Aspectos metodológicos y conceptuales para el conocimiento de las áreas anegables del Chaco Oriental

En el Oriente Chaqueño la dinámica del escurrimiento es clave para comprender el funcionamiento del paisaje de la llanura

Sinopsis ecológica y estado actual del Chaco Oriental

The Eastem Chaco landscape comprises the autochthonous flatland basin of the chaquean región. This subtropical area (82,700 km2), where rivers with seasonal regime are frequent, have streams with autumnal floods and dry periods at the end of the winter. The rainfall distribution in these subtropical flatplains is the most important cause of the "continuum” vegetation with the cattail-swamps and mixed-woods in both gradient's ends. This landscape continuity is the same as that of the river basins in the Eastern Chaco. This continuity is given from headwaters to mouth in their bio-physical environments with a widespread water changes in their chemical, physical and biotic features even in spatial and temporal series. Climatic, hydrologic, physiographic, limnologic, vegetation and other features, are discussed and some considerations on the rational management of the ecosystems, are made. The purpose of this paper is to emphasize in the ecological value of the flatland basins as descriptors of the landscape dynamics in a regional limnological approach.The Eastem Chaco landscape comprises the autochthonous flatland basin of the chaquean región. This subtropical area (82,700 km2), where rivers with seasonal regime are frequent, have streams with autumnal floods and dry periods at the end of the winter. The rainfall distribution in these subtropical flatplains is the most important cause of the "continuum” vegetation with the cattail-swamps and mixed-woods in both gradient's ends. This landscape continuity is the same as that of the river basins in the Eastern Chaco. This continuity is given from headwaters to mouth in their bio-physical environments with a widespread water changes in their chemical, physical and biotic features even in spatial and temporal series. Climatic, hydrologic, physiographic, limnologic, vegetation and other features, are discussed and some considerations on the rational management of the ecosystems, are made. The purpose of this paper is to emphasize in the ecological value of the flatland basins as descriptors of the landscape dynamics in a regional limnological approach

Los bosques fluviales del Chaco Oriental: Primera aproximación

The structure and distribution of the gallery forests from the Eastern Chaco and their economical possibilities, are studied. It was analized using the Quarter Method (Cottan and Curtis, 1956) in 316 samples. The entire clear bole, diameters, coverage, stratification, total tree-heights and the present species in each stand, were measured. Transgressive species from river habitats and the Chaco landscapes, were identified. Difameters variability and heights, are characteristic of these irreguiar forests. Differences among the present stands due to many factors, were verified: stripping, presence of animáis, frequence and intensity of floods. This fact less affects the protection function of the margins, but it does with the availability of merchandable lumber resources. The application of management techniques would allow to better the quali and quantitative possibilities of the forest utilization.The structure and distribution of the gallery forests from the Eastern Chaco and their economical possibilities, are studied. It was analized using the Quarter Method (Cottan and Curtis, 1956) in 316 samples. The entire clear bole, diameters, coverage, stratification, total tree-heights and the present species in each stand, were measured. Transgressive species from river habitats and the Chaco landscapes, were identified. Difameters variability and heights, are characteristic of these irreguiar forests. Differences among the present stands due to many factors, were verified: stripping, presence of animáis, frequence and intensity of floods. This fact less affects the protection function of the margins, but it does with the availability of merchandable lumber resources. The application of management techniques would allow to better the quali and quantitative possibilities of the forest utilization

Distribución de las aves en el valle del río Paraná. Relación con el régimen pulsátil y la vegetación

Freshwater birds are important in the floodplains because its role in trophic nets and their influence on distribution of other organisms. In the Parana riverine system alnost four guilds way are identified: 1-Birds feeding while walking; 2-Birds feeding swimning of diving; 3-Birds that see their food flying or from snare for birds; 4-Birds that capture their food on stems and leanes. Therefore, they live in relationships to the landscape units that are also influenced by the water level fluctuation as a macrofactor that determine fast influence on the distribution and abundance of bird communities. The amplitude, frequency, and phase recurrence whithin the hydrological regime conform a key factor for understanding the amplitude of niches, and periodicity patterns of aquatic birds inhabiting on a very open environments where the seasonality are mainly conferred by hydrological pulses.Freshwater birds are important in the floodplains because its role in trophic nets and their influence on distribution of other organisms. In the Parana riverine system alnost four guilds way are identified: 1-Birds feeding while walking; 2-Birds feeding swimning of diving; 3-Birds that see their food flying or from snare for birds; 4-Birds that capture their food on stems and leanes. Therefore, they live in relationships to the landscape units that are also influenced by the water level fluctuation as a macrofactor that determine fast influence on the distribution and abundance of bird communities. The amplitude, frequency, and phase recurrence whithin the hydrological regime conform a key factor for understanding the amplitude of niches, and periodicity patterns of aquatic birds inhabiting on a very open environments where the seasonality are mainly conferred by hydrological pulses

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

Atenuación del escurrimiento fluvial por bosques de Tessaria

The flow interference effect of the Tessaria integrifolia forest intwo islands of the Paraná River, located dounstream of the Paraná-Paraguay rivers confluence, was studied. Current velocity, suspended sediments, channel depth, water transparency, tree density, tallness and coverage, were measured in cross sections of the stream. The atenuation of the running water by trees can be assumed as a "biological roughness" of the vegetation. It produce a strong decrease in the grain-size distribution of the islands superficial sediments as concequence of the flow interference. In central areas of the islands occuped by forest with 20-30 ind/m*, current velocity was 10 times lower than similar (depth, slope) Coastal sites without vegetation, while the suspended load resulted lesser than the half. The erodability coefficient decrease proportionally to the square of the current velocity diminishing. Owing to the forest extensión and coverage in rivers of the De la Plata basin, it is advisable to consider their effect during flood periods.The flow interference effect of the Tessaria integrifolia forest intwo islands of the Paraná River, located dounstream of the Paraná-Paraguay rivers confluence, was studied. Current velocity, suspended sediments, channel depth, water transparency, tree density, tallness and coverage, were measured in cross sections of the stream. The atenuation of the running water by trees can be assumed as a "biological roughness" of the vegetation. It produce a strong decrease in the grain-size distribution of the islands superficial sediments as concequence of the flow interference. In central areas of the islands occuped by forest with 20-30 ind/m*, current velocity was 10 times lower than similar (depth, slope) Coastal sites without vegetation, while the suspended load resulted lesser than the half. The erodability coefficient decrease proportionally to the square of the current velocity diminishing. Owing to the forest extensión and coverage in rivers of the De la Plata basin, it is advisable to consider their effect during flood periods