have required more than 60 million hardwood ties every year, each tie being about 8 to 10 feet (2.5 to 3 meters) long and 6 by 7 or 8 inches (15 by 18 or 23 centimeters) in cross-section. The railroads also consumed wood to produce steam, though as early as the 1870s many had switched to coal, using wood only as kindling. This all created an enormous demand for lumber.

Many railroad companies started tree plantations to provide timber and to stop erosion on steep road cuts and serve as an example of tree planting to ameliorate the climate of the open, treeless prairies. Between 1872 and 1873 the Saint Paul and Pacific Railroad planted or sowed 4 million trees along its rights-of-way in Minnesota, mainly willow, ash, boxelder, oak, and maple. The effort flagged, however, in the ensuing years, when the company changed hands and embarked on a “shortsighted scheme of economy.” In Nebraska, the Burlington and Missouri Railroad Company planted 460,000 trees on 186 acres (75 hectares) along 28.5 miles (45 kilometers). These included honeylocust, soft maple, boxelder, sugar maple, white elm, laurel willow (Salix pentandra–not native), cottonwood (Populus sp.), and “evergreens.” Norway spruce was not a success, but the others grew rapidly, offering evidence that trees could survive the conditions on the windswept prairies.32 The progeny of these trees continues to affect the species composition of these and nearby woodlots; their origin may not be apparent without the historical perspective, and thus changes may erroneously be attributed to other causes. For example, the non-native laurel willow has become widely naturalized.

Railroads and other roadways exerted a direct effect on the lands through which they passed. Sparks from locomotives were a major source of forest and grassland fires in the late nineteenth and early twentieth centuries, and many other fires started from careless use of fire by travelers. Roads and railroads also directly used land: as early as 1875, some 2.6 percent of the land area in Massachusetts was devoted to roads and railroads. Trees planted along roads for beautification and shade—sugar maples and elms in the eastern United States, for example—served as seed sources for forest regeneration when the adjacent farms were abandoned.33 When roads were moved, the line of old, open-grown trees often continued to mark the location of the old roadbed.

All forms of transport allowed species to be distributed farther than they could have gone on their own. Canals served as distribution corridors for aquatic and other wetland plants in addition to fish and other aquatic animals. (p.166) Railroads carried grain contaminated with weeds like Bromus tectorum.34 Automobiles carried weed seeds, insect egg cases, and other stowaways in their tires and other parts.

The ability of humans to move quickly and travel far by means of transportation other than their own legs has developed through the years as an additional means of transport for many species as well as a way of intensifying and extending the impact of humans on the land. To trace the rate of spread of organisms one must incorporate the variable rates at which they have been carried by people and their intrinsic potential rates of spread.

Urban Agglomeration

A logical consequence of agriculture, convenient transportation, and trade has been the concentration of people in towns and cities. The independent development of urban areas has been as widespread as the rise of agriculture and has a long history, from the great cities of Asia Minor and Mesopotamia by 3000 BCE to those of the Maya of Guatemala by 250 BCE. Many have been abandoned over the millennia, the ancient sites now buried beneath vegetation or wind-blown deposits. Using new methods, especially lidar, archaeologists continue to find more of these remains, from the Mississippi River basin to the tropics. Much research has focused on factors that led to the rise and fall of these centers of civilization, but more recent research has also uncovered their very extensive impacts on local landscapes. Cities required the production and transport of food surpluses and building materials imported from far and wide and have included permanent shelters, storage pits and bins, refuse heaps, burial mounds, and roads. Refuse from the cities fertilized local fields, increasing their productivity, with some changes in soil lasting to the current day.35 The consequences for resulting landscapes are often buried deep in history, but interdisciplinary studies can bring to light their importance for current ecosystems.

While many cities have disappeared, leaving only traces that archaeologists must decipher to reveal details of life deep in the past, others have thrived, layering new construction onto old, burying the past beneath newer structures. The lost cities raise many historical ecological questions, not the least of which is why they were abandoned. Recent research in many areas, especially in the Americas, is beginning to indicate that changed climate has been a major factor in the failure of these cities.36 The next step is to study the impact of the climate change on regional vegetation both away from and near the urbanized areas, and to assess the relative importance of climate change and recovery from heavy disturbance on the vegetation. How resilient (p.167) was the vegetation? Were some species more likely to colonize disturbed areas as climate changed, and has community structure changed? Was there a return to pre-urban conditions, or was succession also so affected by climate that one cannot discern the processes of recovery?

