Meta-analysis reveals that hydraulic traits explain cross-species patterns of drought-induced tree mortality across the globe

Abstract

Drought-induced tree mortality has been observed globally and is expected to increase under climate change scenarios, with large potential consequences for the terrestrial carbon sink. Predicting mortality across species is crucial for assessing the effects of climate extremes on forest community biodiversity, composition, and carbon sequestration. However, the physiological traits associated with elevated risk of mortality in diverse ecosystems remain unknown, although these traits could greatly improve understanding and prediction of tree mortality in forests. We performed a meta-analysis on species' mortality rates across 475 species from 33 studies around the globe to assess which traits determine a species' mortality risk. We found that species-specific mortality anomalies from community mortality rate in a given drought were associated with plant hydraulic traits. Across all species, mortality was best predicted by a low hydraulic safety margin-the difference between typical minimum xylem water potential and that causing xylem dysfunction-and xylem vulnerability to embolism. Angiosperms and gymnosperms experienced roughly equal mortality risks. Our results provide broad support for the hypothesis that hydraulic traits capture key mechanisms determining tree death and highlight that physiological traits can improve vegetation model prediction of tree mortality during climate extremes.meta-analysis | climate change | carbon cycle | climate extremes | biodiversity F orests assimilate and sequester ∼2.4 Pg carbon per year (1), equivalent to 25% of anthropogenic emissions, and provide manifold goods and services to society (2). Climate extremes, such as severe drought, could trigger abrupt and irreversible changes in Earth's forests (3, 4), which would have profound implications for their biodiversity, ecosystem services, and carbon storage (5). Episodes of widespread tree mortality in response to drought and/or heat stress have been observed across the globe in the past few decades (4). In addition, drought severity and frequency are projected to increase with temperature-driven rises in evaporative demand (6). There is fundamental concern that increased climate-induced mortality of trees (7) could offset carbon sinks currently yielded in old growth and regrowth forests alike (8).Predicting plant demographic rates, such as mortality, using physiological traits is a central aim of ecology with critical importance for modeling climate change impacts and the carbon cycle (9). Drought-induced tree mortality has been particularly challenging to model and predict because of uncertainty in traits and mechanisms underlying the physiology of tree death (10, 11). Despite this uncertainty (12, 13), the failure of the plant vascular hydraulic transport system is considered to be a central pathway to mortality (7,(14)(15)(16)(17). This failure happens through embolism of a tree's water transport elements by air bubbles during high xylem tensions induced by low soil moisture and/or high atmospheric evaporative demand during...

Key drivers of ecosystem recovery after disturbance in a neotropical forest

“…This result may look strange given that drought has often been identified as one of the main climate drivers of tropical forest dynamics Wagner et al 2012Wagner et al , 2013Wagner et al , 2014Wagner et al , 2016, with large mortality events among tropical trees during El Nino years for instance (Phillips et al 2009) that have not only immediate but also long-term and cumulative impacts on the carbon cycle (Doughty et al 2015). Those large mortality events are associated with tree hydraulic traits, the most susceptible species being those having a low hydraulic safety margin (Anderegg et al 2016). In this context, why do the most intense dry season generate the lowest carbon losses?…”

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

“…Nowadays, there is a growing scientific interest on forest reactions to drought across different biomes to discern which growth features or functional traits better characterize different species-specific responses to these climate extremes (Anderegg et al, 2013(Anderegg et al, , 2015(Anderegg et al, , 2016Vicente-Serrano et al, 2013;Gazol et al, 2017a). In this sense, annual growth rings provide short-(e.g., years) and long-term (e.g., decades) information on how trees respond to drought (e.g., Anderegg et al, 2015;Camarero et al, 2015b;Gazol and Camarero, 2016;Gazol et al, 2017c).…”

Differences in functional and xylem anatomical features allow Cistus species to co-occur and cope differently with drought in the Mediterranean region

“…Hydraulic failure of the water transport system of the plant is now seen as one of the causes of these changes in species distribution since it is the main mechanism leading drought-induced plant mortality (Brodribb and Cochard 2009, Barigah et al 2013, Salmon et al 2015, Anderegg et al 2016. Plant hydraulic failure is mostly due to the formation of gas bubbles (emboli) in the xylem conduits that break the continuum of the water column and lead to a reduction in hydraulic conductance.…”