Articles de revues : « Drought-Induced tree mortality »

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Shenkin, Alexander, Benjamin Bolker, Marielos Peña-Claros, Juan Carlos Licona, Nataly Ascarrunz et Francis E. Putz. « Interactive effects of tree size, crown exposure and logging on drought-induced mortality ». Philosophical Transactions of the Royal Society B : Biological Sciences 373, n^o 1760 (8 octobre 2018) : 20180189. http://dx.doi.org/10.1098/rstb.2018.0189.

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Large trees in the tropics are reportedly more vulnerable to droughts than their smaller neighbours. This pattern is of interest due to what it portends for forest structure, timber production, carbon sequestration and multiple other values given that intensified El Niño Southern Oscillation (ENSO) events are expected to increase the frequency and intensity of droughts in the Amazon region. What remains unclear is what characteristics of large trees render them especially vulnerable to drought-induced mortality and how this vulnerability changes with forest degradation. Using a large-scale, long-term silvicultural experiment in a transitional Amazonian forest in Bolivia, we disentangle the effects of stem diameter, tree height, crown exposure and logging-induced degradation on risks of drought-induced mortality during the 2004/2005 ENSO event. Overall, tree mortality increased in response to drought in both logged and unlogged plots. Tree height was a much stronger predictor of mortality than stem diameter. In unlogged plots, tree height but not crown exposure was positively associated with drought-induced mortality, whereas in logged plots, neither tree height nor crown exposure was associated with drought-induced mortality. Our results suggest that, at the scale of a site, hydraulic factors related to tree height, not air humidity, are a cause of elevated drought-induced mortality of large trees in unlogged plots. This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications'.

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Arend, Matthias, Roman M. Link, Rachel Patthey, Günter Hoch, Bernhard Schuldt et Ansgar Kahmen. « Rapid hydraulic collapse as cause of drought-induced mortality in conifers ». Proceedings of the National Academy of Sciences 118, n^o 16 (12 avril 2021) : e2025251118. http://dx.doi.org/10.1073/pnas.2025251118.

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Understanding the vulnerability of trees to drought-induced mortality is key to predicting the fate of forests in a future climate with more frequent and intense droughts, although the underlying mechanisms are difficult to study in adult trees. Here, we explored the dynamic changes of water relations and limits of hydraulic function in dying adults of Norway spruce (Picea abies L.) during the progression of the record-breaking 2018 Central European drought. In trees on the trajectory to drought-induced mortality, we observed rapid, nonlinear declines of xylem pressure that commenced at the early onset of xylem cavitation and caused a complete loss of xylem hydraulic conductance within a very short time. We also observed severe depletions of nonstructural carbohydrates, though carbon starvation could be ruled out as the cause of the observed tree death, as both dying and surviving trees showed these metabolic limitations. Our observations provide striking field-based evidence for fast dehydration and hydraulic collapse as the cause of drought-induced mortality in adult Norway spruce. The nonlinear decline of tree water relations suggests that considering the temporal dynamics of dehydration is critical for predicting tree death. The collapse of the hydraulic system within a short time demonstrates that trees can rapidly be pushed out of the zone of hydraulic safety during the progression of a severe drought. In summary, our findings point toward a higher mortality risk for Norway spruce than previously assumed, which is in line with current reports of unprecedented levels of drought-induced mortality in this major European tree species.

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Wang, Weifeng, Changhui Peng, Daniel D. Kneeshaw, Guy R. Larocque et Zhibin Luo. « Drought-induced tree mortality : ecological consequences, causes, and modeling ». Environmental Reviews 20, n^o 2 (juin 2012) : 109–21. http://dx.doi.org/10.1139/a2012-004.

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Drought-induced tree mortality, which rapidly alters forest ecosystem composition, structure, and function, as well as the feedbacks between the biosphere and climate, has occurred worldwide over the past few decades, and is expected to increase pervasively as climate change progresses. The objectives of this review are to (1) highlight the likely ecological consequences of drought-induced tree mortality, (2) synthesize the hypotheses related to drought-induced tree mortality, (3) discuss the implications of current knowledge for modeling tree mortality processes under climate change, and (4) highlight future research needs. First, we emphasize the likely ecological consequences of tree mortality from ecosystem to biome to continental scales. We then document and criticize multiple non-exclusive tree mortality hypotheses (e.g., carbon starvation — carbon supply is less than carbon demand; and hydraulic failure — desiccation from failed water transport) from a more comprehensive ecological perspective. Next, we extend a forest decline concept model, Manion’s framework, by considering new emerging environmental conditions, for a more thorough understanding of the effects of climate change on forest decline. We find that an increase in drought frequency and (or) climate-change-type droughts may trigger increased background tree mortality rates and severe forest dieback events, accelerating species turnover and ecological regime shifts. The contribution of CO2 fertilization, rising temperature within the optimal growth range, and increased nitrogen deposition may defer or reduce this trend in tree mortality, but such contributions will vary between locations, species, and tree sizes. Multiple hypotheses proposed for drought-induced tree mortality are discussed, but coupling carbon and water cycles could help resolve the debate. The absence of a physiological understanding of tree mortality mechanisms limits the predictive ability of current models from stand-level process-based models to dynamic global vegetation models. We thus suggest that long-term observations, experiments, and models should be tightly interwoven during the research process to better forecast future climate changes and evaluate their impacts on forests.

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Hajek, Peter, Roman M. Link, Charles A. Nock, Jürgen Bauhus, Tobias Gebauer, Arthur Gessler, Kyle Kovach et al. « Mutually inclusive mechanisms of drought‐induced tree mortality ». Global Change Biology 28, n^o 10 (17 mars 2022) : 3365–78. http://dx.doi.org/10.1111/gcb.16146.

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Anderegg, William R. L., Alan Flint, Cho-ying Huang, Lorraine Flint, Joseph A. Berry, Frank W. Davis, John S. Sperry et Christopher B. Field. « Tree mortality predicted from drought-induced vascular damage ». Nature Geoscience 8, n^o 5 (30 mars 2015) : 367–71. http://dx.doi.org/10.1038/ngeo2400.

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Zheng, Wuji, Xiaohua Gou, Jiajia Su, Haowen Fan, Ailing Yu, Wenhuo Liu, Yang Deng, Rubén D. Manzanedo et Patrick Fonti. « Physiological and Growth Responses to Increasing Drought of an Endangered Tree Species in Southwest China ». Forests 10, n^o 6 (17 juin 2019) : 514. http://dx.doi.org/10.3390/f10060514.

