Chilean Andes Research Articles

New Records of the Andean Cat (Leopardus jacobita) in the Central Andes of Chile: Filling Gaps in the Distribution Range through Private-Social Partnerships.

Simple SummaryThe Andean cat is an endangered medium-sized felid with grey fur and a characteristic long tail with black rings. It is found only in cold and arid regions of the high Andes of Argentina, Bolivia, Chile, and Peru. As part of a collaboration between the Andean Cat Alliance (AGA) and Parque Andino Juncal (PAJ), we conducted a monitoring program from December 2020 to May 2021 using eight trail cameras in PAJ in the central Andes of Chile, an area where few records of the species have been described. We obtained records of Andean cats which fill a gap on the species distribution map, specifically in the area located between two previously identified evolutionary significant units (ESU) which are populations with different evolutionary histories that should be monitored, managed, and protected separately. Based on this new information, a comprehensive ESU reassessment across the range is currently being conducted by AGA. This will allow for a better understanding of the number of distinct populations across the range and the connectivity (i.e., current gene flow) among them, enabling the prioritization of small and isolated populations or units (i.e., higher extinction risk) and recommendations for evidence-based conservation strategies across the distribution.The Andean cat (Leopardus jacobita) is one of the most endangered and least known wild cat species in the Americas and the world in general. We describe new records of the Andean cat in the central Andes of Chile, in Parque Andino Juncal, obtained as part of a monitoring program conducted from December 2020 to May 2021 using eight trail cameras. The cameras were active for 135 days (sampling effort 1080 camera-trap days). We recorded Andean cats in two different cameras, corresponding to two independent events in January and March 2021, respectively (0.19% capture success). Our new records are relevant since they fill a gap on the species distribution map, specifically in the area located between the two previously identified evolutionarily significant units (ESU) (26–35° S) which has been prioritized by the Andean Cat Alliance (AGA). We highlight the relevance of private protected areas in ecosystems of high biodiversity and fragility such as Parque Andino Juncal and also of strategic private-social partnerships for successful collaborative efforts to monitor the presence of rare, elusive, and endangered species. Our next steps will be to collect scats from this newly identified site and conduct genetic analyses to determine whether these animals are part of previously identified ESUs or a yet unidentified potentially distinct ESU or MU requiring special conservation measures.

The tabular Strathbogie batholith in central Victoria

The southern boundary of the high level, discordant, Devonian Strathbogie batholith in central Victoria includes two near-linear sections that strike east–west, and one north–south. Field mapping has delineated the 100 km southern boundary with 2200 waypoints taken where granite and hornfels are within 10 m of one another. There is 790 m of topographic relief along the southern boundary and, where the mapping is overlain on contours, there are intervals that reflect a steep-dipping contact and others that reflect near-horizontal contacts. Of the latter, some reflect the granite roof and others the floor. Complementary evidence from mineralogic and textural data indicates a strong correlation between the interpreted roof of the granite and the abundance of tourmaline, aplite and pegmatite. When combined, the roof and floor intervals indicate a batholith thickness up to 350 m; nowhere along the southern boundary can a thickness of 1 km be demonstrated. Along the southern boundary, at least, the batholith shape is a thin, tabular and extensive composite granite sheet analogous to a pizza rather than a pipe. The roof of the granite is nearly horizontal in both east–west and north–south sections, and the plateaux today are close to the batholith roof. On regional and local scales, granite emplacement was determined by pre-existing anisotropies, such as master joint sets, across which the propagation of magma-filled fractures (granite sheets) was arrested. The emplacement records a fine balance between magma pressure, and the interplay of lower confining (overburden) pressures and pre-existing anisotropies that also facilitated roof uplift. The opportunistic magmas used the slightest variations of those parameters. This interpretation of the Strathbogie batholith matches examples in the Himalaya and Chilean Andes but differs markedly from the portrayal of very large batholiths beneath Cu–Au porphyry systems. KEY POINTS The boundary of the Strathbogie batholith can be mapped in moderately outcropping terrain to an accuracy of 10 m or better. Steep intervals of the boundary are interspersed with near-horizontal intervals that delineate the granite floor and roof along the 100 km of the southern boundary. The batholith, at least near its southern boundary, comprises near-horizontal sheets of <500 m aggregate thickness. The boundary determined by geophysics is adequate for regional studies but has been misleading in three-dimensional interpretations.

Fossil pigments and environmental conditions in the oligotrophic Laja Lake in the Chilean Andes

Interactions among climate change, ozone depletion, and ultraviolet radiation affect aquatic ecosystems. Meteorological and biological monitoring is often too brief, however, to record the magnitudes of past changes in ultraviolet fluxes and their effects. This study presents an analysis of fossil pigments and environmental conditions in the oligotrophic Laja Lake in the Chilean Andes over a 60-year period. The age of the sediment core was determined using high-efficiency gamma spectrometry and dated with lead-210 (210Pb). Analysis of the total and specific fossil pigments from a sediment core utilized a combination of analytical methods, spectrophotometry, and high-performance liquid chromatography. Environmental variables, such as stratospheric ozone concentration, temperature, precipitation, and ultraviolet radiation explained changes in the fossil pigment scytonemin. Results showed that low cloud cover over the high mountain lake predominated, with high ultraviolet radiation and temperature values during summer months. The most abundant group was Bacillariophyceae (diatoms). The highest concentrations of the pigments (canthaxanthin echinenone, myxoxanthophyll, aphanizophyll zeaxanthin and scytonemin) that represent the cyanobacteria groups were found in the upper part of the core (cm 0–15). The trend analysis further suggested that the influence of environmental features enabled generation of ultraviolet radiation-shielding pigment in the algae communities in the high mountain lake.This study advances understanding of the interactive effects of climate change, ozone depletion, and ultraviolet radiation on aquatic ecosystems. Fossil pigments proved to be good indicators of lake-ecosystem response to climate/environmental changes, which are necessary for predicting possible effects of future climate change.

Application of a Cloud Removal Algorithm for Snow-Covered Areas from Daily MODIS Imagery over Andes Mountains

Snow cover area is dramatically decreasing across the Los Andes Mountains and the most relevant water reservoir under drought conditions. In this sense, monitoring of snow cover is key to analyzing the hydrologic balance in snowmelt-driven basins. MODIS Snow Cover daily products (MOD10A1 and MYD10A1) allow snow cover to be monitored at regular time intervals and in large areas, although the images often are affected by cloud cover. The main objective of this technical note is to evaluate the application of an algorithm to remove cloud cover in MODIS snow cover imagery in the Chilean Andes mountains. To this end, the northern region of Chile (Pulido river basin) during the period between December 2015 and December 2016 was selected. Results were validated against meteorological data from a ground station. The cloud removal algorithm allowed the overall cloud cover to be reduced from 26.56% to 7.69% in the study area and a snow cover mapping overall accuracy of 86.66% to be obtained. Finally, this work allows new cloud-free snow cover imagery to be produced for long term analysis and hydrologic models, reducing the lack of data and improving the daily regional snow mapping.

De-icing landsystem model for the Universidad Glacier (34° S) in the Central Andes of Chile during the past ~660 years

Reconstructing latest Holocene (<1000 years) glacial landscape development in the Central Andes of Chile (30–35° S) is key for understanding the response of the cryosphere during periods of negative glacier mass balance, such as the current one. The excellently preserved glacial landscape produced during the latest ice advance and retreat cycle is of particular interest for examining the detailed response of glaciers to deglaciation. To establish a conceptual model of glacier behavior under warm and dry climatic conditions, we reconstructed and dated the recent glacial history of the Universidad Glacier (34° S) through detailed geomorphological mapping and 10Be cosmogenic surface exposure dating. Our mapping describes a landsystem that spans from the current ice front to ~3 km down-valley, where a mosaic of glacial landforms includes mounded relief; sinkholes; debris-filled stripes; moraine belts; flutings; and a prominent basal till plain. Our 10Be ages suggest that the Universidad Glacier has fluctuated in its forefield since the 13th – 15th centuries CE. We propose that the glacier evolved from a clean glacier to a debris-covered glacier, to an ice-cored moraine, and finally, to a massive dead-ice topography. This deglacial evolution intermittent and potentially reset by multiple standstills and/or re-advances during the overall retreat. The implication is that phases of active ice were followed by stagnation associated with progressive melting of dead ice under the supraglacial debris layer. Similar geomorphic features and processes are recorded in the present-day Universidad Glacier ablation zone, denoting a recurrent reconditioning over time analogous to the glacier's evolution during the latest Holocene.

