Plant species diversity in remnant grasslands on arable soils in the cropping Pampa

Abstract

In order to provide a baseline for management decisions, we evaluated vegetation heterogeneity among 38 remnant grasslands located on high agronomic potential soils along a five degree-eastwest transect in the cropping Pampa. This extensive region has been cultivated for well over a century, small-scale traditional forms of agriculture were progressively replaced with large-scale industrial forms and its cropped area has more than doubled in the last 25 years, threatening the maintenance of biodiversity associated to productive soils. We characterized the diversity of this grassland patches, identified its main environmental drivers and searched for factors that favor their invasion by exotic plant species. Vegetation samples were analysed through Canonical Correspondence Analysis, proportional distribution of functional groups was compared and regression models were estimated to identify variables associated with exotic species importance. Water availability, determined by climate and soil characteristics, was the main driving factor of floristic heterogeneity in these grasslands. Exotic richness, mostly of Eurasian species, increases toward the east, related to proximity to the entrance port. The functional group of C 4 native grasses seems to be responsible for biotic resistance to invasion. More than 80% of the species recorded during the first vegetation registers in 1930 are still present, while the number of exotics was seven-fold increased. Despite covering small areas as isolated stands, these are hot spots of native biodiversity and must be the object of increasing attention for conservation and restoration in order to protect the biodiversity of an extensive agricultural landscape.

Woody Plant Invasions in Pampa Grasslands: A Biogeographical and Community Assembly Perspective

“…Common genera include Stipa, Poa, Piptochaetium, Melica, Briza, Bothriochloa, Aristida, Panicum, and Paspalum . Exotic herbaceous forbs are common throughout the region (Ghersa and León 1999 ;Perelman et al 2001 ;Burkart et al 2011 ) . The Pampas comprise fi ve phytogeographic districts ( Fig.…”

“…The potential vegetation is a " fl echillar" with a species-rich mixture of C 3 and C 4 tussock grasses (Cabrera 1976 ;Soriano 1992 ) . Yet seminatural grasslands occupy only a small fraction of the area, and no relicts of native grassland exist today (Parodi 1947 ;Burkart et al 2011 ) .…”

“…Prescribed burning is used as a management tool in the drier western areas. The dominant community is a steppe-like " fl echillar" with tall-tussock grasses forming dense, species-poor, homogeneous stands (Burkart et al 2011 ) .…”

Guests and gatecrashers in a New World’s banquet: Old World plant species introduced from the Mediterranean Basin enriched the flora of grasslands and croplands in the Pampas of Argentina

“…The northern limit is set by a xerophytic forest known as 'espinal', whereas the region is bounded westward by a shrub land named 'monte' (Cabrera 1976). Pristine vegetation corresponded to mesic tussock grasslands dominated by a rich mixture of C3 and C4 grass species (Parodi, 1930(Parodi, , 1947Burkart & al. 2011).…”

“…2013). Species from Fabaceae are underrepresented in the native pampa grasslands in comparison to the European flora (Cabrera & Zardini 1978;Burkart & al. 2011).…”