Search

Mountain shrublands are widespread habitats of the European Alps. Shrub encroachment into above treeline grazed lands profoundly modifies biodiversity and ecosystem functioning. Yet, mountain shrublands remain overlooked in vegetation distribution modeling because it is difficult to distinguish them from productive grasslands. Here, we used the pigment-sensitive spectral indices based on Sentinel-2 bands within a specific phenological window, to produce a high-resolution distribution map of mountain shrublands in the French Alps. We evaluated the performance of our classification using a large dataset of vegetation plots and found that our model is highly sensitive to Ericaceous species which constitute most of the dense alpine shrublands in the French Alps. Our analysis of topoclimatic and land use factors limiting the shrubland distribution at regional scale found that, consistent with the ecophysiology of shrubs, expansion is limited by a combination of water deficit and temperature. We discussed the past and current land-use implications in the observed distribution and put forward hypotheses combining climate and land-use trajectories. Our work provides a baseline for monitoring mountain shrub dynamics and exploring the response of shrublands to past and ongoing climate and land use changes.

X-ray computed tomography (XRCT) imaging allows non-destructive visualization of the structure of various materials. Applied to wooden objects, it allows determination of their morphologies or manufacturing techniques, but also measurement of growth ring widths. We have applied XRCT to a selection of 38 mummy labels. This funerary furniture, made up of endemic or imported tree species, has survived thanks to environmental conditions in very large quantities in regions in Middle and Upper Egypt and is featured now in museum collections across the globe. Mummy labels thus represent a unique and abundant data source to build floating or absolutely dated dendrochronological chronologies for this period. Here we discuss the possible contributions and limitations of XRCT for the analysis of these artifacts and show that the approach allows identification of discriminating markers for the identification of certain species on the transverse plane, but that the insufficient resolution of the tangential and radial planes normally prevents formal identification of species. By contrast, XRCT undeniably enhances the visibility of toolmarks (in terms of numbers and depth), and thereby allows highlighting marks that remain invisible to the naked eye; XRCT also provides key insights into cutting methods and the calibers used and yields new information on silvicultural practices and the knowhow of Egyptian craftsmen. Finally, the measurement of ring widths on XRCT imagery is also more accurate than what can be achieved by traditional dendrochronological measurements, especially in the case of cuts realized on a slab. The approach also confirms the limited potential of local broadleaved species for dendrochronological approaches due to unreadable or poorly visible tree rings and mostly short tree-ring sequences. [ABSTRACT FROM AUTHOR]

The trade winds cause strong upwelling in the eastern equatorial Pacific, and create the eastern Pacific Cold Tongue (EPCT) that has far‐reaching impacts on global climate. However, large discrepancies persist in quantifying 20th‐century EPCT sea surface temperature (SST) changes across different instrumental data sets. Here we synthesize four coral Sr/Ca‐SST records from the tropical central‐eastern Pacific to develop a Cold Tongue Index (CTI) reconstruction for 1887–1997. The coral CTI record shows a rapid 20th century warming of the EPCT, suggesting an underestimation of warming trends in instrumental CTI records. The decadal to multidecadal changes in reconstructed EPCT SST show an association with the Walker Circulation. Our reconstruction indicates that recent EPCT cooling during the global warming hiatus is not unusual in the context of the 20th century. Our results provide new evidence for 20th century EPCT SST changes and an observational constraint for predicting future tropical climate changes. Plain Language Summary: The tropical Pacific exhibits an asymmetric pattern of sea surface temperatures (SST) along the equator, with a warm pool in the west and a cold tongue in the east. The Eastern Pacific Cold Tongue (EPCT) plays a crucial role in influencing global climate. To date, however, considerable disagreement persists about changes and causes of the EPCT SST over the 20th century due to the sparse instrumental observations before ∼1960. Here we synthesize published coral Sr/Ca‐SST records from the tropical central‐eastern Pacific to develop a coral Cold Tongue Index (CTIcoral) for the period 1887–1997. The CTIcoral record correlates significantly with instrumental data since 1960, and thus allows reliable assessment of 20th century EPCT SST changes. Our record exhibits a rapid 20th century warming trend of the EPCT, indicating an underestimation of warming trends in instrumental CTI records. The decadal to multidecadal changes in CTIcoral also show an association with the Walker Circulation. Comparing the magnitude of the 1992–2011 trend in instrumental CTI with our reconstruction reveals that recent EPCT cooling during the global warming hiatus is not anomalous in the context of 20th century. Our findings have implications for predicting future EPCT SST changes by offering a constraint for model simulations. Key Points: Synthesizing coral Sr/Ca‐SST records yields robust estimates of 20th century warming trend in the eastern Pacific Cold Tongue (EPCT)A coral‐based reconstruction indicates an underestimation of 20th century EPCT warming trends in instrumental SST recordsRecent EPCT cooling during the global warming hiatus is not anomalous in the context of the 20th century [ABSTRACT FROM AUTHOR]

Glacier mass balance reconstructions provide a means of placing relatively short observational records into a longer-term context. Here, we use multiple proxies from Pinus cembra trees from God da Tamangur, combining tree ring anatomy and stable isotope chronologies to reconstruct seasonal glacier mass balance (i.e., winter, summer, and annual mass balance) for the nearby Silvretta Glacier over the last 2 centuries. The combination of tree ring width, radial diameter of earlywood cell lumina, and latewood radial cell wall thickness provides a highly significant reconstruction for summer mass balance, whereas for the winter mass balance, the correlation was less significant but still robust when radial cell lumina were combined with δ18O records. A combination of the reconstructed winter and summer mass balances allows the quantification of the annual mass balance of the Silvretta Glacier for which in situ measurements date back to 1919. Our reconstruction indicates a substantial increase in glacier mass during the first half of the 19th century and an abrupt termination of this phase after the end of the Little Ice Age. Since the 1860s, negative glacier mass balances have been dominant and mass losses accelerate as anthropogenic warming picks up in the Alps. [ABSTRACT FROM AUTHOR]

Over large regions exposed to natural disasters, cascading effects resulting from complex or concatenated natural processes may represent a large portion of total risk. Populated high‐mountain environments are a major concern, and methods for large‐scale quantitative risk analyses are urgently required to improve risk mitigation. This article presents a comprehensive quantitative rockfall risk assessment over a large archetypal valley of the Andean mountains, in Central Chile, which integrates a wide spectrum of elements at risk. Risk is expressed as an expected damage both in monetary terms and casualties, at different scales relevant for decision making. Notably, total rockfall risk is divided into its main drivers, which allows quantifying seismically induced rockfall risk. For this purpose, the local seismic hazard is quantified and the yield acceleration, that is, acceleration required to initiate rockfall, is determined at the regional scale. The probability of failure is thereafter derived in terms of annual frequency of rockfall initiation and integrated in the quantitative risk assessment (QRA) process. Our results show the significant role of seismic activity as the triggering mechanism of rockfalls, and highlight elements at risk that have a major contribution to the total risk. Eventually a sensitivity analysis is conducted to (i) assess the robustness of obtained risk estimates to the data and modeling choices and (ii) identify the most influential assumptions. Our approach evidences the feasibility of large‐scale QRAs in sensitive environments and opens perspectives for refining QRAs in similar territories significantly affected by cascading effects and multihazards. [ABSTRACT FROM AUTHOR]