Skynet’s New Observing Mode: The Campaign Manager

Built in 2004, the Skynet robotic telescope network originally consisted of six 0.4 m telescopes located at the Cerro-Tololo Inter-American Observatory in the Chilean Andes. The network was designed to carry out simultaneous multi-wavelength observations of gamma-ray bursts (GRBs) when they are only tens of seconds old. To date, the network has been expanded to ≈20 telescopes, including a 20 m radio telescope, that span four continents and five countries. The Campaign Manager (CM) is a new observing mode that has been developed for Skynet. Available to all Skynet observers, the CM semi-autonomously and indefinitely scales and schedules exposures on the observer’s behalf while allowing for modification to scaling parameters in real time. The CM is useful for follow up to various transient phenomena including gravitational-wave events, GRB localizations, young supernovae, and eventually, sufficiently bright Argus Optical Array and Large Synoptic Survey Telescope events.

Contrasting Sources and Conditions of Shallow Reservoirs of the Fui Group Small Eruptive Centres Associated with the Liquiñe-Ofqui Fault Zone (Chilean Andes)

Contrasting Sources and Conditions of Shallow Reservoirs of the Fui Group Small Eruptive Centres Associated with the Liquiñe-Ofqui Fault Zone (Chilean Andes)

Meteorological Export and Deposition Fluxes of Black Carbon on Glaciers of the Central Chilean Andes

Meteorological Export and Deposition Fluxes of Black Carbon on Glaciers of the Central Chilean Andes

Combination of Aerial, Satellite, and UAV Photogrammetry for Quantifying Rock Glacier Kinematics in the Dry Andes of Chile (30°S) Since the 1950s

The diachronic analysis of aerial and satellite imagery, uncrewed aerial vehicle (UAV) andin situsurveys obtained between 1956 and 2019 are employed to analyse landform surface kinematics for the Tapado site located in the Dry Andes of Chile. A feature tracking procedure was used between series of orthorectified and co-registered images to calculate surface velocities on several ice-debris landforms, including rock glaciers and debris-covered glaciers. For the active rock glaciers, the results exhibit typical viscous flow, though local destabilisation process seems to occur, increased velocities since 2000 (&amp;gt;1 m/yr) and terminus advance. Nevertheless, the debris-covered glaciers displays heterogeneous spatial patterns of surface velocities, together with collapse (downwasting) associated with the development of thermokarst depressions and supraglacial ponds. Our findings show that surface kinematics and multitemporal observations derived from different sensors are valuable tools for differentiating between glacial and periglacial features. The pluri-decadal time series since 1956 constitute a unique dataset for documenting the surface kinematics of creeping mountain permafrost in the Southern Hemisphere. The approach developed in this work offers a way forward to reconstruct the recent behaviour of glacial and periglacial features in the Andes, where archival aerial photographs are available but have not previously been processed rigorously to obtain an accurate assessment of landform kinematics.

Volcanic activity accompanying the emplacement of dacitic lava domes and effusion of lava flows at Nevados de Chillán Volcanic Complex – Chilean Andes (2012 to 2020)

Nevados de Chillán volcanic complex (NChVC) is one of the most active volcanoes in Chile having 4 eruptive episodes within the previous century. All of this activity has been concentrated within Las Termas sub-complex, the last eruption before the current reactivation occurred in 2008 characterized by a lava flow toward the east side of the edifice. The first surficial manifestation was an explosive event occurred on January 8, 2016, NChVC has been in eruption since then and continuing today. Seismicity has shown a variety of waveforms and types: Long Period (LP), Tornillo (TO), Very Long Period (VLP), spasmodic tremor, harmonic tremor and Volcano Tectonic (VT) earthquakes. Reactivation was marked by an increase in LP seismicity accompanied by a more regular VT activity. Based on seismicity, morphological changes and some petrological features it has determined five phases of activity, from hydrothermal dominance up to different magmatic episodes. It includes a lava dome extrusion, alternate growing and destruction of it, effusion of four lava flows. It is remarkable the low flow rates observed on extrusion and effusion of lava bodies (0.008 m3/s-0.04 m3/s), the constant vulcanian type eruptions of low and middle intensity, the occurrence of piroclastic flows mainly toward north and northeast to the crater and deformation process absent in the lava dome extrusion and very clear during lava flows effusion. This work makes a broad description of multiparametric data acquired by the monitoring network from 2012 to 2020, in order to illuminate the internal and external processes acting during the NChVC crisis and a hypothetical model of the magmatic plumbing system is proposed. This model states the presence of a magma plug in the shallow (0.5–1.1 km) conduit reactivated by at least two intrusive processes from 4 to 6 km depth magma chamber following the trend of a major fault structure, Cortaderas fault, which controls the distribution of eruptive centers of the complex. Our results could contribute also, to understand the behavior of the magmatic systems that produce dacitic lava domes with low volume and low growing rates.

Snow model comparison to simulate snow depth evolution and sublimation at point scale in the semi-arid Andes of Chile

Abstract. Physically based snow models provide valuable information on snow cover evolution and are therefore key to provide water availability projections. Yet, uncertainties related to snow modelling remain large as a result of differences in the representation of snow physics and meteorological forcing. While many studies focus on evaluating these uncertainties, no snow model comparison has been done in environments where sublimation is the main ablation process. This study evaluates a case study in the semi-arid Andes of Chile and aims to compare two snow models with different complexities, SNOWPACK and SnowModel, at a local point over one snow season and to evaluate their sensitivity relative to parameterisation and forcing. For that purpose, the two models are forced with (i) the most ideal set of input parameters, (ii) an ensemble of different physical parameterisations, and (iii) an ensemble of biased forcing. Results indicate large uncertainties depending on forcing, the snow roughness length z0, albedo parameterisation, and fresh snow density parameterisation. The uncertainty caused by the forcing is directly related to the bias chosen. Even though the models show significant differences in their physical complexity, the snow model choice is of least importance, as the sensitivity of both models to the forcing data was on the same order of magnitude and highly influenced by the precipitation uncertainties. The sublimation ratio ranges are in agreement for the two models: 36.4 % to 80.7 % for SnowModel and 36.3 % to 86.0 % for SNOWPACK, and are related to the albedo parameterisation and snow roughness length choice for the two models.

Evaluación de dos perturbaciones simultáneas en bosques de Araucaria-Lenga, usando diferencias de índices espectrales

This study assessed the impact produced by a wildfire and an infectious outbreak led by an oomycete pseudofungi, both occurred in 2015, on the state of Araucaria-Lenga forests of the China Muerta Reserve, placed in the southern Andes of Chile. To do this, a greenness vegetation spectral index was calculated over a multitemporal set of Landsat-8 images, acquired biannually on near-anniversary dates, which was subject to subtractions between ex-ante (2013) and ex-post dates (2015, 2017, 2019). Results show the magnitude and temporal progression of both disturbances, highlighting the celerity and aggressiveness of the wildfire. Although the affected vegetation land covers currently show values close to the recovery of the primal biomass, the inclusion of field-based data to deepen the possible composition and structure variations of these forests is needed.

