Abstract:

During 2004 to 2008, weed surveys were conducted in 373 wheat fields of two different cropped areas (southwest [SW] and southeast [SE]) of the southern region of Buenos Aires Province of Argentina where different weed communities were expected because of changes in cropping practices over time, including tillage, crop sequence, fertilizers, and herbicides applied. Weed communities differed between regions, with greater numbers of native species for the SW. Weed community diversity was also greater for the SW region, probably due to the more diverse land use that resulted in greater landscape heterogeneity. Rush skeletonweed, sand rocket, yellow starthistle and turnipseed occurred at higher constancy (proportion of fields in which a given species is present) in the SW region, whereas common chickweed, false bishop's weed, corn speedwell, and common lambsquarters were present more frequently in the SE region. Compared with the 1982 survey, constancy of weeds increased, but those species with high constancy in 1982 were also with high constancy in the recent surveys. Diversity (species richness) was greater in conventional than in a no-tillage system. The constancy of Italian ryegrass, sand rocket, and yellow starthistle was lower under no-till than conventional tillage. Surveys allow identification of changes in weed community related to different agricultural systems. Rotation of crops and livestock avoid the homogenization of the environment at the landscape level. Management strategies will be necessary to prevent the increase of weeds populations' size, preserving plant diversity and the properties of the agroecosystem.

Author affiliation: Scursoni, Julio Alejandro. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal; Argentina

Author affiliation: Gigón, Ramón. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Bordenave; Argentina

Author affiliation: Martin, Andrés Nelson. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Vigna, Mario Raul. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Bordenave; Argentina

Author affiliation: Leguizamon, Eduardo Sixto. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Istilart, Carolina María. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Lopez, Ricardo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Bordenave; Argentina

Abstract:

Este trabajo describe la composición específica y la diversidad del sotobosque de <i>Nothofagus antarctica</i> (ñire) en función de la estructura del bosque. El estudio se realizó en el noroeste de Chubut, donde se clasificó al bosque en 10 tipos forestales según la altura y la cobertura. Realizamos censos de la vegetación que nos permitieron investigar los diferentes tipos forestales en términos de su riqueza específica, diversidad, dominancia y cobertura del sotobosque (total y según origen y hábito). Se registraron 105 especies (73% nativas y 27% exóticas) distribuidas en 43 familias. En todas las estructuras analizadas se registró una elevada cobertura de especies herbáceas. En los tipos forestales de mayor altura se registró la mayor cobertura total, que bajo dosel denso estuvo compuesta por especies nativas propias del bosque, en tanto que en bosques abiertos se registró una mayor cobertura de especies exóticas, típicas de ambientes alterados. En los bosques bajos, donde coexisten especies de ambiente altoandino, estepa, alterado y bosque, se registró mayor diversidad y riqueza de especies.

We describe the species composition and diversity of the understory of <i>Nothofagus antarctica</i> (ñire) forest depending on the forest structure. The study was conducted in the northwest of Chubut, where the forest was classified into 10 forest types, taking into account the forest height and the canopy cover. On the basis of vegetation inventory, we studied the differences among forest types in terms of species richness, diversity, dominance and understory cover (total and by origin and life form). We recorded 105 species (73% native and 27% exotic) distributed in 43 families. In all the structures analyzed high coverage of herbaceous species was recorded. In the forest type with the highest tree-height the highest coverage were recorded, composed of native species typical of the forest under dense canopies, and of exotic species, typical of disturbed environments, in open forests. In the forest type with the lowest tree-height, where species of the forest, of disturbed environments, and of the steppe coexist, there was greater diversity and species richness.

