The European Long-Term Ecosystem, Critical Zone, and Socio-Ecological Research Infrastructure (eLTER RI) aims to provide a continental-scale, site-based network for observing, understanding, and addressing major ecological, geochemical, and socio-ecological challenges. A core element of eLTER RI is the implementation of the eLTER Standard Observations (SOs), which establish a harmonised framework for the systematic collection and analysis of long-term environmental data across a diverse range of ecosystems. Ensuring methodological consistency and interoperability by the SOs is imperative in order to create a shared observational basis. Such a basis is essential for large-scale synthesis and international collaboration, particularly within the context of Critical Zone Science.The eLTER Standard Observations adopt a multidisciplinary perspective, integrating biological, hydrological, geochemical, climatic, soil-related, and socio-economic variables. Core thematic domains include biodiversity, primary production, water quality, nutrient and carbon cycling, soil processes, and climate dynamics. This integrated design explicitly supports Critical Zone Science by enabling the coupled analysis of processes spanning the Earth’s surface, from the vegetation canopy through soils and groundwater to the underlying geology, while simultaneously accounting for human influences. Standardisation across sites and regions ensures data comparability over space and time, facilitating cross-site analyses, model development, and the identification of patterns and drivers of change.The SOs are closely aligned with the concept of Essential Variables (EVs) and cover key elements of Essential Climate Variables (ECVs), Essential Biodiversity Variables (EBVs), and Essential Socio-Economic Variables (ESVs). Through this coverage, the SOs provide a comprehensive observational foundation to assess ecosystem status, track long-term trends, and analyse human–nature interactions. By harmonising observations and explicitly linking Critical Zone processes to existing EV frameworks, eLTER strengthens connections between national and international research initiatives and enhances the contribution of European long-term ecosystem research to global observation systems.This presentation will outline the scope, methodology, and scientific relevance of the eLTER Standard Observations, with a particular emphasis on their role in fostering international collaboration in Critical Zone Science. It will demonstrate how the SOs support integrative ecosystem research and contribute to addressing global challenges such as climate change, biodiversity loss, and sustainable resource management through coordinated, long-term, and comparable observations.

Abstract The development of harmonized, standardized, and integrated environmental observation systems is a key challenge in Earth system science. Such capability is essential for advancing the interdisciplinary research needed to improve understanding of the Earth system and support global sustainability. The Integrated European Long‐Term Ecosystem, Critical Zone and Socio‐ecological Research Infrastructure (eLTER RI) is a recently developed pan‐European network of in situ research sites that facilitates the collection long‐term, comprehensive observation, analysis, and modeling of environmental and ecosystem change. This initiative focuses on Europe's primary ecosystems, encompassing the atmosphere, geosphere, hydrosphere, biosphere, and their socio‐ecological interactions with the anthroposphere. A fundamental prerequisite for effective environmental monitoring and observation is a standardized and harmonized design that facilitates consistent and comparable environmental data across diverse spatial and temporal scales. The objective of this paper is to introduce the eLTER Framework of Standard Observations (eLTER SO) as a harmonized conceptual and operational standard for long‐term, integrated in situ environmental observations, and to demonstrate how it supports consistent cross‐sphere monitoring and international collaboration in environmental research. The eLTER SO delineates essential ecosystem variables, their measurement methods, and protocols. These Standard Observations (SOs) constitute the conceptual foundation of eLTER RI and provide a basis for overcoming existing disciplinary barriers to the international harmonization of environmental research and a foundation for cross‐sphere observation concepts. The eLTER SO combines the scientific‐academic perspective, as known from “classical” Essential Variable concepts, with the operational perspective required for the establishment and long‐term operation of in situ observatories.

The Earth is facing several environmental challenges on a global scale, often called “Grand Challenges” (https://www.wcrp-climate.org/grand-challenges/). The growing population (https://pdp.unfpa.org) needs fresh air, fresh water, food and energy, while at the same time climate is changing, many cities have challenges with air quality, biodiversity is decreasing and supplies of fresh water, food and energy are diminishing. Since these Grand Challenges are highly connected and interlinked, not only with each other but also with e.g. pandemics, they cannot be solved separately since potential solutions are tightly coupled with each other. However, the solutions may also include unexpected trade-offs. Therefore, integrated, comprehensive, big open data are required, together with a research and innovation framework in which a multidisciplinary research with critical mass of scientists utilising proper resources is connected to fast-tracked policy making and wide stakeholder community. This allows aiming for practical solutions based on deep scientific understanding. The global challenges are intimately linked to interactions and feedbacks between the different compartments of the planet Earth at different spatial and temporal scales. Fundamentally, the atmosphere is closely interconnected with various other parts of the Earth, including biosphere, hydrosphere, cryosphere and lithosphere as well as urban surfaces over a range of time and spatial scales varying from seconds to millennia. The sources, sinks and atmospheric concentrations of reactive trace gases, greenhouse gases and aerosol particles depend strongly on each other via physical, chemical and biological processes. Furthermore, both human actions and natural feedback mechanisms between the biosphere and atmosphere have substantial impacts on interactions between these atmospheric constituents and their influences on air quality and climate. To be able to meet global grand challenges we need comprehensive open data with proper metadata, along with open science. The large data sets from ground-base in situ observations, ground and satellite remote sensing and multiscale modelling need to be utilized seamlessly. Here we demonstrate the power of the SMEAR (Station for Measuring Earth surface – Atmosphere Relations) concept via several examples, such as detection of new particle formation and their subsequent growth, quantifying atmosphere-ecosystem feedback loops, combining comprehensive observations with emergency science and services, as well as studying the effect of COVID restrictions on different air quality and climate variables. Furthermore we show how from feedback loop analyses we develop CarbonSink+ concept. The future needs and the potential of comprehensive observations of the environment are also summarized.

