Designing the eLTER Research Infrastructure: representativity, priority regions and recommendations for development
Authors: Ohnemus Thomas , Mollenhauer Hannes , Mirtl Michael , Zacharias Steffen 
Published: March 2021

&lt;p&gt;The integrated European Long-Term Ecosystem, critical zone and socio-ecological Research Infrastructure (eLTER RI) was accepted onto the ESFRI roadmap in 2018. While several existing thematic environmental RIs in Europe focus on impacts of climate change and/or other elements of environmental change, eLTER RI will be the only research infrastructure embracing holistically the integrated impacts of such stressors on a wide variety of European benchmark ecosystems (major geo-eco-sociological systems across the continent&amp;#8217;s ecoclimatological zones and Earth&amp;#8217;s critical zone). In the beginning of 2020 eLTER RI entered the preparatory phase aiming at the development of the legal, financial and technical maturity required for an ESFRI Research Infrastructure.&lt;/p&gt;&lt;p&gt;The core of the eLTER RI will be ca. 200 selected sites covering all biogeographical zones in Europe, where biological, biogeochemical, hydrological and socio-ecological data will be collected - according to common standards - and analyzed. The European landscape of LTER sites and national networks has mainly been developed in a bottom-up manner. The sites have mostly been established for different monitoring and research purposes and are heterogeneous in terms of investigated ecosystem types, scales of investigation, complexity and instrumentation. Consequently, the transformation of the selected elements of the eLTER RI into a harmonized, high-performance, complementary and interoperable infrastructure is one of the key challenges of eLTER. Achieving the best possible representativity is on the major building blocks in eLTER&amp;#8217;s design strategy.&lt;/p&gt;&lt;p&gt;To evaluate the representativity of eLTER a novel statistical approach combining information on biogeographical, ecological and socio-economic gradients with the management-relevant distribution of established sites was developed aiming at &amp;#160;i) identification of areas in Europe that are geographically underrepresented by the existing eLTER RI site network, ii) definition of priority regions for the geographical extension of the eLTER site network and, iii) development of suggestions for conceptual and infrastructural upgrades for existing less developed eLTER sites.&lt;/p&gt;&lt;p&gt;Reference datasets depicting biogeographical, ecological and socio-economical gradients were used to describe underrepresentation with a summation parameter called Aggregated Representedness. This statistical criterion was then used to classify five types of &amp;#8220;priority regions&amp;#8221; from very low to very high priority for geographical and/or conceptual extension. In a second step this information on priority regions was refined using additional information describing the geographical distribution based on Euclidean distances between established eLTER sites. &amp;#160;The combination of these two analyses allowed to identify less developed eLTER sites most suitable for conceptual and infrastructural upgrades. Thus, the presented analysis provides important information for the development of the design strategy for eLTER RI on the continental scale.&lt;/p&gt;&lt;p&gt;Concluding, a novel approach combining information on biogeographical, ecological and socio-economic gradients with the management-relevant information on the geographical distribution of established sites was developed. This tool allows to evaluate the strategies for further extension of established site networks.&amp;#160;&lt;/p&gt;