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Research Highlights: We compared annually resolved records of tree-ring width and stable isotope of dead and surviving Fokienia hodginsii (Dunn) Henry et Thomas trees. We provide new insights into the relationships and sensitivity of tree growth to past and current climate, and explored the underlying mechanism of drought-induced mortality in F. hodginsii. Background and Objectives: Drought-induced tree decline and mortality are increasing in many regions around the world. Despite the high number of studies that have explored drought-induced decline, species-specific responses to drought still makes it difficult to apply general responses to specific species. The endangered conifer species, Fokienia hodginsii, has experienced multiple drought-induced mortality events in recent years. Our objective was to investigate the historical and current responses to drought of this species. Materials and Methods: We used annually resolved ring-width and δ13C chronologies to investigate tree growth and stand physiological responses to climate change and elevated CO2 concentration (Ca) in both dead and living trees between 1960 and 2015. Leaf intercellular CO2 concentration (Ci), Ci/Ca and intrinsic water-use efficiency (iWUE) were derived from δ13C. Results: δ13C were positively correlated with mean vapor pressure deficit and PDSI from previous October to current May, while ring widths were more sensitive to climatic conditions from previous June to September. Moreover, the relationships between iWUE, basal area increment (BAI), and Ci/Ca changed over time. From 1960s to early 1980s, BAI and iWUE maintained a constant relationship with increasing atmospheric CO2 concentration. After the mid-1980s, we observed a decrease in tree growth, increase in the frequency of missing rings, and an unprecedented increase in sensitivity of 13C and radial growth to drought, likely related to increasingly dry conditions. Conclusions: We show that the recent increase in water stress is likely the main trigger for the unprecedented decline in radial growth and spike in mortality of F. hodginsii, which may have resulted from diminished carbon fixation and water availability. Given that the drought severity and frequency in the region is expected to increase in the future, our results call for effective mitigation strategies to maintain this endangered tree species.

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Hillabrand, Rachel M., Uwe G. Hacke et Victor J. Lieffers. « Defoliation constrains xylem and phloem functionality ». Tree Physiology 39, n^o 7 (17 mai 2019) : 1099–108. http://dx.doi.org/10.1093/treephys/tpz029.

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AbstractInsect defoliation contributes to tree mortality under drought conditions. Defoliation-induced alterations to the vascular transport structure may increase tree vulnerability to drought; however, this has been rarely studied. To evaluate the response of tree vascular function following defoliation, 2-year-old balsam poplar were manually defoliated, and both physiological and anatomical measurements were made after allowing for re-foliation. Hydraulic conductivity measurements showed that defoliated trees had both increased vulnerability to embolism and decreased water transport efficiency, likely due to misshapen xylem vessels. Anatomical measurements revealed novel insights into defoliation-induced alterations to the phloem. Phloem sieve tube diameter was reduced in the stems of defoliated trees, suggesting reduced transport capability. In addition, phloem fibers were absent, or reduced in number, in stems, shoot tips and petioles of new leaves, potentially reducing the stability of the vascular tissue. Results from this study suggest that the defoliation leads to trees with increased risk for vascular dysfunction and drought-induced mortality through alterations in the vascular structure, and highlights a route through which carbon limitation can influence hydraulic dysfunction.

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MacAllister, Sarah, Maurizio Mencuccini, Ulf Sommer, Jasper Engel, Andrew Hudson, Yann Salmon et Kyle G. Dexter. « Drought-induced mortality in Scots pine : opening the metabolic black box ». Tree Physiology 39, n^o 8 (21 juin 2019) : 1358–70. http://dx.doi.org/10.1093/treephys/tpz049.

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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.

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Sun, Shoujia, Lanfen Qiu, Chunxia He, Chunyou Li, Jinsong Zhang et Ping Meng. « Drought-Affected Populus simonii Carr. Show Lower Growth and Long-Term Increases in Intrinsic Water-Use Efficiency Prior to Tree Mortality ». Forests 9, n^o 9 (13 septembre 2018) : 564. http://dx.doi.org/10.3390/f9090564.

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The Three-North Shelter Forest (TNSF) is a critical ecological barrier against sandstorms in northern China, but has shown extensive decline and death in Populus simonii Carr. in the last decade. We investigated the characteristics—tree-ring width, basal area increment (BAI), carbon isotope signature (13Ccor), and intrinsic water-use efficiency (iWUE)—of now-dead, dieback, and non-dieback trees in TNSF shelterbelts of Zhangbei County. Results from the three groups were compared to understand the long-term process of preceding drought-induced death and to identify potential early-warning proxies of drought-triggered damage. The diameter at breast height (DBH) was found to decrease with the severity of dieback, showing an inverse relationship. In all three groups, both tree-ring width and BAI showed quadratic relationships with age, and peaks earlier in the now-dead and dieback groups than in the non-dieback group. The tree-ring width and BAI became significantly lower in the now-dead and dieback groups than in the non-dieback group from 17 to 26 years before death, thus, these parameters can serve as early-warning signals for future drought-induced death. The now-dead and dieback groups had significantly higher δ13Ccor and iWUEs than the non-dieback group at 7–16 years prior to the mortality, indicating a more conservative water-use strategy under drought stress compared with non-dieback trees, possibly at the cost of canopy defoliation and long-term shoot dieback. The iWUE became significantly higher in the now-dead group than in the dieback group at 0–7 years before death, about 10 years later than the divergence of BAI. After the iWUE became significantly different among the groups, the now-dead trees showed lower growth and died over the next few years. This indicates that, for the TNSF shelterbelts studied, an abrupt iWUE increase can be used as a warning signal for acceleration of impending drought-induced tree death. In general, we found that long-term drought decreased growth and increased iWUE of poplar tree. Successive droughts could drive dieback and now-dead trees to their physiological limits of drought tolerance, potentially leading to decline and mortality episodes.

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Klein, T. « Drought-induced tree mortality : from discrete observations to comprehensive research ». Tree Physiology 35, n^o 3 (1 mars 2015) : 225–28. http://dx.doi.org/10.1093/treephys/tpv029.

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Hosseini, Ahmad, Seyed M. Hosseini et Juan C. Linares. « Site factors and stand conditions associated with Persian oak decline in Zagros mountain forests ». Forest Systems 26, n^o 3 (31 janvier 2018) : e014. http://dx.doi.org/10.5424/fs/2017263-11298.

