Methodological issues and outputs of the REINFFORCE network - a unique transnational infrastructure of tree species arboreta for the adaptation of planted forests to future climate Predicting the future responses of productive forests and choosing the best-adapted regeneration material to climate change requires transnational infrastructures that provide evidence-based knowledge of the response of multiple tree species under a wide range of climatic conditions. This is why REINFFORCE http://reinfforce.iefc.net was established as a unique network of demonstration sites to test the field performance and adaptation of 32 tree species from all over the world, including currently established and alternative productive species/provenances. The network made of 38 arboreta with common genetic material distributed along the European Atlantic arc (latitudes 37° to 58° N).This latitudinal gradient, covering a large diversity of climate and soil conditions, allows assessing the response of 120,000 tested trees from 176 provenances to current and anticipated future climatic conditions outside their current distribution range. We present methodological issues for the establishment, maintenance and coordination of the transnational network between the multiple partners, based on the common protocols and consolidated database for long-term monitoring and knowledge sharing. The latest outputs in methodological innovation include a harmonized field protocol for phenology assessment, height measurements with drone technology, and the use of the arboreta network as sentinels for emerging pests and diseases.The successful experience of the REINFFORCE network provides a strategic research platform for transnational cooperation and creates synergies with other research initiatives on forest adaptation to climate change. The latest research findings provides evidences and decision support for multiple forest stakeholders to increase the adaptation of the planted forests facing future climate uncertainty. 30/09/2019 Curitiba IUFRO World Congress - B4g: Long-Term Forest Monitoring Networks for Evaluating Responses to Environmental Change - I https://app.oxfordabstracts.com/events/691/program-app/submission/92135 Christophe Orazio Hernan Serrano-León