Why is Tree Drought Mortality so Hard to Predict?

Trugman, Anna T.; Anderegg, Leander D. L.; Anderegg, William R. L.; Das, Adrian J.; Stephenson, Nathan L.

doi:10.1016/j.tree.2021.02.001

Cited by 139 publications

(136 citation statements)

References 109 publications

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“…Each interacting organism experiences its own physiological response to drought (e.g., Lau and Lennon 2012) with a characteristic death spiral. Accounting for where and when these separate death spirals intersect is critical if our goal is to better predict plant mortality (Trugman et al 2021) and scale this concept from individual plants to ecosystems.…”

Section: Discussionmentioning

confidence: 99%

Friend or foe? The role of biotic agents in drought-induced plant mortality

et al. 2021

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Plant mortality is a complex process influenced by both biotic and abiotic factors. In recent decades, widespread mortality events have been attributed to increasing drought severity, which has motivated research to examine the physiological mechanisms of drought-induced mortality, particularly hydraulic failure. Drought-based mortality mechanisms are further influenced by plant interactions with biota such as neighboring plants, insect pests, and microbes. In this review, we highlight some of the most influential papers addressing these biotic interactions and their influence on plant mortality. Plant-plant interactions can be positive (facilitation), neutral, or negative (competition), depending on drought intensity and neighbor identity. For example, standscale mortality likely increases with basal area (an index of competition). However, the diversity of forest stands matters, as more diverse forests suffer less mortality from drought than species-poor forests. Dense forest stands also increase bark beetle attack frequency, which can exacerbate drought stress and mortality, particularly for fast-growing species with lower defense allocation. In some cases, however, drought stress can alleviate biotic attack, depending on feedbacks between plant and pest physiology. Finally, plant interactions with beneficial microorganisms can increase drought tolerance, reduce the likelihood of mortality, and even extend plant distributions into drier habitats. Our review suggests more work is needed in natural herbaceous plant communities as well as dry tropical ecosystems where mortality mechanisms are less understood. Overall, relatively few studies directly link biotic interactions with the physiological mechanisms of mortality. Simultaneous manipulations of biotic interactions and measurements of physiological thresholds (e.g., xylem cavitation) are needed to fully represent biotic interactions in predictive models of plant mortality.

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Section: Discussionmentioning

confidence: 99%

Friend or foe? The role of biotic agents in drought-induced plant mortality

et al. 2021

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“…Physiology experiments have so far failed to find a consistent link between vulnerability to drought-induced embolism and conduit diameter, and likely as a result, recent reviews of the causes of forest mortality do not mention a possible vulnerability-conduit diameter link at all, suggesting that the link is not regarded as a significant potential player (Anderegg et al, 2015(Anderegg et al, , 2016Adams et al, 2017;Breshears et al, 2018;Stovall et al, 2019;Liang et al, 2020;Trugman et al, 2021). Some physiology experiments show a strong correlation, with the widest vessels in a given stem segment clearly being the first to embolize (Hargrave et al, 1994;Cai and Tyree, 2010).…”

Section: Experimental Data Are Inconsistent With Regard To the Linkmentioning

confidence: 99%

“…Another aspect that a vulnerability-diameter link might help explain is the observation that one individual can die when apparently similar individuals in similar conditions survive (Trugman et al, 2021). A vulnerability-diameter link could help identify vulnerable individuals as those with relatively wide conduits for a given height.…”

Section: Why Some Individuals Die Whereas Others Do Notmentioning

confidence: 99%

“…A major effort is underway to understand the causes of death of millions of trees worldwide under climate change-induced drought (Breshears et al, 2013(Breshears et al, , 2018Allen et al, 2015;Anderegg et al, 2015Anderegg et al, , 2016Adams et al, 2017;Choat et al, 2018;Trugman et al, 2018Trugman et al, , 2021Brodribb et al, 2020). These studies reveal a multitude of factors involved in forest mortality, from the failure of water transport in the wood, to insect or fungal attack and fire.…”

Section: Introductionmentioning

confidence: 99%

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Tree Mortality: Testing the Link Between Drought, Embolism Vulnerability, and Xylem Conduit Diameter Remains a Priority

Anfodillo

Olson

2021

Front. For. Glob. Change

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Global climate change-induced droughts are provoking events of forest mortality worldwide, with loss of tree biomass and consequent ecosystem services. Ameliorating the effects of drought requires understanding the causes of forest mortality, with failure of the hydraulic system being an important contributor. Comparative anatomical data strongly suggest that, all else being equal, wider conduits are more vulnerable to drought-induced embolism than narrow ones. However, physiology experiments do not provide consistent support for such a link. If a vulnerability-diameter link exists, though, it would contribute not only to explaining and predicting forest mortality but also to interventions to render individual trees more drought resistant. Given that xylem conduits scale with plant height, taller plants have wider conduits. If there is a vulnerability-diameter link, then this would help explain why taller plants are often more vulnerable to climate change-induced drought. Links between conduit diameter, plant height, and vulnerability would also provide guidance for standardizing sampling of hydraulic variables across individuals and suggest that selecting for relatively narrow conduits at given height from the tree top could produce more drought resistant varieties. As a result, given current ambiguities, together with the potential importance of a link, it is important to maintain the vulnerability-diameter link as a research priority.

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“…Predictions of dieback and tree mortality based on physiological approaches are not accurate enough because momentaneous physiological variables do not contain sufficient information about the ecology of trees, which are long-lived, complex organisms and which interact with their environment and other organisms (Trugman et al 2021). An improved mechanistic understanding of droughtinduced dieback is imperative.…”

Section: Process-based Bottom-up Approaches: Hydraulics Has Low Predictive Power Of Dieback and Mortalitymentioning

confidence: 99%

The drought‒dieback‒death conundrum in trees and forests

Camarero

2021

Plant Ecology & Diversity

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Background: Climate warming is amplifying and exacerbating drought stress worldwide. Long-term trends of increasing evaporative demand and decreasing soil moisture availability occur superimposed on severe spells of drought. These rare, extreme droughts have triggered episodes of forest dieback that have led to reduced productivity and rising mortality rates, usually at small scales (dieback hotspots), but affecting biomes worldwide. Aims: This review summarizes and discusses the drivers, patterns and mechanisms of forest dieback caused by drought. Methods: I review studies on forest dieback and tree death linked to dry spells with a focus on tools to forecast dieback. Results: Several mechanisms have been described as physiological drivers of dieback, including hydraulic failure and carbon starvation, however hydraulics-based models have shown little predictive power of dieback and mortality. Field proxies of tree vigour, including changes in canopy defoliation and water content, combined with surrogates of tree functioning (tree-ring growth, wood anatomy, tree-ring δ 13 C or δ 18 O composition) may improve predictions of forest dieback or at least render early-warning signals of impending tree death. Conclusions: Drought-induced dieback and mortality are concerning phenomena which lack forecasting tools with sufficient predictive power. Surrogates of tree vigour, growth and functioning should be used to build more accurate models of tree death in response to extreme climate events linked to drought. Here, I argue for combining and comparing those surrogates to better forecast forest dieback.

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Why is Tree Drought Mortality so Hard to Predict?

Cited by 139 publications

References 109 publications

Friend or foe? The role of biotic agents in drought-induced plant mortality

Friend or foe? The role of biotic agents in drought-induced plant mortality

Tree Mortality: Testing the Link Between Drought, Embolism Vulnerability, and Xylem Conduit Diameter Remains a Priority

The drought‒dieback‒death conundrum in trees and forests

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