Tree mortality across biomes is promoted by drought intensity, lower wood density and higher specific leaf area

Abstract

Drought events are increasing globally, and reports of consequent forest mortality are widespread. However, due to a lack of a quantitative global synthesis, it is still not clear whether droughtinduced mortality rates differ among global biomes and whether functional traits influence the risk of drought-induced mortality. To address these uncertainties, we performed a global metaanalysis of 58 studies of drought-induced forest mortality. Mortality rates were modelled as a function of drought, temperature, biomes, phylogenetic and functional groups and functional traits. We identified a consistent global-scale response, where mortality increased with drought severity [log mortality (trees trees À1 year À1 ) increased 0.46 (95% CI = 0.2-0.7) with one SPEI unit drought intensity]. We found no significant differences in the magnitude of the response depending on forest biomes or between angiosperms and gymnosperms or evergreen and deciduous tree species. Functional traits explained some of the variation in drought responses between species (i.e. increased from 30 to 37% when wood density and specific leaf area were included). Tree species with denser wood and lower specific leaf area showed lower mortality responses. Our results illustrate the value of functional traits for understanding patterns of drought-induced tree mortality and suggest that mortality could become increasingly widespread in the future.

Drought-induced oak decline in the western Mediterranean region: an overview on current evidences, mechanisms and management options to improve forest resilience

“…For example, recent studies evidenced how some functional traits as wood density (Greenwood et al 2017), stand conditions as inter-and intra-specific competition, the level of crown transparency or the size and age of plants, co-act with drought in leading to decline. In fact, in accordance with Martínez-Vilalta et al (2011), intra-and interspecific competition exacerbates the negative effects of drought predisposing plants to decline.…”

“…For instance, Greenwood et al (2017) concluded that tree mortality increased with drought severity, but functional traits as wood density explained less than 10% of the variation in drought responses, although tree species with denser wood showed lower mortality responses. Remarkably, only 17% of their 58 study cases considered oak species.…”

A High Resolution Dataset of Drought Indices for Spain

“…Gridded drought indices have been widely used in a variety of systems to identify drought impacts, including tree morbidity and mortality at various spatial scales [43,44], crop yield reductions and crop failures [45], forest fires [46,47], and decreased vegetation activity [48,49]. The developed …”

Forest Growth Responses to Drought at Short- and Long-Term Scales in Spain: Squeezing the Stress Memory from Tree Rings

“…Since dry spells reduce forest productivity and tree growth and often weaken trees by deteriorating their vigor, drought effects on forests may last for several years (Peltier et al, 2016). Recent studies suggest that forest resilience to drought, i.e., the capacity to resist and recover after a drought, mainly depends on drought intensity, but such resilience may also depend on climate types (Zhang et al, 2017), tree species or specific functional traits (Greenwood et al, 2017). Furthermore, tree species and individuals can vary in their strategies to cope with drought (Gazol et al, 2017a,b) modifying forest growth responses to drought, which may be reflected in tree-ring width variability.…”