Entries entitled "Habitat Loss in North America" in: Conservation and Environmentalism,
"Snow as Habitat"
"Habitat Loss in North America"
Conservation and Environmentalism,
William O. Pruitt, Jr.
Department of Zoology,
The University of Manitoba,
Winnipeg, Manitoba, Canada
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Pruitt, W.O., Jr. 1995. Entries entitled "Habitat Loss in North America" (pp. 339-342) and "Snow as Habitat" (pp. 593-594) in: Paehlke, R. (Editor): Conservation and Environmentalism, An Encyclopaedia. Garland Publ. Co., New York and London: 771 pp.
Habitat Loss in North America
When speaking of habitat loss it is necessary to differentiate between actual "loss" and "change" in habitat. An initial loss, such as the effects of clearcutting on a stable-age forest, is usually followed by a seral succession of different habitats. Eventually sometimes only after hundreds of years the stable-age condition may be reestablished. In other cases in which the original community was relict an entirely different community becomes established. This is real habitat loss.
It is important to remember that habitat loss or change is not the only factor involved in species loss. In Canada, for example, hunting or trapping was the sole factor leading to the loss in historic times of the four now-extinct species/subspecies of mammals and the three now-extinct species/subspecies of birds. It has been calculated that of the fourteen species of endangered birds in Canada, hunting and/or human persecution are the major causes of endangerment in the case of nine species; of the nineteen species/subspecies of endangered mammals, hunting and/or human persecution can be blamed in the case of eighteen. Factors other than clearcutting or hunting can deny an area to some organisms. Biocides, erosion, or air pollution can make an area uninhabitable by different species for varying periods of time.
Human history represents the story of a long series of cultures that outgrew the carrying capacity of their region, and collapsed or were succeeded by another culture that employed a different set of resources. One also encounters the myth of the "noble savage" who walked lightly upon the land and who inhabited North America for thousands of years but caused no environmental damage. In actual fact, however, pre-contact native North Americans lived in a world they and their ancestors had changed dramatically. Amerindian corn fields, unused for nearly 1,000 years, are still identifiable as such by the reduced tilth and fewer nutrients in the soil. There is fairly clear evidence that early humans in North America were at least partially responsible for the extinction of at least twenty and possibly as many as forty species of medium to large mammals including two or three species of bison, horses, tapirs, camels, llamas, mammoths, giant deer, moose-deer, saiga antelope, ground sloths, giant peccaries, and several species of "shrub oxen." For most of these species we no longer have even common names.
When Europeans invaded North America they encountered not an untouched continent teeming with life to its maximum but one with a depauperate and already-ravaged fauna. Because they came from another continent that had been ravaged by their own ancestors even more, they considered North America absurdly prolific with wildlife. They were, however, just one of the waves of human invaders to hit North America, who in their turn also obeyed the basic rule of virtually all human societies to date: "Cut and get out." Because of more efficient weapons and a social/religious ethic of "Dominion over the beasts of the field" the Europeans have been able to accomplish in 400 years even more destruction than that which had taken the earlier human invasions some 10,000 years to achieve.
It would be helpful then to look at some of North America's most important types of habitat in relation to the impacts of human activities. Some of the habitat types discussed here (including tropical rainforests, rangelands, and old-growth forests) are treated elsewhere in this volume, but several are not.
Eastern and Central Forests
North American forests have been devastated by human activity sweeping from east to west. At the time of the European invasion there were about 6,000 square kilometers cleared by the aboriginal inhabitants of Canada and the United States. Since then, approximately 641,000 square kilometers have been cleared. Most of the early European clearing was done to secure fuelwood. In some regions the trend of increasing annual amounts of forest destruction was reversed between 1920 and 1978 because of farm abandonment and concentration, but since then the destruction has intensified.
The exact amount of habitat loss is impossible to calculate. For example, the area of the Great Lakes "cutover lands" reached 127,000 square kilometers in 1920 but today most of this has regenerated to forest. To be sure, this is not the original pine- beech-hemlock forest, but it is forest nonetheless. Elsewhere in the Eastern Deciduous Forest only a few tiny bits survive. There is much regrowth, some of which now has a species composition approaching that of the original forest, but lacking the size.
North American Grasslands and Savannas
North American grasslands and savannas have been almost completely converted to cropland and pastures, totaling 956,000 square kilometers. Tallgrass prairie has been hit especially hard. In Manitoba, for example, less than 1 percent of the original tallgrass prairie remains, consisting of a few areas each less than 10 hectares in size. This is typical.
