Plant community patterns in a gypsum area of NE Spain. II. Effects of ion washing on topographic distribution of vegetation

A model, based on the physico-chemical properties of gypsum, is postulated in order to interpret the regular distribution of plant communities associated with the topography and the main environmental stresses to which each vegetation type is subjected in a landscape unit.The leaf chemical composition of 28 representative plant species supports the main predictions of the model: species from low areas present large concentrations of Na, N and ash but low contents of Ca. It is demonstrated that the strong nutrient and salt downwashing in the hilly terrain is an important cause of the vegetation segregation observed on a large spatial scale.     

Streamflow variability and its relationship with climate indices in western rivers of Argentina

The objective of this study was to examine the streamflow variability of Argentinean Andean basins (22°–52°S). Trends and step changes of seven hydrological variables were analysed. In addition, relationships between the hydrological variables and Pacific Decadal Oscillation (PDO), Niño 3.4, and Southern Annular Mode (SAM) indices were analysed. Most streamflow variables showed upward trends in the northwest and central-western basins, while downward trends were identified in the Patagonia (southwestern) region. Streamflow of the central-western and Patagonian basins was positively correlated with the Niño 3.4 index. Moreover, an inverse relationship with the SAM was found in watersheds south of 37°S. Positive step changes associated with the PDO phases in the north and central-western basins in the mid-1970s were detected, while negative step changes resulted in Patagonia between 1970 and 2000. This research provides new evidence of the influence of major climate modes on streamflow variability in the western rivers of Argentina.