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Aim of study: Drought and stand structure are major and interconnected drivers of forest dynamics. Water shortage and tree-to-tree competition may interact under the current climate change scenario, increasing tree mortality. In this study, we aimed to investigate climate trends, site and stand structure effects on tree mortality, with the main hypothesis that drought-induced mortality is higher as competition increases.Area of study: Persian oak forests from Zagros Range, western Iran.Material and Methods: We split the study area into 20 topographical units (TUs), based on aspect, slope and elevation. In each TU, three 0.1 ha plots were established to quantify site and stand characteristics, namely the diameter of all trees and shrubs, stand density and basal area, canopy dieback and mortality. In addition, soil profiles were analyzed to obtain physical and chemical soil properties. Six transects 100 m length were established per TU to measure tree-to-tree competition for alive and dead trees.Main Results: The highest mortality rates and crown dieback were found at higher elevations and southern and western aspects. Our findings confirm increasing rates of tree mortality in stands with higher tree density and shallow soils. As regard links between climate change and forest decline, our results suggest that changing forest structure may have a significant impact on dust emission.Research highlights: Despite severe dry years occurred recently the study area, they are not significantly different than those recorded in the past. Stand structure appears as a modulating factor of climate change effects, linked to competition-related tree vulnerability to drought.

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Hartmann, Henrik. « Carbon starvation during drought-induced tree mortality – are we chasing a myth ? » Journal of Plant Hydraulics 2 (18 novembre 2015) : e005. http://dx.doi.org/10.20870/jph.2015.e005.

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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.

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Adams, Henry D., Maite Guardiola-Claramonte, Greg A. Barron-Gafford, Juan Camilo Villegas, David D. Breshears, Chris B. Zou, Peter A. Troch et Travis E. Huxman. « Temperature sensitivity of drought-induced tree mortality portends increased regional die-off under global-change-type drought ». Proceedings of the National Academy of Sciences 106, n^o 17 (13 avril 2009) : 7063–66. http://dx.doi.org/10.1073/pnas.0901438106.

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Large-scale biogeographical shifts in vegetation are predicted in response to the altered precipitation and temperature regimes associated with global climate change. Vegetation shifts have profound ecological impacts and are an important climate-ecosystem feedback through their alteration of carbon, water, and energy exchanges of the land surface. Of particular concern is the potential for warmer temperatures to compound the effects of increasingly severe droughts by triggering widespread vegetation shifts via woody plant mortality. The sensitivity of tree mortality to temperature is dependent on which of 2 non-mutually-exclusive mechanisms predominates—temperature-sensitive carbon starvation in response to a period of protracted water stress or temperature-insensitive sudden hydraulic failure under extreme water stress (cavitation). Here we show that experimentally induced warmer temperatures (≈4 °C) shortened the time to drought-induced mortality in Pinus edulis (piñon shortened pine) trees by nearly a third, with temperature-dependent differences in cumulative respiration costs implicating carbon starvation as the primary mechanism of mortality. Extrapolating this temperature effect to the historic frequency of water deficit in the southwestern United States predicts a 5-fold increase in the frequency of regional-scale tree die-off events for this species due to temperature alone. Projected increases in drought frequency due to changes in precipitation and increases in stress from biotic agents (e.g., bark beetles) would further exacerbate mortality. Our results demonstrate the mechanism by which warmer temperatures have exacerbated recent regional die-off events and background mortality rates. Because of pervasive projected increases in temperature, our results portend widespread increases in the extent and frequency of vegetation die-off.

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Chen, Zhicheng, Shan Li, Junwei Luan, Yongtao Zhang, Shidan Zhu, Xianchong Wan et Shirong Liu. « Prediction of temperate broadleaf tree species mortality in arid limestone habitats with stomatal safety margins ». Tree Physiology 39, n^o 8 (17 mai 2019) : 1428–37. http://dx.doi.org/10.1093/treephys/tpz045.

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Abstract A growing body of evidence highlights the occurrence of increased widespread tree mortality during climate change-associated severe droughts; however, in situ long-term drought experiments with multispecies communities for the prediction of tree mortality and exploration of related mechanisms are rather limited in natural environments. We conducted a 7-year afforestation trial with 20 drought-resistant broadleaf tree species in an arid limestone habitat in northern China, where the species displayed a broad range of survival rates. The stomatal and xylem hydraulic traits of all the species were measured. We found that species’ stomatal closure points were strongly related to their xylem embolism resistance and xylem minimum water potential but not to their survival rates. Hydraulic failure of the vascular system appeared to be the main cause of tree mortality, and the stomatal safety margin was a better predictor of tree mortality than the traditionally considered xylem embolism resistance and hydraulic safety margin. We recommend the stomatal safety margin as the indicator for predicting drought-induced tree mortality and for selecting tree species in future forest restorations in arid regions.

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Li, Duan, Jianhua Si, Xiaoyou Zhang, Yayu Gao, Chunlin Wang, Huan Luo, Jie Qin et Guanlong Gao. « Hydraulic Characteristics of Populus euphratica in an Arid Environment ». Forests 10, n^o 5 (10 mai 2019) : 407. http://dx.doi.org/10.3390/f10050407.

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Stable hydraulic conductivity in forest trees maintains healthy tree crowns and contributes to productivity in forest ecosystems. Drought conditions break down this relationship, but the mechanisms are poorly known and may depend on drought severity. To increase the understanding of changes in hydraulic conductivity during drought, we determined hydraulic parameters in Populus euphratica Oliv. (P. euphratica) in naturally arid conditions and in a simulated severe drought using a high-pressure flow meter. The results showed that leaf-specific hydraulic conductance (LSC) of leaf blades was less variable in mild drought, and increased significantly in severe drought. Plants attempted to maintain stability in leaf blade LSC under moderate water stress. In extreme drought, LSC was enhanced by increasing hydraulic conductance in plant parts with less hydraulic limitation, decreasing it in other parts, and decreasing leaf area; this mechanism protected the integrity of water transport in portions of tree crowns, and induced scorched branches and partial mortality in other parts of crowns. We conclude that limitation in water supply and elastic regulation of hydraulic characteristics may drive the mortality of tree branches as a result of severe drought. Evaluation of adaptive water transport capacity in riparian plants in arid areas provides a scientific basis for riparian forest restoration.