Abstract:

Tall grassland landscapes in the Paraná River floodplain are associated with a particular natural fluctuation, and to anthropic disturbances that determine their floristic assemblages. This paper addresses tall-grasslands of Panicum prionitis and evaluates the relationship between its floristic composition and the occurrence of fire, hydrological pulses and soil texture. Fifty-eight plots of tall grasslands of 25m2 each were analyzed in eight patches; abundance-cover of each species was recorded. Of the plots, 15 were distributed in three of the eight patches. The three patches had different fire histories: 7 months, 4 years and 14 years from the last fire event. In the eight patches, sediment samples of 0-20cm depth were collected and 20 topographic readings were performed. Vegetation was analyzed by applying classification and indirect ordination multivariate techniques. One hundred and eighteen species distributed in four floristic groups were found. No statistically significant differences in diversity and floristic composition were identified among tall grasslands with different fire history. Differentiation in floristic groups was mainly associated with hydrological pulses and soil texture. Fire does not generate significant changes in species richness, diversity or structure in Panicum prionitis tall grasslands. From the conservation perspective, we believe it is appropriate to suggest that to maintain the permanence of the Panicum prionitis tall grasslands the fire events should not be avoided.

Los paisajes de pajonales en la planicie inundable del Río Paraná se encuentran asociados a fluctuaciones naturales particulares y a disturbios antrópicos que determinan sus ensambles florísticos. En este trabajo se estudia el pajonal de Panicum prionitis y se evalúa la relación entre su composición florística y la ocurrencia de incendios, los pulsos hidrológicos y la textura del suelo. Se analizaron 58 censos de pajonales de 25m2 cada uno, distribuidos en ocho parches y la abundanciacobertura de cada una de las especies ha sido registrada. Del total de censos, 15 fueron distribuidos en tres de los ocho parches. Los tres parches tuvieron diferentes historias de fuego: 7 meses, 4 años y 14 años desde el último evento de fuego. En los ocho parches se colectaron muestras de sedimentos hasta 20cm de profundidad y se realizaron 20 lecturas topográficas.La vegetación fue analizada aplicando técnicas multivariadas de clasificación y ordenación indirecta. Se identificaron 118 especies pertenecientes a cuatro grupos florísticos. No hubo diferencias estadísticamente significativas en la diversidad y composición específica de los pajonales con diferentes historias de incendios. La diferenciación de grupos florísticos estuvo asociada principalmente a los pulsos hidrológicos y a la textura de los suelos. Los incendios no generaron cambios significativos en la riqueza, diversidad y estructura de los pajonales de Panicum prionitis. Desde una perspectiva de conservación, creemos que es apropiado sugerir que para mantener la permanencia de los pajonales de Panicum prionitis los eventos de fuego no deberían ser evitados.

Author affiliation: Marchetti, Zuleica Yael. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; Argentina

Author affiliation: Aceñolaza, Pablo Gilberto. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; Argentina

Abstract:

Understanding the importance of biotic community structure on ecosystem functioning, and whether communities inhabiting different microhabitats in highly heterogeneous areas provide different ecological functions is a challenge in ecological research in the face of biodiversity and habitat loss. Biological soil crusts (BSCs) have been largely treated as unique entities, and have been mostly examined in interspaces between perennial plants, limiting current understanding of their role as drivers of ecosystem functioning and their relative contribution in comparison to vascular plants. We assessed the role of BSCs on ecosystem functioning in vegetated patches and interspaces, and how individual soil functions and ecosystem multifunctionality are related to changes in BSC species- and community-level attributes. We contemplated nine ecosystem functions associated with soil water dynamics, nutrient cycling and erosion potential. We found that vegetated patches improve infiltration rates, soil stability and net potential nitrogen (N) mineralization compared to interspaces, and thus dominate multifunctionality. However, well-developed BSCs improve soil moisture and N pool in both microsites, and are multifunctional stabilizing soils and regulating soil moisture and infiltration in the interspaces. BSC surface microstructure, including changes in total cover, species richness, morphological functional groups and surface discontinuities, has significant effects on soil moisture. Differences in soil N and phosphorous are mostly related to the presence of BSC-lichens. The effect of BSCs on multifunctionality varies in dependence of the particular set of functions that are sought to simultaneously maximize. Our results suggest that vascular plants and BSCs have idiosyncratic effects on different key ecosystem functions and multifunction, and BSCs substitute vascular plants in stabilizing soils and regulating water dynamics in the interspaces. BSCs greatly contribute to small-scale heterogeneity in the functioning of vegetated patches and interspaces, hence consideration of BSCs in different microsites is essential for enhancing our understanding of their functional relevance at a regional scale. In addition, quantification of BSC microstructure is crucial, owing to the contrasting effects of BSC species- and community-level attributes on different functions and multifunction. A plain language summary is available for this article.

