When we look at regions that are now considered marginal and wonder why they frequently have had a long history of human settlement it is necessary to try and imagine the environmental conditions that existed for early settlers. At the time of the early development of agriculture valley bottoms which are now favoured for agriculture would have been filled with lakes, gravel beds, rivers and marshes as they had not yet received the sediment loads from mountain erosion that have now created extensive flat and fertile alluvial plains. The amelioration of valley bottoms in some cases is relatively recent and still taking place. In Iceland the flat fields that lie below the mountains only appeared in the one thousand years since the first settlement of Iceland and after the upland soils had eroded as a result of excessive human disturbance (Fig. 11.30). Similarly, islands and other maritime areas that now seem remote and exposed had coastal fringes where soils were more easily drained and woodlands more readily cleared than in the interior regions with dense vegetation. Many early migrations both in North America and Europe were made by sea and therefore the concept of geographical inaccessibility that we now have in relation to offshore islands and isolated archipelagos is not relevant to these earlier landscapes.

With the passage of time other sites would have become available that appear potentially more productive and rewarding. However, history demonstrates that competition for fertile land is intense, and subsequent migrants, possibly better equipped than the autochthonous populations, may have been more successful in capturing the better land. In South America the high-altitude mountain valleys remain the preserve of the Quechua-speaking population of the Andes. A similar situation exists for the Sherpas of Nepal. The more ancient indigenous populations having adapted to their original chosen habitat are able to survive there in what other people might consider suboptimal or marginal conditions. We must admire the territorial tenacity of those who continue to people peripheral regions in that they enrich the world culturally and preserve the diversity of the human race (Fig. 11.31). In just the same manner, the plant populations that survive in marginal habitats throughout the world enrich the flora and preserve these unique habitats.

Fig. 12.1 The Athabasca Glacier ice front in late July 2006. The glacier flows from the Columbian ice field (altitude 3491 m) of the Canadian Rockies and has retreated 1500 m in the last century. Since 1980 there has been a noted acceleration of this retreat. (Photo Professor R. J. Abbott.)

Summary and conclusions

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