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Hereş, Ana-Maria, Jordi Voltas, Bernat Claramunt López et Jordi Martínez-Vilalta. « Drought-induced mortality selectively affects Scots pine trees that show limited intrinsic water-use efficiency responsiveness to raising atmospheric CO2 ». Functional Plant Biology 41, n^o 3 (2014) : 244. http://dx.doi.org/10.1071/fp13067.

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Widespread drought-induced tree mortality has been documented around the world, and could increase in frequency and intensity under warmer and drier conditions. Ecophysiological differences between dying and surviving trees might underlie predispositions to mortality, but are poorly documented. Here we report a study of Scots pines (Pinus sylvestris L.) from two sites located in north-eastern Iberian Peninsula where drought-associated mortality episodes were registered during the last few decades. Time trends of discrimination against 13C (Δ13C) and intrinsic water-use efficiency (WUEi) in tree rings at an annual resolution and for a 34 year period were used to compare co-occurring now-dead and surviving pines. Results indicate that both surviving and now-dead pines significantly increased their WUEi over time, although this increase was significantly lower for now-dead individuals. These differential WUEi trends corresponded to different scenarios describing how plant gas exchange responds to increasing atmospheric CO2 (Ca): the estimated intercellular CO2 concentration was nearly constant in surviving pines but tended to increase proportionally to Ca in now-dead trees. Concurrently, the WUEi increase was not paralleled by a growth enhancement, regardless of tree state, suggesting that in water-limited areas like the Mediterranean, it cannot overcome the impact of an increasingly warmer and drier climate on tree growth.

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Schellenberg, Konstantin, Thomas Jagdhuber, Markus Zehner, Sören Hese, Marcel Urban, Mikhail Urbazaev, Henrik Hartmann, Christiane Schmullius et Clémence Dubois. « Potential of Sentinel-1 SAR to Assess Damage in Drought-Affected Temperate Deciduous Broadleaf Forests ». Remote Sensing 15, n^o 4 (11 février 2023) : 1004. http://dx.doi.org/10.3390/rs15041004.

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Understanding forest decline under drought pressure is receiving research attention due to the increasing frequency of large-scale heat waves and massive tree mortality events. However, since assessing mortality on the ground is challenging and costly, this study explores the capability of satellite-borne Copernicus Sentinel-1 (S-1) C-band radar data for monitoring drought-induced tree canopy damage. As droughts cause water deficits in trees and eventually lead to early foliage loss, the S-1 radiometric signal and polarimetric indices are tested regarding their sensitivities to these effects, exemplified in a deciduous broadleaf forest. Due to the scattered nature of mortality in the study site, we employed a temporal-only time series filtering scheme that provides very high spatial resolution (10 m ×10 m) for measuring at the scale of single trees. Finally, the anomaly between heavily damaged and non-damaged tree canopy samples (n = 146 per class) was used to quantify the level of damage. With a maximum anomaly of −0.50 dB ± 1.38 for S-1 Span (VV+VH), a significant decline in hydrostructural scattering (moisture and geometry of scatterers as seen by SAR) was found in the second year after drought onset. By contrast, S-1 polarimetric indices (cross-ratio, RVI, Hα) showed limited capability in detecting drought effects. From our time series evaluation, we infer that damaged canopies exhibit both lower leaf-on and leaf-off backscatters compared to unaffected canopies. We further introduce an NDVI/Span hysteresis showing a lagged signal anomaly of Span behind NDVI (by ca. one year). This time-lagged correlation implies that SAR is able to add complementary information to optical remote sensing data for detecting drought damage due to its sensitivity to physiological and hydraulic tree canopy damage. Our study lays out the promising potential of SAR remote sensing information for drought impact assessment in deciduous broadleaf forests.

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Batllori, Enric, Francisco Lloret, Tuomas Aakala, William R. L. Anderegg, Ermias Aynekulu, Devin P. Bendixsen, Abdallah Bentouati et al. « Forest and woodland replacement patterns following drought-related mortality ». Proceedings of the National Academy of Sciences 117, n^o 47 (2 novembre 2020) : 29720–29. http://dx.doi.org/10.1073/pnas.2002314117.

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Forest vulnerability to drought is expected to increase under anthropogenic climate change, and drought-induced mortality and community dynamics following drought have major ecological and societal impacts. Here, we show that tree mortality concomitant with drought has led to short-term (mean 5 y, range 1 to 23 y after mortality) vegetation-type conversion in multiple biomes across the world (131 sites). Self-replacement of the dominant tree species was only prevalent in 21% of the examined cases and forests and woodlands shifted to nonwoody vegetation in 10% of them. The ultimate temporal persistence of such changes remains unknown but, given the key role of biological legacies in long-term ecological succession, this emerging picture of postdrought ecological trajectories highlights the potential for major ecosystem reorganization in the coming decades. Community changes were less pronounced under wetter postmortality conditions. Replacement was also influenced by management intensity, and postdrought shrub dominance was higher when pathogens acted as codrivers of tree mortality. Early change in community composition indicates that forests dominated by mesic species generally shifted toward more xeric communities, with replacing tree and shrub species exhibiting drier bioclimatic optima and distribution ranges. However, shifts toward more mesic communities also occurred and multiple pathways of forest replacement were observed for some species. Drought characteristics, species-specific environmental preferences, plant traits, and ecosystem legacies govern postdrought species turnover and subsequent ecological trajectories, with potential far-reaching implications for forest biodiversity and ecosystem services.

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Fensham, Roderick J., Boris Laffineur et Craig D. Allen. « To what extent is drought-induced tree mortality a natural phenomenon ? » Global Ecology and Biogeography 28, n^o 3 (9 janvier 2019) : 365–73. http://dx.doi.org/10.1111/geb.12858.

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Hartmann, Henrik, Henry D. Adams, William R. L. Anderegg, Steven Jansen et Melanie J. B. Zeppel. « Research frontiers in drought-induced tree mortality : crossing scales and disciplines ». New Phytologist 205, n^o 3 (12 janvier 2015) : 965–69. http://dx.doi.org/10.1111/nph.13246.

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Gessler, Arthur, Marcus Schaub et Nate G. McDowell. « The role of nutrients in drought-induced tree mortality and recovery ». New Phytologist 214, n^o 2 (28 novembre 2016) : 513–20. http://dx.doi.org/10.1111/nph.14340.