In cities that have continued to flourish, there have been multilayered impacts on the environment over time. Plants and animals that have thrived in cities include both those that residents have grown for their use or pleasure, such as garden flowers and chickens, and those that are usually regarded as pests, such as weeds and rats. Early cities like those in Mesopotamia included land for gardens, both for beauty and for food. In fact, city and other home gardens usually have very high productivity because of the concentrated effort spent on them. Cities have provided unique new habitats and growing conditions, as lots fertilized by human wastes have been abandoned and the wide diversity of species that have been introduced by trade met and mingled in revegetating vacant land.37

A comparative study of the plant communities in gardens and uncultivated areas reveals some of the complexity of the ecology of these kinds of urban sites. The city of Bariloche in northwestern Patagonia was built a century ago in an area without a history of permanent agriculture. Weeds found there are mainly exotics. Similarly, the plants growing without intentional cultivation are predominantly exotics in Christchurch, New Zealand, and Santiago, Chile, neither of which has a long history of agriculture. On the other hand, the weeds found in gardens in Mexico City, Mexico; Paris, France; and Sheffield, England, all of which have very long histories of agriculture, are mainly species that were present before the cities arose. Around Mexico City, there is a substantial decrease in the number of noncultivated species per hectare along a gradient from suburbs to downtown, while the opposite pattern, an increase with nearness to a city, characterizes Hertfordshire, England. The reasons for these differences are related to the different kinds of plants that have been cultivated in the different regions as well as to the effect of intensive agriculture on species diversity in England. The importance of the evolution of species that favor disturbance is also highlighted by these comparisons. The significance of these differences may overwhelm the consequences of more regional or global environmental changes, depending on the scale. Urban habitats often exist at finer scales than more rural habitats, and the causes of changes may be buried in historical, political, and economic demands.38

In addition to gardens and vacant lots, urban/suburban areas usually include woodlots or forest areas that have been preserved for various reasons, often for recreation. A study of nine forest stands along a gradient from New York City to Connecticut indicated several consequences for forests of proximity (p.168) to cities. The stands were all at least sixty years old, occurred on similar geological substrates, and were dominated by species of oaks. There is no analysis of the earlier history of the sites, for example, whether some grew on abandoned farmland. Although the forests were smaller the closer they were to the city, rates of litter decomposition and potential nitrogen mineralization were higher close to the city, most likely because of the inputs of nitrogen from the urban environment. The history of these sites, in addition to their similar minimum age, might reveal further explanations for differences. Forests closer to the city were more apt to have had a longer influence of urban disturbances and to have been free of farm uses like pasturing or collecting wood longer than those located farther into the countryside. While plant species richness tends to increase with increasing urbanization because the introduction of exotic species exceeds extinction of natives, animal species richness decreases.39

The attitudes of city and suburban residents affect plant and animal communities under their influence. Many city dwellers see themselves as insulated from and independent of nonhuman nature.40 The forces of nature, storms and droughts, for example, are not as clearly relevant to life as they are for farmers. The current Western attitude that one is in control of nature developed at least in part in medieval Europe as cities grew, beginning in the twelfth century. Where food supplies and other necessities of life arrive abundantly into a city, city dwellers are little aware of their dependence on the produce of the land. As the city spreads from its small original perimeter, it engulfs fertile agricultural soils with little regard for the loss of potential productivity. Many cities themselves are located on rich alluvial soil, while others expand over drained marshland. Some unbuilt land is perhaps treated less as a commodity than as a museum, neither for active use nor for change. If someone moves from the city to the surrounding land that is focused on the city, it is to enjoy this more natural environment. The buying of property for its amenity value, dissociated from more natural bonds with its productivity, leads to suburbanization, as more people leave the city, facilitated by the increasing convenience of transportation.41

As long as people’s lives are not tied to the land in some direct way, there is no natural check on overpopulating the land or destroying its natural ecosystems. Suburban dwellers want to see “nature” but are unaware that by building close to it or even on it, they are destroying the very thing that attracted them in the first place. These activities lead to different kinds of treatment of the land than does active exploitation, with varying results for ecosystems. For example, in 1988, 75 percent of the owners of parcels of forest in rural northern New Jersey were white-collar workers or retirees. Forty-five percent (p.169) came from communities with populations greater than fifteen thousand, while only about 20 percent came from a rural background. In 1972, about 12 percent had harvested trees from their forest land, but by 1988, almost all had cut timber. The change was related both to international events such as an oil embargo, which led people to cut firewood, and to local infestation of a non-native insect, the gypsy moth, which led to salvage cutting.42 This example is illustrative of the volatility of land-use decisions by those who do not depend on the land for survival (though those hired to do the salvage cutting most likely did depend on forestry for their livelihoods). Owners of land can change their use quickly to respond to different conditions, leading to a very discontinuous history of impacts on the land over time.

Salt-marsh habitat near the present city of New York persisted until the end of the nineteenth century, under intensive use for agriculture. In one area, between 1750 and 1850, farmers had built salt ponds for evaporation, a mill driven by tidal flow, and dikes to control tidal flow for harvest of salt hay. Salt hay production utilized native salt-marsh grasses and the natural ebb and flow of the tides modified by dikes. However, in the late nineteenth and early twentieth centuries, construction of oil refineries and storage tanks, disposal of waste from these activities, and shoreline extension into the surrounding waters almost completely obliterated the native ecosystems and shoreline. Disassociating use from the natural system resulted in a landscape that most likely could never be restored to its predevelopment condition.

