Search for: All records

Abstract AimClimate change is transforming mountain summit plant communities worldwide, but we know little about such changes in the High Andes. Understanding large‐scale patterns of vegetation changes across the Andes, and the factors driving these changes, is fundamental to predicting the effects of global warming. We assessed trends in vegetation cover, species richness (SR) and community‐level thermal niches (CTN) and tested whether they are explained by summits' climatic conditions and soil temperature trends. LocationHigh Andes. Time periodBetween 2011/2012 and 2017/2019. Major taxa studiedVascular plants. MethodsUsing permanent vegetation plots placed on 45 mountain summits and soil temperature loggers situated along a ~6800 km N‐S gradient, we measured species and their relative percentage cover and estimated CTN in two surveys (intervals between 5 and 8 years). We then estimated the annual rate of changes for the three variables and used generalized linear models to assess their relationship with annual precipitation, the minimum air temperatures of each summit and rates of change in the locally recorded soil temperatures. ResultsOver time, there was an average loss of vegetation cover (mean = −0.26%/yr), and a gain in SR across summits (mean = 0.38 species m²/yr), but most summits had significant increases in SR and vegetation cover. Changes in SR were positively related to minimum air temperature and soil temperature rate of change. Most plant communities experienced shifts in their composition by including greater abundances of species with broader thermal niches and higher optima. However, the measured changes in soil temperature did not explain the observed changes in CTN. Main conclusionsHigh Andean vegetation is changing in cover and SR and is shifting towards species with wider thermal niche breadths. The weak relationship with soil temperature trends could have resulted from the short study period that only marginally captures changes in vegetation through time. 

Abstract Seamounts and ridges are often invoked to explain subduction‐related phenomena such as flat slab generation, but the extent of their involvement remains controversial. An analysis of seismicity in the region of the Pampean flat slab through an application of an automated catalog generation algorithm resulted in 35,924 well constrained local earthquake hypocenters and a total of 12,172 focal mechanisms. Several new features related to the subduction of the Juan Fernandez Ridge (JFR) were discovered, including (a) a series of parallel lineaments of seismicity in the subducted Nazca plate separated by about 50 km and trending about 20°, and (b) a strong spatial correlation between these deeper (>80 km depth) regions of intense seismicity and concentrations of activity in the crust almost directly above it. Focal mechanisms of the deeper events are almost exclusively (∼81%) normal, while those in the crust are predominantly (∼70%) reverse. The deeper lineaments mirror the orientation and spacing of several seamount chains seen on the Nazca plate, suggesting that these patterns are caused by the same types of features at depth. This would imply that relatively minor features persist as slab anomalies long after they are subducted. The correlation of the deeper seismicity that defines these features with seismicity in the mid to lower crust suggests a genetic relation between the two. We postulate that volatiles from the subducted ridges percolate into the South American crust and induce seismicity essentially by fracking it.