Floristic heterogeneity of flooding Pampa grasslands: a multi-scale analysis

Abstract

The present paper describes vegetation heterogeneity at contrasting spatial scales in order to analyse patterns of floristic diversity and vegetation -environment relations in the Flooding Pampa grasslands of Argentina. The overall grassland flora contains a large proportion of exotic species, which are mostly annual forbs. At a regional scale, there is a latitudinal turnover in relative abundance of major grass tribes, and C 3 grasses become increasingly common in grasslands at higher latitudes. The principal gradients in overall vegetation composition were associated with landscape-level changes in topography and soil chemistry. Both native and exotic species richness increased with topographic elevation, and markedly decreased in flood-prone habitats with acidic or saline soils. In remnants of tussock grassland, the predominant physiognomy of the Pampas in pre-settlement times, the presence of the tall native grass Paspalum quadrifarium is a strong determinant of local community structure, reducing the percentage of exotic species. Heterogeneity analysis at the community scale revealed a fine-grained species packing that was in sharp contrast with spatial mosaics observed in other grasslands under livestock grazing. At this scale, spatial variation in floristic composition correlated with changes in various soil parameters, but not with subtle differences in topographic relief. The studied grasslands possess some unique features that contribute towards a better understanding of how current vegetation heterogeneity is controlled by historical, environmental and management factors.

Climatic and land‐use drivers along a latitudinal gradient: species diversity in temperate grasslands on agricultural soils

“…To the south (Flooding Pampa), it is a large plain with low morphogenetic potential as a result of a very slight slope, with endorheic drainage leaving free water surfaces and extensive areas with lengthy flooding during winter (Chaneton et al. ).…”

“…It is a vast and continuous plain formed by a deep mantle of loessic sediments of Pleistocene age deposited over a crystalline structure, which lies at a depth of 300-5000 m. To the north (Rolling and Mesopotamic Pampas) the relief is gently rolling with an extensive exoreic drainage network of rivers and valleys. To the south (Flooding Pampa), it is a large plain with low morphogenetic potential as a result of a very slight slope, with endorheic drainage leaving free water surfaces and extensive areas with lengthy flooding during winter (Chaneton et al 2005).…”

Linking vegetation heterogeneity and functional attributes of temperate grasslands through remote sensing

“…Exhaustive vegetation surveys identified four main vegetation units based on different species composition. These vegetation units differ in their position in the landscape and in their soil characteristics (for more details see Burkart et al 1990;Perelman et al 2001;Chaneton et al 2005). In addition, we considered vegetated ponds (Vervoorst 1967), a habitat not included in previous surveys.…”

“…Species richness increases from halophytic steppes and humid prairies to mesophytic meadows, while the relative abundance of C 4 grasses showed the opposite trend. C 4 grasses relative cover may reach up to 80% in halophytic steppes (Chaneton et al 2005). In addition, we distinguished four agricultural communities: winter (mainly wheat) and summer crops (mainly maize), implanted pastures and Eucalyptus spp.…”

“…The Flooding Pampa grassland in Buenos Aires province, Argentina, is one of the many areas around the world where livestock production depends on natural forage (Hidalgo & Cauhepé 1991;Soriano et al 1991;Diaz et al 1992;Milchunas & Laurenroth 1993;Adler & Morales 1999;Cingolani et al 2004;Aragón et al 2005). Edaphic and climatic factors have limited agricultural development and, as a consequence, the Flooding Pampa represents the largest area of remnant natural or seminatural grasslands in this region (Soriano et al 1991;Chaneton et al 2005).…”