Author affiliation: Garibotti, Irene Adriana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina

Author affiliation: Gonzalez Polo, Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina

Author affiliation: Tabeni, Maria Solana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; Argentina

Abstract:

El Parque Nacional Campos del Tuyú, ubicado en el extremo sur de la Bahía de Samborombón, es un área protegida creada para conservar el venado de las pampas (<i>Ozotoceros bezoarticus celer</i>). Los antecedentes sugieren que la protección del venado de las pampas dependería, entre otros factores, de la disponibilidad y calidad de la oferta forrajera provista por las dos comunidades preferidas como hábitat de alimentación: el monte de tala y el espartillar. Con el fin de mejorar la oferta de forraje se diseñaron y evaluaron prácticas de manejo específicas para las dos comunidades: a) exclusión del ganado en los montes de tala del establecimiento ganadero aledaño, luego de una defoliación intensa a fin de verano, y b) defoliaciones mecánicas periódicas en los espartillares. La defoliación intensa a fin del verano seguida por la exclusión al pastoreo del ganado entre marzo y agosto en los montes de tala del establecimiento vecino promovió la aparición o aumentó la contribución de los pastos nativos invernales <i>Bromus catharticus</i>, <i>Bromus auleticus</i> y <i>Elymus scabrifolius</i>, de los estivales <i>Bothriochloa laguroides</i> y <i>Paspalum dilatatum</i> y de la leguminosa <i>Melilotus officinalis</i>. La defoliación periódica del espartillar durante el período de crecimiento de la especie dominante, <i>Spartina densiflora</i>, incrementó la contribución de los pastos invernales nativos <i>Elymus scabrifolius</i>, <i>Chaetotropis elongata</i> y <i>Phalaris angusta</i>, y de la leguminosa <i>Melilotus officinalis</i>, y disminuyó la cobertura de la paja <i>Cortaderia selloana</i>. En ambas comunidades se registró un aumento del valor zootécnico ya que las especies que elevaron su contribución fueron pastos y leguminosas de alto valor nutritivo, mientras que las especies que disminuyeron su cobertura fueron herbáceas de escaso valor nutritivo.

Campos del Tuyú National Park, located at the southern part of the Samborombón Bay, is a protected area created to promote the recovery of an endangered species, the pampas deer (<i>Ozotoceros bezoarticus celer</i>). Previous studies suggest that deer protection is related to the availability and nutritive value of forage provided by <i>Celtis tala</i> and <i>Spartina densiflora</i> communities, both preferred as feeding habitat. With the aim of enhace forage offer for pampa deer, specific management practices were designed: a) high intensity biomass defoliation in late summer followed by cattle exclusion from March to August in the <i>Celtis</i> community of the neighbor cattle farm, and b) periodic biomass defoliation of the Spartina densiflora Brongn community in the protected area. Defoliation in late summer followed by cattle exclusion from March to August in the <i>Celtis</i> community promoted the establishment or increased the contribution of the native cool-season grasses <i>Bromus catharticus</i>, <i>Bromus auleticus</i> and <i>Elymus scabrifolius</i> and warm-season grasses <i>Bothriochloa laguroides</i> and <i>Paspalum dilatatum</i>, and the legume <i>Melilotus officinalis</i>. Periodic defoliation of the <i>Spartina densiflora</i> community during its growing period increased the contribution of the native cool-season grasses <i>Elymus scabrifolius</i>, <i>Chaetotropis elongata</i> and <i>Phalaris angusta</i> and of the legume <i>Melilotus officinalis</i>, while decrease basal cover of the cordgrass <i>Cortaderia selloana</i>. Forage value increased in both communties because grasses and legumes species of high nutritive value increased their contribution, while herbaceous species of low nutritive value decrease their proportion.

