Pampas
Vegetation

The dominant vegetation types are grassy prairie and grass steppe, in which numerous species of the grass genus Stipa are particularly conspicuous. "Pampas grass" (Cortaderia selloana) is an iconic species of the Pampas. Vegetation typically includes perennial grasses and herbs. Different strata of grasses occur because of gradients of water availability.

Why the pristine pampas were treeless regions has been much debated. Perhaps the most commonly cited explanation is seasonal drought. A related hypothesis is that grass roots compete for water and exclude tree seedlings. The effect might be increased by heavy, clayed soils which limit tap root penetration. Other causes that have been proposed are fires set by indigenous peoples for land clearance; the existence of heavy-bodied herbivores; and that the pampas are relicts of drier past climates. These explanations have been criticised as mono-causal. "Overall, we expect that low propagule pressure, abiotic stresses, biotic resistance, and a paucity of specific symbionts might have exerted a synergistic influence in slowing tree invasion rates ".

The World Wildlife Fund divides the Pampas into three distinct ecoregions. The Uruguayan Savanna lies east of the Paraná River, and includes all of Uruguay, most of Entre Ríos and Corrientes provinces in Argentina, and the southern portion of Brazil's state of Rio Grande do Sul. The Humid Pampas include eastern Buenos Aires Province, and southern Entre Ríos Province. The Semiarid Pampas includes western Buenos Aires Province and adjacent portions of Santa Fe, Córdoba, and La Pampa provinces. The Pampas are bounded by the drier Argentine Espinal grasslands, which form a semicircle around the north, west, and south of the Humid Pampas.

Winters are cold to mild, and summers are hot and humid. Rainfall is fairly uniform throughout the year but is a little heavier during the summer. Annual rainfall is heaviest near the coast and decreases gradually further inland. Rain during the late spring and summer usually arrives in the form of brief heavy showers and thunderstorms. More general rainfall occurs the remainder of the year as cold fronts and storm systems move through. Although cold spells during the winter often send nighttime temperatures below freezing, snow is quite rare. In most winters, a few light snowfalls occur over inland areas.

Central Argentina boasts a successful agricultural business, with crops grown on the Pampas south and west of Buenos Aires. Much of the area is also used for cattle, and more recently, to cultivate vineyards in the Buenos Aires wine region. The area is also used for farming honey using European honeybees. These farming regions are particularly susceptible to flooding during thunderstorms. The weather averages out to be 16 °C (60 °F) year-round in the Pampas.
keywords:existence, startend:end_checker