Jérôme Poulenard

Rapid glacier retreat is transforming mountain landscapes, exposing terrain where postglacial ecosystems emerge while new opportunities for infrastructure development also arise. These newly ice-free areas are therefore becoming socio-ecological frontiers in which ecosystem development, land use and conservation frameworks increasingly overlap. Yet spatially explicit evidence of where these overlaps occur remains scarce, limiting the ability of governance systems to anticipate emerging conflicts. Here, using the European Alps as a data-rich case study, we pair satellite-derived land cover mapping with inventories of ski infrastructure, hydropower reservoirs and protected areas within the end-of-Little Ice Age glacier footprint. We show that newly exposed terrain already contains emerging vegetated and freshwater habitats, whose regional distribution is mainly modulated by temperature gradients. Concomitantly, ski and hydropower infrastructures already occupy parts of postglacial terrain, even within strictly protected areas, revealing mismatches between formal conservation status and land-use decisions. Emerging postglacial ecosystems fall into a de facto legal vacuum, as current tools encourage reactive, piecemeal decisions that fail to safeguard ecosystem functions and services. We argue for anticipatory stewardship that recognizes glacier and postglacial ecosystems in law and planning as a single transforming system. These regional findings foreshadow a global governance challenge that will intensify as deglaciation expands in regions where deglaciation exposes land to competing ecological, economic and political interests.

Over the past four decades, seasonal snow cover has declined rapidly in temperate alpine regions. However, the fine-scale dynamics of snowmelt preceding the ongoing warming period remain largely unknown, limiting our understanding of the long-term influence of past snow cover on alpine ecosystems. Here we rely upon the spatial similarities in melt-out patterns and a temperature-based model of fractional snow cover area, to reconstruct fine-scale snow cover changes over the past 250 years in instrumented catchments of the southwestern Alps. We provide evidence that, until the 1980s, prolonged snow cover in many late-lying snowfields delayed ecosystem development and explain why current vegetation cover, soil organic matter content, and mineral weathering are significantly lower in these areas than in surrounding ecosystems. These findings highlight the long-term legacy of snow cover on alpine landscapes and underscore the need to re-evaluate its effects on ecosystem structure, functioning, and responsiveness to ongoing changes.

Summary: Increasing climate warming and summer droughts are known to affect mountain plant communities, their functional traits and life strategies. However, little is known about how strongly and efficiently communities respond to climate change, and how tightly plant responses are linked to responses of ecosystem functions. To test this, we transplanted alpine plant communities to subalpine conditions, exposing them to warming and drying. We compared these transplanted communities to alpine and subalpine control communities to assess their responses. Five years after transplantation, we found slower growth (e.g. lower leaf nitrogen) and more outsourcing strategies (e.g. lower specific root length) in the warmer and drier subalpine control communities compared to the alpine controls, probably due to drought. Traits of warmed alpine communities shifted toward subalpine controls. However, neither below‐ nor aboveground traits nor productivity of plants fully acclimated to subalpine conditions. Nevertheless, standard litter decomposition rates, arbuscular colonization and bacterial biomass showed no acclimation lag to the subalpine controls. Significant but insufficient acclimation of plant functional traits and strategies is prone to result in maladapted plant productivity, impairing competitiveness with better adapted subalpine species and leading to the temporally delayed loss of ecosystem features specific to alpine environments.

Soil health degradation is a major threat to European food security, biodiversity, and climate stability. While scientists have debated how to define soil health during recent decades, a quantifiable framework for monitoring, management, and policy remains lacking. We introduce SHERPA (Soil Health Evaluation, Rating Protocol, and Assessment) as a framework and present a first assessment across Europe. Surprisingly, soil health of grasslands is as negatively impacted as cropland soils. Soil erosion, nutrient surplus, and pesticide risk are largely driving poor soil health aligning with reported high biodiversity loss in agricultural land. Forest soils are also surprisingly low in health, mainly because of nitrogen surplus, reflecting documented widespread forest decline from nutrient imbalances. Interactive maps highlight specific threats to soil health across Europe, offering valuable insights for targeted action.

Mountains are particularly vulnerable to climate change, as they are warming at a rate that exceeds the global average, significantly impacting cold‐adapted ecosystems. In these environments, soil organic matter (SOM) stocks are often considerably larger than at lower elevations. These stocks are therefore highly susceptible to global warming and the associated risk of greenhouse gas (GHG) (CO₂, CH₄, N₂O) emissions driven by temperature‐induced increases in SOM mineralisation. In order to quantify these emissions and the change of mineralisation rates under warming, it is necessary to gain an understanding of the annual mineralisation balance. We investigated how warming impacts the duration and intensity of mineralisation in different seasons. The main aim of this study is to quantify alpine SOM mineralisation rates and GHG production under a range of seasonal conditions, including those associated with warming. An in vitro approach was employed to expose alpine topsoils (0–10 cm) to the conditions of key seasonal periods: snow cover, growing season and rainfall/snowmelt. This was achieved by experimentally varying temperature and inflow of precipitation water. Additionally, the soil samples were subjected to a temperature increase of 4°C. The short‐term responses of carbon (C), nitrogen (N) and phosphorus (P) mineralisation and GHG production were monitored. The results demonstrated that alpine soil respiration rates exhibited a twofold increase with a 4°C warming, while the relative proportion of labile SOM demonstrated a decline with rising temperatures. Water saturation from simulated rain and snowmelt played a crucial role in organic matter mineralisation and increased the mineralisation of carbon (+12% to +53%), nitrogen (+20% to +80% of net ammonification) and phosphorus (+50% of net phosphate production). This suggests that nutrients present in the snowpack or the rain were added to the soil. In contrast, soil–water saturation decreased net nitrate production by between 10% and 90%. The results of this study highlight the potential for alpine soil warming to release labile SOM and demonstrate the influence of the snow regime on nutrient and carbon fluxes.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous persistent organic pollutants that accumulate in soils because of their high affinity for soil organic matter (SOM). As these pollutants are toxic to humans and the environment, a better understanding of their fate in the environment is required. This study aimed to assess the PAH distribution within soils according to different soil fractions: the free particulate organic matter (fPOM), the occluded particulate organic matter (oPOM) and the mineral‐associated organic matter (MaOM). PAH contents were measured in bulk soils and SOM fractions of alpine soils along an elevation gradient in the French Alps (Lautaret) from 1920 m to 2840 m a.s.l. A specific PAH distribution was identified, with highest PAH contents in the oPOM, followed by the fPOM, then the MaOM. Organic matter (OM) contents of each fraction can partly explain this distribution, but results of nuclear magnetic resonance (NMR) spectroscopy on fPOM and oPOM also highlighted a correlation between the PAH contents and the degree of decomposition of SOM. This indicates that the PAH distribution may be linked to the formation and transformation of fractions: (i) PAHs in the fPOM correspond to relatively recent deposits and mainly reflect the background contamination, (ii) in the oPOM are the PAHs that resist biodegradation during the transformation of fPOM into oPOM and accumulate in the oPOM; this accumulation may be further enhanced by the formation of aggregates. Finally, (iii) in the MaOM, the lower PAH contents can be explained by the different formation pathway of this fraction and its high degree of decomposition. As the PAH distribution may have an impact on their dynamics in soils, it should be taken into consideration in future research.

Arthropods play a vital role in ecosystems; yet, their distributions remain poorly understood, particularly in mountainous regions. This study delves into the modelling of the distribution of 31 foliar arthropod genera in the French Alps, using a comprehensive approach encompassing multi‐trophic sampling, community DNA metabarcoding and random forest models. The results underscore the significant importance of vegetation structure, such as herbaceous vegetation density, and forest density and heterogeneity, along with climate, in shaping the distributions of most arthropods. These responses to environmental gradients are consistent across trophic groups, with the exception of nectarivores, whose distributions are more sensitive to landscape structure and water availability. By leveraging community DNA metabarcoding, this study sheds light on the understudied drivers of arthropod distributions, emphasizing the importance of modelling across diverse trophic groups to anticipate arthropod responses to global change.

The global retreat of glaciers is dramatically altering mountain and high-latitude landscapes, with new ecosystems developing from apparently barren substrates^1,2,3,4. The study of these emerging ecosystems is critical to understanding how climate change interacts with microhabitat and biotic communities and determines the future of ice-free terrains^1,5. Here, using a comprehensive characterization of ecosystems (soil properties, microclimate, productivity and biodiversity by environmental DNA metabarcoding⁶) across 46 proglacial landscapes worldwide, we found that all the environmental properties change with time since glaciers retreated, and that temperature modulates the accumulation of soil nutrients. The richness of bacteria, fungi, plants and animals increases with time since deglaciation, but their temporal patterns differ. Microorganisms colonized most rapidly in the first decades after glacier retreat, whereas most macroorganisms took longer. Increased habitat suitability, growing complexity of biotic interactions and temporal colonization all contribute to the increase in biodiversity over time. These processes also modify community composition for all the groups of organisms. Plant communities show positive links with all other biodiversity components and have a key role in ecosystem development. These unifying patterns provide new insights into the early dynamics of deglaciated terrains and highlight the need for integrated surveillance of their multiple environmental properties⁵.

Summary: The development of terrestrial ecosystems depends greatly on plant mutualists such as mycorrhizal fungi. The global retreat of glaciers exposes nutrient‐poor substrates in extreme environments and provides a unique opportunity to study early successions of mycorrhizal fungi by assessing their dynamics and drivers. We combined environmental DNA metabarcoding and measurements of local conditions to assess the succession of mycorrhizal communities during soil development in 46 glacier forelands around the globe, testing whether dynamics and drivers differ between mycorrhizal types. Mycorrhizal fungi colonized deglaciated areas very quickly (< 10 yr), with arbuscular mycorrhizal fungi tending to become more diverse through time compared to ectomycorrhizal fungi. Both alpha‐ and beta‐diversity of arbuscular mycorrhizal fungi were significantly related to time since glacier retreat and plant communities, while microclimate and primary productivity were more important for ectomycorrhizal fungi. The richness and composition of mycorrhizal communities were also significantly explained by soil chemistry, highlighting the importance of microhabitat for community dynamics. The acceleration of ice melt and the modifications of microclimate forecasted by climate change scenarios are expected to impact the diversity of mycorrhizal partners. These changes could alter the interactions underlying biotic colonization and belowground–aboveground linkages, with multifaceted impacts on soil development and associated ecological processes.

A major feature of the Anthropocene is the drastic increase in global soil erosion. Soil erosion is threatening Earth habitability not only as soils are an essential component of the Earth system but also because societies depend on soils. However, proper quantification of the impact of human activities on erosion over thousands of years is still lacking. This is particularly crucial in mountainous areas, where the highest erosion rates are recorded. Here we use the Lake Bourget catchment, one of the largest in the European Alps, to estimate quantitatively the impact of human activities on erosion. Based on a multi-proxy, source-to-sink approach relying on isotopic geochemistry, we discriminate the effects of climate fluctuations from those of human activities on erosion over the last 10,000 years. We demonstrate that until 3800 years ago, climate is the only driver of erosion. From that time on, climate alone cannot explain the measured rates of erosion. Thanks to an unprecedented regional paleoenvironmental reconstruction, we highlight that the development of pastoralism at high altitudes from the Bronze Age onwards and the extension of agriculture starting in the Middle Ages were key factors in the drastic increase in erosion observed in the Alps.