Browsing by Author "Gutierrez, Alvaro G."

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    A Self-Calibrated Non-Parametric Time Series Analysis Approach for Assessing Insect Defoliation of Broad-Leaved Deciduous Nothofagus pumilio Forests
    (2019) Chavez, Roberto O.; Rocco, Ronald.; Gutierrez, Alvaro G.; Estay Cabrera, Sergio Andrés; Dorner, Marcelo.
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    Ecological impacts of different harvesting scenarios for temperate evergreen rain forest in southern Chile -: A simulation experiment
    (2007) Rueger, Nadja; Gutierrez, Alvaro G.; Kissling, W. Daniel; Armesto, Juan J.; Huth, Andreas
    Current forestry practices in Chile largely rely on exotic tree plantations, and limited management experiences are available for the species-rich native evergreen rain forests. Yet, conservationists and forest scientists call for sustainable management of native forests as an alternative to plantations so as to maintain important ecosystem services. We parameterised the process-based forest growth model FORMIND for a Valdivian coastal temperate rain forest in Chiloe Island, Chile, to assess the ecological implications of different logging practices including selective logging and strip-cutting. We tested the model by comparing simulation results with field data from the study site and carried out an extensive sensitivity analysis to explore the impacts of parameter values on model results. Simulated logging practices were compared in regard to expected timber harvest and long-term impacts on forest structure and composition.
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    MODIS Time Series Reveal New Maximum Records of Defoliated Area by Ormiscodes amphimone in Deciduous Nothofagus Forests, Southern Chile
    (2023) Estay, Sergio A.; Chavez, Roberto O.; Lastra, Jose A.; Rocco, Ronald; Gutierrez, Alvaro G.; Decuyper, Mathieu
    Outbreaks of the Ormiscodes amphimone moth are among the largest biotic disturbances in South America, defoliating vast areas of native Nothofagus pumilio forests in the Chilean and Argentinian Patagonia in the last decade. Using MODIS 16-day composites of the enhanced vegetation index and the new functions of the latest release of the "npphen" R-package, we identified new maximum records of continuously defoliated area in the Aysen region (Chilean Patagonia). This approach allowed us to detect 55,193 ha and 62,344 ha of extremely defoliated N. pumilio forest in 2019 and 2022, respectively, in an area locally known as "Mallin Grande". Extreme defoliation was accounted for by means of negative EVI anomalies with values falling among 5% of the lowest EVI records of the reference period (2000-2010). These new 2019 and 2022 outbreaks in Mallin Grande were the largest reported insect outbreaks in South American Patagonia in this century.
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    Recent increase in autumn temperature has stabilized tree growth in forests near the tree lines in Chilean Patagonia
    (2022) Gibson-Carpintero, Stephanie; Venegas-Gonzalez, Alejandro; Urra, Vinci D.; Estay, Sergio A.; Gutierrez, Alvaro G.
    It is widely accepted that global warming is affecting forests near the tree line by increasing tree growth in these cold-limited environments. However, since about 1970, a reduction in tree growth near the tree line has been observed in response to warming and increased drought stress. This reduction in tree growth has been mainly reported in forests of the northern hemisphere but less studied in southern forests. In this study, we investigated tree populations of Nothofagus pumilio located near the arboreal altitudinal limit in the central Patagonian Andes (45-47 degrees S, Aysen region, Chile). In this region, warming has been accompanied by increased drought conditions since the 2000s. We explored whether this climatic variability has promoted or reduced tree growth at the regional scale in tree lines of these broadleaved temperate forests of central Patagonia. We constructed tree-ring chronologies and determined common growth patterns and trends, and then analyzed the influence of recent climate. We detected a significant change in the slope of regional growth trends between the periods 1955-1985 and 1985-2015. We found that positive growth trends in the period 1955-1985 were associated with warmer and drier springs. However, after 1985, we found a stabilization in N. pumilio growth associated with a steady increase in temperature in autumn. Our results support the idea that more frequent warm autumns, with very thin or no snow cover, have stabilized tree growth due to water deficit at the end of the growing season of N. pumilio. The predicted climate change scenario of increasing temperatures and drought in central Patagonia may increase competition among trees for water, particularly at the end of the growing season. Consequently, we could expect a decreasing forest growth trend in central Patagonia, potentially impacting forest dynamics of these southern forests.
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    Regeneration patterns and persistence of the fog-dependent Fray Jorge forest in semiarid Chile during the past two centuries
    (2008) Gutierrez, Alvaro G.; Barbosa, Olga; Christie, Duncan A.; Del-Val, Ek; Ewing, Holly A.; Jones, Clive G.; Marquet, Pablo A.; Weathers, Kathleen C.; Armesto, Juan J.
    The persistence of rainforest patches at Fray Jorge National Park (FJNP) in semiarid Chile (30 degrees 40'S), a region receiving approximately 147 mm of annual rainfall, has been a source of concern among forest managers. These forests are likely dependent on water inputs from oceanic fog and their persistence seems uncertain in the face of climate change. Here, we assessed tree radial growth and establishment during the last two centuries and their relation to trends in climate and canopy disturbance. Such evaluation is critical to understanding the dynamics of these semiarid ecosystems in response to climate change. We analyzed forest structure of six forest patches (0.2-22 ha) in FJNP based on sampling within 0.1 ha permanent plots. For the main canopy species, the endemic Aextoxicon punctatum (Aextoxicaceae), we used tree-ring analysis to assess establishment periods, tree ages, growing trends and their relation to El Nino Southern Oscillation (ENSO), rainfall, and disturbance. The population dynamics of A. punctatum can be described by a continuous regeneration mode. Regeneration of A. punctatum was sensitive to different canopy structures. Growth release patterns suggest the absence of large scale human impact. Radial growth and establishment of A. punctatum were weakly correlated with rainfall and ENSO. If water limits forests patch persistence, patches are likely dependent on the combination of fog and rain water inputs. Forest patches have regenerated continuously for at least 250 years, despite large fluctuations in rainfall driven by ENSO and a regional decline in rainfall during the last century. Because of the positive influence on fog interception, forest structure should be preserved under any future climate scenario. Future research in FJNP should prioritize quantifying the long-term trends of fog water deposition on forests patches. Fog modeling is crucial for understanding the interplay among physical drivers of water inputs under climate change.