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Anderegg, William R. L., Tamir Klein, Megan Bartlett, Lawren Sack, Adam F. A. Pellegrini, Brendan Choat et Steven Jansen. « Meta-analysis reveals that hydraulic traits explain cross-species patterns of drought-induced tree mortality across the globe ». Proceedings of the National Academy of Sciences 113, n^o 18 (18 avril 2016) : 5024–29. http://dx.doi.org/10.1073/pnas.1525678113.

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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.

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González de Andrés, Ester, et Jesús Julio Camarero. « Disentangling Mechanisms of Drought-Induced Dieback in Pinus nigra Arn. from Growth and Wood Isotope Patterns ». Forests 11, n^o 12 (16 décembre 2020) : 1339. http://dx.doi.org/10.3390/f11121339.

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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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Sun, ShouJia, Shuai Lei, HanSen Jia, Chunyou Li, JinSong Zhang et Ping Meng. « Tree-Ring Analysis Reveals Density-Dependent Vulnerability to Drought in Planted Mongolian Pines ». Forests 11, n^o 1 (13 janvier 2020) : 98. http://dx.doi.org/10.3390/f11010098.

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Population density influences tree responses to environmental stresses, such as drought and high temperature. Prolonged drought negatively affects the health of Mongolian pines in forests planted by the Three-North Shelter Forest Program in North China. To understand the relationship between stand density and drought-induced forest decline, and to generate information regarding the development of future management strategies, we analyzed the vulnerability to drought of planted Mongolian pines at three stand densities. A tree-ring width index for trees from each density was established from tree-ring data covering the period 1988–2018 and was compared for differences in radial growth. Resistance (Rt), recovery (Rc), resilience (Rs), and relative resilience (RRs) in response to drought events were calculated from the smoothed basal area increment (BAI) curves. The high-density (HDT) group showed a consistently lower tree-ring width than the border trees (BT) and low-density (LDT) groups. The BAI curve of the HDT group started to decrease five years earlier than the LDT and BT groups. Pearson correlation analysis revealed that the radial growth of all of the groups was related to precipitation, relative humidity (RH), potential evapotranspiration (ET0), and standardized precipitation evapotranspiration index (SPEI) in the previous October and the most recent July, indicating that Mongolian pine trees of different densities had similar growth–climate relationships. Over the three decades, the trees experienced three severe drought events, each causing reduced tree-ring width and BAI. All of the groups showed similar Rc to each drought event, but the HDT group exhibited significantly lower Rt, Rs, and RRs than the BT group, suggesting that the HDT trees were more vulnerable to repeated drought stress. The RRs of the HDT group decreased progressively after each drought event and attained <0 after the third event. All of the groups showed similar trends regarding water consumption under varying weather conditions, but the HDT group showed significantly reduced whole-tree hydraulic capability compared with the other two groups. From these results, HDT trees exhibit ecophysiological memory effects from successive droughts, including sap flux dysfunction and higher competition index, which may prevent recovery of pre-drought growth rates. HDT trees may be at greater risk of mortality under future drought disturbance.

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Rayachhetry, Min B., George M. Blakeslee et Ted D. Center. « Predisposition of Melaleuca (Melaleuca quinquenervia) to Invasion by the Potential Biological Control Agent Botryosphaeria ribis ». Weed Science 44, n^o 3 (septembre 1996) : 603–8. http://dx.doi.org/10.1017/s0043174500094418.

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Enhancement of the canker causing ability of Botryosphaeria ribis on melaleuca was studied with respect to stress from simulated drought, low temperature, and defoliation treatments. Low xylem water potential was related to increased level of canker development and subsequent tree mortality. Canker development was enhanced by low temperature treatments with alternating exposure to 6 C for 3 d followed by 4 d at 30 (±5) C for 8 wk. Partial defoliation did not affect canker development but complete defoliation of B. ribis-inoculated ramets resulted in tree mortality within 4 wk. Callusing of melaleuca wounds was either reduced or prevented in stressed trees. These observations suggest that stress induced on the tree enhances the tree-killing efficacy of this fungus.

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Malone, Sparkle. « Monitoring Changes in Water Use Efficiency to Understand Drought Induced Tree Mortality ». Forests 8, n^o 10 (26 septembre 2017) : 365. http://dx.doi.org/10.3390/f8100365.

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Sala, Anna, Frida Piper et Günter Hoch. « Physiological mechanisms of drought-induced tree mortality are far from being resolved ». New Phytologist 186, n^o 2 (25 mars 2010) : 274–81. http://dx.doi.org/10.1111/j.1469-8137.2009.03167.x.

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Redmond, Miranda D., et Nichole N. Barger. « Tree regeneration following drought- and insect-induced mortality in piñon-juniper woodlands ». New Phytologist 200, n^o 2 (17 juin 2013) : 402–12. http://dx.doi.org/10.1111/nph.12366.

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Peng, Changhui, Zhihai Ma, Xiangdong Lei, Qiuan Zhu, Huai Chen, Weifeng Wang, Shirong Liu, Weizhong Li, Xiuqin Fang et Xiaolu Zhou. « A drought-induced pervasive increase in tree mortality across Canada's boreal forests ». Nature Climate Change 1, n^o 9 (20 novembre 2011) : 467–71. http://dx.doi.org/10.1038/nclimate1293.

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Adams, Henry D., Melanie J. B. Zeppel, William R. L. Anderegg, Henrik Hartmann, Simon M. Landhäusser, David T. Tissue, Travis E. Huxman et al. « A multi-species synthesis of physiological mechanisms in drought-induced tree mortality ». Nature Ecology & ; Evolution 1, n^o 9 (7 août 2017) : 1285–91. http://dx.doi.org/10.1038/s41559-017-0248-x.

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Redmond, Miranda D., Neil S. Cobb, Michael J. Clifford et Nichole N. Barger. « Woodland recovery following drought-induced tree mortality across an environmental stress gradient ». Global Change Biology 21, n^o 10 (19 juin 2015) : 3685–95. http://dx.doi.org/10.1111/gcb.12976.

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Zhang, Xiongqing, Yuancai Lei, Yong Pang, Xianzhao Liu et Jinzeng Wang. « Tree mortality in response to climate change induced drought across Beijing, China ». Climatic Change 124, n^o 1-2 (26 février 2014) : 179–90. http://dx.doi.org/10.1007/s10584-014-1089-0.

