Central Tierra Del Fuego Research Articles

Patterns of Vegetation and Climatic Conditions Derived from Satellite Images Relevant for Sub-Antarctic Rangeland Management

Sub-Antarctic rangelands are characterized by weather seasonality and abundant winter snowfall. These climate factors determine most livestock management decisions. Nonetheless, data on these weather patterns are only available for some areas of the region, and management is entirely empirically-derived. The aim of this study was twofold: to compile spatial and temporal environmental information of rangelands in the Magallanes Region of Chile by using satellite images and to provide an example for local purposes through a simple evaluation of current grazing systems of four ranches in central Tierra del Fuego using satellite-derived image products and a known thermal comfort zone for sheep. To determine the environmental conditions of the region, we processed a 12-year (2000–2011) series of three MODIS-Terra platform products: Normalized Difference Vegetation Index (NDVI) as an index of photosynthetic activity, snow cover index, and Land Surface Temperature (LST). Results indicate that data obtained from satellite images follow the known seasonality of the region and deliver spatial and temporal environmental information (e.g., temperature at large scale) for most ranching areas of the region where it was formerly unavailable. The determined grazing period of analyzed ranches for winter range was May 8 to September 29. These tools show promise to encourage management innovation from simple applications to combine platforms and models for forage monitoring and ranch management in Sub-Antarctic rangelands.

Spatial abundance models and seasonal distribution for guanaco (Lama guanicoe) in central Tierra del Fuego, Argentina.

Spatially explicit modelling allows to estimate population abundance and predict species’ distribution in relation to environmental factors. Abiotic factors are the main determinants of a herbivore´s response to environmental heterogeneity on large spatiotemporal scales. We assessed the influence of elevation, geographic location and distance to the coast on the seasonal abundance and distribution of guanaco (Lama guanicoe) in central Tierra del Fuego, by means of spatially explicit modelling. The estimated abundance was 23,690 individuals for the non-breeding season and 33,928 individuals for the breeding season. The factors influencing distribution and abundance revealed to be the elevation for the non-breeding season, and the distance to the coast and geographic location for the breeding season. The southwest of the study area presented seasonal abundance variation and the southeast and northeast presented high abundance during both seasons. The elevation would be the driving factor of guanaco distribution, as individuals move to lower areas during the non-breeding season and ascend to high areas during the breeding season. Our results confirm that part of the guanaco population performs seasonal migratory movements and that the main valleys present important wintering habitats for guanacos as well as up-hill zones during summer. This type of study would help to avoid problems of scale mismatch and achieve better results in management actions and is an example of how to assess important seasonal habitats from evaluations of abundance and distribution patterns.

Postglacial environments in the southern coast of Lago Fagnano, central Tierra del Fuego, Argentina, based on pollen and fungal microfossils analyses

We analyzed a peat-bog sequence from the central region of Tierra del Fuego, southernmost Patagonia, to reconstruct the environmental changes over the past 15,000years. Postglacial vegetation was mainly composed by grasslands and shrubby communities with sparsely distributed Nothofagus trees under dry conditions. The predominance of Glomus sp. and Gelasinospora sp. may also indicate less humid conditions related to the steppe communities. The presence of herbivorous grazers is suggested by the record of ascospores of coprophilous Sordaria-type and Sporormiella-type throughout the profile. Between 11,200 and 6500calyr BP, the Nothofagus woodland established under warmer and wetter climate than before. However, precipitation must have remained below present-day levels. Most fungal remains (Gaeumannomyces sp., Glomus sp., Gelasinospora sp., Microthyriaceae, Spegazzinia tessarthra, Alternaria sp.) are likely associated with the development of forest-steppe ecotone communities. Following 6500calyr BP, when climate conditions were more humid and colder than before, the closed-canopy forest dominated the landscape, and Microthyriaceae remains prevailed among fungi. During the last 1000years, the record showed open forest communities accompanied by the presence of Glomus sp. These palaeoenvironmental changes observed along the sequence suggested variations in the amount of precipitation of westerly origin related to shifts in the position and/or strength of the southern margin of the westerlies. This study revealed that fungal remains complement pollen/spores analysis by providing important independent information on the palaeoenvironmental and palaeoclimate conditions that prevailed during the late Pleistocene-Holocene in the Lago Fagnano area.

Late Quaternary palaeoenvironmental reconstruction of central Tierra del Fuego (Argentina) based on pollen and fungi

This paper presents the main palaeoenvironmental results obtained from two sites located in the eastern (La Correntina peat bog) and southern (Terra Australis peat bog) sectors of the Lake Fagnano area, situated at 54° S on the Tierra del Fuego island, at the southernmost extreme of Patagonia. Here, we provide an overview of the postglacial ecosystem and vegetation dynamics on both slopes of the Fuegian Andes by combining palynological records of pollen and fungal remains analyses, supported by radiocarbon datings and multivariate statistics. The pollen data from the two sites indicate initial shrubby and herbaceous vegetation with scattered trees, under drier and colder climate conditions than today. Expansion of Nothofagus forest began about 11,200 cal BP in the Terra Australis area, while an open vegetation of grasslands and shrubs developed around La Correntina site by 11,500 cal BP followed by the establishment of the forest-steppe ecotone after 9400 cal BP. These vegetation changes implied a modification of the climate toward warmer and drier climate conditions than present. At both sites, the predominance of the mycorrhizal Glomus was related to the presence of open ground grassland, indicating relatively dry local conditions. Closed-canopy forests dominated the landscape after 6500 cal BP at Terra Australis, and after 5000 cal BP at La Correntina, suggesting relatively cold and wet environmental conditions. However, the fungal assemblage in Terra Australis shows high abundances of epiphyllous Microthyriaceae, pointing that the Nothofagus trees grew closer than at La Correntina. These findings allow us to conclude that both mires have experienced dissimilar trends in the environmental evolution since Late-glacial times, probably due to their locations in two distinct flanks of the Andean range.

