Descomposición de la hojarasca en un bosque nativo y en una plantación de Grevillea robusta del Chaco Oriental

Litter fall and decomposition were simultaneously studied in a mixed natural forest in an adjacent stands of Grevlllea robusta (22 years oíd), near Makalló City (20*07'S; 59*21’W) where annual rainfall mean is 1100 mm with a humid period at the end of summer and a dry period in winter time. Simultaneously, a strong seasonality in the litter fall could be recorded by biweekly sampling operations. The annual fine litter fall was estimated in 6.96 tn/ha/yr in a native forest. The water storage was different in both soil sites as a consequence of a higher density and lower infiltration in Grevillea forest. Thirty litter bags with 10g of dead leaves, and 30 cellulose bagswere placed in each site in order to estímate the organic matter decomposition. Using the Olson equation, we obtained faster valúes in the natural forest: 173 days for haif-life time, compared with Grevillea forest:750 days for haif-life time. Similar trend could be observed in cellulose decomposition: remaining dry weight of 5 % was found at 220 and 968 days in native and Grevlllea forest, respectívety. Compiementary.the actívity of microbiota funtional groups were calculated (as cellulotítis, nitrifiers, and soil algae) demónstrate that the biological actívity in the decomposition procesess is mainly related with two key factors: different litter quality and dfferent water budget in the soil surface. After only two decades of implantad Grevillea forest, the fluxestand ralease of nutrient and organic matter is quite different.Litter fall and decomposition were simultaneously studied in a mixed natural forest in an adjacent stands of Grevlllea robusta (22 years oíd), near Makalló City (20*07'S; 59*21’W) where annual rainfall mean is 1100 mm with a humid period at the end of summer and a dry period in winter time. Simultaneously, a strong seasonality in the litter fall could be recorded by biweekly sampling operations. The annual fine litter fall was estimated in 6.96 tn/ha/yr in a native forest. The water storage was different in both soil sites as a consequence of a higher density and lower infiltration in Grevillea forest. Thirty litter bags with 10g of dead leaves, and 30 cellulose bagswere placed in each site in order to estímate the organic matter decomposition. Using the Olson equation, we obtained faster valúes in the natural forest: 173 days for haif-life time, compared with Grevillea forest:750 days for haif-life time. Similar trend could be observed in cellulose decomposition: remaining dry weight of 5 % was found at 220 and 968 days in native and Grevlllea forest, respectívety. Compiementary.the actívity of microbiota funtional groups were calculated (as cellulotítis, nitrifiers, and soil algae) demónstrate that the biological actívity in the decomposition procesess is mainly related with two key factors: different litter quality and dfferent water budget in the soil surface. After only two decades of implantad Grevillea forest, the fluxestand ralease of nutrient and organic matter is quite different

Aspectos ecológicos de la ficoflora de ambientes acuáticos del Chaco Oriental (Argentina)

The present study describes the al gal flora of some streams and tropical swamps ("esteros") settled in the Eastern Chaco between the Pilcomayo (25°15'S; 57°45'W) and Amores (28°15'S; 59°30'W) rivera towards the Paraguay-Paraná axis. Samples taken during 1984 at different hydrometric levels within the annual hydrologic re gime, were compared. The quali and quantitative study of the phytoplankton was carried out, as well as the periphytic flora from natural substrates with addition of SEM analyses. Counts of phytoplankton were done by the Utermohl method. Phytoplankton density was low during the high water period (between 15 and 280 ind.ml-1), and high species richness were found. During the low water period the phytoplankton density ranged from 20 to 1746 ind.ml-1. The highest density was recorded in highly salinitized water bodies with blooms of halophilous species (Glenodinium balticum and Protoperidinium achromaticum).  In response to high salinity and alkalinity diatoms such as Nitzschia acicularis var. closterioides, Surirella striatula, Campylodiscus clypeus and Bacillaria paradoxa were found in the phytoplankton. Besides, Audouinella sp. (Rhodophyta) and Enteromorpha sp. (Chlorophyta) were observed in the periphyton. In the tropical swamps the phytoplankton density ranged from 22 to 525 ind.ml-1 with high species number of Euglenophyta. Acidity indicators species (within Chrysophyceae, Xanthophyceae and Diatomophyceae) were recorded in the periphyton. Thus, local populations showed strong differences with respect to other regional waterbodies of the Northeastem of Argentina.The present study describes the al gal flora of some streams and tropical swamps ("esteros") settled in the Eastern Chaco between the Pilcomayo (25°15'S; 57°45'W) and Amores (28°15'S; 59°30'W) rivera towards the Paraguay-Paraná axis. Samples taken during 1984 at different hydrometric levels within the annual hydrologic re gime, were compared. The quali and quantitative study of the phytoplankton was carried out, as well as the periphytic flora from natural substrates with addition of SEM analyses. Counts of phytoplankton were done by the Utermohl method. Phytoplankton density was low during the high water period (between 15 and 280 ind.ml-1), and high species richness were found. During the low water period the phytoplankton density ranged from 20 to 1746 ind.ml-1. The highest density was recorded in highly salinitized water bodies with blooms of halophilous species (Glenodinium balticum and Protoperidinium achromaticum).  In response to high salinity and alkalinity diatoms such as Nitzschia acicularis var. closterioides, Surirella striatula, Campylodiscus clypeus and Bacillaria paradoxa were found in the phytoplankton. Besides, Audouinella sp. (Rhodophyta) and Enteromorpha sp. (Chlorophyta) were observed in the periphyton. In the tropical swamps the phytoplankton density ranged from 22 to 525 ind.ml-1 with high species number of Euglenophyta. Acidity indicators species (within Chrysophyceae, Xanthophyceae and Diatomophyceae) were recorded in the periphyton. Thus, local populations showed strong differences with respect to other regional waterbodies of the Northeastem of Argentina

Mapping and characterizing social-ecological land systems of South America

Humans place strong pressure on land and have modified around 75% of Earth’s terrestrial surface. In this context, ecoregions and biomes, merely defined on the basis of their biophysical features, are incomplete characterizations of the territory. Land system science requires classification schemes that incorporate both social and biophysical dimensions. In this study, we generated spatially explicit social-ecological land system (SELS) typologies for South America with a hybrid methodology that combined data-driven spatial analysis with a knowledge-based evaluation by an interdisciplinary group of regional specialists. Our approach embraced a holistic consideration of the social-ecological land systems, gathering a dataset of 26 variables spanning across 7 dimensions: physical, biological, land cover, economic, demographic, political, and cultural. We identified 13 SELS nested in 5 larger social-ecological regions (SER). Each SELS was discussed and described by specific groups of specialists. Although 4 environmental and 1 socioeconomic variable explained most of the distribution of the coarse SER classification, a diversity of 15 other variables were shown to be essential for defining several SELS, highlighting specific features that differentiate them. The SELS spatial classification presented is a systematic and operative characterization of South American social-ecological land systems. We propose its use can contribute as a reference framework for a wide range of applications such as analyzing observations within larger contexts, designing system-specific solutions for sustainable development, and structuring hypothesis testing and comparisons across space. Similar efforts could be done elsewhere in the world