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

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

Long-term monitoring of thinning for silvopastoral purposes in Nothofagus antarctica forests of Tierra del Fuego, Argentina

Aim of the study: To analyse the effectiveness of thinning on tree growth, forest structure and microclimatic variables along seven years after cuttings in a secondary Nothofagus antarctica forest in Southern Patagonia. Area of study: Five hectares of homogeneous stand of secondary forests (54º15’46” SL, 66º59’41” WL) in Tierra del Fuego, Argentina. Material and methods: One control and two thinning levels were established, and forest structure, growth, crown dynamic and microclimate variables in long-term permanent plots were evaluated. Main comparisons were made using multiple ANOVAs. Main results: Intensive thinning in secondary forests allowed to increase tree individual growth rates by doubling the radiation levels at the understory level that enhances the silvopastoral management. These forests showed a desirable resilience to the forest interventions and natural disturbances (e.g. heavy defoliator attack), with a rapid reaction in the canopy cover growth. Research highlights: Monitoring of thinning for silvopastoral management must include easy and cheap measuring variables, e.g. diameter growth as a proxy for timber production objectives and hemispherical photos (crown cover and radiation) as a proxy for pasture production. Long-term monitoring allowed to identify reliable indicators that assist new sustainable management alternatives

Reciente invasión del Archipiélago de Tierra del Fuego por la avispa Vespula germanica (Hymenoptera: Vespidae)

Vespula germanica es una especie invasora de nivel mundial que ha sido detectada en la Patagonia continental de la Argentina y Chile. En este trabajo, ampliamos el rango de distribución de este véspido de la Patagonia, al Archipiélago de Tierra del Fuego. Indicamos ubicación, año y ambiente de cada avistamiento y/o captura. El patrón de expansión indicaría que esta especie está bien establecida tanto en áreas naturales como antrópicas, y probablemente ha dependido del transporte humano para llegar desde el continente. Esta comunicación breve sirve también para tomar medidas prácticas de mitigación y control de esta especie, incluyendo información básica para que la ciudadanía tome conciencia sobre su presencia y esto ayude a evitar su transporte a nuevos lugares. Finalmente, se recomienda mayor investigación para el manejo y control de esta especie invasora en Tierra del Fuego

Survival and growth of Nothofagus pumilio seedlings under several microenvironments after variable retention harvesting in southern Patagonian forests

International audience& Context Variable retention prescriptions for Nothofagus pumilio forests provide for biodiversity conservation and natural regeneration by controlled opening of the canopy. Harvesting generates different microenvironments which present dissimilar conditions for seedling establishment, due to positive or negative influences over biotic and abiotic factors. & Aims This study evaluated seedling survival and perfor-mance in different microenvironments within the harvested stands. Tested hypotheses stated that seedling stress and per-formance were influenced by harvesting due to changes in forest structure, microclimate, soil properties, and nutrient availability. & Methods In the stands harvested by variable retention, five contrasting microenvironments were selected as treatments for the experiments and sampling. Environmental variables were related to ecophysiological, seedling survival, and performance. & Results The modification of forest structure (crown cover and tree density) and the presence of coarse woody debris greatly affect the effective rainfall and global radiation reaching understorey level, influencing seedling stress and consequently survival and performance. Harvesting also mod-ifies soil properties (e.g., soil bulk density) and coarse woody debris accumulation which in turn influences soil mois-ture and/or solar radiation levels. Analyses showed that seedlings received benefits of microenvironment varia-tion after harvesting. Areas covered with middle or fine woody debris presented regeneration with better eco-physiological response and seedling performance, al-though dispersed retention areas (far away from remnant trees) and roads could also present suitable conditions for seedling survival and performance. & Conclusions The proportion of different microenviron-ments in the harvested forests will determine the amount of natural recruitment of regeneration and consequently the suc-cess of proposed silvicultural management. Forest practices must be manipulated to increase the proportion of favorable microenvironments (e.g., woody debris), allowing greater nat-ural regeneration success during the first years after harvesting

Provincia de Tierra del Fuego, Antártida e Islas del Atlántico Sur

El cambio del uso del suelo y la expansión de la agricultura ha llevado a un incremento récord de los rendimientos nacionales, sin embargo, debe hacernos reflexionar acerca de cómo planificar para el futuro la actividad, pues compromete la estructura y funcionalidad de ecosistemas frágiles y pueden afectar servicios ecológicos. La degradación ambiental por sobrepastoreo constituye uno de los grandes temas a resolver a partir de un ordenamiento del uso del suelo en nuestro territorio. El Capítulo presenta las buenas prácticas de Conservación del Suelo y del Agua en Áreas de Secano de la provincia de Tierra del Fuego, describiendo las principales prácticas de manejo del suelo y del agua probadas exitosamente en los sistemas de producción agrícola y ganadera.Fil: Oliva, Gabriel Esteban. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Livraghi, Enrique. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Frers, Enrique. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Ferrante, Daniela. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Utrilla, Victor. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Rivera, Emilio H.. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Sturzenbaum, María V.. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Diaz, Boris Gastón. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Humano, Gervasio. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Peri, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentina. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Ormaechea, Sebastián Gabriel. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Martínez Pastur, Guillermo José. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Monelos, Lucas Humberto. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Soler Esteban, Rosina Matilde. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Gargaglione, Veronica Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Bahamonde, Héctor Alejandro. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Fundacion Para la Educacion la Ciencia y la Cultura.; ArgentinaFil: Mattenet, Francisco Javier. Fundacion Para la Educacion la Ciencia y la Cultura.; Argentin

A review of silvopastoral systems in native forests of Nothofagus antarctica in southern Patagonia, Argentina

Silvopastoral systems in Nothofagus antarctica (ñire) forest have become an economical, ecological and productive alternative in Patagonia. Southern Patagonia’s experience over the past 12 years with silvopastoral systems is reviewed. The productivity and nutritive value (crude protein content and dry matter digestibility) of the understorey grassland were dependent on the interaction of environmental (mainly soil water availability and light intensity) and management factors under the trees and in turn determined animal performance. A method developed for carrying capacity estimation at the paddock level was based on the potential aboveground net primary production, and values ranged from 85 to 2200 kg DM ha−1 year−1. Planned thinning in secondary forest stands provides wood production and also improves the undestorey DM production by increasing incoming radiation. Within a management plan, a stand’s water stress conditions as well as the use of Reineke’s stand density index are proposed to assist in determining thinning intensities. Livestock production is the main annual income of silvopastoral systems where cattle and mixed livestock production (cattle + sheep) is the main activity. Animal performance at the whole farm scale is presented by comparing traditional extensive grazing management with an adaptive silvopastoral management that included strategic separation in homogeneous areas (grass steppe, forest and riparian meadows), stocking rate adjustment to grassland net primary production and the protection of regeneration from herbivores browsing. Data from litter decomposition, nutrient cycling and carbon storage studies also are presented. Finally, aspects related to the criteria and indicators to assess ñire forest’s sustainability under silvopastoral use along with biodiversity conservation issues are presented.Fil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Sur; Argentina. Universidad Nacional de la Patagonia Austral. Unidad Académica Río Gallegos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Bahamonde, Héctor Alejandro. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Sur; Argentina. Universidad Nacional de la Patagonia Austral. Unidad Académica Río Gallegos; ArgentinaFil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Gargaglione, Veronica Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Sur; Argentina. Universidad Nacional de la Patagonia Austral. Unidad Académica Río Gallegos; ArgentinaFil: Soler Esteban, Rosina Matilde. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Ormaechea, Sebastián Gabriel. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Sur; ArgentinaFil: Martínez Pastur, Guillermo José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentin