scholarly journals Dead or dying? Quantifying the point of no return from hydraulic failure in drought‐induced tree mortality

2019 ◽  
Vol 223 (4) ◽  
pp. 1834-1843 ◽  
Author(s):  
William M. Hammond ◽  
Kailiang Yu ◽  
Luke A. Wilson ◽  
Rodney E. Will ◽  
William R. L. Anderegg ◽  
...  
Keyword(s):  
Tree Mortality ◽  
Hydraulic Failure ◽  
Point Of No Return

scholarly journals Carbon starvation during drought-induced tree mortality – are we chasing a myth?

2015 ◽  
Vol 2 ◽  
pp. e005 ◽  
Author(s):  
Henrik Hartmann
Keyword(s):  
Tree Mortality ◽  
Stomatal Closure ◽  
Carbon Starvation ◽  
Carbon Limitation ◽  
Functional Roles ◽  
C Storage ◽  
Hydraulic Failure ◽  
Lethal Level ◽  
Potential Link ◽  
C Assimilation

Drought-induced tree mortality has received much attention in the recent past. McDowell et al.’s (2008) hydraulic framework links tree hydraulics with carbon dynamics and proposes two non-exclusive mortality mechanisms: carbon starvation (CS) and hydraulic failure (HF). CS is often referred to as the (partial) depletion of non-structural carbohydrates (NSC) in response to stomatal closure, reduced C assimilation and sustained C storage dependency during longer droughts. HF describes a lethal level of xylem dysfunction from runaway embolism during severe droughts. While HF can be readily inferred from the percentage loss of conductivity in vascular tissues at the time of death, CS is much more difficult to assess.Starvation is usually defined as a lack of food leading to suffering or death. In plants photosynthetic sugars play many functional roles, not only as a source of catabolic energy. For example, sugars are important for osmotic regulation of cell pressure and recent studies suggest a potential link between xylem parenchyma sugars and embolism repair following drought. Hence, carbon limitation could have a direct impact on tree hydraulics and HF; however, empirical evidence for such a mechanism is still inconclusive.Although HF appears to be predominant during drought mortality, our limited understanding of the roles of NSC in hydraulic function precludes any premature refutation of CS as a mechanism in drought-induced tree mortality.

scholarly journals Differences in Near Isohydric and Anisohydric Behavior of Contrasting Poplar Hybrids (I-101 (Populus alba L.) × 84K (Populus alba L. × Populus glandulosa Uyeki)) under Drought-Rehydration Treatments

Forests ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 402 ◽  
Author(s):  
Li Zhang ◽  
Li Liu ◽  
Han Zhao ◽  
Zaimin Jiang ◽  
Jing Cai
Keyword(s):  
Tree Mortality ◽  
Slow Growth ◽  
Threshold Value ◽  
Carbon Starvation ◽  
Populus Alba ◽  
Growth Strategies ◽  
Fast Growing ◽  
Hydraulic Failure ◽  
Hydraulic Safety ◽  
Slow Growing

Carbon starvation and hydraulic failure are considered important factors in determining the mechanisms associated with tree mortality. In this study, iso/anisohydric classification was used to assess drought resistance and mortality mechanisms in two contrasting poplar species, as it is generally believed that isohydric species are more susceptible to carbon starvation, while anisohydric species are more susceptible to hydraulic failure. However, these assumptions are rarely tested in poplar genotypes with contrasting growth strategies. Thus, we subjected potted poplar genotypes (I-101 (Populus alba L.) × 84K (Populus alba L. × Populus glandulosa Uyeki)) with fast and slow growth rates to drought–rehydration treatments. The slow-growing genotype maintained higher stomatal conductance and lower predawn leaf water potential than the fast-growing genotype, thus exhibiting a near-anisohydric stomatal behavior throughout the treatment period. The nonstructural carbohydrate (NSC) content indicated that the two genotypes had the same trend of carbon change (e.g., the NSC content in the leaves increased with drought and then decreased). However, when NSC content data were combined with the growth and photosynthetic data, it was observed that the slow-growing genotype mobilized carbon to maintain hydraulic safety, while the NSC content of the fast-growing genotype among tissues was static. The percent loss of hydraulic conductivity in the branches during treatments indicated that the fast-growing genotype could recover more quickly from xylem embolism than the slow-growing genotype. The slow-growing genotype with a slow growth recovery after rehydration showed a significant increase in carbon consumption, combined with a significant increase in the hydraulic safety threshold value, indicating that there may be drought tolerance. In comparison, the fast-growing genotype showed a faster hydraulic recovery ability that had no effect on the NSC content in the leaves and roots. Our findings demonstrate intraspecific isohydric behavior in poplar; however, the trade-off between carbon distribution and stomatal regulation should be considered separately within genotypes of the same species. In addition, NSC plays an important role in water–carbon balance in the drought–rehydration cycle.

scholarly journals Drought response strategies and hydraulic traits contribute to mechanistic understanding of plant dry-down to hydraulic failure

2019 ◽  
Vol 39 (6) ◽  
pp. 910-924 ◽  
Author(s):  
Chris J Blackman ◽  
Danielle Creek ◽  
Chelsea Maier ◽  
Michael J Aspinwall ◽  
John E Drake ◽  
...  
Keyword(s):  
Drought Tolerance ◽  
Tree Mortality ◽  
Stomatal Closure ◽  
Safety Margin ◽  
Critical Levels ◽  
Response Strategies ◽  
Hydraulic Failure ◽  
Dry Down ◽  
Leaf Succulence ◽  
And Function

Abstract Drought-induced tree mortality alters forest structure and function, yet our ability to predict when and how different species die during drought remains limited. Here, we explore how stomatal control and drought tolerance traits influence the duration of drought stress leading to critical levels of hydraulic failure. We examined the growth and physiological responses of four woody plant species (three angiosperms and one conifer) representing a range of water-use and drought tolerance traits over the course of two controlled drought–recovery cycles followed by an extended dry-down. At the end of the final dry-down phase, we measured changes in biomass ratios and leaf carbohydrates. During the first and second drought phases, plants of all species closed their stomata in response to decreasing water potential, but only the conifer species avoided water potentials associated with xylem embolism as a result of early stomatal closure relative to thresholds of hydraulic dysfunction. The time it took plants to reach critical levels of water stress during the final dry-down was similar among the angiosperms (ranging from 39 to 57 days to stemP88) and longer in the conifer (156 days to stemP50). Plant dry-down time was influenced by a number of factors including species stomatal-hydraulic safety margin (gsP90 – stemP50), as well as leaf succulence and minimum stomatal conductance. Leaf carbohydrate reserves (starch) were not depleted at the end of the final dry-down in any species, irrespective of the duration of drought. These findings highlight the need to consider multiple structural and functional traits when predicting the timing of hydraulic failure in plants.

scholarly journals Water stress-induced xylem hydraulic failure is a causal factor of tree mortality in beech and poplar

2013 ◽  
Vol 112 (7) ◽  
pp. 1431-1437 ◽  
Author(s):  
Têtè Sévérien Barigah ◽  
Olivia Charrier ◽  
Marie Douris ◽  
Marc Bonhomme ◽  
Stéphane Herbette ◽  
...  
Keyword(s):  
Water Stress ◽  
Tree Mortality ◽  
Causal Factor ◽  
Hydraulic Failure

scholarly journals Drought-induced mortality in Scots pine: opening the metabolic black box

2019 ◽  
Vol 39 (8) ◽  
pp. 1358-1370
Author(s):  
Sarah MacAllister ◽  
Maurizio Mencuccini ◽  
Ulf Sommer ◽  
Jasper Engel ◽  
Andrew Hudson ◽  
...  
Keyword(s):  
Scots Pine ◽  
Natural Enemies ◽  
Tree Mortality ◽  
Aromatic Amino Acids ◽  
Metabolic Effects ◽  
Severe Drought ◽  
Hydraulic Failure ◽  
Effects Of Drought ◽  
Eurasian Species ◽  
Increased Susceptibility

Abstract Forests are sensitive to droughts, which increase the mortality rate of tree species. Various processes have been proposed to underlie drought-induced tree mortality, including hydraulic failure, carbon starvation and increased susceptibility to natural enemies. To give insights into these processes, we assessed the metabolic effects of a mortality-inducing drought on seedlings of Pinus sylvestris L. (Scots Pine), a widespread and important Eurasian species. We found divergence over time in the foliar metabolic composition of droughted vs well-watered seedlings, with the former showing increased abundance of aromatic amino acids and decreases in secondary metabolism associated with defence. We observed no significant differences amongst provenances in these effects: seedlings from drought-prone areas showed the same foliar metabolic changes under drought as seedlings from moist environments, although morphological effects of drought varied by provenance. Overall, our results demonstrate how severe drought prior to death may target particular primary and secondary metabolic pathways, weakening defences against natural enemies and contributing to the risk of drought-induced mortality in P. sylvestris.

scholarly journals Mutually inclusive mechanisms of drought-induced tree mortality

2020 ◽  
Author(s):  
Peter Hajek ◽  
Roman M. Link ◽  
Charles Nock ◽  
Jürgen Bauhus ◽  
Tobias Gebauer ◽  
...  
Keyword(s):  
Mortality Risk ◽  
Tree Mortality ◽  
Tree Height ◽  
Summer Drought ◽  
Species Identity ◽  
Pest Infestation ◽  
Hydraulic Failure ◽  
Safety Margins ◽  
Structural Carbohydrate ◽  
Inclusive Processes

AbstractAn extreme summer drought caused unprecedented tree dieback across Central Europe in 2018, highlighting the need for a better mechanistic understanding of drought-induced tree mortality. While numerous physiological risk factors have been identified, the principal mechanisms, hydraulic failure and carbon starvation, are still debated. We studied 9,435 trees from 12 temperate species planted in a diversity experiment in 2013 to assess how hydraulic traits, carbon dynamics, pest infestation, tree height and neighbourhood competition influence individual mortality risk. We observed a reduced mortality risk for trees with wider hydraulic safety margins, while a rising sugar fraction of the non-structural carbohydrate pool and bark beetle infestation were associated with higher risk. Taller trees had a lower mortality risk. The sign and magnitude of neighbourhood effects on mortality risk depended on the species-identity of the involved trees, with most species having beneficial and some having deleterious effects on their neighbours. While severe tissue dehydration causing hydraulic failure precedes drought-induced tree mortality, we show that the probability of this event depends on a series of mutually inclusive processes including pest infestation and starch depletion for osmotic adjustment, and is modulated by the size and species identity of a tree and its neighbours.

What makes a tree die? - Bark beetle-induced mortality causes abrupt declines in tree diameter

2021 ◽  
Author(s):  
Samuli Junttila ◽  
Teemu Hölttä ◽  
Ninni Saarinen ◽  
Mikko Vastaranta
Keyword(s):  
Diurnal Variation ◽  
Bark Beetle ◽  
Water Demand ◽  
Tree Mortality ◽  
Atmospheric Water ◽  
Tree Diameter ◽  
Hydraulic Failure ◽  
Diameter Variation ◽  
Investigation Period ◽  
In The Beginning

<p>The climate change has brought better environmental conditions for numerous bark beetles to reproduce in unmet amounts. Large-scale tree mortality events have been witnessed globally due to mass outbreaks of phloem feeding pest insects, such as <em>Ips typographus</em> (L.), that are jeopardizing numerous ecosystem services forests provide. To be able to assess the current and future bark beetle-induced tree mortality, we need more profound understanding of the processes that occur after the infestation of a tree, eventually leading to tree mortality. We measured the diurnal variation in tree stem diameter from four healthy and four infested trees trees during an <em>I. typographus</em> infestation in Helsinki, Finland, of which the four infested trees died during the investigation period between June and September in 2020. The condition of the tree crowns was also visually assessed in the beginning and the end of the study period.</p><p>We found that the amplitude of diurnal diameter variation was considerably smaller in the infested trees compared to healthy trees indicating smaller diurnal variation in the water content of the stem. The decrease in diurnal diameter variation was followed by abrupt and irreversible declines in tree diameter likely indicating tissue damage due to hydraulic failure. The declines were triggered largely by increased atmospheric water demand during the hottest days of the investigation period. The condition of the tree crown in the beginning of the study did not reflect the timing of the decline in tree diameter, but one of the most visually vital trees declined first.</p><p>The results indicate that hotter summer temperatures will increase and hasten bark beetle-induced tree mortality. This happens because irreversible hydraulic failure seems to occur in a cross pressure of bark beetle-induced stress and increased atmospheric water demand. Trees are likely more vulnerable to bark beetle-related hydraulic failure in the future because of increasing atmospheric water demand and more intense droughts. The triggers and processes that cause bark beetle-related tree mortality need more careful investigation to incorporate them into models that forecast tree mortality.</p>

