Agricultural sustainability in marginal areas

Marginal areas frequently show signs that their limited resources are being over exploited, or else managed in such a way as to cause a gradual and sustained deterioration of the environment. This is not a recent phenomenon. Evidence of soil exhaustion around early agricultural settlements is often noted in archaeological excavations. The proximate cause of abandonment around 1500 BC of an early settlement at the Scord of Brouster in Shetland (see Section 1.8) has been attributed to a combination of soil erosion, podzol formation and increased stoniness of the remaining eroded soil (Whittle et al., 1986).

During the second millennium BC, in the Bronze Age, a considerable expansion of agriculture took place. In Scotland this was particularly notable in upland areas which are inherently vulnerable to even minor fluctuations in climate and human mismanagement through soil impoverishment from clearing, grazing and over exploitation (Cowie & Shepherd, 1997). Thus, a climatic downturn in the latter part of the second millennium, when the climate of Scotland became much colder and wetter, resulted in the abandonment of many of the earlier Bronze Age settlements. Studies of tree-ring chronologies have suggested that the catalyst in bringing about this retreat from upland areas may have been a series of cataclysmic volcanic eruptions. Volcanic eruptions, wherever they occur, spread their dust worldwide in the upper atmosphere from where it disappears only slowly. Despite the global spread the dust produces its most severe effects on climate at higher latitudes, where due to the low angle of incidence of solar radiation towards the poles any

Ecological Limits

Fig. 11.4 Fair Isle, an isolated island lying midway between Orkney and Shetland with a population of approximately 70 inhabitants. Marginal farming as practised here and elsewhere in the Highlands and Islands of Scotland is termed crofting and provides legal security of tenure for small tenant farmers. The economy of this isolated island is aided by the fame of its knitwear and the opportunities it provides for bird-watching.

Fig. 11.4 Fair Isle, an isolated island lying midway between Orkney and Shetland with a population of approximately 70 inhabitants. Marginal farming as practised here and elsewhere in the Highlands and Islands of Scotland is termed crofting and provides legal security of tenure for small tenant farmers. The economy of this isolated island is aided by the fame of its knitwear and the opportunities it provides for bird-watching.

additional attenuation can effect a marked climatic alteration.

In more recent times Scotland, together with Finland, Scandinavia, Estonia and Iceland suffered the

'seven ill years' due to volcanic eruptions. This began in AD 1693 with an enormous eruption of Hekla, which had a wide effect across the North Atlantic and into Scandinavia. This was followed in the same year with

Fig. 11.5 Crofting on Fair Isle. Hay drying on the trestles illustrates the difficulties of securing good-quality hay in a humid oceanic environment.

Serua in Indonesia and Komaga-Take in Japan, and in 1694 by Aboina in Indonesia (Luterbacher et al., 2001). These eruptions took place in the Little Ice Age during a time referred to as the Maunder Minimum c. 16451715 when sun spot activity was particularly low and solar radiation was already reduced (Langematz et al., 2005). The result at the end of the seventeenth century was a succession of harvest failures that caused widespread famine and large losses of population in all these northern lands. The great famine of Estonia in 1694-97

is particularly remembered for the extensive loss of human life from winter starvation. Such was Scotland's plight that it finally brought about political union with England and the departure of its Parliament to London.

Through historical palaeontological research it is possible to quantify the deterioration of agricultural areas either from records of reduction in productivity or else loss of biodiversity. In oceanic areas with high rainfall, the expansion of poor acid grasslands as a result of a long history of mismanagement and overstocking and erosion has long been a problem. In more arid parts of the world population pressure on the land, both for cultivation and for wood for fuel, has also led to soil erosion and desertification. In many areas limited water resources aggravate this degradation. The alternation of wet and dry seasons can clear the land of plant cover after harvest which then leads to rapid erosion when the rains return.

In conclusion to this study of plants in marginal areas, it is pertinent to consider the varying consequences of human settlement in areas where climatic or soil resources are potentially limiting and where the dual impact of climatic warming and increasing human exploitation may combine to irreversibly damage the plant communities on which the landscape depends for its stability. The inclusion of an historical element in this appraisal is an essential background to understanding the present-day needs for conserving species, habitats and productivity. Marginal areas also attract considerable conservation interest due to their perceived wilderness status and presumed fragility in relation to climatic change. Unfortunately, few marginal areas are true wildernesses, and when they show signs of ecological fragility it is frequently due to denial of sufficient space and time for the proper function of natural regeneration cycles.

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