Sistemas agrícolas y silvopastoriles en el Chaco Semiárido. Impactos sobre la productividad primaria

La productividad primaria neta (PPN) se define como la tasa a la cual se acumula biomasa por unidad de área y de tiempo, y se la considera una variable integradora del funcionamiento de los ecosistemas. El desmonte y los cambios en el uso del suelo que afectan gran parte de la región del Chaco Semiárido pueden impactar sobre las ganancias totales de C y su estacionalidad. Trabajos previos en la región utilizan índices espectrales de vegetación como subrogado de la PPN. Sin embargo, arriban a resultados dispares y sólo se circunscriben a lo que sucede con la parte aérea (PPNA), sin considerar los cambios que ocurren en la porción subterránea (PPNS), que suele variar entre tipos fisonómicos de vegetación. Sobre la base del modelo de eficiencia en el uso de la radiación, de información espectral derivada de sensores remotos y de relaciones PPNS/PPN de la bibliografía, el objetivo de este trabajo fue cuantificar el efecto de la transformación en el uso y la cobertura del suelo sobre la PPN, y su variación estacional. En particular, se evaluó el cambio de la PPN en sistemas agrícolas y silvopastoriles con un componente leñoso variable, respecto del bosque original. En general, se observó que los usos del suelo que presentaban una mayor productividad aérea mostraban, al mismo tiempo, los menores niveles de productividad subterránea. El doble cultivo trigo-maíz presentó la mayor PPN total, significativamente superior a la de los sistemas silvopastoriles entre 5 y 25% de cobertura arbórea, y a los cultivos de trigo-soja y soja de primera. Sin embargo, su productividad no varió significativamente de la del bosque, las pasturas megatérmicas y el maíz de primera. Los resultados obtenidos no sólo aportan información sustancial para concluir cuantitativamente en términos de la magnitud del cambio en unidades de materia seca, sino que también permiten establecer un orden o ranking más apropiado de las coberturas y usos del suelo en cuanto a la productividad total

Variabilidad fenotípica de Berberis microphylla G. Forst. en poblaciones naturales de Tierra del Fuego, una especie frutal forestal no maderable con posibilidad de diversificar la producción agroforestal patagónica

Las especies nativas de la Patagonia como las del género Berberis L., llamadas «calafates» o «michay», han hecho una importante contribución a la alimentación y la salud de las culturas locales. En los últimos años, se ha incrementado la demanda de frutos de estos arbustos y en particular de B. microphylla, tanto para el consumo en fresco como para la elaboración de diversos productos como dulces y jaleas, pulpas para la elaboración de helados, bebidas sin alcohol, a su vez que se emplean en productos cosméticos.A esto debe sumarse el hecho que se ha incorporado al Código Alimentario Argentino por Resolución Conjunta 22/2006 y 409/2006. Estos hechos ponen de manifiesto la necesidad de estudiar la variabilidad fenotípica de esta especie en diferentes ambientes en donde crece naturalmente con el objetivo general de contribuir al conocimiento, la conservación, el mejoramiento y posterior uso sustentable de los recursos vegetales de la Patagonia para generar nuevas alternativas productivas para la región y a nivel internacional. Como objetivos específicos se propusierona) realizar una caracterización morfológica y bioquímica de flores y frutos, b) estudiar la fenología y eficiencia reproductiva y c) correlacionar todas las variables estudiadas para determinar la variabilidad fenotípica de B. microphylla intra e inter poblaciones en Tierra del Fuego y su relación con las condiciones ambientales. Se seleccionaron de 10 a 12 plantas adultas de B. microphylla que crecen naturalmente en 3 sitios con características ambientales diferentes en Tierra del Fuego, Argentina. Se ha encontrado plasticidad fenotípica en algunos caracteres morfológicosy bioquímicos de las flores y frutos entre poblaciones y plantas, a la vez que entre las estaciones de crecimiento analizadas. Además, se identificaron plantas con un comportamiento destacado para ser propagadas clonalmente y evaluadas ex situ para el inicio de un programa de mejoramiento

Habitat-specific vegetation and seasonal drivers of bird community structure and function in southern Patagonian forests

Biodiversity conservation requires knowledge about the factors that influence the structure and function of biotic assemblages. In southern Patagonian Nothofagus forests, birds are the most abundant and diverse vertebrates and are known to have different requirements for nesting, breeding and feeding. Therefore, we chose this group to analyze key drivers of avian community dynamics; for conservation purposes, this information is requisite to manage Nothofagus forest landscapes and their associated biota. We first characterized forest structure and understory floristic composition in open and closed canopy broadleaved forests of mixed deciduous (MD) and mixed deciduous-evergreen (MDE) species on the southern coast of Tierra del Fuego National Park, Argentina. For each habitat, bird assemblages were assessed using point counts, checklists and mistnetting. We used ANOVAs and multivariate methods to analyze changes in bird species richness, density, and biomass as a function of habitat and seasonal characteristics. Forest structure and understory plant communities influenced avian assemblage and density; MDE forests had significantly greater species richness, but lower density than MD. Plus, particular species were associated with specific understory conditions, such as Anairetes parulus and Zonotrichia capensis whose presence was related to shrubs. Additionally, variations observed between seasons apparently were related to differential uses of each habitat type during certain times of year. Finally, it was not possible to define a single forest type with greater conservation value for birds; each had a specific bird species assemblage. Consequently, our results suggest the importance of a full representation of habitats to preserve the region’s bird diversity, which also has been described for forest invertebrates and understory plants