Preface to Advances in the Jurassic of Argentina

Mocho-Choshuenco Volcanic Complex (MCVC) is one of the most hazardous volcanoes in Chile's Southern Volcanic Zone (SVZ). It is located at 40°S 72°W in Los Ríos Region, Chile, where the SVZ coexists with the margin-parallel Liquiñe-Ofqui Fault System (LOFS) and with NW-striking Andean Transverse Faults (ATF). The LOFS is 1200 km-long intra-arc strike-slip fault system located between 38° and 46°S, and partially controls the occurrence, spatial distribution and geometry of major stratovolcanoes. The fault-fracture networks induced by crustal deformation plays an essential role in the generation of pathways, facilitating the transport and emplacement of magmas. Thus, the Chilean Andes provides one of the best natural laboratories in the world to assess the link between tectonics and volcanism. In this study, we provide new structural, kinematic and dynamic insights, which would condition the formation and evolution of the MCVC and laying foundations for future works.Structural field data was collected and analyzed from regional and local scales. The strain analysis shows heterogeneous deformation. The stress field analysis at a regional scale indicates a strike-slip dominated transpressional regime with N61°E-trending σ1 and N26°W-trending σ3, which is consistent with the actual oblique convergence. Deformation driven by this oblique convergence is partially partitioned, where the margin-parallel component originates the dextral strike-slip in LOFS. Results are consistent with reactivation of preexisting NW-striking faults under the regional stress field, facilitating hydrothermal fluid flow and magma migration, associated with volcanoes, dikes and minor eruptive centers present in the study area. As a final result, we propose a simplified, three-dimensional model for the MCVC's basement, contributing to the understanding of the system and the way in which the different factors interact.

Dynamic and kinematic characterization of the basement structures of the Mocho-Choshuenco Volcanic Complex, Southern Andes, Chile

Mocho-Choshuenco Volcanic Complex (MCVC) is one of the most hazardous volcanoes in Chile's Southern Volcanic Zone (SVZ). It is located at 40°S 72°W in Los Ríos Region, Chile, where the SVZ coexists with the margin-parallel Liquiñe-Ofqui Fault System (LOFS) and with NW-striking Andean Transverse Faults (ATF). The LOFS is 1200 km-long intra-arc strike-slip fault system located between 38° and 46°S, and partially controls the occurrence, spatial distribution and geometry of major stratovolcanoes. The fault-fracture networks induced by crustal deformation plays an essential role in the generation of pathways, facilitating the transport and emplacement of magmas. Thus, the Chilean Andes provides one of the best natural laboratories in the world to assess the link between tectonics and volcanism. In this study, we provide new structural, kinematic and dynamic insights, which would condition the formation and evolution of the MCVC and laying foundations for future works.Structural field data was collected and analyzed from regional and local scales. The strain analysis shows heterogeneous deformation. The stress field analysis at a regional scale indicates a strike-slip dominated transpressional regime with N61°E-trending σ1 and N26°W-trending σ3, which is consistent with the actual oblique convergence. Deformation driven by this oblique convergence is partially partitioned, where the margin-parallel component originates the dextral strike-slip in LOFS. Results are consistent with reactivation of preexisting NW-striking faults under the regional stress field, facilitating hydrothermal fluid flow and magma migration, associated with volcanoes, dikes and minor eruptive centers present in the study area. As a final result, we propose a simplified, three-dimensional model for the MCVC's basement, contributing to the understanding of the system and the way in which the different factors interact.

Assessment of CMIP6 Performance and Projected Temperature and Precipitation Changes Over South America

We evaluate the performance of a large ensemble of Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) over South America for a recent past reference period and examine their projections of twenty-first century precipitation and temperature changes. The future changes are computed for two time slices (2040–2059 and 2080–2099) relative to the reference period (1995–2014) under four Shared Socioeconomic Pathways (SSPs, SSP1–2.6, SSP2–4.5, SSP3–7.0 and SSP5–8.5). The CMIP6 GCMs successfully capture the main climate characteristics across South America. However, they exhibit varying skill in the spatiotemporal distribution of precipitation and temperature at the sub-regional scale, particularly over high latitudes and altitudes. Future precipitation exhibits a decrease over the east of the northern Andes in tropical South America and the southern Andes in Chile and Amazonia, and an increase over southeastern South America and the northern Andes—a result generally consistent with earlier CMIP (3 and 5) projections. However, most of these changes remain within the range of variability of the reference period. In contrast, temperature increases are robust in terms of magnitude even under the SSP1–2.6. Future changes mostly progress monotonically from the weakest to the strongest forcing scenario, and from the mid-century to late-century projection period. There is an increase in the seasonality of the intra-annual precipitation distribution, as the wetter part of the year contributes relatively more to the annual total. Furthermore, an increasingly heavy-tailed precipitation distribution and a rightward shifted temperature distribution provide strong indications of a more intense hydrological cycle as greenhouse gas emissions increase. The relative distance of an individual GCM from the ensemble mean does not substantially vary across different scenarios. We found no clear systematic linkage between model spread about the mean in the reference period and the magnitude of simulated sub-regional climate change in the future period. Overall, these results could be useful for regional climate change impact assessments across South America.