The distinct effects of cities on the surrounding nonbuilt land are also important and in many cases very difficult to reverse. City dwellers place a large demand on water supplies, both for direct human use and for manufacturing. When a city is near the sea, such demand often leads to pumping a deep water table down so that saltwater intrusion contaminates wells. Wastes produced by people and industry pollute surface water, so cities must turn to water supplies far from their locales, and cities are often not built where there is a sufficient local supply of potable water. The Romans built large aqueducts to carry water from the countryside or mountains to the cities, the cities of southern Germany rely on water from Lake Constance, and the cities of coastal California rely on water from the distant Sierra Nevada Mountains.

Reliance on distant water supplies may lead to efforts to protect the water supplies as well as to a depletion of the supply in the source areas. Water supplies for Newark, New Jersey; Boston; and New York come from large forested areas west and north of the cities. Protection of the watersheds of these water supplies is in the interest of the city dwellers, even if those who live in the vicinity of the watersheds may prefer other uses for the land. A (p.170) twentieth-century mayor of Newark claimed that governmental action was appropriate to “save the best stands of intact forest in the New York metropolitan area before they are lost to sprawl.” The goal of the management of these forests was preservation of a good water supply, which has led to management that concentrated on preventing erosion rather than on use of the timber resources, thus obscuring and reversing a long history of logging for industrial purposes, such as production of charcoal and tanbark.43

The impact of cities on local aquatic systems can, however, be quite severe. Studies of urban effects on aquatic environments suggest major impacts that may not be obvious. In Guatemala, a decline of the pollen of forest taxa relative to herbaceous taxa about 3000 BCE signals Mayan agriculture and urbanization. A combination of archeological and stratigraphic studies suggests that there was major erosion of local riparian soils at the same time, leading to transport of soil as well as phosphorous, probably derived from both human waste and the surface of the soil. The phosphorous-loading of the lakes did not lead to their eutrophication, possibly because the amount of suspended silt in the water decreased light penetration sufficiently to prevent overproductivity. At the same time, the accumulation rate of inorganic material in the sediment increased as much as ten times. Similar kinds of impacts have occurred in many parts of the world, leaving a legacy of lakes that are greatly modified by past human activities.44

Sulfur and nitrogen compounds in the air have changed the chemistry of rainfall and the water of many lakes, leading to losses of species that are sensitive to acidification or nutrient enrichment. These changes in lakes have been superimposed on changes that occur naturally over time, so that studies of the causes of current changes must rely on sedimentary studies of change over millennia, not just decades. Quantitative analyses of indicators of lake chemistry, such as diatoms and chironomids, have shown that the changes that lakes undergo over time are complex, related to watershed chemistry and vegetation as well as climate and anthropogenic inputs. These studies have, however, shown that recent anthropogenic inputs have made major contributions to recent changes in lake chemistry, and these must be considered to arrive at an understanding of the dynamics of the lake ecosystems.45

Marshes have long been regarded as entirely negative environments, to be drained and filled or used as dumping grounds for wastes produced by cities. Few coastal marshes near cities do not have drainage canals, built for a variety of purposes, from mosquito control to pasture or hay production to feed the large herds of cattle needed to supply milk and other products to the nearby cities. On the Nile delta, large lagoons were drained and converted to agriculture as early as Hellenistic times, especially in the vicinity of the city (p.171) of Alexandria, and by the first millennium BCE, the large number of river channels in the delta had been reduced to two by excavation, changing the shape of the coast. The large concentrations of people in cities created new demands on the land that required more intensification of use. Even when the use changed, these former activities left distinctive marks on the ecosystems they had disturbed.46

Historical ecology can reveal pre-urban patterns of interest in surviving cities as well. In the Mannahatta project, researchers have used historical documents to describe the landscape of Manhattan before European colonization. Similar efforts have provided a glimpse into the past of the San Francisco Bay region.47 Residents and visitors alike find it intriguing to be able to visualize these built landscapes as they were before swamps were drained and built on, forests were cut down, streams put into conduits, and so on. A few small remnants of the precolonial vegetation persists, for example, the hemlock grove at the New York Botanical Garden (though the hemlock has recently succumbed to an insect infestation). These glimpses into the past can inform efforts at restoration as well as reveal past ecosystems that may have been all but obliterated by urbanization.

Conclusion

Many apparently “pristine” landscapes have a long-buried history of human activities that have changed over time, along with climate. While it may not be surprising that many impacts of past agricultural use or logging have been nearly obliterated by natural processes of ecological succession, it is perhaps unexpected that succession has erased evidence of dense settlements and built landscapes. Traces of the past, however, do persist, so that the drivers of current landscape patterns and ecosystem patterns include the consequences of these past human activities. Some of these activities have created ecosystems that are today very diverse, belying the notion that human impact on environments is always negative. However, whether positive or negative, they must be taken into account as drivers of the present. We can see that dissociation of human activities from the natural processes may lead to changes that are obviously very difficult to reverse, but more subtle influences, especially those caused by dense populations in the past, may also be critical to interpreting current patterns and processes. It is only by reconstructing the past of a site that an ecologist can assemble the whole panoply of factors affecting it, and thus arrive at explanations for the current systems. (p.172)

Notes: