Altered fire regimes modify lizard communities in globally endangered Araucaria forests of the southern Andes

Wildfire regimes are being altered in ecosystems worldwide. The density of reptiles responds to fires and changes to habitat structure. Some of the most vulnerable ecosystems to human-increased fire frequency are old-growth Araucaria araucana forests of the southern Andes. We investigated the effects of wildfires on the density and richness of a lizard community in these ecosystems, considering fire frequency and elapsed time since last fire. During the 2018/2019 southern summer season, we conducted 71 distance sampling transects to detect lizards in Araucaria forests of Chile in four fire “treatments”: (1) unburned control, (2) long-term recovery, (3) short-term recovery, and (4) burned twice. We detected 713 lizards from 7 species. We found that the density and richness of lizards are impacted by wildfire frequency and time of recovery, mediated by the modification of habitat structure. The lizard community varied from a dominant arboreal species (L. pictus) in unburned and long-recovered stands, to a combination of ground-dwelling species (L. lemniscatus and L. araucaniensis) in areas affected by two fires. Araucaria forests provided key habitat features to forest reptiles after fires, but the persistence of these old-growth forests and associated biodiversity may be threatened given the increase in fire frequency.

Rainfall-Induced Landslide Early Warning System based on corrected mesoscale numerical models: an application for the Southern Andes

Rainfall-Induced Landslide Early Warning Systems (RILEWS) are critical tools for reducing and mitigating economic and social damages related to landslides. Despite this critical need, the Southern Andes does not yet possess an operational-scale system to support decision-makers. We propose RILEWS using a logistic regression system in the Southern Andes. The models were forced by corrected simulations of precipitation and geomorphological features. We evaluated the precipitation using the Weather and Research Forecast (WRF) model on an hourly scale. The precipitation was corrected using bias correction approaches with daily data from 12 meteorological stations. Four logistic and probabilistic models were then calibrated using Logit and Probit distributions. The predictor variables used were combinations of the slope, corrected daily precipitation and data preceding the events (7 and 30 days previous) for 57 Rainfall-Induced Landslides (RIL); validation was by ROC analysis. Our results showed that WRF does not represent the spatial variability of the precipitation. This situation was resolved by bias correcting. Specifically, the PP_M4a method with Bernoulli distribution for the occurrence and Gamma for the intensity produced lower MAE and RMSE values and higher correlation values. Finally, our RILEWS had a high predicting capacity with an AUC of 0.80 using daily precipitation data and slope. We conclude that our methodology is suitable at an operational level in the Southern Andes. Our contribution could become a useful tool in the mitigation of impacts related to climate change.

Debris flow event on Osorno volcano, Chile, during summer 2017: new interpretations for chain processes in the southern Andes

Debris flow generation in volcanic zones in the southern Andes has not been widely studied, despite the enormous economic and infrastructure damage that these events can generate. The present work contributes to the understanding of these dynamics based on a study of the 2017 Petrohué debris flow event from two complementary points of view. First, a comprehensive field survey allowed us to determine that a rockfall initiated the debris flow due to an intense rainfall event. The rockfall lithology corresponds to lava blocks and autobrecciated lavas, predominantly over 1500 m a.s.l. Second, the process was numerically modelled and constrained by in situ data collection and geomorphological mapping. The event was studied by back analysis using the height of flow measured on Route CH-255 with errors of 5 %. Debris flow volume has a high sensitivity with the initial water content in the block fall zone, ranging from 4.7×105 up to 5.5×105 m3, depending on the digital elevation model (DEM) used. Therefore, debris flow showed that the zone is controlled by the initial water content available previous to the block fall. Moreover, our field data suggest that future debris flows events can take place, removing material from the volcanic edifice. We conclude that similar events could occur in the future and that it is necessary to increase the mapping of zones with autobrecciated lava close to the volcano summit. The study contributes to the understanding of debris flows in the southern Andes since the Osorno volcano shares similar features with other stratovolcanoes in the region.

RADIOCARBON VS. LUMINESCENCE DATING OF ARCHAEOLOGICAL CERAMICS IN THE SOUTHERN ANDES: A REVIEW OF PAIRED DATES, BAYESIAN MODELS, AND A PILOT STUDY

ABSTRACT Archaeologists have been using luminescence to date pottery in South America since the late 1970s, inspired by early success in northern Chile. However, luminescence dates have not been rigorously compared to independent dating methods, which this paper’s goal. First, we present a compilation of 94 paired 14C and luminescence dates from the southern Andes, which reveals discrepancies across a range of contexts and ages. Second, we compare two Bayesian models of sets of 14C and thermoluminescence (TL) dates from three ceramic styles in the Azapa Valley, Chile, and the Inca occupation of Mendoza, Argentina. We find that only the 14C models produce results that agree with expectations based on independent data. Third, we present results from a pilot study in Mendoza that dated 6 sherds with 3 luminescence methods each and closely associated 14C dates. The reasons for disagreement between methods remain unclear, but Andean sediments with low and unstable luminescence sensitivity seem to be an important factor. Even though some luminescence ages are accurate, the clear trend of inconsistent results leads us to recommend that archaeologists use 14C rather than luminescence dates to build cultural chronologies.