Environmental drivers of plant community assembly in Isla de los Estados at Southern Atlantic Ocean

The comprehensive assessment of environmental gradients influencing species assemblages is important for implementing new conservation strategies under climate change. This study aims to determine the multi-scale effect of altitudinal and longitudinal gradients as drivers of richness and plant community assembly in mountain landscapes of Isla de los Estados (Argentina) to identify areas with greater conservation value in Southern Patagonia. We chose three fjords across the island that extends from West to East and we categorized landscapes into four ecosystem types according to their vegetation type (forests and open-lands) and elevation (lower lands, 0-100 m.a.s.l. and upper lands, 300-400 m.a.s.l.). Forest structure, soil cover (woody debris, rocky outcrop and bare soil) and vegetation cover (vascular and non-vascular), including richness and growthforms (trees, shrubs, prostrate and erect herbs, tussock and rhizomatous grasses, ferns and inferior plants) were measured in 60 sampling areas (3 fjords × 2 vegetation types × 2 elevations × 5 replicates). ANOVAs and multivariate methods were used to analyse heterogeneity in forest structure, plant richness, and life-form. In addition, species richness and the Simpson’s diversity index were calculated to understand plant assembly at multiple-scales (α, β and γ). Our results showed that environmental gradients (altitudinal and longitudinal) are more important drivers of change of ecosystem type than forest spatial structure. Furthermore, forest structure significantly varied with altitudinal and longitudinal gradients affecting most of the studied variables. A greater similarity (in richness and cover) between open-lands of lower and higher elevations was detected, as well as between forests. Fjords showed a West-East gradient, where the western and center fjords were more closely related to each other than to the eastern fjord. A multi-scale diversity approach may play central role in improving our understanding the main environmental drivers of richness and plant community assembly in these forests, both theoretical and empirical, and may be used to identify the spatial scale at which ecosystem types have greater conservation value. This study indicates that for southern forest conservation at regional level, efforts must cover all environmental gradients, including the different vegetation types to assure ful conservation of all the species assemblages. | Supporting Information Supporting Information </supplementary-material

MASTREE+ : time-series of plant reproductive effort from six continents

Significant gaps remain in understanding the response of plant reproduction to environmental change. This is partly because measuring reproduction in long-lived plants requires direct observation over many years and such datasets have rarely been made publicly available. Here we introduce MASTREE+, a data set that collates reproductive time-series data from across the globe and makes these data freely available to the community. MASTREE+ includes 73,828 georeferenced observations of annual reproduction (e.g. seed and fruit counts) in perennial plant populations worldwide. These observations consist of 5971 population-level time-series from 974 species in 66 countries. The mean and median time-series length is 12.4 and 10 years respectively, and the data set includes 1122 series that extend over at least two decades (≥20 years of observations). For a subset of well-studied species, MASTREE+ includes extensive replication of time-series across geographical and climatic gradients. Here we describe the open-access data set, available as a.csv file, and we introduce an associated web-based app for data exploration. MASTREE+ will provide the basis for improved understanding of the response of long-lived plant reproduction to environmental change. Additionally, MASTREE+ will enable investigation of the ecology and evolution of reproductive strategies in perennial plants, and the role of plant reproduction as a driver of ecosystem dynamics

MASTREE+: Time-series of plant reproductive effort from six continents.

Significant gaps remain in understanding the response of plant reproduction to environmental change. This is partly because measuring reproduction in long-lived plants requires direct observation over many years and such datasets have rarely been made publicly available. Here we introduce MASTREE+, a data set that collates reproductive time-series data from across the globe and makes these data freely available to the community. MASTREE+ includes 73,828 georeferenced observations of annual reproduction (e.g. seed and fruit counts) in perennial plant populations worldwide. These observations consist of 5971 population-level time-series from 974 species in 66 countries. The mean and median time-series length is 12.4 and 10 years respectively, and the data set includes 1122 series that extend over at least two decades (≥20 years of observations). For a subset of well-studied species, MASTREE+ includes extensive replication of time-series across geographical and climatic gradients. Here we describe the open-access data set, available as a.csv file, and we introduce an associated web-based app for data exploration. MASTREE+ will provide the basis for improved understanding of the response of long-lived plant reproduction to environmental change. Additionally, MASTREE+ will enable investigation of the ecology and evolution of reproductive strategies in perennial plants, and the role of plant reproduction as a driver of ecosystem dynamics

Forty years of silvicultural management in southern Nothofagus pumilio primary forests

