Prolonged drought duration, not intensity, reduces growth recovery and prevents compensatory growth of oak trees

Abstract

Global forests suffer from increasing drought pressure, as drought are more intense, and last for longer, and occur more frequently, but how drought intensity and duration affect post-drought growth recovery and compensatory growth is still poorly known. Understanding the immediate and subsequent impacts of drought on tree growth is key to predict future forest dynamics. Here, we used a network of tree-ring data of 735 Quercus mongolica trees from 27 sites of North China representing a large portion of its distribution to study the effects of drought intensity and duration on radial growth. We analyzed growth resistance, recovery, and resilience of Q. mongolica by linking it to drought intensity and duration, and further quantified the post-drought growth trajectories. Our results confirmed that current summer drought is a major influence on radial growth of Q. mongolica across its distribution. While drought occurrence was related to decreased growth even for incipient droughts, we found no differences in growth decline with drought severity. Although drought intensity did not alter growth decline in dry years, drought intensity was positively related to recovery and resilience indices. The damage of recovery is due to the extension of drought duration rather than drought intensity. However, post-drought growth was even more strongly related to drought duration and not intensity. Q. mongolica showed compensatory growth in the year following single-year droughts before returning to pre-drought growth-levels, while multi-year drought led to little to no compensatory growth and prolonged growth reductions. Hence, multi-year drought is the key to predict post-drought recovery of Q. mongolica including compensatory growth in an increasingly arid climate.