Human Imprints on the Primeval Landscape
Antony R. Orme
No physical geography is complete without some evaluation of the changes wrought on the natural landscape by human activity. Such impacts reflect the practical needs, cultural ethos, and technical abilities of people, all of which change over time. For North America, as elsewhere, a useful distinction may be made between the role of prehistoric peoples with simple needs and limited skills, and historic peoples who, armed with more advanced technology, have made increasing demands on the landscape and its resources. Unlike in Asia and Europe, however, the dividing time line between prehistoric and historic cultures came quite late in North America, where only in the last few centuries, more recently in some areas, have human imprints become truly significant.
The theme of this chapter is vast, so the approach here is necessarily selective. After reviewing the peopling of the continent, the discussion moves from an evaluation of impacts on plants and animals, through the effects of mining, to impacts on water resources. This order has a certain logic because plants and animals are the first resources that, for reasons of survival, people normally use. Later, as technology improves, these resources, with minerals and water, are exploited more thoroughly until in many areas the primeval landscape all but disappears, replaced by the agricultural, industrial, and urban landscapes. However, the sequence is not rigid. For example, twentieth-century oil drillers in Alaska invaded the wilderness directly, whereas water resources were impacted from the earliest human encounters with plants and animals, but not to the extent that they would be later.
Although eschewing environmental determinism, it is stressed that human impacts on the North American landscape have been staged against a changing natural backcloth that has variably influenced human activity. Thus fluctuating ice sheets and sea levels clearly influenced late Pleistocene human immigration to North America. Later, the early Holocene retreat of tundra before advancing forest and the prairie expansion into former forest areas challenged human survival skills, just as later Holocene changes in forest and grassland distributions called for further adjustments. A warm interlude between A.D. 800 and 1200, linked to the climatic anomaly so well documented in medieval Europe, favored Norse settlements in Greenland that later succumbed to advancing permafrost and glaciers. Climatic variability also increased along the Pacific coast around this time, reflected in higher sea-surface temperatures and alternations of rainy periods with prolonged drought, which affected prehistoric subsistence patterns and social organization in California. Similarly, increasing drought in the Great Plains and the Southwest after 1200, and cold stormy conditions along the eastern seaboard during the Little Ice Age (≈1500–1850), challenged the survival of settled farming communities, regardless of other human impacts. Recent human impacts on climate, through the