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Abstract
A test of the Midcontinent Plains as a climatically defined grassland stretching from Canada to the Rio Grande is offered in the vegetation reconstructions of a series of models beginning with Köppen, Thornthwaite, and Holdridge, and extended more recently by efforts to simulate biomes using global climate models.  Current attempts to derive grasslands (and other biomes) from climate models are concerned with environmental change likely to result from increased levels of CO2. The former emphasis placed on precipitation deficiency as defining characteristics of grasslands has given way to a greater interest in temperature patterns because of the link between CO2 and climate change.  Regional interpretations based on the Köppen, Thornthwaite, and Holdridge models have been challenged because these models are based on the mapped correspondence of climate and vegetation patterns rather than on biochemical theories aout plant growth processes.  The photosynthetic pathways corresponding to the processes used by plants to fix carbon and plant height lead to the definition of C3, C4 shortgrass, and C4 tallgrass groupings of Plains grasses.  Abundance maps based on the three groups show a regional differentiation only roughly corresponding to climatic differences.  spatial statistical analysis reveals that local variability can be as great as variability within the entire region. Broad, climate-based regionalizations may be less important than topographic position or other site factors in explaining the existence and distribution of grasses.

Key words: Grasslands, Midcontinent Plains, biome models, photosynthetic types,
grassland region maps, climate change.

View or download entire article 29 pages, including 13 maps, two figures, and 1 table.

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