• Energy Research

ABSTRACTMountain areas are biodiversity hotspots and provide a multitude of ecosystem services of irreplaceable socio‐economic value. In the European Alps, air temperature has increased at a rate of about 0.36°C decade−1 since 1970, leading to glacier retreat and significant snowpack reduction. Due to these rapid environmental changes, this mountainous region is undergoing marked changes in spring phenology and elevational distribution of animals, plants and fungi. Long‐term monitoring in the European Alps offers an excellent natural laboratory to synthetize climate‐related changes in spring phenology and elevational distribution for a large array of taxonomic groups. This review assesses the climatic changes that have occurred across the European Alps during recent decades, spring phenological changes and upslope shifts of plants, animals and fungi from evidence in published papers and previously unpublished data. Our review provides evidence that spring phenology has been shifting earlier during the past four decades and distribution ranges show an upwards trend for most of the taxonomic groups for which there are sufficient data. The first observed activity of reptiles and terrestrial insects (e.g. butterflies) in spring has shifted significantly earlier, at an average rate of −5.7 and −6.0 days decade−1, respectively. By contrast, the first observed spring activity of semi‐aquatic insects (e.g. dragonflies and damselflies) and amphibians, as well as the singing activity or laying dates of resident birds, show smaller non‐significant trends ranging from −1.0 to +1.3 days decade−1. Leaf‐out and flowering of woody and herbaceous plants showed intermediate trends with mean values of −2.4 and −2.8 days decade−1, respectively. Regarding species distribution, plants, animals and fungi (N = 2133 species) shifted the elevation of maximum abundance (optimum elevation) upslope at a similar pace (on average between +18 and +25 m decade−1) but with substantial differences among taxa. For example, the optimum elevation shifted upward by +36.2 m decade−1 for terrestrial insects and +32.7 m decade−1 for woody plants, whereas it was estimated to range between −1.0 and +11 m decade−1 for semi‐aquatic insects, ferns, birds and wood‐decaying fungi. The upper range limit (leading edge) of most species also shifted upslope with a rate clearly higher for animals (from +47 to +91 m decade−1) than for plants (from +17 to +40 m decade−1), except for semi‐aquatic insects (−4.7 m decade−1). Although regional land‐use changes could partly explain some trends, the consistent upward shift found in almost all taxa all over the Alps is likely reflecting the strong warming and the receding of snow cover that has taken place across the European Alps over recent decades. However, with the possible exception of terrestrial insects, the upward shift of organisms seems currently too slow to track the pace of isotherm shifts induced by climate warming, estimated at about +62 to +71 m decade−1 since 1970. In the light of these results, species interactions are likely to change over multiple trophic levels through phenological and spatial mismatches. This nascent research field deserves greater attention to allow us to anticipate structural and functional changes better at the ecosystem level.

AbstractHuman impacts such as habitat loss, climate change and biological invasions are radically altering biodiversity, with greater effects projected into the future. Evidence suggests human impacts may differ substantially between terrestrial and freshwater ecosystems, but the reasons for these differences are poorly understood. We propose an integrative approach to explain these differences by linking impacts to four fundamental processes that structure communities: dispersal, speciation, species‐level selection and ecological drift. Our goal is to provide process‐based insights into why human impacts, and responses to impacts, may differ across ecosystem types using a mechanistic, eco‐evolutionary comparative framework. To enable these insights, we review and synthesise (i) how the four processes influence diversity and dynamics in terrestrial versus freshwater communities, specifically whether the relative importance of each process differs among ecosystems, and (ii) the pathways by which human impacts can produce divergent responses across ecosystems, due to differences in the strength of processes among ecosystems we identify. Finally, we highlight research gaps and next steps, and discuss how this approach can provide new insights for conservation. By focusing on the processes that shape diversity in communities, we aim to mechanistically link human impacts to ongoing and future changes in ecosystems.

