Tree defence and bark beetles in a drying world : carbon partitioning, functioning and modelling

Drought has promoted large-scale, insect-induced tree mortality in recent years, with severe consequences for ecosystem function, atmospheric processes, sustainable resources and global biogeochemical cycles. However, the physiological linkages among drought, tree defences, and insect outbreaks are still uncertain, hindering our ability to accurately predict tree mortality under ongoing climate change. Herewepropose an interdisciplinary research agenda for addressing these crucial knowledge gaps. Our framework includes field manipulations, laboratory experiments, and modelling of insect and vegetation dynamics, and focuses on how drought affects interactions between conifer trees and bark beetles. We build upon existing theory and examine several key assumptions: (1) there is a trade-off in tree carbon investment between primary and secondary metabolites (e.g. growth vs defence); (2) secondary metabolites are one of the main component of tree defence against bark beetles and associated microbes; and (3) implementing conifer-bark beetle interactions in current models improves predictions of forest disturbance in a changing climate. Our framework provides guidance for addressing a major shortcoming in current implementations of large-scale vegetation models, the under-representation of insect-induced tree mortality.JH, AH, DK, JG, and HH were funded by Max Planck Society. AMT and HDA were supported by the National Science Foundation, Division of Integrative Organismal Systems, Integrative Ecological Physiology Programme (no. 1755346). AMT recognizes contributions from the USDA National Institute of Food and Agriculture Hatch project (MONB00389). HDA recognizes support from the Office of the Vice President for Research at Oklahoma State University. RS acknowledges support from the Austrian Science FundFWFthroughSTARTgrant Y895- B25. KFR acknowledges the University of Wisconsin-Madison Vilas-Sorenson Professorship from the College of Agricultural and Life Sciences the Graduate School. D.G was funded by the Los Alamos National Laboratory Centre for Space and Earth Science and Exploratory Research program.CXwas funded by theUC-Lab Fees Research Program (grant nos. LFR18-542511).http://www.newphytologist.comam2020Forestry and Agricultural Biotechnology Institute (FABI)Zoology and Entomolog