Clouds play a vital role in the Earth's radiation budget, with low-level clouds having a net cooling effect. Evidence shows that forests alter low-level clouds' formation and physical properties (e.g., [1-3]). In their turn, clouds modify radiation transfer, influencing near-surface variables and forest carbon uptake. Shallow cumulus clouds can enhance photosynthesis due to the diffuse fertilization effect, and the relative increase in photosynthesis is most significant in boreal forests compared to other ecosystems [4]. All this evidence suggests a strong atmosphere-biosphere link for boreal forests. We use long-term observations at SMEAR II station in Finland and satellite data sets to study how air mass transformation over boreal forests changes the optical properties of low-level clouds. Further, we assess the dynamics of photosynthesis and net ecosystem exchange in response to changing cloud properties and near-surface variables under different low-level clouds. We show that stratus clouds dampen photosynthesis, and the effect is amplified with the time spent by an air mass over a forest. Oppositely, cumulus clouds enhance photosynthesis compared to the clear sky conditions. If an air mass is exposed to the boreal forest for several days, and cumulus clouds form during the daytime, photosynthesis is efficient, and clouds' transmittance somewhat decreases. Our results suggest that shallow cumulus clouds formed in an air mass interacting with boreal forest can become more reflective. At the same time, these clouds provide ideal conditions for enhanced boreal forest carbon uptake.References[1] Teuling, A. J., Taylor, C. M., Meirink, J. F., Melsen, L. A., Miralles, D. G., van Heerwaarden, C. C., Vautard, R., Stegehuis, A. I., Nabuurs, G.-J., and de Arellano, J. V.-G.: Observational evidence for cloud cover enhancement over western European forests, Nat. Commun., 8, 14065, 2017. [2] Yli-Juuti, T., Mielonen, T., Heikkinen, L., Arola, A., Ehn, M., Isokääntä, S., Keskinen, H.-M., Kulmala, M., Laakso, A., Lipponen, A., Luoma, K., Mikkonen, S., Nieminen, T., Paasonen, P., Petäjä, T., Romakkaniemi, S., Tonttila, J., Kokkola, H., and Virtanen, A.: Significance of the organic aerosol driven climate feedback in the boreal area, Nat. Commun., 12, 5637, 2021. [3] Petäjä, T., Tabakova, K., Manninen, A., Ezhova, E., O'Connor, E., Moisseev, D., Sinclair, V. A., Backman, J., Levula, J., Luoma, K., Virkkula, A., Paramonov, M., Räty, M., Äijälä, M., Heikkinen, L., Ehn, M., Sipilä, M., Yli-Juuti, T., Virtanen, A., Ritsche, M., Hickmon, N., Pulik, G., Rosenfeld, D., Worsnop, D. R., Bäck, J., Kulmala, M., and Kerminen, V.-M.: Influence of biogenic emissions from boreal forests on aerosol–cloud interactions, Nat. Geosci., 15, 42–47, 2022. [4] Zhou, H., Yue, X., Lei, Y., Zhang, T., Tian, C., Ma, Y., & Cao, Y.: Responses of gross primary productivity to diffuse radiation at global FLUXNET sites. Atmospheric Environment, 244, 117905, 2021.

To tackle the planetary environmental and climate crisis and meet the United Nations’ Sustainable Development Goals (SDGs), we must fully leverage the potential of Earth observations (EO). This involves integrating globally sourced data on the atmosphere, hydrosphere, cryosphere, lithosphere, along with ecological and socio-economic information. By harmonizing and integrating these diverse data sources, we can more effectively incorporate observational data into multi-scale modeling and artificial intelligence (AI) frameworks. This paper is based on discussions from the “Towards Global Earth Observatory” workshop held from May 8–10, 2023, organized by the World Meteorological Organization (WMO) and the Atmosphere and Climate Competence Center (ACCC), in collaboration with the Institute for Atmospheric and Earth System Research (INAR) at the University of Helsinki. The current state of EO and data repositories is fragmented, highlighting the need for a more integrated approach to establish a new global Ground-Based Earth Observatory (GGBEO). Here, we summarize the current status of selected in-situ and ground-based remote sensing observation systems and outline future actions and recommendations to meet scientific, societal, and economic needs. In addition, we identify key steps to create a coordinated and comprehensive GGBEO system that leverages existing investments, networks, and infrastructures. This system would integrate regional and global ground-based in situ and remote sensing systems, marine, and airborne observational data. An integrated approach should aim for seamless coordination, interoperable and harmonized data repositories, easily searchable and accessible data, and sustainable long-term funding.