<p>Warmer climate and more frequent extreme droughts will pose major threats to forest ecosystems. Persistence of intra-specific populations of tree species will depend on their tolerance and adaptive capacities to forthcoming climate conditions. However, past demography processes due to post-glacial recolonization can also contribute to the genetic-based differences in growth responses among provenances. In this study, we investigated the impact of climatic conditions on growth traits among 18 provenances of silver fir (<em>Abies alba </em>Mill.) from west, south and eastern Europe growing in two provenance trials established in Switzerland in 1980s. We further assessed whether the differences in growth-related traits across provenances were linked to their genetic differences due to recolonization history and natural selection processes.</p><p>In total 250 individuals were measured and cored for dendrochronological analyses, and different growth-related traits were calculated: i) total tree height and diameter at breast height (DBH), ii) growth-climate relationships using correlations between tree-ring width and monthly climate parameters as well as levels of autocorrelation, and iii) short-term responses to extreme drought using resilience components (resilience, resistance, and recovery) to the severe drought that occurred in the study area in 2003. We also genotyped all the individuals in 150 putatively neutral single nucleotide polymorphisms to define the neutral genetic structure of the population, the neutral genetic differentiation among provenances (<em>F<sub>ST</sub></em>) and the genetic variation among provenances in relation to the total genetic variance in a trait (<em>Q<sub>ST</sub></em>). Signs of natural selection were assessed by two approaches: i) Pearson correlations between the least-square means of provenances of the traits and bioclimatic variables from the seed origin, and ii) <em>Q<sub>ST</sub>-F<sub>ST</sub></em> comparison.</p><p>The studied provenances grouped into three longitudinal clusters reassembling the genetic lineages of refugia from the last glacial maximum: the provenance of the Pyrenees as a sole member of the westernmost cluster, the Central European provenances representing the central cluster and all the eastern European provenances forming the eastern cluster. These three lineages showed differences in growth performance traits (height and DBH), with the trees from the eastern cluster being the top performers. The Pyrenees cluster showed significantly lower recovery and resilience to the extreme drought of 2003 as well as lower values of growth autocorrelation. A <em>Q<sub>ST</sub>-F<sub>ST</sub></em> and correlation analyses with climate of provenance origin suggest that the differences among provenances found in some traits result from natural selection. Our study suggests that post-glacial re-colonization and natural selection are the major drivers explaining the intra-specific variability in growth of silver fir across Europe. These findings provide insights to support assisted gene flow to ensure the persistence of the species in European forests.</p>

Summary Microclimatic effects (light, temperature) are often neglected in phenological studies and little information is known about the impact of resource availability (nutrient and water) on tree’s phenological cycles. Here we experimentally studied spring and autumn phenology in four temperate trees in response to changes in bud albedo (white‐painted vs black‐painted buds), light conditions (nonshaded vs c. 70% shaded), water availability (irrigated, control and reduced precipitation) and nutrients (low vs high availability). We found that higher bud albedo or shade delayed budburst (up to +12 d), indicating that temperature is sensed locally within each bud. Leaf senescence was delayed by high nutrient availability (up to +7 d) and shade conditions (up to +39 d) in all species, except oak. Autumn phenological responses to summer droughts depended on species, with a delay for cherry (+7 d) and an advance for beech (−7 d). The strong phenological effects of bud albedo and light exposure reveal an important role of microclimatic variation on phenology. In addition to the temperature and photoperiod effects, our results suggest a tight interplay between source and sink processes in regulating the end of the seasonal vegetation cycle, which can be largely influenced by resource availability (light, water and nutrients).

Climate change is shifting the growing seasons of plants, affecting species performance and biogeochemical cycles. Yet how the timing of autumn leaf senescence in Northern Hemisphere forests will change remains uncertain. Using satellite, ground, carbon flux, and experimental data, we show that early-season and late-season warming have opposite effects on leaf senescence, with a reversal occurring after the year’s longest day (the summer solstice). Across 84% of the northern forest area, increased temperature and vegetation activity before the solstice led to an earlier senescence onset of, on average, 1.9 ± 0.1 days per °C, whereas warmer post-solstice temperatures extended senescence duration by 2.6 ± 0.1 days per °C. The current trajectories toward an earlier onset and slowed progression of senescence affect Northern Hemisphere–wide trends in growing-season length and forest productivity.

ABSTRACTLong‐term phenological data in alpine regions are often limited to a few locations and thus, little is known about climate‐change‐induced plant phenological shifts above the treeline. Because plant growth initiation in seasonally snow‐covered regions is largely driven by snowmelt timing and local temperature, it is essential to simultaneously track phenological shifts, snowmelt, and near‐ground temperatures. In this study, we make use of ultrasonic snow height sensors installed at climate stations in the Swiss Alps to reveal the phenological advance of grassland ecosystems and relate them to climatic changes over 25 years (1998–2023). When snow is absent, these snow height sensors additionally provide information on plant growth at a uniquely fine temporal scale. We applied a two‐step machine learning algorithm to separate snow‐ from plant‐height measurements, allowing us to determine melt‐out for 122 stations between 1560 and 2950 m a.s.l., and to extract seasonal plant growth signals for a subset of 40 stations used for phenological analyses. We identified the start of growth and calculated temperature trends, focusing particularly on thermal conditions between melt‐out and growth initiation. We observed an advance of green‐up by −2.4 days/decade coinciding with strong warming of up to +0.8°C/decade. Although the timing of snowmelt has not changed significantly over the study period in this focal region, phenological responses to early melt‐out years varied due to differing influences of photoperiodic and thermal constraints, which were not equally important across elevations and communities. Phenological shifts of alpine grasslands are thus likely to become even more pronounced if snowmelt timing advances in the future as predicted. As climate change continues to reshape mountain ecosystems, understanding the interplay between phenological changes and species turnover will be essential for predicting future biodiversity patterns and informing conservation strategies in alpine regions.