Environmental isotope concepts of precipitation and surface water and groundwater in the Central Andes: A review

A preliminary review of existing information on the isotopic composition of oxygen (δ18O) and hydrogen (δ2H) of the water molecule in the northern sector of the Chilean Andes, between 17°30´ S and 25°30´ S, is presented. During the austral summer, the winds from the east favour the arrival of Atlantic humidity, dominantly through the Amazonas Basin, which produces more than the 80% of the annual precipitation. The Central Andes cordillera acts as a barrier to the wet air from the south-eastern Atlantic and in the Chilean northern coast produces the driest climatic area of the Earth. What is known about isotopic hydrology is briefly reviewed. This knowledge has allowed answers to questions such as the origin of precipitation, the possible links between basins, and the detection of processes that modify water isotopy, such as evaporation and geothermal effects. It has been observed in the surface water, groundwater and rainfall of northern Chile, that there is an enrichment in heavy isotopes in the north-south direction, from the region of Arica and Parinacota to the Antofagasta region. Continuing the research on precipitation and surface and groundwater isotopy is essential to achieve sustainable management of water resources and to understand current climate conditions and the past and future variations.

Stable isotope and anthropogenic tracer signature of waters in an Andean geothermal system

In the present study, we combined stable isotopes and anthropogenic tracers to investigate the origin, residence times, and evolution of thermal waters in the Lonquimay-Tolhuaca Volcanic Complex (LTVC) of the southern Chilean Andes. A total of 20 water samples from springs discharging at a broad range of temperatures (8–96 °C) were collected and analyzed for major ion geochemistry, stable isotope ratios (δ2H, δ18O, δ13CTDIC), dissolved chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6). In addition, we compiled all available data on the isotopic composition of precipitation in the region to derive the local meteoric water line. Coupled with a Rayleigh-fractionation model of precipitation, we provide constraints on the elevation at which infiltration and recharge to the system is produced. δ13CTDIC values are consistent with the bulk of dissolved inorganic carbon being derived from the addition of soil CO2 to an atmospheric source, while magma degassing and boiling processes are evidenced in samples discharging directly on the flanks of volcanoes. The isotopic composition of thermal water, once heated at depth, is further modified by CO2 degassing and carbonate precipitation during ascent. All geothermal samples contain low but detectable concentrations of CFC-11, CFC-12, CFC-113, and SF6, suggesting the addition of only a small fraction (2–22%) of modern meteoric water. The discharge temperature of naturally outflowing springs in the LTVC correlates directly with the age distribution of the water samples. This difference in residence times is attributed to the distinct subsurface circulation pathways of each water type—i.e., the shallow, diffuse flow of cold groundwater vs. the deep, focused circulation of thermal water along fault zones. Conduit flow along high vertical permeability networks allows hydrothermal fluid to remain relatively unmixed with shallow meteoric water during ascent. Data from this study confirm that fault-fracture meshes with different orientations exert a first order control on the residence times, ascent, and mixing rates of thermal waters in this segment of the Andean Cordillera, thus modulating their chemical and isotopic signature. Additionally, our results show that the combined use of conventional hydrogeochemical and isotopic data with environmental tracers, including anthropogenic CFCs and SF6, is a powerful tool to better understand the dynamics of geothermal systems.