Ice-nucleating particles (INPs) facilitate the heterogeneous freezing of cloud droplets and thus modify cloud properties. Hence, it is important to understand the sources of INPs. During the HyICE-2018 campaign, which took place in the boreal forest of Hyytiälä, substantial concentrations of airborne heat-sensitive biological INPs were observed, despite many potential biological sources of INPs being snow-covered. A potential source of INPs that were not covered in snow was lichens that grow on trees; hence, we investigated these lichens as a potential source of biological INPs in this boreal forest environment. INPs derived from lichen sampled during HyICE-2018 are shown to nucleate ice at temperatures as warm as −5 °C with 103 INPs per gram of lichen. Successive filtration to smaller sizes removes some of the most active INPs in suspension, but substantial activity remains, even when filtering to 0.1 µm. The small size of the INPs from lichen means they have the potential to either be emitted directly into the atmosphere or be associated with larger particles, such as lichenous reproductive aerosol types (spores or diaspores). We also show that the INPs from lichens from Hyytiälä are sensitive to heat, which is similar to the INPs sampled from the atmosphere of Hyytiälä and consistent with the presence of ice-active proteins. Adding to previous evidence of lichenous INPs, this study shows that lichens from a European boreal forest in Hyytiälä harbour INPs. This novel finding may be especially important in this snow-covered habitat where few, if any, other biological INP sources are available. The great terrestrial abundance of lichens in Hyytiälä, and around the world, calls for further research to combine their ice-nucleating ability with dispersal studies to evaluate the flux of lichenous INPs into the atmosphere, as well as to what extent these particles reach heights and locations where they might influence cloud properties.

In an era of unprecedented environmental change, the need for long-term, integrated ecosystem research has never been more urgent. The first eLTER Science Conference brings together a vibrant community of researchers, site and platform coordinators, and visionaries dedicated to understanding and safeguarding the complex systems that sustain life on Earth. This proceeding includes all contributions to the first eLTER Science Conference in June 2025 in Tampere, Finland. The Conference is a pivotal moment in our shared journey toward deeper understanding, collaboration, and stewardship of our planet's complex socio-ecological systems. It marks an important milestone in the scientific work towards the Whole Systems Approach that is the unique foundation of the eLTER RI, addressing the Earth system at different spatial and temporal scales in order to answer many of the burning scientific and societal questions of our time. In the Anthropocene, environmental research is ever more challenged to develop a holistic approach for understanding the compounded impacts of the multiple stressors on our ecosystems, including, e.g., climate change, biodiversity loss, soil degradation, pollution, and unsustainable resource use. No scientific community can address these challenges in isolation from others. Therefore, the eLTER Science Conference is a unique opportunity to hear and see how different communities and disciplines gather forces to study not only the different spheres (geo-, hydro-, bio-, atmo-, and socio-sphere), but especially the linkages amongst them on the habitable skin of the Earth. The high-level scientific and social programme of the Conference encourages diversity of approaches, exchange between generations of scientists, and inclusivity in the spirit of promoting inter- and trans-disciplinarity. The presentations highlight the key elements of eLTER’s vision: advancing integrated, long-term environmental research, promoting interdisciplinary collaboration, and supporting policy-relevant science for sustainability. The workshops offer a chance for hands-on engagement with various practical subjects while also exploring themes through artistic perspectives. The Conference week is composed of high-level keynote lectures, oral and poster sessions, inspirational exhibitions, workshops, and field trips, relevant for researchers from Europe and globally. The transdisciplinary dialogue is forming an important, cross-cutting element to the Conference program. Altogether 335 participants from 44 countries and 226 institutions will contribute their latest findings to the programme. The 25 prominent Keynotes will address their own research themes in a broad and comprehensive manner. Early career researchers (83) ensure fresh perspectives and energy to continue the ongoing renewal of the scientific enterprise. Interestingly, a common thread runs through many of the sessions: the word ‘Integration’ features in the titles of seven of them. This highlights a strong, shared ambition among participants to deepen collaboration not just within their own disciplines, but across the wider research landscape. It underscores a collective push toward developing harmonised methods and tools that can support more impactful, high-quality science. At the same time, it sends a clear message to the broader environmental science community: eLTER is open for collaboration and eager to connect. Beyond the rich scientific agenda, the eLTER Science Conference offers a diverse and engaging social programme, including Conference dinner on a charming Viikinsaari island and four guided excursions, each offering a unique perspective on Finland's diverse ecosystems and long-term ecological research initiatives, and providing participants with immersive experiences into Finland's ecological research and conservation efforts. The Scientific Committee ensured the high-level scientific content of the Conference. The Organising Committee was led by Jaana Bäck and Jerome Gaillardet, and included Paulina Rajewicz, Nina Hobbhahn, Alexandra Tzvetkova, and Michael Mirtl; in addition, Benat Olascoaga Gracia, Allan Souza, Janne Korhonen, and Syed Ashraful Alam and the 12 conference assistants contributed to making the Conference a success. With this Proceedings, we welcome all authors and other attendees to the first eLTER Science Conference, a landmark event in shaping the future of integrated ecosystem, critical zone, and socio-ecological research across Europe and beyond. We thank all contributors and participants for their valuable insights and commitment, and we look forward to continuing this journey — united in eLTER’s vision for a more sustainable and resilient future. The conference is organised by the EU-funded eLTER PLUS Advanced Community project (Grant Agreement No. 871128) and supported financially by the University of Helsinki Fig. 1, the Federation of Finnish Learned Societies Fig. 2, Metsämiesten Säätiö Foundation Fig. 3, and the Atmosphere and Climate Competence Center (ACCCFig. 4) Flagship of the Research Council of Finland.

Research Infrastructures (RIs) are key to face the grand environmental challenges humanity encounters by providing standardized, large-scale data. However, the in-situ facilities of RIs frequently exhibit a sampling bias. A promising and cost-efficient approach to mitigate sampling bias is ”co-location”, i.e. the usage of in-situ facilities by more than one RI.We investigated the bias mitigation potential of co-location in Europe exemplarily for eLTER RI. Therefore, we added 50 candidate facilities from seven pan-European RIs and peer networks to the eLTER RI and investigated bias reduction for current environmental conditions and anticipated changes under RCP4.5 and RCP8.5. Additionally, we investigated which facilities contribute to bias reduction.It required 5, 10 and 25 of 832 candidate facilities, respectively, to reduce sampling bias for RCP8.5, RCP4.5 and current conditions. However, after the addition of 50 sites, 60 % (RCP4.5) to 80 % (current conditions) of the initial bias remained. Bias reduction was most conclusive in Eastern Europe and Fennoscandia, while bias in the Mediterranean was only removed for RCP4.5. The analysis recommended 197 candidate facilities for bias reduction, 156 in Fennoscandia, Poland, Lithuania and Spain.Thus, co-location alone can mitigate but not overcome bias in eLTER RI. The mitigation potential was limited by the small number of candidate facilities in the Iberian Peninsula. Therefore, for eLTER RI we recommend: (i) aim to co-locate the facilities recommended by this analysis, (ii) search for or establish further facilities in the Iberian Peninsula and (iii) mitigate bias in data analyses by using less biased or unbiased subsets.

The distributed Integrated European Long-Term Ecosystem, critical zone and socio-ecological Research Infrastructure – eLTER RI – comprises ecosystem research sites and socio-ecological research platforms. The in-situ facilities are designed to measure standardized observation variables for each of the five ecosystem spheres – sociosphere, atmosphere, hydrosphere, geosphere, biosphere. Optimisation of the spatial distribution of in-situ facilities within a research infrastructure is often based on analyses of transferability or representativity revealing under-, well or overrepresented conditions and locations. However, these current conditions shift dramatically due to Global Change, posing fundamental research challenges. For eLTER RI, land use change (LUC) and climate change manifesting as climatic pressures on ecosystems were identified as important emerging research challenges. Therefore, we investigated both the current coverage of environmental and socio-ecological gradients by the eLTER RI as well as its fitness for research challenges. To investigate the current state, we (i) conducted a survey to describe the emerging eLTER RI and (ii) identified the most critical gaps in its coverage of six Reference Parameters. To investigate the suitability of the eLTER RI to address the two key research challenges, we iii) derived metrics that reflect said research challenges, iv) estimated eLTER RI’s fitness for these future research challenges, and v) compared the eLTER RI's coverage of current environmental and socio-ecological gradients with its fitness for future research challenges. Finally, we vi) derived recommendations for the further development of the eLTER RI. In its current state, three distinct geospatial gaps were identified: the Iberian Gap, the Eastern Gap, and the Nordic Gap. These gaps resulted mainly from the underrepresentation of agricultural lands, regions with low economic density, mesic and dry regions as well as the Mediterranean, Continental and Boreal biogeoregions. The patterns of underrepresentation appeared to be driven by access to funding resources. Several sites that responded to the survey but do currently not fulfil the infrastructural requirements of the eLTER RI bear potential to contribute to gap closure. Additionally, incorporating research facilities from other research infrastructures or monitoring networks into the eLTER RI could cost-efficiently counteract gaps. Regarding the fitness for research challenges, the derived metrics depicted the relevant research challenges well and spatial patterns of the emerging research challenges were consistent between scenarios. The eLTER RI covers all facets of emerging research challenges, but is tremendously spatially biased. Climatic hotspots regarding biotemperature and the seasonality of water availability will be overemphasised by the eLTER RI, while precipitation and LUC hotspots are underrepresented. Gaps that were assumed to be stable for a variety of potential futures manifested in the Southern Iberian Peninsula, Poland, Finland, Sweden and Norway. Closing gaps regarding the current coverage of environmental and socio-ecological gradients is of highest priority for the spatial network development. Primarily, regions where overlap to gaps in the Fitness for Research Challenges exists should be targeted. Consequently, this work suggests that the development of the eLTER RI and other research infrastructure should be adapted based on current and anticipated future conditions, since the spatial design can and should be optimised for both simultaneously.

We explore how the Global Ecosystem Research Infrastructure (GERI) proposes a pathway for other Networks and Networks-of-Networks (NoNs) can work together and accelerate collaborations and data harmonization to address global environmental challenges. Recognizing that contemporary environmental issues transcend geopolitical boundaries, we advocate for collaborative frameworks that integrate top-down structured ecosystems research infrastructures (ERIs) with bottom-up environmental networks (ENs). We highlight the unique characteristics of ERIs, including their long-term data collection capabilities and structured governance, in contrast to the flexible and innovative nature of ENs. We address the technical and organizational barriers that hinder effective collaboration and data sharing among these entities and draw upon two use cases: ecological drought; and the integration of Mexican ENs into a NoNs framework. ecological drought; and the integration of Mexican ENs into a NoNs framework. Through workshops and strategic leadership tools, we established a shared understanding and collective identity among these diverse stakeholders, and fosteri sustainable organizational practices and enhance global environmental observations. Our findings underscore the importance of addressing cultural dynamics and building mutual trust to ensure the long-term sustainability of collaborative efforts in ecological research and data integration. Together top-down ERIs that support standardized and long-term observational continuity, and bottom-up ENs that introduce new perspectives and data types, provide the complementarity to support the data and human capital required to address the Grand Challenges of global environmental change.

Plant biogenic volatile organic compounds (BVOCs) play a critical role in atmospheric chemistry by forming ozone and secondary organic aerosols, making them key agents in regulating air quality and influencing climate. However, current models usually rely on limited site-specific data and indirect inputs, introducing significant uncertainties in BVOC predictions. We propose remote sensing of photosynthetic optical signals, such as the carotenoid-sensitive photochemical reflectance index (PRI) and Chl/carotenoid index (CCI) and sun-induced fluorescence (SIF), to help reduce these uncertainties. These indices are functionally linked, albeit indirectly for SIF, to isoprenoid BVOC emissions via carotenoid biosynthesis. In this Viewpoint, we explore the potential of this connection to estimate and constrain BVOC emissions at multiple scales. We synthesize key aspects, recent advances, and research uncertainties, and propose empirical and scaling roadmaps for integrating optical signals with BVOCs, highlighting their connectivity under abiotic stress (e.g. drought, heat) and across seasonal dynamics. This integration represents a critical step toward reducing model uncertainties, improving large-scale BVOC monitoring, and enhancing our understanding of their role in atmospheric chemistry and climate. By providing a more comprehensive framework for linking plant physiological processes to atmospheric chemistry, this approach strengthens our ability to predict ecosystem responses to climate change.

Observational data collected in December 2014 at the base camp of Mount Everest, Nepal, indicated frequent new particle formation events of pure biogenic origin. Those events were speculated to be controlled by the along-valley winds forming in the valley connecting the Indo-Gangetic plain to the observational site, the Nepal Climate Observatory-Pyramid. The valley winds funnel highly oxygenated organic molecules of biogenic origin to higher elevations where they nucleate. The mechanism was referred to as "The Himalayan aerosol factory". Its geographical extent and climate implications are currently unknown. In view of this, we conducted numerical chemical model simulations to corroborate the presence of the mechanism, and to quantify its geographical extent. Our numerical simulations confirmed that biogenic emissions located in the valleys can be converted into ultra-low volatility organic compounds, transported to the observational site by the along-valley winds, and therein nucleate. The overall time scale of the process, from the release of biogenic emissions to the conversion to ultra-low volatile organic compounds to the arrival time at the observational site, was found to be around 4 hours, consistent with the predicted along-valley winds intensity and the geographical distribution of biogenic emissions. A first estimation of the maximum injection height of biogenic particles, and highly oxygenated organic molecules, indicated the presence of efficient nucleating gases and biogenic particles at an elevation as high as 5000-6000 m a.s.l. These results suggest that the Himalayan chain, under specific weather conditions, is a main contributor to the biogenic aerosol loads in the free troposphere. Considering these findings, field campaigns, especially at the entrance of the valley's floors, and research consortia supporting atmospheric research in Asian mountain regions, are highly encouraged.

