The eLTER Research Infrastructure: Current Network Design and Fitness for Research Challenges
Authors: Ohnemus Thomas , Dirnböck Thomas , Gaube Veronika , Mollenhauer Hannes , Bäck Jaana , Mirtl Michael , Zacharias Steffen 
Published: March 2024

The distributed Integrated European Long-Term Ecosystem, critical zone and socio-ecological Research Infrastructure &#8211; eLTER RI &#8211; 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 &#8211; 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&#8217;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.