Cross-scale vegetation patterns of Flooding Pampa grasslands

Sb. Perelman et al., Cross-scale vegetation patterns of Flooding Pampa grasslands, J ECOLOGY, 89(4), 2001, pp. 562-577
Citations number
Categorie Soggetti
Journal title
ISSN journal
0022-0477 → ACNP
Year of publication
562 - 577
SICI code
1 The spatial pattern of vegetation heterogeneity across different scales m ay indicate the major environmental controls on vegetation structure. and t hus guide strategies for the conservation of biodiversity. 2 We analysed cross-scale vegetation patterns in a 90000-km(2) area of natu ral grasslands in the Flooding Pampa, Argentina. We assessed the contributi on of regional (latitudinal) and landscape (topographic) patterns of specie s turnover to overall heterogeneity using data from 749 censuses. 3 A large proportion of the variation in species composition across the ent ire region was observed at very fine spatial scales (0.1-10 km(2)), associa ted with subtle topographic features and soil salinity gradients. Latitudin al 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 d egrees 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 compos ed of rare (satellite) species that occurred in less than 10% of the sample s, 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 amo ng the zonal communities located in well-drained soils where differences in relative cover of C-3 and C-4 grasses were seen. However, photosynthetic p athways still varied more along salinity or topographic gradients than acro ss regions. A latitudinal pattern in abundance of the different Poaceae tri bes was also consistent with their climatic classification. 7 Alpha diversity showed a threefold variation among different stands withi n a landscape: it increased from low topographic positions and high soil sa linity to high topographic positions and low salinity. However, it was cons tant among surveys within the region. 8 Nearly 25% of the species were exotic, mostly European, whose invasion wa s 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.