Adaptability is a feature of mankind, with the result that even the most marginal habitats are seldom devoid of human settlements. Furthermore, once having populated a peripheral area the community often appears reluctant to abandon what they have come to consider as their home territory, even when deteriorating environmental conditions have brought prolonged periods of hardship. Ecologically, the range of habitats in which prehistoric human settlements developed knew few boundaries. There is increasing evidence that the first human beings to cross into North America used coastal migration routes even before the late Pleistocene ice had retreated from the Beringian shores (Shreeve, 2006). It is therefore not surprising that many early human communities can be found on offshore islands, marshes, and flood-prone deltas. Archaeological records from the poles to the tropics have revealed the rapidity with which our early ancestors spread through an astonishing range of marginal environments.
Peripheral areas can present both opportunities and risks for their human inhabitants. On one hand, historical and archaeological records provide numerous examples where fluctuating climatic conditions opened up areas of opportunity, which attracted migration and settlement. On the other hand, fluctuating conditions could lead to crop failure or the collapse of other resources such as hunting or fishing and force the abandonment of areas that were formerly attractive. Such events are taking place today at an ever-increasing rate, particularly in regions where large human populations are having their agricultural and pastoral activities destroyed by prolonged droughts, possibly connected with global warming. For others, rising sea levels threaten to erode or inundate their lands.
Current climatic warming is, however, not universally damaging for agriculture. In many northern regions there is a feeling that at last they are free from the adverse effects of the Little Ice Age (Fig. 11.1). The growing season for grass is extending and wheat and other crops are being cultivated further north than ever before. Boreal forest timber production is also benefiting in many locations due to increased tree growth.
In marginal settlements, irrespective of whether they are inland or coastal, there have always been special characteristics which enable the inhabitants to survive in potentially insecure and variable habitats. The essential aspect common to them all is the ability to plan for the future and foresee the possibility that times of plenty can be followed by times of hardship. Man's unique ability to anticipate the future is particularly relevant in the Arctic. The hunter-gatherer communities that live in the far north are obliged to store food for the winter and so have had to develop a large number of social strategies, including the control of property, together with scheduling, and co-ordinating labour to a degree that is not required in tropical or temperate climates (Ingold, 1982).
The development of a viable lifestyle for these early pre-agricultural communities, wherever they were, was influenced by the nature of the vegetation and the animals that it supported. This is well illustrated in the Late Glacial and early Holocene period when the inhabitants of polar regions, with the exception of the coastal regions where marine resources were available, relied on the larger herbivores (mammoth, reindeer, musk oxen) for their nutritional demands, and these animals in turn required substantial plant forage.
The archaeological history of Homo sapiens in the Late Pleistocene reveals that hunters spread across northern Eurasia and Alaska to the edges of the ice sheets in pursuit of the 'megafauna'. These large herbivorous mammals were dependent on a single hyper-zone of vegetation described botanically as tundra-steppe that existed where today there is modern steppe, taiga, and tundra (see below).
With the development of agriculture, many examples can be found where prehistoric peoples showed considerable resourcefulness in adapting to habitats in areas that today might be considered marginal for agriculture. In the semi-arid montane regions of South America, ancient, specialized agricultural traditions maintained extensive human populations in a region where readily cultivable land and rainfall is severely restricted. In the Andes, a tradition of irrigation and terrace-farming long predates the Inca civilization, with evidence of terrace construction beginning probably as early as 2400 BC (see Denevan, 2001).
Many other marginal habitats have long histories of human habitation, where either early agriculture was practised using specialized techniques, or where use was made of the natural plant communities to compensate for a limited ability to grow crops. Marshes, mangrove swamps, storm-swept coasts, and drylands in many parts of the world have supported individualistic forms of human settlement. Striking examples of human ingenuity of extracting crop productivity out of marginal habitats are found in the raised fields of the wetlands around Lake Titicaca in the Bolivian Highlands (Denevan, 2001), the lazy beds of the Celtic western fringe of the British Isles and Ireland, and the ancient settlements (possibly dating back to the time of Sumerians in the fourth millennium BC) of the Marsh Arabs on the wetlands of the Tigris-Euphrates alluvial salt marshes.
Africa provides numerous and varied cases of peoples who live in semi-arid lands with the constant risk of rain failure and ensuing starvation. The transition zones between forest and savanna, and savanna and semi-desert, are physically very fragile and delicately balanced ecosystems. In these marginal areas, human activity can damage the ecosystems beyond their limits for recovery. Excessive soil trampling of the ground by livestock compacts the soil, increases the proportion of fine material, and reduces the percolation of rainfall. The increasing run-off when the rains return brings about erosion, first by water and then by wind. Excessive grazing and the collection of firewood in periods of drought reduce or even eliminate the plants that help to bind the soil. Consequently, in many regions it is the increased human population and livestock pressure that has caused desertification and not climate change.
In times of drought nomads tend to move to less arid areas and thus disrupt the local ecosystem and increase the rate of erosion of the land. In trying to escape the desert the nomads bring the desert with them. Sometimes the habitat degradation that is caused by the drought is described as desertification. However, this is a misconception and can be misleading, as the natural vegetation of these semi-deserts is well adapted to withstand periodic rain failure and prolonged drought. Well-managed lands can recover from drought when the rains return. It is land abuse during drought that causes the degradation and desertification.
Despite these evident hazards, marginal areas have nevertheless always attracted human occupation. In most cases the inhabitants are well aware of the dangers and have developed lifestyles that minimize the impact of the risks to which they are periodically exposed. The motivation for accepting these conditions can vary. Escape from oppression or persecution, avoidance of competition with other peoples and tribes, and a sense of independence and pride in their own fortitude in overcoming obstacles that are a deterrent to less adventurous neighbours, are all factors that contribute to the continued occupancy of marginal regions.
The following pages examine some individual case histories in an attempt to assess their relative vulnerability and the role of plants in sustaining human occupation of these peripheral areas. How long such human communities will survive in a modern world with a global economy and changing climatic conditions will depend in great measure on the strength of cultural attachment of the inhabitants to these peripheral lands and the value that is placed on the maintenance of their individualistic lifestyles, cultures, and perceived freedom.
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