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 centralTierra del Fuego (54º18’ S, 67º49’ 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 rainfall.Key words: regeneration; forest management; crown cover; regional climate; modelling; Tierra del Fuego.

Detrital zircon SHRIMP U–Pb age study of the Cordillera Darwin Metamorphic Complex of Tierra del Fuego: sedimentary sources and implications for the evolution of the Pacific margin of Gondwana

Abstract: The Cordillera Darwin Metamorphic Complex in the southernmost Andes includes a basement of probable Palaeozoic age, a mid-Jurassic and younger volcano-sedimentary cover, and a suite of Jurassic granites, all of which were jointly metamorphosed during the Cretaceous. Detrital zircon ages presented here show that some of the amphibolite-facies metamorphic rocks previously mapped as basement have a Jurassic protolith. Overall the detrital zircon age patterns for samples of the Cordillera Darwin basement differ from those of the Madre de Dios Terrane of the western Patagonian Andes with which they had been correlated; instead, they are more comparable with those from the Eastern Andes Metamorphic Complex, which apparently developed in a passive margin setting. The paucity of Cambrian detrital zircons indicates that the meta-igneous basement of the Magallanes foreland basin of central and northern Tierra del Fuego was not the main source of detritus for the protolith of the Cordillera Darwin Metamorphic Complex. The possibility is envisaged that the Magallanes Fagnano transform fault boundary between the Scotia and South America plates resulted from reactivation of an older, pre-Jurassic suture zone between the basement terranes of north–central Tierra del Fuego and Cordillera Darwin. Supplementary material: Geographical coordinates of analysed samples, sensitive high-resolution ion microprobe U–Th–Pb analytical data and representative cathodoluminescence images of zircon grains analysed are available at http://www.geolsoc.org.uk/SUP18397 .

Paleocomunidades vegetales del centro de Tierra Del Fuego durante el Holoceno temprano y tardío

Plant Palaeocommunities of Central Tierra del Fuego during the Early and Late Holocene. This study presents new data for the history of vegetation of central Tierra del Fuego. The goal is to identify the vegetation types before and after the middle Holocene, having in mind previous studies proposing a forest expansion started in early Holocene times following a SW-NE precipitation gradient. Two segments of a Sphagnum peat bog profile (R-2: 54°32’S, 67°04’W), now surrounded by the Nothofagus pumilio (Poepp et Endl.) deciduous forest, were analyzed. The following results were obtained through the modern analogs method: steppe and woodland were found in the older segment and open and closed forest in the younger segment. We concluded that an asynchronous establishment of the involved plant communities occurred. In fact, ca. 7000 years BP, while in other sites of the central island forests were already established, in R-2, located eastwards from those sites, the steppe-woodland ecotone dominated. On the other hand, from ca. 2000 years AP to modern times both open and closed forests covered the central area. The humidity carried by the Southern Westerlies could have influenced the late development of Nothofagus. This study represents an advancement in the knowledge of the vegetation history, and provides new data about the asynchrony in the establishment of communities.

Contrasting styles of superposed deformation in the southernmost Andes

Brittle fault arrays, regional structural patterns, and marine multichannel seismic reflection profiles across the Magallanes basin near 53°S latitude show contrasting styles of superposed extensional, contractional, and transtensional deformation. Below the northeastern end of a NE‐SW transect of the basin, seismic reflection profiles show deepening levels of pre‐Late Jurassic basement and Upper Jurassic to Lower Cretaceous volcanic horizons toward the southwest. This trend is associated with apparent normal fault offsets that may be attributed to a widespread Late Jurassic‐Early Cretaceous extensional event. Contrastingly, below the southwestern end of Magallanes basin subsurface depths of basement and volcanic horizons shallow to the southwest. Integration of seismic reflection data with published seismic refraction data, geologic mapping, and satellite gravity anomaly data suggest that this shallowing trend is controlled structurally by craton‐vergent, basement‐involved contractional deformation. This style of shortening contrasts with thin‐skinned styles of thrusting in the northern and central parts of the basin on Tierra del Fuego. Structural relationships, stratigraphic data, and previously published metamorphic data indicate that basement‐involved contraction occurred during latest Cretaceous to early Tertiary time. Overprinting all contractional structures, steep Tertiary strike‐slip and oblique‐slip faults in the central and southern parts of the Magallanes basin display oblique‐normal (mostly down‐to‐the‐southwest) offsets across WNW‐ESE trending segments of the South American‐Scotia transform plate boundary on the South American continent. Newly discovered features along the plate boundary segment include sediment‐filled grabens and half grabens up to 7 km wide that occur between subparallel fault splays in the Magallanes fault zone. Kinematic analyses of fault‐slip data indicate that sinistral transtensional motion occurred within this fault zone between the eastern arm of the Straits of Magellan and central Tierra del Fuego. Together these data indicate that (1) the southernmost Andes were under compression during rapid cooling and exhumation of unique high‐pressure (∼8 kbars) basement rocks now exposed in the Darwin Metamorphic Complex (DMC) near 55°S latitude and (2) final exhumation of basement rocks in the DMC occurred during a shift away from compression toward transtension during late Tertiary crustal relaxation. We suggest that preexisting structural anisotropies formed during basement‐involved contractional deformation and the initiation of seafloor spreading south of South America during the Oligocene controlled late Tertiary sinistral transtensional patterns in the Magallanes fault zone.