The timing of drought coupled with pathogens may boost tree mortality

Drought severity and frequency (Luce et al. 2016) affect tree growth and mortality (Allen et al. 2010, Martinez-Vilalta et al. 2012, Cailleret et al. 2017, Trugman et al. 2018). Recently our understanding of the importance of the timing of drought has increased considerably. The expected increase in variability in precipitation extremes (Jentsch et al. 2007, Dai 2013) will shift the timing of drought (Anderegg et al. 2013) and potentially induce drought stress during key physiological and growth stages of trees. This may negatively affect tree functioning and their ability to recover from abiotic and biotic stresses (Anderegg et al. 2013, Forner et al. 2018). For example, changes in the synchrony of the timing of drought and spring growth phenology in temperate trees may restrain leaf and canopy development (Misson et al. 2011, Forner et al. 2018), or new sapwood growth (Anderegg and Callaway 2012, D’Orangeville et al. 2018, Forner et al. 2018), increasing tree vulnerability to additional drought events. The timing of drought can thus critically affect tree functioning and, ultimately, the likelihood of tree mortality (Miao et al. 2009, Anderegg et al. 2013, Huang et al. 2018).