Azorella Cushion Plants and Aridity are Important Drivers of Soil Microbial Communities in Andean Ecosystems

Cushion plants are specialized keystone species of alpine environments that can have a positive effect on ecosystem structure and function. However, we know relatively little about how cushion plants regulate the diversity and composition of soil microbial communities, major drivers of soil processes and ecosystem functioning. Identifying what factors drive the diversity and composition of soil microbial communities in high-elevation ecosystems is also fundamental to predict how global changes will affect their conservation and the services and functions they provide. Thus, we sampled four sites along the southern Andes following the vegetation belt of Azorella cushion species. The field sites spread along a latitudinal gradient and had contrasting levels of aridity, UV-B radiation, mean temperature and soil properties. Overall, Azorella, as well as aridity and UV-B radiation, were the major drivers of the distribution, composition and diversity of soil microbial communities in the studied ecosystems of the Chilean Andes. UV-B radiation affected particularly soil fungi, while soil properties such as pH, total C and N content, essential predictors of microbial diversity globally, had a much lower effect on the composition of soil microbial communities. Understanding the factors driving the structure and composition of microbial communities, particularly the role of cushion plants and the feedbacks between plant, climate and soil is of uttermost importance for the preservation of the functionality of high-elevation ecosystems threatened by climate change.

Climate response and drought resilience of Nothofagus obliqua secondary forests across a latitudinal gradient in south-central Chile

The climate response and resilience of tree growth to drought events have been widely reported for forests from the Northern Hemisphere. However, studies are much scarcer in the extra-tropical forests of southern South America. Mediterranean and Temperate forests of Chile are suffering from a moderate warming and a sustained precipitation decrease, occurring on top of an unprecedented megadrought since 2010. This study evaluated tree-growth patterns, the climate response and drought resilience of nine secondary Nothofagus obliqua forests across a latitudinal gradient from Mediterranean to Temperate climate in the Andes of Chile (35.7° to 40.3° S). Moreover, to improve the understanding of the spatial variation in productivity patterns, this research assessed trends in the maximum Normalized Difference Vegetation Index (peak in the NDVI) across the gradient for 2001–2018. Tree-growth patterns were highly influenced by stand dynamics, with steep decreasing trends in most of the stands related to a gradual canopy closure. Productivity trends had a flat pattern north of 38oS, but positive trends south of this latitude, which were mostly attributed to stand development. Tree growth was positively related to precipitation in all the sites, with annual and summer rainfall being more important in the north (Mediterranean climate) and south (Temperate climate), respectively. Conversely, maximum temperature had a negative effect on growth in most of the studied forests. This implies that projected warmer and drier conditions may have a detrimental effect on N. obliqua growth during coming decades. The two northern stands, located at the species dry range edge, were among the most resilient to drought and have not been strongly affected by the current megadrought in the area. Overall climate conditions, however, do not define the tolerance of stands to droughts, likely because local environmental and forests conditions play a key role. Although droughts have not strongly impacted the growth of N. obliqua across its distribution so far, future studies should assess the effects of the current long-term megadrought on growth resilience, and physiological studies should address the impacts of droughts and heat waves on forest function beyond what growth can unveil.

Dendrochronological potential of Prumnopitys andina (Podocarpaceae) at the southern limit of its range in the Chilean Andes

ABSTRACT Prumnopitys andina is a South American podocarp with a restricted distribution in southern Andean temperate forests, and is severely threatened due to habitat loss. Despite much dendrochronological work on other temperate South American conifers, little is known about the dendrochronological potential of P. andina. Here, we examine the main features of P. andina tree rings and evaluate the potential of this species for yielding tree-ring chronologies sensitive to climatic variability. In a population at the southern range limit of the species, we collected tree cores and cross-section samples of P. andina for analyses following standard dendrochronological techniques. 76 tree-ring series from 45 trees were examined, 32 (42%) of which were successfully cross-dated and included in a chronology. We found that the species forms well-defined tree rings with distinct boundaries delimiting annual growth. The chronology began in 1778, with notable periods of suppression and release occurring in the late nineteenth and early twentieth centuries, respectively. The chronology showed a high inter-series correlation value of 0.51, suggesting a strong common signal among trees. December to January precipitation showed a positive relationship with radial growth. Conversely, maximum and mean temperature showed negative relationships with radial growth during the austral summer and autumn. These significant relationships of climate variables with radial growth of P. andina indicate that tree-ring series of this species are suitable for dendroclimatological studies.