Monitoring global tree mortality patterns and trends : report from the VW symposium 'Crossing scales and disciplines to identify global trends of tree mortality as indicators of forest health'

From the 21st to the 23rd June 2017, the Herrenhausen castle in Hannover/Germany hosted a diverse and large crowd with more than 70 tree physiologists, forest ecologists, forest inventory experts, remote-sensing scientists, and vegetation modelers. Participants from six continents and from more than 20 countries gathered to discuss how to improve the scientific determination of global-scale patterns, drivers, and trends of a threatening phenomenon: the apparent emergence of recent widespread tree mortality events in diverse forests around the world. Continuing the theme of a workshop held at the Max-Planck Institute for Biogeochemistry in Jena (Germany) in 2014 (Hartmann et al., 2015), the Hanover meeting intended to develop approaches, tools and collaborative actions to accelerate progress in addressing regional patterns and trends of tree mortality (Williams et al., 2013). Over the last decade climate change related tree mortality events have been increasingly reported around the globe (van Mantgem et al., 2009; Carnicer et al., 2011; Peng et al., 2011; Brienen et al., 2015), but to what degree this is a global trend, amplifying under increasing climate change, remains uncertain.