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Yao, Yitong, Emilie Joetzjer, Philippe Ciais, Nicolas Viovy, Fabio Cresto Aleina, Jerome Chave, Lawren Sack et al. « Forest fluxes and mortality response to drought : model description (ORCHIDEE-CAN-NHA r7236) and evaluation at the Caxiuanã drought experiment ». Geoscientific Model Development 15, n^o 20 (24 octobre 2022) : 7809–33. http://dx.doi.org/10.5194/gmd-15-7809-2022.

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Abstract. Extreme drought events in Amazon forests are expected to become more frequent and more intense with climate change, threatening ecosystem function and carbon balance. Yet large uncertainties exist on the resilience of this ecosystem to drought. A better quantification of tree hydraulics and mortality processes is needed to anticipate future drought effects on Amazon forests. Most state-of-the-art dynamic global vegetation models are relatively poor in their mechanistic description of these complex processes. Here, we implement a mechanistic plant hydraulic module within the ORCHIDEE-CAN-NHA r7236 land surface model to simulate the percentage loss of conductance (PLC) and changes in water storage among organs via a representation of the water potentials and vertical water flows along the continuum from soil to roots, stems and leaves. The model was evaluated against observed seasonal variability in stand-scale sap flow, soil moisture and productivity under both control and drought setups at the Caxiuanã throughfall exclusion field experiment in eastern Amazonia between 2001 and 2008. A relationship between PLC and tree mortality is built in the model from two empirical parameters, the cumulated duration of drought exposure that triggers mortality, and the mortality fraction in each day exceeding the exposure. Our model captures the large biomass drop in the year 2005 observed 4 years after throughfall reduction, and produces comparable annual tree mortality rates with observation over the study period. Our hydraulic architecture module provides promising avenues for future research in assimilating experimental data to parameterize mortality due to drought-induced xylem dysfunction. We also highlight that species-based (isohydric or anisohydric) hydraulic traits should be further tested to generalize the model performance in predicting the drought risks.

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Wang, Yongkang, et Jia Song. « Field-Measured Hydraulic Traits and Remotely Sensed NDVI of Four Subtropical Tree Species Showed Transient Declines during the Drought–Heatwave Event ». Forests 14, n^o 7 (11 juillet 2023) : 1420. http://dx.doi.org/10.3390/f14071420.

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Unpredictable drought–heatwave events occur frequently worldwide, causing low water availability (drought) and high temperatures (hot), with consequences for forest decline and mortality. Our knowledge of the potential instantaneous reactions and subsequent recovery of water-related physiological processes and vegetation indices in hot drought events remains unclear. Here, we investigated how the 2022 summer drought–heatwave event in the subtropical regions of China affected hydraulic traits and NDVI values in the forests of four common subtropical tree species. During the hot drought, the NDVI values of all four forests decreased (−31%~−23%), accompanied by leaf scorch and tree crown dieback. Among the four species, a hot drought event caused an instantaneous descent in hydraulic conductivity (Ks, −72%~−31%), stomatal conductance (gs, −94%~−50%), and midday water potential (−40%~−169%), with severe drought-induced stem xylem embolism. A trade-off was found between resistance and resilience in hot-drought-induced hydraulic dysfunction, as species with lower declines in Ks and gs during the hot drought had a shorter recovery in the post-stress phase. This study highlights that the 2022 hot drought event had severe negative instantaneous impacts on the forests of four subtropical tree species, which were reflected both in water-related physiological processes in the field and in remote sensing data from satellites.

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Suarez, María L., et Thomas Kitzberger. « Recruitment patterns following a severe drought : long-term compositional shifts in Patagonian forests ». Canadian Journal of Forest Research 38, n^o 12 (décembre 2008) : 3002–10. http://dx.doi.org/10.1139/x08-149.

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Severe droughts have the potential of inducing transient shifts in forest canopy composition by altering species-specific adult tree mortality patterns. However, permanent vegetation change will occur only if tree recruitment patterns are also affected. Here, we analyze how a massive mortality event triggered by the 1998–1999 drought affected adult and sapling mortality and recruitment in a mixed Nothofagus dombeyi (Mirb.) Blume – Austrocedrus chilensis (D. Don) Flor. et Boult. forests of northern Patagonia. Comparing drought-induced and tree-fall gaps, we assessed changes in forest composition, microenvironments, and seedling density and survival of both species. Drought-kill disturbance shifted species composition of both canopy and sapling cohorts in favour of A. chilensis. Drought gaps were characterized by a shadier and more xeric environment, affecting the recruitment pattern of N. dombeyi seedlings. The seedling cohort was composed mostly of A. chilensis, and its survival was always higher than that of N. dombeyi. Additionally, A. chilensis seedlings showed higher plasticity than N. dombeyi seedlings, increasing its root to shoot ratios in drought gaps. The results suggest that extreme drought itself is a strong driving force in forest dynamics, with important imprints on forest landscapes. Future climate-change scenarios, projecting an increased in frequency and severity of droughts, alert us about expected long-term compositional shifts in many forest ecosystems.

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Gessler, Arthur, Maxime Cailleret, Jobin Joseph, Leonie Schönbeck, Marcus Schaub, Marco Lehmann, Kerstin Treydte, Andreas Rigling, Galina Timofeeva et Matthias Saurer. « Drought induced tree mortality - a tree-ring isotope based conceptual model to assess mechanisms and predispositions ». New Phytologist 219, n^o 2 (6 avril 2018) : 485–90. http://dx.doi.org/10.1111/nph.15154.

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Zhang, Shubin, Guojing Wen et Daxin Yang. « Drought-Induced Mortality Is Related to Hydraulic Vulnerability Segmentation of Tree Species in a Savanna Ecosystem ». Forests 10, n^o 8 (17 août 2019) : 697. http://dx.doi.org/10.3390/f10080697.

