Globally accelerating trends in societal development and human environmental impacts since the mid-twentieth century are known as the Great Acceleration and have been discussed as a key indicator of the onset of the Anthropocene epoch . While reports on ecological responses (for example, changes in species range or local extinctions) to the Great Acceleration are multiplying , it is unknown whether such biotic responses are undergoing a similar acceleration over time. This knowledge gap stems from the limited availability of time series data on biodiversity changes across large temporal and geographical extents. Here we use a dataset of repeated plant surveys from 302 mountain summits across Europe, spanning 145 years of observation, to assess the temporal trajectory of mountain biodiversity changes as a globally coherent imprint of the Anthropocene. We find a continent-wide acceleration in the rate of increase in plant species richness, with five times as much species enrichment between 2007 and 2016 as fifty years ago, between 1957 and 1966. This acceleration is strikingly synchronized with accelerated global warming and is not linked to alternative global change drivers. The accelerating increases in species richness on mountain summits across this broad spatial extent demonstrate that acceleration in climate-induced biotic change is occurring even in remote places on Earth, with potentially far-ranging consequences not only for biodiversity, but also for ecosystem functioning and services.

Upward migration of plant species due to climate change has become evident in several European mountain ranges. It is still, however, unclear whether certain plant traits increase the probability that a species will colonize mountain summits or vanish, and whether these traits differ with elevation. Here, we used data from a repeat survey of the occurrence of plant species on 120 summits, ranging from 2449 to 3418 m asl, in south-eastern Switzerland to identify plant traits that increase the probability of colonization or extinction in the 20th century. Species numbers increased across all plant traits considered. With some traits, however, numbers increased proportionally more. The most successful colonizers seemed to prefer warmer temperatures and well-developed soils. They produced achene fruits and/or seeds with pappus appendages. Conversely, cushion plants and species with capsule fruits were less efficient as colonizers. Observed changes in traits along the elevation gradient mainly corresponded to the natural distribution of traits. Extinctions did not seem to be clearly related to any trait.Our study showed that plant traits varied along both temporal and elevational gradients. While seeds with pappus seemed to be advantageous for colonization, most of the trait changes also mirrored previous gradients of traits along elevation and hence illustrated the general upward migration of plant species. An understanding of the trait characteristics of colonizing species is crucial for predicting future changes in mountain vegetation under climate change.

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A simple center-of-mass avalanche model that accounts for avalanche flow in forests is presented. The model applies the principle of conservation of energy to calculate the deceleration of avalanches caused by tree fracture, overturning and debris entrainment. The model relates the physical properties of forests (tree spacing, tree age, tree type, soil conditions) to avalanche flow. Modified dry-Coulomb and velocity-dependent friction parameters commonly used in avalanche runout calculations are derived. Example calculations demonstrate how the model can be applied to back-calculate observed avalanche events. The model quantitatively explains why large avalanches can destroy forests without significant deceleration. Furthermore, it shows why tree fracture consume/little of the avalanche’s energy. Finally, the model reveals how protective forests in avalanche tracks can be maintained over time to provide the best protective capacity against snow avalanches.

Eighty-four mature Norway spruce (Picea abies L. Karst), silver fir (Abies alba Mill) and Scots pine (Pinus sylvestris L.) trees were winched over to determine the maximum resistive turning moment (M(a)) of the root-soil system, the root-soil plate geometry, the azimuthal orientation of root growth, and the occurrence of root rot. The calculation of M(a), based on digital image tracking of stem deflection, accounted not only for the force application and its changing geometry, but also for the weight of the overhanging tree, representing up to 42% of M(a). Root rot reduced M(a) significantly and was detected in 25% of the Norway spruce and 5% of the silver fir trees. Excluding trees with root rot, differences in M(a) between species were small and insignificant. About 75% of the variance in M(a) could be explained by one of the four variables--tree mass, stem mass, stem diameter at breast height squared times tree height, and stem diameter at breast height squared. Among the seven allometric variables assessed above ground, stem diameter at breast height best described the root-soil plate dimensions, but the correlations were weak and the differences between species were insignificant. The shape of the root-soil plate was well described by a depth-dependent taper model with an elliptical cross section. Roots displayed a preferred azimuthal orientation of growth in the axis of prevailing winds, and the direction of frequent weak winds matched the orientation of growth better than that of rare strong winds. The lack of difference in anchorage parameters among species probably reflects the similar belowground growth conditions of the mature trees.

Question To determine long‐term vegetation changes in revisitation studies, it is crucial to know how much of measured species turnover over time can be attributed to pseudo‐turnover (i.e. turnover caused by imperfect data acquisition), and which factors contribute to observation bias and pseudo‐turnover. Independent simultaneous surveys provide a powerful tool to quantify pseudo‐turnover and to indentify factors causing it, which may vary strongly between lowland and mountain areas. Location Alpine mountain summits (2616 m to 3418 m a.s.l.) in the southeastern Swiss Alps. Methods Plant inventories of 48 summits were collected by two independent observers simultaneously. Pseudo‐turnover between observers was compared to species turnover over one century based on historical species lists of the same summits. Variables linked to observer characteristics and external (observer‐independent) factors were tested for their influence on pseudo‐turnover and number of species missed by one of the observers, and plant characteristics were tested for their effect on species detection probability. Results Mean pseudo‐turnover between observers (13.6%) was almost three times smaller than species turnover over one century (41.4%). Pseudo‐turnover and the number of species missed increased with difference in botanizing time between observers and with a longer ascent to the summit, especially in combination with a high species richness on the summit. Species had a higher probability to be missed if occurring on many summits but with a low abundance, if small in stature and if belonging to certain taxonomic plant groups (e.g. Asteraceae). Conclusions Our critical evaluation of turnover over time vs pseudo‐turnover confirms that floristic changes on alpine summits over time represent an ecological pattern. In mountainous terrain, factors related to observer characteristics play a major role, as we found the best correspondence between simultaneous records when the difference in botanizing time was small and the ascent was short. Our results help to improve data quality in mountainous terrain by pointing out possible causes for observation bias. Long‐term vegetation studies in alpine ecosystems should make a strong effort to identify and minimize such causes in advance, for instance by reducing between‐observer differences in botanical skills, fitness and time management through appropriate training.

Abstract. The damage caused by snow avalanches to property and human lives is underestimated in many regions around the world, especially where this natural hazard remains poorly documented. One such region is the Argentinean Andes, where numerous settlements are threatened almost every winter by large snow avalanches. On 1 September 2002, the largest tragedy in the history of Argentinean mountaineering took place at Cerro Ventana, Northern Patagonia: nine persons were killed and seven others injured by a snow avalanche. In this paper, we combine both numerical modeling and dendrochronological investigations to reconstruct this event. Using information released by local governmental authorities and compiled in the field, the avalanche event was numerically simulated using the avalanche dynamics programs AVAL-1D and RAMMS. Avalanche characteristics, such as extent and date were determined using dendrochronological techniques. Model simulation results were compared with documentary and tree-ring evidences for the 2002 event. Our results show a good agreement between the simulated projection of the avalanche and its reconstructed extent using tree-ring records. Differences between the observed and the simulated avalanche, principally related to the snow height deposition in the run-out zone, are mostly attributed to the low resolution of the digital elevation model used to represent the valley topography. The main contributions of this study are (1) to provide the first calibration of numerical avalanche models for the Patagonian Andes and (2) to highlight the potential of Nothofagus pumilio tree-ring Correspondence to: A. Casteller (casteller@lab.cricyt.edu.ar) records to reconstruct past snow-avalanche events in time and space. Future research should focus on testing this combined approach in other forested regions of the Andes.