Optimisation of the spatial arrangement of distributed in-situ research infrastructures is often based on analyses of the transferability or representativity of its current site network. However, current conditions shift dramatically due to Global Change, posing fundamental challenges for the establishment of research infrastructures. Climate and land use change (LUC) are among the ecologically most relevant Global Change aspects. This study analysed how well the geographical distribution of the Integrated European Long-Term Ecosystem, critical zone and socio-ecological Research Infrastructure (eLTER RI) represents these future changes at European scale. Therefore, we (i) derived ecologically meaningful metrics depicting both changes and identified associated hotspots, (ii) estimated eLTER RI's fitness for these Global Change aspects, and (iii) compared the eLTER RI's coverage of current environmental and socio-ecological gradients with its representation of climate change and LUC. Climate change and LUC were quantified as Pressures, expressing changes in biotemperature (BT Pressure), precipitation (P Pressures), seasonal water availability (SPEI Pressure) and Land Use (Land Use Change Pressure) relative to a location's baseline conditions. Individual Pressures revealed consistent spatial patterns of different magnitude between the RCP4.5 and RCP8.5 scenarios. The eLTER RI covers a wide variety of Pressures, but is spatially biased. BT and SPEI Pressure Hotspots are overrepresented by the eLTER RI, while P Pressure and Land Use Change Pressure Hotspots are underrepresented. Gaps in eLTER RI coverage manifested in both RCP scenarios in the Southern Iberian Peninsula, Poland, and Fennoscandia. Gap locations are assumed to be consistent under various potential futures and they largely overlap with gaps already identified for current conditions. Therefore, we recommend primarily targeting overlapping gaps, with an additional focus on underrepresented hotspot areas. Consequently, incorporating future conditions allows sharpening of the network design of RI's in-situ facilities. This is a key step to transfer local measurements into continental-scale policy support.

Introduction The IRISCC ( Integrated Research Infrastructure Services for Climate Change risks, www.iriscc.eu ) project delivers scientific and knowledge-based services aimed to support society’s capacity to address and strengthen resilience to climate change. IRISCC will establish a comprehensive service catalogue for research, innovation, training, and digital services related to climate risks and their determinants (hazards, exposures and vulnerabilities) (Fig. 1). Services are offered by 93 service providers through national and international research infrastructures (RIs), eLTER being one of them. IRISCC is an EU funded 4,5-year project (project number 101131261) launched in spring 2024 and coordinated by Natural Resources Institute Finland (Luke). It brings together 79 partners representing various research domains, including Earth systems, environmental health and social sciences. IRISCC will establish a “one-stop-shop” on climate risk related RI services and offer transnational and virtual access through open calls during years 2025–2027. Approach In the core of IRISCC is the provision of robust RI services geared towards climate change risk research. These services include transnational access (TA) to research facilities and virtual access (VA) to harmonised data, as well as standardised methodologies and cutting-edge tools for understanding climate change driven risks. The integrated approach merges the analysis of hazards, exposure, and vulnerability, enabling a comprehensive understanding of climate change driven risks. By fostering multi-, inter-, and transdisciplinary collaboration, IRISCC aims to empower users to predict, mitigate, and adapt to the risks and impacts posed by climate change on human, production and natural systems. The IRISCC project will develop its services from first release of multidisciplinary services towards interdisciplinary and transdisciplinary approaches by science demonstrators and service design labs. IRISCC and eLTER With 25 of eLTER research facilities included in the IRISCC Catalogue of Services, eLTER is one of the 14 RIs contributing to the services provided through IRISCC. eLTER is also involved in providing strategic leadership as a member in the project’s internal board, IRISCC Infrastructure Board. eLTER contributes to co-creation of novel research services thus advancing our understanding of socio-ecological transformations. Conclusions By summer 2025, IRISCC has launched its first suite of services and the first TA call is open. The services will gradually increase. The second release taking place in spring 2026 will include more integrated RI services and the third release in spring 2027 will include transdisciplinary by integrating knowledge services co-designed with societal actors. The IRISCC Catalogue of Services marks a milestone in the project's contribution to advancing environmental science, transdiciplinary and resilience-building efforts. This presentation will showcase the newly released IRISCC services and the applications of the follow up service releases in advancing research on climate risks, disaster risk reduction, and cross-sectoral environmental integration. It will also discuss how IRISCC can support transformative change and emphasises the role of integrated RIs in delivering actionable knowledge to researchers, policymakers, and society. The IRISCC approach not only supports multi- and transdisciplinary research but also strengthens the pathways for translating scientific advancements into effective policies and practical solutions. IRISCC is positioned as a pivotal contributor in the quest to predict, mitigate, and adapt to the complex challenges arising from climate change. We encourage eLTER Science Conference participants to familiarizing themselves with IRISCC services for climate change related risks and, when feasible, applying for transnational and virtual access through IRISCC: https://www.iriscc.eu/catalogue-of-services, https://www.iriscc.eu/open-calls.

Forests deliver essential ecosystem services that can be impacted by climate, land use and above ground biodiversity changes. Assessment of such impacts can be achieved through ecosystem modeling of interlinked above- and below-ground processes. In this study, the one-dimensional Integrated Critical Zone (1D-ICZ) model was used to simulate the soil functions of two mature forested ecosystems: Zöbelboden in Austria and Hyytiälä in Finland. Both are long-term ecosystem research (LTER) sites with extensive monitoring data. The model was initialized and calibrated using long-term observations and simulated the gross primary production (GPP), the total soil C stock and the concentrations of several components of soil chemistry. The C and N content of Zöbelboden soils (82.55 tC/ha and 3.76 tN/ha) are higher than Hyytiälä (38.61 tC/ha and 1.33 tN/ha) reflecting higher particulate organic matter (POM) accumulation. Temperature and light were found to be the primary limiting factors of plant growth in both sites, and precipitation a limiting factor only at Hyytiälä. Regarding the quantification of soil functions at Zöbelboden, GPP was 15.6 tC/ha/yr, soil C stock 82.6 tC/ha, N stock 3.8 tN/ha and soil CO2 flux 0.04 tC/ha/yr while for Hyytiala, GPP was 11.6 tC/ha/yr, soil C stock 38.6 tC/ha, N stock 1.3 tN/ha and soil CO2 flux 0.03 tC/ha/yr. The model can be used to understand the limitations of plant growth and carbon sequestration, processes significant to climate mitigation.