To achieve sustainability of a forest system it is necessary to apply appropriate silvicultural management, including preservation measures. The characterization of the status and development of the harvested stands, as well as the timber potential of the unmanaged ones, is necessary to achieve a sustainable forest management. In southern Patagonia, Nothofagus forests are the basis for the sawmill industry. Since European colonization, different silvicultural management regimes have been applied in primary forests. Forestry policies and available sawmill technologies have also been involved. There is little knowledge about the consequences of the different silvicultural systems implemented, as well as about the regeneration status of the harvested stands and future possibilities of the managed forests. The objective of this work is to analyse the logged, affected from harvesting and current forest structures, as well as the regeneration development during the last 40 years and the consequences derived to forests of southern Patagonia. The harvesting was applied irregularly between the studied decades (30 ± 15% of the original basal area was removed) creating an irregular forest structure. Large quantities of sawn logs were abandoned in the forest floor and a high percentage of the remaining forest structure was damaged during the harvesting. Negligent management and wind throw produced a huge amount of wasted timber, resulting in a scarce standing log volume of very low quality. Nevertheless, regeneration was successfully installed (222 ± 185 thousands/ha) within the harvested stands. No differences in the harvesting intensity were found with the different theoretical silvicultural methods applied through the years (selective cuts, clear-cuts or shelterwood cuts). As a result, the forests present a low current and future economical potential. Hence, the status of the secondary forest must be improved and regulated in order to achieve sustainability. Otherwise, the local forest industry will suffer from negative consequences, and this valuable resource will not be profitable in the future. © 2004 Elsevier B.V. All rights reserved

Site quality influence over understory plant diversity in old-growth and harvested Nothofagus pumilio forests

<p><em>Aim of study:</em> The effects and interactions of shelterwood forest harvesting and site qualities over understory plant species diversity and composition were compared among primary and harvested <em>Nothofagus pumilio</em> forests.</p><p><em>Area of study: </em>Tierra del Fuego (Argentina), on three pure conditions (one and six year-old harvested, and primary without previous harvesting forests) and three site qualities (high, medium and low).</p><p><em>Material and Methods: </em>Understory richness and cover (%) were registered in five replicates of 1 hectare each per treatment. Taxonomic species were classified in categories (groups, origin and life forms). Two-way ANOVAs and multivariate analyses were conducted.</p><p><em>Main results:</em> Shelterwood harvesting and site quality significantly influenced understory cover and richness, which allow the introduction of native and exotic species and increasing of dicot and monocot covers. In dicots, monocots, exotics and total groups, higher richness and covers were related to time. Meanwhile, cover reached similar high values in all site qualities on dicot, native and total groups. On the other hand, monocot and exotic richness and cover remain similar in primary and recently harvested forests, and greatly increased in old harvested forests. Mosses and ferns were among the most sensitive groups.</p><p><em>Research highlights: </em>Impacts of shelterwood cut depend on site quality of the stands and time since harvesting occurs. For this, different site quality stands should received differential attention in the development of conservation strategies, as well as variations in the shelterwood implementation (as irregularity and patchiness) should be considered to better promote understory plant species conservation inside managed areas.</p><p><em>Key words:</em> plant species conservation; years after harvesting; forest management; Tierra del Fuego.</p

Seed production and recruitment in primary and harvested Nothofagus pumilio forests: Influence of regional climate and years after cuttings

Aim of study: Harvesting proposals (e.g. variable retention) for Nothofagus pumilio forests are based on canopy opening, to increase recruitment and enhance seedling growth, by modifying light and soil moisture. Seed production and seedling recruitment will define the success of harvesting, where remnant forest structure are the main influence factors, as well as biotic and abiotic factors. The objective was to analyse seed production, seedling recruitment and recruitment efficiency in primary and harvested forests through variable retention along the first 10 years after harvesting, as well as the influence of regional climate. Area of study: The study were conducted in a pure Nothofagus pumilio forest located in central Tierra del Fuego (54°18’ S, 67°49’ W), where harvested stands with variable retention and unmanaged forests were sampled in long-term permanent plots. Material and methods: Data of forest regeneration plots were used (n = 72) (2007 a 2014), and forest structure and seed production (2006 a 2013) were also measured. Regional climate was characterised for these years from satellite images (Sea Surface Temperature) and climate re-analysis models (rainfall and temperature of land surface). Main results: Harvesting modified forest structure; however, aggregated retention maintained some characteristics of the primary unmanaged forests. These changes influenced seed production and recruitment. Seed production and recruitment were related to crown cover and the amount of seed production; however, recruitment efficiency was not affected by harvesting. The studied variables significantly changed along the years after harvesting. Seed production and recruitment were also related to regional climate factors, where it was possible to explain their variations through temperature (e.g. summer temperature) and rainfall (e.g. winter rainfall) for the different retention types in harvested forests and the primary forests. Research highlights: Variable retention harvesting generated different micro-conditions that influence seed production and recruitment. These variables were related to canopy cover. However, recruitment efficiency was not affected by harvesting. Seed production and recruitment (primary forests and harvested stands) were related to regional climate factors and their variations can be explained from variables related to temperature and rainfallPeer reviewe