The eLTER research infrastructure: Current design and coverage of environmental and socio-ecological gradients

Addressing global change requires standardised observations across all ecosystem spheres. To that end, the distributed Integrated European Long-Term Ecosystem, critical zone and socio-ecological Research Infrastructure (eLTER RI) strives for an optimal observational design of its over 200 in-situ facilities. Their spatial distribution should be unbiased to scale local data to its continental target region. Therefore, we assessed biases in the emerging eLTER RI in-situ facility network. We (i) conducted a survey describing the emerging eLTER RI, (ii) detected critical gaps in its coverage of Reference Parameters by identifying biases in a six-dimensional thematic space and determined regions, where these biases cluster spatially, and (iii) derived recommendations to further develop the eLTER RI network. Three distinct gaps were identified: the Iberian, Eastern and Nordic Gap. They resulted mainly from underrepresentation of agricultural lands, mesic and dry regions with low economic density and the Mediterranean, Continental and Boreal biogeoregions. The patterns of underrepresentation are driven by various factors including the thematic context of site establishment over the past decades, operations logistics and funding constraints. We consider closing these gaps of highest priority for spatial network development. Mitigating the biases in the eLTER RI network is crucial to enable confident scaling of local data to the European scale. This will allow the eLTER RI to provide a comprehensive foundation for scientists, policy and decision makers to face global change. Next, a comprehensive dataset of possible additional research sites over Europe must be analysed to derive site- and country-specific recommendations for cost-efficient gap mitigation.