Hydraulic failure and tree mortality: from correlation to causation

2021 ◽  
Author(s):  
Marylou Mantova ◽  
Stéphane Herbette ◽  
Hervé Cochard ◽  
José M. Torres-Ruiz
Keyword(s):  
Tree Mortality ◽  
Hydraulic Failure

scholarly journals Forecasting of droughts and tree mortality under global warming: a review of causative mechanisms and modeling methods

2020 ◽  
Vol 11 (3) ◽  
pp. 600-632 ◽  
Author(s):  
Jeongwoo Han ◽  
Vijay P. Singh
Keyword(s):  
Global Warming ◽  
Tree Mortality ◽  
Drought Forecasting ◽  
Temperature Changes ◽  
Mortality Forecasting ◽  
Forecasting Models ◽  
Global Mean Temperature ◽  
Hydraulic Failure ◽  
Global Mean

Abstract Droughts of greater severity are expected to occur more frequently at larger space-time scales under global warming and climate change. Intensified drought and increased rainfall intermittency will heighten tree mortality. To mitigate drought-driven societal and environmental hazards, reliable long-term drought forecasting is critical. This review examines causative mechanisms for drought and tree mortality, and synthesizes stochastic, statistical, dynamical, and hybrid statistical-dynamical drought forecasting models as well as theoretical, empirical, and mechanistic tree mortality forecasting models. Since an increase in global mean temperature changes the strength of sea surface temperature (SST) teleconnections, forecasting models should have the flexibility to incorporate the varying causality of drought. Some of the statistical drought forecasting models, which have nonlinear and nonstationary natures, can be merged with dynamical models to compensate for their lack of stochastic structure in order to improve forecasting skills. Since tree mortality is mainly affected by a hydraulic failure under drought conditions, mechanistic forecasting models, due to their capacity to track the percentage of embolisms against available soil water, are adequate to forecast tree mortality. This study also elucidates approaches to improve long-term drought forecasting and regional tree mortality forecasting as a future outlook for drought studies.

scholarly journals Disentangling Mechanisms of Drought-Induced Dieback in Pinus nigra Arn. from Growth and Wood Isotope Patterns

Forests ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1339
Author(s):  
Ester González de Andrés ◽  
Jesús Julio Camarero
Keyword(s):  
Water Use ◽  
Radial Growth ◽  
Tree Mortality ◽  
Pinus Nigra ◽  
Growth Patterns ◽  
Natural Forests ◽  
Northern Spain ◽  
Hydraulic Failure ◽  
Intrinsic Water Use Efficiency ◽  
Growth Decline

The increased frequency and intensity of warming-induced droughts have triggered dieback episodes affecting many forest types and tree species worldwide. Tree plantations are not exempt as they can be more vulnerable to drought than natural forests because of their lower structural and genetic diversity. Therefore, disentangling the physiological mechanisms leading to growth decline and tree mortality can provide tools to adapt forest management to climate change. In this study, we investigated a Pinus nigra Arn. plantation situated in northern Spain, in which some trees showed canopy dieback and radial-growth decline. We analyzed how radial growth and its responses to drought events differed between non-declining (ND) and declining (D) trees showing low and high canopy defoliation, respectively, in combination with carbon (δ13C) and oxygen (δ18O) isotope ratios in tree rings. The radial growth of P. nigra was constrained by water availability during the growing season and the previous autumn. The radial growth of D trees showed higher sensitivity to drought than ND trees. This fact is in accordance with the lower drought resilience and negative growth trends observed in D trees. Both tree classes differed in their growth from 2012 onwards, with D trees showing a reduced growth compared to ND trees. The positive δ13C-δ18O relationship together with the uncoupling between growth and intrinsic water-use efficiency suggest that D trees have less tight stomatal regulation than ND trees, which could involve a high risk of xylem embolism in the former class. Our results suggest that different water use strategies between coexisting ND and D trees were behind the differences in growth patterns and point to hydraulic failure as a possible mechanism triggering dieback and growth decline.

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