Abstract:

En un cultivo de manzanos en la provincia de Mendoza, Argentina, se observó la presencia de las comunidades dominadas por Cynodon dactylon y Galinsoga parviflora localizadas entre y bajo las copas de los árboles frutales, en coincidencia con una toposecuencia de relieves de altos y bajos, respectivamente. Ante el hecho de estar frente a un interesante ejemplo agronómico de establecimiento de comunidades arvenses se las analizó fisonómica, florística y sociológicamente, relacionándolas con las condiciones ecológicas, físico-químicas de los suelos y bioclimáticas de los sitios que las contienen. Mientras la comunidad de Cynodon dactylon presente en los altos o entre plantas resultó más luminosa, cálida, seca y menos fértil, la de Galinsoga parviflora en los bajos fue más sombría, fría, húmeda y más fértil. En esta última, la alta concentración de materia orgánica, nutrientes minerales y humedad de los suelos parece estar relacionada con la presencia de plantas anuales bajo las copas. Los resultados obtenidos muestran la importancia de las toposecuencias de relieves de altos y bajos en la distribución, estructura y composición florística de las comunidades vegetales arvenses, las cuales pueden resultar potenciadas con las coberturas de las copas de los árboles frutales.

In an apple orchard in the province of Mendoza, Argentina, the presence of plant communities dominated by Cynodon dactylon and Galinsoga parviflora was observed between and underneath fruit-tree canopies, coinciding with a toposequence of higher and lower reliefs respectively. Being an interesting example of weed establishment, these plant communities were physiognomically, floristically and sociologically analyzed, and related to the physicochemical and ecological conditions of soils, as well as to the bioclimatic conditions of the environments where they occur. The site occupied by the Cynodon dactylon community on the higher reliefs was more luminous, warmer, drier and less fertile, whereas that occupied by Galinsoga arviflora on the lower reliefs was more shaded, colder, and more humid and fertile. In the latter community, the high concentration of organic matter, mineral nutrients and soil moisture seems to be related to the high presence of annual plants beneath canopies. Results obtained show the importance of higher and lower reliefs in the distribution, structure and floristic composition of weed communities, which may expand with the cover of fruit-tree canopies.

Author affiliation: Méndez, Eduardo. Instituto Argentino de Investigaciones de las Zonas Áridas. Botánica y Fitosociología <IADIZA>

Abstract:

El objetivo de este trabajo fue determinar la composición florística y el aporte de minerales a la dieta animal para la producción de carne bovina de los pastizales de Andropogon lateralis Nees (PAL) y Sorghastrum setosun (Griseb.) Hitchc. (PSS), analizados mediante espectrometría ICP-AES en dos series de suelo de la provincia de Corrientes, Argentina. El mayor aporte de materia seca lo realizan A. lateralis y S. setosum. El aporte de leguminosas es bajo. El perfil de elementos minerales esenciales, probablemente esenciales y los de función incierta, cubren parcialmente los requerimientos del ganado bovino productor de carne, excepto para Mn. Las relaciones entre elementos, Ca/P, Na/K (mEq), Cu/Mo y Cu/Fe son aceptables. Las relaciones K/Mg, K/Ca+Mg (mEq) y Na/Mg (mEq) no son adecuadas, pues existe deficiencia de Mg.