Driven by the increasing awareness that innovative approaches to solving the problems at hand in our complex human-environment interactions require closer collaboration among scientific disciplines and communities, inter- and transdisciplinary integration is continuously gaining importance in R&D agendas and Research Infrastructure (RI) development strategies. In addition, the complexity and costs of RIs have substantially increased in many realms triggered by technological developments and the need to organize beyond national and continental boundaries. This suggests multi-, inter- and transdisciplinary collaborations, sharing and multiple usage of infrastructures. Alignments of infrastructure developments needed for this purpose require a conceptual framework for disciplinary integration suited for identifying common approaches and resulting infrastructure design and service components. The talk reports recent advancements in building a common theoretical base between major communities that is - inter alia - underlying the ongoing implementation of the Integrated European Ecosystem, critical zone and socio-ecological Research Infrastructure (eLTER RI). An overview of considered theories on within- and cross-scale interactions and feedback loops will be given and the pathway to the eLTER "Whole System Approach” will be presented. We will also expand on the potential of such a unifying approach in theory-guided integration and division of tasks amongst related environmental RIs. Expected practical implications are answers to questions like where concretely existing and planned European environmental RIs are challenged to interact in response to common overarching questions, and what practical fora and mechanisms (across RIs) would be needed to bridge the gap between research teams driven (bottom-up) efforts and the centralistic RI design and operations.

Introduction Cosmic-ray neutron sensors (CRNSs) have been used worldwide to assess soil moisture changes continuously and non-destructively at scales of less than kilometers. The method is based on inverse correlation between cosmic-ray neutron intensity and soil moisture, as low-energy neutron intensity above the soil depends greatly on the hydrogen content of the soil (Zreda 2008). On the field scale, the effective range of the sensor is from 130 to 240 m and penetration depth from 15 to 83 cm depending on soil moistness, decreasing exponentially with distance from the sensor (Köhli 2015). CRNSs have been used in diverse environments, such as grasslands, agricultural fields and forest ecosystems, various climatic zones and more than ten years in Europe (Bogena 2022). Here we attempt to calibrate the CRNS soil moisture estimation process for three boreal coniferous forests stands in southern and northern Finland and compare the results with data from point measurements of soil moisture sensors. Since most of the CRNS research has been conducted further south in Europe, these will be novel results from CRNS measurements of boreal forests in northern Europe, partly even further north than the Arctic Circle. Materials and methods Three CRNSs (StyX Neutronica Black Puppet SP; Fig. 1) were installed in 2022 at two University of Helsinki field sites, two at the Station for Measuring Ecosystem-Atmosphere Relations (SMEAR) II (61.51°N, 24.17°E, 181 a.s.l) near Hyytiälä forest station in southern Finland and one at SMEAR I (67°46’N, 29°35’E, 390 a.s.l) on Kotovaara hill, near Värriö subarctic research station in eastern Finnish Lapland. SMEAR II in southern Finland has two sensors, one located to call “hill” and other called “hollow” sites. The forest around CRNS “hill” is a 63-years-old Scots pine ( Pinus sylvestris L.) stand with undergrowth of Norway spruce ( Picea abies (L.) Karst.), and around “hollow” is dominated by 60–100-years-old Norway spruces (Kolari 2022). The soil above the bedrock around “hill” sensor is haplic podsol on glacial till (FAO 1988), and the soil depth is approximately 0.5–1.0 m. “Hollow” site has a small a stream flowing in wet seasons near the sensor. Forest around SMEAR I in northern Finland is naturally generated Scots pine stand, which has estimated to be on average approximately 70–80 years old (Matkala 2021). Soil type is haplic podsol on sandy till (FAO 1988), and the soil depth is approximately 0.5 m. Moisture calibration was conducted by taking volumetric soil samples from different directions, distances and various depths from the sensors, based on Schrön (2017). Moisture content of the samples was determined gravimetrically. Soil samples from SMEAR II “hill” were collected from six different directions at 7, 40 and 100 meters from the sensor in August 2022. Soil samples from SMEAR II “hollow” were collected from four different directions at 4, 24 and 70 meters from the sensor in August 2023. Humus layer was sampled, and soil samples were sampled from 5 or 6 different depths up to 30 cm. Soil samples from SMEAR I were collected from six different directions at 3.5, 49 and 114 meters from the sensor in June 2023. Humus layer height was measured, and soil samples were collected from 6 different depths up to 30 cm. Additionally, soil organic matter (SOM) and carbon (SOC) were determined for soil samples. Calculations were conducted with an open-source Python tool “crspy” (Power 2021). Results Preliminary results from the assessment of soil moisture using CRNS from the first measurement years 2022–2024 are shown in the eLTER conference. We aim to evaluate the performance of CRNS in our measurement areas by comparing the results with environmental variables, such as, soil moisture measured continuously with soil sensors at different depths and different locations near the CRNSs, precipitation and snow depth in the area. The purpose is to detect whether the results of CRNS and point measurements are in line or if there are divergent patterns during the year(s) or discrepancies in some conditions that might affect the validity of either measurement method.

