The vegetation of seasonal wetlands in extratropical and orotropical South America
Deil, Ulrich; Alvarez, Miguel; Bauer, Eva-Maria; Ramírez, Carlos
Until now, the vegetation of seasonal wetlands in South America has only been studied on local to regional scales. A synoptic view is lacking and the distribution of vegetation types remains unknown. Hence we attempt here to detect floristic patterns on the spatial dimension of the subcontinent and to identify the environmental factors behind them. All plot-related floristic data (phytosociological relevés) available to us were collected and stored in a TURBOVEG-database. The study area included both extratropical South America (austral-temperate and subantarctic climatic zones) and the orotropical biome of the Andean Highlands, because the amphibic habitats in the two areas have some taxa in common. Tropical lowlands were more dissimilar and thus were excluded. In total we found 573 vegetation samples in 28 bibliographic sources, published between 1960 and 2008. To achieve a consistent nomenclature was a major problem, and the taxonomic treatment of a number of habitat specific taxa is obviously in need of improvement. Classification and ordination were performed with the total data set as well as just the diagnostic taxa. The floristic structure was analysed using non-metric multidimensional scaling (nMDS) and procrustes rotation techniques to compare species combinations at the species and genus levels. The interpretation of the results is limited by the substantial floristic and ecological heterogeneity of the data (varying plot size, plots including an inundation gradient etc.) and by the spatially uneven distribution of the data. The classification revealed a higher diversity of communities than expected: 11 clusters with precise species combinations, ecology and distribution emerged from the classification: A) Plagiobothryo-Acaenion platyacanthae and B) Pration repentis are distributed in Southern Patagonia in seasonal lagoons, respectively on inundated turfs. Moorland pools and inundated bog hollows in hard cushion mires of the Andean belt have a number of genera in common, but separate on the species level into C) Muhlenbergia fastigiata-Distichlis humilis-communities in the semi-desert highlands of NW Argentina, D) Gentiana sedifolia-Carex bonplandii and Gentiano-Oritrophion-communities in the Super-Páramo belt of Venezuela, E) the Lilaeopsion andinae in the altiplano extending from S Peru to NE Chile and NW Argentina, and F) Limosella-communities ranging from E Bolivia to Central Andean Peru. Lakeshores in the super-forest belt of the wet tropical Andes and in the mountainous parts of extratropical South America are colonized by the Crassuletalia peduncularis-venezuelensis (cluster G), the amphibic zone of lakes in the temperate climate of Chile and Argentina by Littorellion australis- and Senecioni zosteraefolii-Eleocharietalia-communities (cluster H). The vegetation of vernal pools in Mediterranean Chile has been poorly studied until now, but some communities are recorded from the transition zone to temperate Chile. They are grouped in Juncion planifolii (cluster I). Seasonal wetlands in flooded Pampa grassland of Argentina are characterized by the Ludwigia peploides-Luziola peruviana-communities (group J). Muddy river banks of River Paraná are colonized by the Lindernio dubiae-Mecardonietum (cluster K). Strong spatial patterns emerge on the continental scale, not only from vicinismus effects of the matrix vegetation surrounding the small-scale seasonal wetlands, but also for the habitat specific flora and vegetation. The main differentiating environmental factors on large scales are macroclimatic conditions and the trophic level of the substrate. Water depth, inundation duration and germination conditions in the amphibic ecophase result in a local zonation pattern. An azonal character of seasonal wetlands becomes obvious on the super-specific taxonomic rank from genera, that speciated within this environment and evolved geographical vicarious species with similar niches (e.g. Isoëtes, Limosella, Ranunculus, Hypsela, Oritrophium, Littorella, Lilaeopsis, Muhlenbeckia and Crassula).