The Pampa problem: a critical review

Abstract

On the basis of intensive research on the relationship between the distribution of hydroclimatic water balance and the representative natural vegetation in the USA, Thornthwaite (1952) hypothesized the presence of a grassland climate. Similar results were obtained by his collaborators on the Pampa: the grassland is a natural phenomenon, in equilibrium with its climatic environment, and it is possible to explain the presence of grassland on the basis of climate alone without bringing in other aspects such as human activities or fire. Recent hydroclimatological research concluded that the Pampa should have a forest climate, ie mesophytic forest growth in the NE region, a transitional forest in the central region, and treeless steppe-like grassland in the W region, and extensive natural grassland which corresponds with an edaphic climax formation confined in the widespread azonal sites. The concurrence between root systems of grasses and trees in the soil at given sites has also been intensively investigated; the dominance in such a situation lies with the soil condition. In general, grasses dominate if soils are heavy, and trees dominate in light soils. In the Pampa, the boundary between grassland and woodland is approximately in accordance with that of heavy (in the E) and light (in the W) soils. Microscopic research on the soil, especially the humus, also gained remarkable results considering the former vegetation on the Pampa. -from English summary