Despite the influence of drought on ecosystem functions and human well-being, there are significant uncertainties in our understanding of the impacts of drought for ecosystems and humanity. Over the past decade, large Environmental Research Infrastructures (ERIs) have been implemented around the world to advance our understanding in the responses of the biosphere to environmental change. These emergent ERIs now provide a unique opportunity to advance our understanding of ecological processes, such as drought, across continents, decades, and disciplinary boundaries. Against this backdrop, 6 ERIs (SAEON/South Africa, TERN/Australia, CERN/China, NEON/USA, ICOS/Europe, eLTER/Europe) have established an international network-to-network collaboration – the Global Ecosystem Research Infrastructure (GERI). To date, GERI activities have focused on garnering support, establishing baseline pathways for communications across continents and cultures and an initial mapping of each ERI’s data availability to facilitate future research. With recent funding from a U.S. National Science Foundation AccelNet award, GERI is poised to begin harmonizing key drought-related data. Working with stakeholder partners in the The Drought-Net Research Coordination Network’s and International Drought Experiment, we have identified key baseline data products for harmonization capable of driving new discoveries across continents. These data include soil moisture, precipitation, soil texture, and aboveground biomass, water balance, etc. As we advance this project, these harmonized data will be open, findable, searchable, and accessible, and made available to the broader community for research and discovery and stakeholder networks including the International Drought- Network to test and model. Data contributions from these new and emerging networks will be encouraged and streamlined through accessible metadata and standards. Lessons learned from the intersection of global drought data will be applied to the expanding set of environmental data collected by research networks around the world.

Biogenic volatile organic compounds (BVOCs), primarily emitted into the atmosphere by terrestrial vegetation through biochemical processes, have key ecological functions in protecting vegetation from biotic or abiotic stresses. However, accurately quantifying and predicting changes in BVOC emissions in response to long-term environmental changes large spatial scales remain challenging. The appropriate tools for observing the BVOC emissions at large scales are still missing. Remote sensing of optical signals is a promising solution to fill spatial knowledge gap. We hypothesize that the carotenoid-related vegetation index, such photochemical reflectance index (PRI), is a promising method to investigate BVOCs emitted by plants based on their functional links with carotenoids and photosynthetic activity. We conducted a leaf-level experiment in greenhouse during the summer of 2022 to investigate how the relationships between PRI and BVOC emissions change in response to drought or heat stresses in Scots pine and English oak saplings during the peak of growing season. We aim to address the following questions: (1) What factors control the relationships between PRI and BVOC emissions in response to mild/extreme drought or heat; (2) Will these controlling factors differ between vegetation species or BVOC emission types (e.g., isoprene and monoterpenes)? (3) Can PRI or other carotenoid-related vegetation indices capture the changes of BVOC emissions in response to drought or heat stresses? We will present our preliminary results. The expected outcomes will give new insight into leaf-level mechanistic links between PRI and BVOC emissions for plants in response to climate drought or warming.

Boreal forests act as crucial carbon storage, but their management can have important consequences for their carbon dynamics. Thinning of the stand alters carbon storage by removing trees, which affects the overall forest growth. Thinning stimulates growth of the remaining trees and affects soil processes in complex ways, while the overall impacts vary by forest type and site conditions. We applied biometric and soil CO2 flux measurement data to study the changes in carbon storage across multiple forest components in both an upland and a drained peatland forest undergoing thinning operations. Following thinning, the carbon accumulation rate of the aboveground biomass components declined sharply due to the removal of trees but started recovering a year after the thinning, largely driven by forest floor vegetation. Belowground biomass components followed a similar trend. Carbon emissions increased post-thinning, mainly due to decomposition of harvest residues. The upland forest net ecosystem production (NEP) temporarily shifted to a net source of carbon (-43 g C m-2 yr-1) but it recovered the following year to a net carbon sink (164 g C m-2 yr-1). The drained peatland forest NEP remained negative, with thinning further increasing the CO2 emissions (-570 g C m-2 yr-1) and leading to a slow recovery (-488 g C m-2 yr-1) to pre-thinning levels. The tree carbon stocks in both forest type is projected to take over a decade to recover. The effects of thinning on forest carbon dynamics show short-term changes in the upland forest but more lasting consequences in the drained peatland forest due to slower tree growth and persistent emissions.