Intraseasonal variability in South America during the cold season

Intraseasonal (IS) variability in South America is analyzed during the cold season using 10–90 day bandpass filtered OLR anomalies (FOLR). IS variability explains a large percentage of variance with maximum values over Paraguay, northeastern Argentina, and southern Brazil. The leading pattern of FOLR, as isolated from an EOF analysis, (Cold Season IS pattern, CSIS), is characterized by a monopole centered over southeastern South America (SESA) with a northwest-southeast orientation. CSIS induces a large modulation on daily precipitation anomalies, especially on both wet spells and daily precipitation extremes, which are favored during positive (wet) CSIS phases. Large-Scale OLR anomalies over the tropical Indian and west Pacific Oceans associated with CSIS exhibit eastward propagation along tropical latitudes. In addition, circulation anomalies in the Southern Hemisphere reveal the presence of an anticyclonic anomaly over Antarctica with opposite-sign anomalies in middle latitudes 10 days before CSIS is maximum as well as evidence of Rossby wave-like patterns. Positive precipitation anomalies in SESA are favored during wet CSIS phases by the intensification of a cyclonic anomaly located further south, which is discernible over the southeastern Pacific for at least 14 days before CSIS peaks. The cyclonic anomaly evolution is accompanied by the intensification of an upstream anticyclonic anomaly, which remains quasi-stationary near the Antarctica Peninsula before the CSIS peak. We speculate that the stationary behavior of the anticyclonic center is favored by a hemispheric circulation anomaly pattern resembling that associated with a negative southern annular mode phase and a wavenumber 3–4 pattern at middle latitudes.     

Species composition and diversity of woody communities along an elevational gradient in tropical Dwarf Cloud Forest

Elucidating woody community diversity and structure change along environmental gradients is still a central issue of tropical forest ecology. We have evaluated changes in alpha and beta diversity, community composition and structure of woody communities along an elevational gradient in Dwarf Cloud Forests, Southeast Brazil. We selected five areas along an elevational gradient(1,300-1,600 m asl), and randomly allocated 10 plots(10 m × 20 m) in each area in the Ibitipoca State Park(ISP), Serra da Mantiqueira, southeastern Brazil. All woody species(diameter at breast height ≥ 5.0 cm) were collected for taxonomic identification. Thus, we analysed the woody communities based on a phytosociological approach. Overall, 147 species and 37 families were recorded, distributed in 2,303 individuals. No differences in the species richness pattern were observed between areas using the rarefaction and extrapolation curves. Significant differences in species composition and structure between areas were observed. The high beta diversity observed, corroborated by the Jaccard coefficient, increases with decreasing altitude. Our results showed that woody communities in the studied Dwarf Cloud Forests have a higher diversity and structural variability along elevational gradient.