The goal of this work was to determine the floristic composition and the mineral contribution of Andropogon lateralis Nees (PAL) and Sorghastrum setosum (PSS) pastures, in the animal diet for the production of beef, analyzed by ICP-AES spectrometry in two series of soils from the Province of Corrientes, Argentina. The greatest contribution of dry raw matter is provided by A. lateralis and S. setosum. The contribution of legume is low. The profile of essential mineral elements, probably essential ones and of those of uncertain function, partially fulfill the meat producer cattle requirements. The elemental ratios Ca/P, Na/K (mEq), Cu/Mo and Cu/Fe, are acceptable. The K/Mg, K/Ca+Mg (mEq) and Na/Mg (mEq) ratios are not adequate, and there is Mg deficiency.

Author affiliation: Bernardis, Aldo C.. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias

Author affiliation: Villafañe, Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas

Author affiliation: Pellerano, Roberto G.. Universidad Nacional del Nordeste

Author affiliation: Marchevky, Eduardo. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Departamento de Química.

Abstract:

Recently, wetlands have declined worldwide due mainly to habitat loss by human activities. In order to achieve a better understanding of the impacts that are being generated on the Iberá wetland in northeastern Argentina, the objective of this study is to analyze seasonal variation of the environments present in the sandy ridges areas of this wetland. The different environments were identifi ed and characterized according to their topography, vegetation physiognomy and dominance of species. In addition, the seasonal variation in the vegetation communities occurring in the different environments was analyzed and characterized in terms of fl oristic composition, abundance-cover and attributes. A thematic map of environments was generated and validated through the analysis of abundance-cover of the vegetation. Surveys were conducted seasonally, resulting in a total of 600 plots randomly selected. The percentage of dry matter, bare ground, vegetation-free water surface, vegetation height and depth of the water column were determined where appropriate. Six environments were identifi ed: the upland areas, the temporary ponds, the upper and lower transition zones (between aquatic and terrestrial environments), the low-lying area and the ?embalsados? (with aquaticpalustrine species). The environment classifi cation suggests that the topographic gradient and associated edaphic factors would determine the presence of the different communities. The great intra-annual variation in water regime originating from seasonal precipitation in the study area produces a variety of plant communities. The patterns of plant zonation in this wetland are changed from season to season as water levels fluctuate in space and time making the system very susceptible to changes in the hydrometric level.

Author affiliation: Corriale, Maria Jose. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Author affiliation: Picca, Pablo Ignacio. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Biodiversidad y Biologia Experimental. Laboratorio del Grupo de Est.de Plantas Vasculares; Argentina

Author affiliation: Di Francescantonio, Débora. Laboratorio de Ecología Forestal y Ecofisiología; . Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Abstract:

Outcrops around the world enhance biodiversity as they provide heterogeneous environments and varied habitats for species with different requirements than those living in the surroundings, and in this way they increase alpha and beta diversity. We studied the floristic composition of the vegetation of rock outcrops in northwestern Patagonia, Argentina, and compared them to the surrounding matrix of shrubland and steppe. For this we sampled 50 outcrops and 50 matrix plots close to them, identified all the species present, and analyzed their floristic composition with Detrended Correspondence Analysis (DCA). We also analyzed the floras of the north and south faces of the outcrops. The resulting ordinations were related to geographic gradients of the region. The proportions of alien to native species, different life forms, and phylogenetic groups of the outcrop floras were compared to the matrix with G-tests. Our results showed similar dominant families, life form proportions and percentage of alien species in the outcrops and the surrounding matrix. However, species composition of the outcrops was markedly different. North Patagonian outcrops present several taxa not found in the matrix, especially in their southern, less insolated walls. The previously recorded distribution of most of these exclusive species is found in colder areas further south. Thus, we hypothesize that outcrops could be acting as relicts of cold-adapted glacial paleofloras that were probably more extended during glacial times and retreated south after the last glacial maximum. © 2011 Elsevier GmbH.

Author affiliation: Speziale, Karina Lilian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina

Author affiliation: Ezcurra, Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina