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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., Laboratorio de Investigación de Sistemas Ecológicos y Ambientales

Old-growth forests present a mosaic of different conditions resulting from the natural forest structure of the stands. Nothofagus betuloides forests have high spatial variability in regeneration without a clear correlation with overstory, and could be related to location of the stands in the landscape. The objective was to evaluate the influence of macro- and micro-variables over regeneration dynamics in old-growth N. betuloides forests, considering the effect of landscape (altitude and influence of the sea) and microenvironment conditions in the forest floor (closeness to trees, pits, understory cover type and bare soil). A total of four sites and 24 stands were sampled including forest structure, regeneration, understory cover and microclimate variables. Macro- (landscape) and micro- (microenvironment conditions in the forest floor) variables influenced over regeneration dynamics. Natural regeneration values (0.17 million ha−1 in the drier site vs. >4.52 million ha−1 in the other sites) not gre...

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. Fil: Martínez Pastur, Guillermo José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Gallo, E.. Administracion de Parques Nacionales; Argentina Fil: de Cruz, M.. Magellanic Nature Tours; Argentina Fil: Borla, Maria Laura. Magellanic Nature Tours; Argentina Fil: Soler Esteban, Rosina Matilde. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Anderson, Christopher Brian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego; Argentina

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 performance in different microenvironments within the harvested stands. Tested hypotheses stated that seedling stress and performance 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 modifies soil properties (e.g., soil bulk density) and coarse woody debris accumulation which in turn influences soil moisture and/or solar radiation levels. Analyses showed that seedlings received benefits of microenvironment variation after harvesting. Areas covered with middle or fine woody debris presented regeneration with better ecophysiological response and seedling performance, although 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 microenvironments in the harvested forests will determine the amount of natural recruitment of regeneration and consequently the success of proposed silvicultural management. Forest practices must be manipulated to increase the proportion of favorable microenvironments (e.g., woody debris), allowing greater natural regeneration success during the first years after harvesting., Laboratorio de Investigación de Sistemas Ecológicos y Ambientales

Understanding regeneration processes is important for implementing new silvicultural treatments that rely on natural regeneration from seed. Nevertheless, integrated, flower-to-sapling studies of the regeneration cycle evaluating the effect of management factors operating at each reproductive stage are scarce. We analyzed the influence of variable retention harvesting on the biotic and abiotic drivers of regeneration of Nothofagus pumilio forests of Southern Patagonia (Argentina). We quantified losses in reproductive potential caused by biotic and abiotic factors within the landscape mosaic generated by variable retention, including harvested stands with aggregated retention and dispersed retention, and in primary unharvested forests. Overall, pre-dispersal losses were caused by wind and insect predation acting on flowers and developing fruits, whereas post-dispersal losses resulted from stratification during winter, and impact of microclimate and rodent predation upon seeds. Dispersed retention areas modified the main drivers of regeneration as compared to aggregates and control areas. Flowering and fruiting was favored in the dispersed retention treatment, whereas seed and seedling survival were more successful in aggregates and control stands. Aggregates retained within harvested areas maintained most of reproductive processes of primary unharvested forests. The most critical step of the reproductive cycle is associated with the seedling stage to the extent that complete regeneration failure can occur in certain years independently of flower and seed crops. Fil: Martínez Pastur, Guillermo José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Soler Esteban, Rosina Matilde. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Pulido, Fernando. Universidad de Extremadura; España Fil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

Plant-animal interactions at the landscape level become particularly relevant when land use is diversified. Nothofagus forests in southern Patagonia have been used for timber and cattle grazing purposes during the last century, causing livestock to increase (Bos taurus and Ovis aries) and large native herbivores, such as guanaco (Lama guanicoe), either maintained or decreased their populations. Within this scenario, feeding interactions between guanaco and domestic herbivores were analysed in a mosaic of open habitats and different Nothofagus forest types and management histories, whereby a total of six habitat types were identified through satellite image analysis. A total of 205 floristic surveys were conducted to characterize the plant species composition at the landscape level. Diet composition of herbivores was assessed once each season during a year, using microhistological analysis of feces. Results showed higher plant richness in open lands and lower in closed, unmanaged forests. Overall, 43 plant taxa were detected in herbivore feces, which represent 56% of plant richness detected in the field. Both guanacos and domestic herbivores included mainly grasses in their diet, which were found predominantly in open lands. Tree seedlings and saplings were consumed by all herbivores, as well, except during winter. Differential forage use between guanaco and domestic herbivores in southern Patagonian Nothofagus forests did exist. However, competition for available resources among theses herbivores resulted in an alternation of feeding sites, which varied throughout the year. Management plans in southern Southern Patagonia (livestock, silvopastoral plans and timber harvesting) do not consider the direct or indirect consequences on guanaco populations. The challenge, therefore, is to generate management decisions to avoid either guanacos or domestic herbivores from becoming detrimental to the sustainability of managed forested ecosystems. Fil: Soler Esteban, Rosina Matilde. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Martínez Pastur, Guillermo José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Borrelli, Laura Beatriz. Instituto Nacional de Tecnologia Agropecuaria Bariloche; Argentina

The success ofthe reproductive process in trees depends on abiotic and biotic factors that determine the final outcome of natural regeneration. Silviculture alters biotic and abiotic factors and results in secondary forest structures. To effectively manage these forests, it is necessary to understand the bottlenecks in reproductive stages using a whole-cycle approach study. The aim ofthis study was to analyse flowering and seeding patterns in primary, secondary and silvopastoral managed Nothofagus antarctica forests, including investigating the pre-dispersion foraging of insects and birds, as well as abscised biomass production. A high percentage of female flowers produced fruits (95 96%) in which the main loss factor before seeding was the abscission ofimmature fruits (11 14%). Seeding was greater in secondary forests (11.4 million ha1), but managed stands presented a higher percentage offlowers resulting in seeds (82%). However, secondary forests had a better seed quality (17% viable seeds), where the main loss factor was empty seeds in all treatments (39 50%). Biotic factors (foraging by insects and birds) were higher in disturbed than primary forests. Nothofagus antarctica produce large quantities of seeds, but abscised immature fruits and empty seeds due to self-incompatibility mechanisms appeared as the major loss factors. EEA INTA Santa Cruz Fil: Soler Esteban, Rosina Matilde. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Centro Austral de Investigaciones Científicas (CADIC). Ushuaia, Tierra del Fuego; Argentina. Fil: Martínez Pastur, Guillermo José. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Centro Austral de Investigaciones Científicas (CADIC). Ushuaia, Tierra del Fuego; Argentina. Fil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Centro Austral de Investigaciones Científicas (CADIC). Ushuaia, Tierra del Fuego; Argentina. Fil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina. Fil: Peri, Pablo Luis. Universidad Nacional de la Patagonia Austral (UNPA). Santa Cruz; Argentina. Fil: Peri, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Argentina.