Temperate rainforests have undergone a marked reduction in area because of cutting, especially clearcutting. The effect of clearcutting old-growth rainforest on the survival of the spotted owl is well known. At this writing the struggle to save the old-growth forest around Clayoquot Sound (Vancouver Island) continues. The population of Marbled Murrelet in this region showed a 5O percent drop between 1970 and 1990; at the present rate of decline the species will probably be extirpated from the region within fifty years.
Transcontinental Taiga or Northern Coniferous Forest
From Newfoundland to Alaska, the transcontinental taiga or northern coniferous forest is undergoing more change and habitat loss than any other biome type at present. Fires, pulping, logging, spraying, and clearing for agriculture are the major factors. Alberta has committed about 220,000 square kilometers of its taiga to be cut down over the next sixty years. Manitoba has signed over 20 percent of the total area of the province for cutting by a single company. The area signed away consists of 40 percent of the productive taiga in the province or 198,000 square kilometers. This is the equivalent in size to the U.S. state of North Dakota. The contract is for twenty years, renewable for another twenty. The company, Repap, is controlled by one person who owns, 55 percent of the shares. Thus, 40 percent of the productive taiga in Manitoba is now controlled by one person. Most of the deal was concluded in secret by the government of Manitoba without any public environmental assessment.
One of the characteristic large mammals of the taiga is the woodland caribou. Caribou are few in number, have a low reproductive potential, are secretive, live in small bands and are terribly vulnerable to clearcutting, forest fires, ""sports" hunting, poaching, and legal hunting by Treaty Indians. Recent studies in Manitoba have shown that it is not the loss of lichens that first denies a region to woodland caribou but the jackstraw tangle of downed, burned trees that occurs when the roots rot about five years after a fire. The animals show remarkable fidelity to ancestral range until the physical barrier of meter-high tangles stops them. No woodland caribou bands have ever survived a program of even moderately intensive clearcutting in their vicinity. Woodland caribou in Alberta and Manitoba are classified by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as "vulnerable," but they should perhaps be classified as "threatened."
Loss of habitat continues in many regions. In one region of Manitoba the percentage of land cleared and cultivated increased from 58 percent to 85 percent between 1948 and 1974, with most of the increase occurring between 1964 and 1970. In the Interlake region of Manitoba, clearing of mature forest for agriculture makes up as much as 7.5 percent of the total area per year. Most of the clearing is subsidized by provincial and federal agricultural agencies.
Labrador is one of the few remaining areas in North America, other than the tundra, where large areas are unexploited for timber. In recent years much of the change/loss has been instigated by governmental initiatives. For example, in Labrador, since near the turn of the century, government financing has supported a series of large-scale logging and pulp operations. Though all have failed they have managed to cut much of the best and easily-accessible timber. Each failed venture has meant reduced chances for real ecologically-sustainable forest operations because less of the commercial-quality easily-accessible forest remains.
Loss of stable-aged ("old-growth") taiga and temperate rainforest is not just incidental to other uses of the forests. In forest succession, maximum productivity of fiber is in "middle-age." "Old-growth" forests parcel energy and materials into increasingly complex numbers of species and microhabitats rather than adding large amounts of fiber. Consequently the aim of market-driven forestry is to eliminate "old-growth" forests and substitute young, preferably monoculture, "tree farms" for maximum production of fiber when they reach "middle-age." Such management is based on the premise that logged areas will never again be permitted to reach an "old-growth" phase. Preservation of biologically-complex, stable-age conditions by selective logging is thus anathema to unregulated profit-oriented forestry.
Eleven species of tundra animals (eight mammals and three birds) are listed by the International Union for the Conservation of Nature and Natural Resources (IUCN) as "threatened" throughout their world range and there is concern by IUCN for the survival, of twenty-one additional species (eight mammals and thirteen birds). This is a higher percentage than in any other major biome in the world.
Nonetheless tundra is relatively untouched except in certain areas where dramatic changes have occurred. Physical changes such as thermokarst from vehicular traffic are common in restricted lowland or wet areas. Biotic changes are more subtle to detect but do occur. The extensive, misguided wolf poisoning and bounty campaigns in the 1950s and 1960s wreaked havoc not only with wolves, but with colored fox, white fox, wolverine, barrenground grizzly, and raven occurrences. It has been suggested that the musk ox of eastern Ellesmere Island and northwestern Greenland have never fully recovered from the devastation wreaked on them by the explorers and the expeditions in the Rush for the Pole in the early days of this century. Most of the expeditions fed themselves and their dogs on locally-hunted musk ox and caribou. One expedition, led by the American R.E. Peary, actually partly financed itself through the sale of musk ox and polar bear skins it had taken.
On the basis of the number of species involved there are three important types of tundra breeding range: 1) rocky or cliffy areas with talus; 2) rocky or tussocky uplands, including rolling uplands with birch-heath-cottonsedge tussocks; and 3) sandy eskers. There are two important types of summer range: 1) rocky or tussocky uplands, including rolling uplands with birch-heath-cottonsedge tussocks; and 2) lowlands, stream and lake edges. In addition there is one important type of winter range: well-drained ridges and hillsides. When analyzing these requirements in relation to the relative importance of the species to the tundra ecosystem one must also consider specialized types of caribou winter habitat in tundra, caribou winter range in taiga and forest-tundra, and eskers winding sandy ridges which function as caribou migration routes and nesting/denning areas for white fox, colored fox, and wolves. This complexity is critical and the preservation of one or two types of habitat will not be sufficient to ensure species well-being. This example should be kept in mind as regards many species in many other types of habitat.
One might also note that only one tundra type is relatively unimportant for animals: lowlands in winter. There is also a marked correlation between those landscape types that exhibit a wide spectrum of snow cover types and their suitability as animal habitats. The more varied the snow cover (patches of exposed ground, varied drift types, complete cover, hard snow, soft snow, etc.) the more species of animals can use the area. Thus, for the tundra, we know which landscape types to protect in order to maintain species.
Coastal habitats are exceedingly important as breeding or overwintering habitats for a wide variety of organisms. In the United States, for example, 70 percent of the commercial fish and 65 percent of the recreational fish come from estuaries. Habitat change may occur through a range of human activities, seemingly unrelated to the coastal habitat concerned: incoming fresh water, damming, poldering, drainage, pollution (dissolved, particulate, thermal), agricultural (haying, grazing), solar salt production, augmenting recreational beaches, and many other forms of imposition. The total loss is thus considerable. For example, in the state of Louisiana, coastal wetlands are lost at a rate of about 100 square kilometers per year, totaling 3,500 square kilometers of the coastal zone. In Florida, about 10 million m3 of sand have been added to one seventeen-kilometer stretch of recreational beach to increase its width to ninety meters. No information is available on the biological changes caused by the addition or on the source area from which the sand was obtained.
The full potential of the human assault on deserts has not been felt in all desert locations. Prior to air conditioning and water transfers the impacts were minimal. Since the widespread use of water transfers has been initiated the loss of desert habitat to agriculture has been extensive throughout the U.S. West and in recent decades the losses to residential development, golf courses, and the like has been severe, especially in California and Arizona. The plants and animals of this specialized habitat in most cases cannot survive elsewhere; their numbers have thus been severely diminished in many cases, especially perhaps in the case of cacti and succulents.
To offset habitat loss and preserve these valuable resources ways must be found to restrain the encroachment of human settlement and resource extraction on the spaces of nonhuman species of all kinds. If limiting human numbers cannot be restrained and even reduced, somehow limiting the average space assumed by each occupant on a daily basis and/or regulating the amount of resources that may be extracted for food production and recreation may be our only options.
William O. Pruitt, Jr.
Colinvaux, P. The Fates of Nations: A Biological Theory of History. 1980.
Schaefer, J.A., and W.O. Pruitt, Jr. Fire and Woodland Caribou in Southeastern Manitoba. Wildlife Monographs No.116, 1991.
Turner, B.L., et al., eds. The Earth as Transformed by Human Actions. 1990.
Arctic; Bears; Conservation and Habitat; Bison: Conservation and Habitat; Clayoquot Sound; Coastal Marshes, Conservation of; Cougars: Conservation and Habitat; Everglades of South Florida; Florida Panther; Forest Fragmentation and Bird Habitats; Freshwater Wetlands; Habitat Fragmentation, Patches and Corridors; IUCN; Landscape Ecology; Old Growth Forests; Rangelands (U.S.); Snow as Habitat; Top Predators in Canada: An Overview; Ungulates; Wilderness; Wildlife Protection: History; Wolf: A Conservation Challenge.
Snow as Habitat
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This page created March 2, 1999.
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