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Vulnerability segmentation (VS) has been widely suggested to protect stems and trunks from hydraulic failure during drought events. In many ecosystems, some species have been shown to be non-segmented (NS species). However, it is unclear whether drought-induced mortality is related to VS. To understand this, we surveyed the mortality and recruitment rate and measured the hydraulic traits of leaves and stems as well as the photosynthesis of six tree species over five years (2012–2017) in a savanna ecosystem in Southwest China. Our results showed that the NS species exhibited a higher mortality rate than the co-occurring VS species. Across species, the mortality rate was not correlated with xylem tension at 50% loss of stem hydraulic conductivity (P50stem), but was rather significantly correlated with leaf water potential at 50% loss of leaf hydraulic conductance (P50leaf) and the difference in water potential at 50% loss of hydraulic conductance between the leaves and terminal stems (P50leaf-stem). The NS species had higher Huber values and maximum net photosynthetic rates based on leaf area, which compensated for a higher mortality rate and promoted rapid regeneration under the conditions of dry–wet cycles. To our knowledge, this study is the first to identify the difference in drought-induced mortality between NS species and VS species. Our results emphasize the importance of VS in maintaining hydraulic safety in VS species. Furthermore, the high mortality rate and fast regeneration in NS species may be another hydraulic strategy in regions where severe seasonal droughts are frequent.

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Liu, Qiuyu, Changhui Peng, Robert Schneider, Dominic Cyr, Zelin Liu, Xiaolu Zhou et Daniel Kneeshaw. « TRIPLEX-Mortality model for simulating drought-induced tree mortality in boreal forests : Model development and evaluation ». Ecological Modelling 455 (septembre 2021) : 109652. http://dx.doi.org/10.1016/j.ecolmodel.2021.109652.

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Wang, Ye, Ting Liao, Liqin Guo, Guobin Liu et Benye Xi. « Hydraulics Facilitate Urban Forest Establishment by Informing Tree Dynamics under Drought ». Forests 14, n^o 12 (12 décembre 2023) : 2415. http://dx.doi.org/10.3390/f14122415.

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Urban forests provide considerable ecosystem services for city dwellers, yet the function of forest species is increasingly challenged by urban drought. Understanding drought tolerance of urban forest species would facilitate vegetation conservation and establishment within urban ecosystems. Here, we report on the drought resistance of leaves for two exotic and three indigenous tree species common to the Jing-Jin-Ji metropolitan region (covering Beijing, Tianjin, and Hebei province) of north China. Xylem vulnerability to drought-induced embolism and leaf gas exchange, together with various morphological and anatomical traits that potentially relate to plant water use, were measured for pot-grown seedlings. In addition, seedlings were subjected to dry-down at two different drought intensities until death, and the tree mortality rate was recorded. We found that species differ markedly in xylem embolism resistance, with indigenous species showing more negative P50 (the water potential triggering 50% loss of xylem hydraulic conductivity), but less canopy leaf area at a given branch basal diameter, compared with exotic species. Furthermore, P50 well predicted tree mortality rate under protracted drought stress. Species characterized by more negative P50 also exhibited higher maximum leaf photosynthetic rates. In addition, leaf P50 was found to correlate with specific leaf area, while the hydraulic safety margin was related to sapwood density and the thickness of the leaf upper epidermis. Collectively, these results highlight the role of embolism resistance in dictating drought response and the promise of morphological traits as proxies of plant physiological drought resistance. Our findings contribute to understanding drought response for urban tree species and will guide the establishment and management of urban forests.

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Zhang, Qingyin, Ming’an Shao, Xiaoxu Jia et Xiaorong Wei. « Relationship of Climatic and Forest Factors to Drought- and Heat-Induced Tree Mortality ». PLOS ONE 12, n^o 1 (17 janvier 2017) : e0169770. http://dx.doi.org/10.1371/journal.pone.0169770.

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De Kauwe, Martin G., Belinda E. Medlyn, Anna M. Ukkola, Mengyuan Mu, Manon E. B. Sabot, Andrew J. Pitman, Patrick Meir et al. « Identifying areas at risk of drought‐induced tree mortality across South‐Eastern Australia ». Global Change Biology 26, n^o 10 (19 août 2020) : 5716–33. http://dx.doi.org/10.1111/gcb.15215.

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Schwantes, Amanda M., Jennifer J. Swenson et Robert B. Jackson. « Quantifying drought-induced tree mortality in the open canopy woodlands of central Texas ». Remote Sensing of Environment 181 (août 2016) : 54–64. http://dx.doi.org/10.1016/j.rse.2016.03.027.

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Hartmann, Henrik, Catarina F. Moura, William R. L. Anderegg, Nadine K. Ruehr, Yann Salmon, Craig D. Allen, Stefan K. Arndt et al. « Research frontiers for improving our understanding of drought-induced tree and forest mortality ». New Phytologist 218, n^o 1 (28 février 2018) : 15–28. http://dx.doi.org/10.1111/nph.15048.

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Martínez-Vilalta, Jordi, Francisco Lloret et David D. Breshears. « Drought-induced forest decline : causes, scope and implications ». Biology Letters 8, n^o 5 (14 décembre 2011) : 689–91. http://dx.doi.org/10.1098/rsbl.2011.1059.

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A large number of episodes of forest mortality associated with drought and heat stress have been detected worldwide in recent decades, suggesting that some of the world's forested ecosystems may be already responding to climate change. Here, we summarize a special session titled ‘Drought-induced forest decline: causes, scope and implications’ within the 12th European Ecological Federation Congress, held in Ávila (Spain) from 25 to 29 September 2011. The session focused on the interacting causes and impacts of die-off episodes at the community and ecosystem levels, and highlighted recent events of drought- and heat-related tree decline, advances in understanding mechanisms and in predicting mortality events, and diverse consequences of forest decline. Talks and subsequent discussion noted a potentially important role of carbon that may be interrelated with plant hydraulics in the multi-faceted process leading to drought-induced mortality; a substantial and yet understudied capacity of many forests to cope with extreme climatic events; and the difficulty of separating climate effects from other anthropogenic changes currently shaping forest dynamics in many regions of the Earth. The need for standard protocols and multi-level monitoring programmes to track the spatio-temporal scope of forest decline globally was emphasized as critical for addressing this emerging environmental issue.

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Costa, Danilo Pereira, Eduardo Sanches Stuchi, Eduardo Augusto Girardi, Abelmon da Silva Gesteira, Maurício Antonio Coelho Filho, Carlos Alberto da Silva Ledo, André Luiz Fadel et al. « Hybrid Rootstocks for Valencia Sweet Orange in Rainfed Cultivation Under Tropical Savannah Climate ». Journal of Agricultural Science 12, n^o 11 (15 octobre 2020) : 40. http://dx.doi.org/10.5539/jas.v12n11p40.

