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Ecological Factors in the Development of Intensive‐Management Ecosystems in Midwestern United States

Auclair, Allan N.
Ecology 1976 v.57 no.3 pp. 431-444
cropland, developmental stages, ecosystems, energy, forests, highlands, intensive farming, mechanization, models, pastures, principal component analysis, savannas, soil properties, soil types, subsidies, Midwestern United States
This paper quantifies changes in the importance of ecological parameters associated with the development of intensive agriculture in midwestern USA. Changes in the important of 20 edaphic and 31 cover—type parameters were measured for three stages of development: (1) conversion of natural vegetation to pre—intensive agriculture (1833—1934), (2) agricultural intensification associated with chemical subsidies and mechanization (1934—1948), and (3) recent shifts in crop diversity and production (1934—1972). Between 1833 and 1934 all the natural upland vegetation, and two—thirds of the original marshlands were transformed. Of the original prairie surface, 92% was converted to a cropland—temporary pasture system by 1934. Much less of the original savanna was converted to cropland. By 1934 the alteration of savanna to cropland, permanent pasture, and oak forest was in the ratio of 4:3:2. A principal components analysis of the factors significant in the alternation of the natural vegetation indicated strong interactions with soil attributes of the first component. Prairie and cropland were bimodally distributed on the catenal gradient. The distribution of savanna and forest vegetation was related primarily to steep, shallow soil types. Intensification of agricultural production was accompanied by a reduction in the total cropland acreage, and forest cover increased by 10.6% in the 1934—1961 period. With agricultural intensification there was an increase in crop specialization. In fact, crop diversity declined by 35% between 1950 and 1965; since 1965 the tendency toward monoculture increased only slightly. Furthermore, the trend toward monoculture coincided with a shift toward large—stature plant forms. The models of canonical correlation indicated that with agricultural intensification the moisture—related variables became more important while those related to fertility and catena did not. The dependence of intensive agriculture on favorable sites and large energy inputs is discussed from the viewpoint of growing problems of energy supply and population.