サウスオーストラリアの開発と農業の進展

歴史地理学的視点からのレヴュー

抄録

The European settlement of Australia began in 1788. Australian history itself can almost be thought of as the history of its land settlement process into the inland areas. Problems of the settlement and the settlement process of Australia have been actively studied in historical geography. In this paper the author reviews studies of the exploitation of the wheat belt in South Australia.
The first remarkable change of Australian landscape after European settlement was the clearance of forests, woodlands and scrub. The agricultural land spread from the coastal plains to the inland areas after the clearance of native vegetation. Harris' map, based on air photographs, shows the vegetation clearance within the agricultural and of South Australia up until the mid-1970s. The map shows that nearly three-quarters of the land has been stripped. The abundance of agricultural land resulted from a severe decrease in native vegetation.
Since the first European settlement, Australia was adversely affected by drought. The more the agricultural land spread into the inland areas, the greater affect these droughts had on the wheat belt. In particular, severe droughts occurred after the 1920s in the southern part of Australia, and substantial damage was done to crops and sheep. Farmers suffered from the decrease in crop yields.
In early times, on the wheat belt in the southern part of Australia, farmers continued to plant only wheat every year. But the soil fertility decreased gradually until the end of the 19th century. Donald reports that the wheat yield in the southern part of Australia declined from 12.8 bushels per acre in the 1860s to 10.8 bushels in the 1870s, to 8.3 bushels in the 1880s and finally to a desperately low 7.3 bushels in the 1890s. To restore soil fertility, farmers introduced a wheat-fallow system of farming by the early 20th century. With this system, the wheat yield rose to 9.8 bushels in the 1900s, to 10.7 bushels in the 1910s and to 12.0 bushels in the 1920s. Although the yields rose from 7.3 to 12.0 bushels, the system proved unstable, and, in many districts of the southern part of Australia, there was a decline in crop yield from 1920 onwards, because of severe droughts and the extension of wheat growing into climatically and edaphically marginal lands.
The next new farming system, “ley farming”or“pasture legumes”, was introduced into the wheat belt after the mid 1930s. Ley farming is an integrated system of cereal and livestock production. Farmers grow wheat, barley and oats on part of their agricultural land, while sheep and cattle graze the pasture legumes. With the introduction of ley farming, production in the wheat belt increased rapidly. The wheat yield rose from around 12-13 bushels in the 1930s and 1940s to above 17 bushels in the 1960s. By 1950, annual legumes, mainly medics and clovers, were chosen and sown, and the ley farming system had diffused over the wheat belt of South Australia and the other parts of Australia. But other factors, such as disease and soil erosion, have limited yield increase especially after the 1970s.
For the comprehensive reconstruction of the details of changing landscapes in the Australian Wheat belt after the exploitation of its lands, it is necessary to analyse the relations between the European settlement process and the progress of the farming system.