Cross‐scale vegetation patterns of Flooding Pampa grasslands

Abstract

Summary 1The spatial pattern of vegetation heterogeneity across different scales may indicate the major environmental controls on vegetation structure, and thus guide strategies for the conservation of biodiversity. 2 We analysed cross-scale vegetation patterns in a 90 000-km 2 area of natural grasslands in the Flooding Pampa, Argentina. We assessed the contribution of regional (latitudinal) and landscape (topographic) patterns of species turnover to overall heterogeneity using data from 749 censuses. 3 A large proportion of the variation in species composition across the entire region was observed at very fine spatial scales (0.1-10 km 2 ), associated with subtle topographic features and soil salinity gradients. Latitudinal variation played a secondary role. 4 Species turnover among stands occupying different landscape positions at the same latitude was 50% greater than among inventories encompassing two degrees of latitude. The fine-grain heterogeneity determined that an area of 10 km 2 was often sufficient to include 50% of all vascular plant species of the region. 5 Although a large proportion (nearly 70%) of the vascular flora was composed of rare (satellite) species that occurred in less than 10% of the samples, few core species (i.e. those occurring in more than 90% of the samples) were seen at any scale of analysis. 6 Latitude contributed most clearly to variation in species composition among the zonal communities located in well-drained soils where differences in relative cover of C 3 and C 4 grasses were seen. However, photosynthetic pathways still varied more along salinity or topographic gradients than across regions. A latitudinal pattern in abundance of the different Poaceae tribes was also consistent with their climatic classification. 7 Alpha diversity showed a threefold variation among different stands within a landscape: it increased from low topographic positions and high soil salinity to high topographic positions and low salinity. However, it was constant among surveys within the region. 8 Nearly 25% of the species were exotic, mostly European, whose invasion was promoted by livestock grazing. Compared with the native species, exotics were consistently enriched in annuals, particularly forbs, across latitude, and were less tightly associated with landscape heterogeneity than native species.

The relationship between soil characteristics and vegetation as a function of landform position in an area of the Flooding Pampa [Argentina]

“…The phytosociological studies that have been carried out at different latitudes in this subregion describe plant heterogeneity at the landscape scale (León et al, 1979;Burkart et al, 1990). The vegetation patterns of the Flooding Pampa at both the landscape and regional scales have been examined by Perelman et al (2001).…”

A typing error in Tokeshi's test of bimodality

“…Unfortunately, at least three recent studies (Guo et al ., 2000;Van Rensburg et al ., 2000;Perelman et al ., 2001) have referred to the incorrect equation in Collins & Glenn (1997). Applying the correct equation to the data of Van Rensburg et al .…”

Poplar Afforestation Effects on Grassland Structure and Composition in the Flooding Pampas

“…Summer droughts are common and more pronounced in the uplands (Taboada and Lavado 1988). Grassland heterogeneity is explained by this topographic gradient and its interaction with grazing (Perelman et al 2001). In this work, we included communities from uplands and midslope lowlands (communities ''A'' and ''B'' according to Burkart et al 1990), discarding the lowest positions in the landscape, typically occupied by strongly alkaline soils and permanently flooded areas, because of their poor suitability for tree planting.…”

“…A temperate climate with mild winters and uniform precipitation inputs throughout the year warrants the coexistence of C3 and C4 species across the Flooding Pampa (Paruelo et al 1999;Perelman et al 2001). These 2 groups have balanced cover proportions in uplands, whereas C4 species tend to dominate in lowlands (Perelman et al 2001) and in areas subject to excessive or poorly managed grazing (Jacobo et al 2000).…”

“…These 2 groups have balanced cover proportions in uplands, whereas C4 species tend to dominate in lowlands (Perelman et al 2001) and in areas subject to excessive or poorly managed grazing (Jacobo et al 2000). The native grasslands of the Flooding Pampas have their minimum primary production in winter (Sala et al 1981;Paruelo et al 2001), and forage availability during this season often dictates livestock carrying capacity throughout the whole year (Jacobo et al 2000).…”