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The performance of Valencia sweet orange grafted onto 41 hybrid citrus rootstocks was evaluated for 11 years in rainfed cultivation under tropical savannah climate (Aw type) in Brazil, in addition to three selections of the standard drought-tolerant Rangpur lime and two selections of Sunki mandarin. Drought tolerance, assessed by visual score of leaf wilting, was directly related to the mean fruit yield. Indio and Riverside citrandarins, Tropical Sunki mandarin and the hybrid TSKC × CTSW-028 were grouped with the most productive selections of Rangpur lime, all of them inducing large tree size, intermediate fruit production efficiency, and high drought tolerance. The hybrid TSK × TR English-CO was similar except by inducing a higher mean soluble solids concentration in the orange juice. A third group of rootstocks induced high yield and drought tolerance, and a mean 30% reduction in tree size that led to high production efficiency, which comprised the hybrids HTR-053, TSKC × (LCR × TR)-017 and-059, TSKC × CTSW-041, LCR × TR-001 and San Diego citrandarin. The tree mortality on Rangpur lime selections was as least as 46%, while more than 80% of trees grafted onto the aforementioned rootstocks survived without visual symptoms of citrus sudden death disease or graft incompatibility. The selected hybrids and Tropical Sunki mandarin also induced fruit quality, mainly soluble solids, superior to the Rangpur lime and, therefore, are potential rootstocks for rainfed cultivation of Valencia sweet orange.

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Wermelinger, Beat, Andreas Rigling, Doris Schneider Mathis, Marc Kenis et Martin M. Gossner. « Climate Change Effects on Trophic Interactions of Bark Beetles in Inner Alpine Scots Pine Forests ». Forests 12, n^o 2 (25 janvier 2021) : 136. http://dx.doi.org/10.3390/f12020136.

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Increased tree mortality has become a widespread phenomenon and is largely attributed to climate change. Little field research has addressed the complex interactions between trees, herbivores, and their natural enemies as affected by temperature. We recorded the densities of bark insects and their natural enemies emerging from felled trees in Scots pine forests at 17 study sites along 6 elevation gradients encompassing different temperature ranges in 3 regions in Switzerland and Italy. We additionally measured tree resin defense at different elevations. The density of aggressive bark beetles decreased with increasing temperatures while that of non-aggressive species did not respond to temperature. Contrasting patterns were also found for natural enemies, with the densities of most predatory taxa decreasing with increasing temperature whereas densities of parasitoids increased. Consequently, bark beetle mortality by predators decreased and that by parasitoids increased with temperature. Exudation of resin increased with temperature. As the number of resin ducts did not change with temperature, this is assumed a physical effect of reduced viscosity. Despite lower densities of aggressive bark beetles and improved tree resin flow under higher temperatures, the currently experienced drought-induced reduction in tree vigor is likely to increase tree mortality under the ongoing climate warming.

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Baguskas, Sara A., Seth H. Peterson, Bodo Bookhagen et Christopher J. Still. « Evaluating spatial patterns of drought-induced tree mortality in a coastal California pine forest ». Forest Ecology and Management 315 (mars 2014) : 43–53. http://dx.doi.org/10.1016/j.foreco.2013.12.020.

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Szyp-Borowska, Iwona, Joanna Ukalska, Marzena Niemczyk, Tomasz Wojda et Barb R. Thomas. « Effects of Water Deficit Stress on Growth Parameters of Robinia pseudoacacia L. Selected Clones under In Vitro Conditions ». Forests 13, n^o 12 (23 novembre 2022) : 1979. http://dx.doi.org/10.3390/f13121979.

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Rapid screening methods for drought-resistant genotypes are urgently needed in tree improvement programs in the face of current climate change. We used a plant tissue culture technique to assess the phenotypic response of three highly productive genotypes of Robinia pseudoacacia to water deficit induced by mannitol and sucrose in a range of water potentials from 0 MPa to −1.5 MPa in an eight-week experiment. Our study showed genotype-specific responses to induced drought stress, indicating the potential for tree improvement in productivity and stress tolerance. Considering that all plantlets were constantly supplied with carbon, from the medium during the drought-induced experiment, our results suggest that hydraulic failure rather than carbon starvation may be the main cause of drought-induced mortality. Furthermore, our results showed different metabolic pathways of sucrose depending on the concentration of sucrose in the medium and different responses to osmoticum (mannitol vs. sucrose) and its concentration among the clones tested. We believe, that for large-scale breeding programs wanting to select for drought-tolerant genotypes, the use of culture media containing 90 gL−1 mannitol or 90 gL−1 sucrose at an early selection stage should provide satisfactory screening results. However, lab-based screening should be supported by further field trials, preferably at multiple sites, to assess the long-term impact and phenotypic stability of the early selection strategies.

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Adams, Henry D., Matthew J. Germino, David D. Breshears, Greg A. Barron-Gafford, Maite Guardiola-Claramonte, Chris B. Zou et Travis E. Huxman. « Nonstructural leaf carbohydrate dynamics ofPinus edulisduring drought-induced tree mortality reveal role for carbon metabolism in mortality mechanism ». New Phytologist 197, n^o 4 (11 janvier 2013) : 1142–51. http://dx.doi.org/10.1111/nph.12102.

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Sapes, Gerard, Beth Roskilly, Solomon Dobrowski, Marco Maneta, William R. L. Anderegg, Jordi Martinez-Vilalta et Anna Sala. « Plant water content integrates hydraulics and carbon depletion to predict drought-induced seedling mortality ». Tree Physiology 39, n^o 8 (4 juillet 2019) : 1300–1312. http://dx.doi.org/10.1093/treephys/tpz062.

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Abstract Widespread drought-induced forest mortality (DIM) is expected to increase with climate change and drought, and is expected to have major impacts on carbon and water cycles. For large-scale assessment and management, it is critical to identify variables that integrate the physiological mechanisms of DIM and signal risk of DIM. We tested whether plant water content, a variable that can be remotely sensed at large scales, is a useful indicator of DIM risk at the population level. We subjected Pinus ponderosa Douglas ex C. Lawson seedlings to experimental drought using a point of no return experimental design. Periodically during the drought, independent sets of seedlings were sampled to measure physiological state (volumetric water content (VWC), percent loss of conductivity (PLC) and non-structural carbohydrates) and to estimate population-level probability of mortality through re-watering. We show that plant VWC is a good predictor of population-level DIM risk and exhibits a threshold-type response that distinguishes plants at no risk from those at increasing risk of mortality. We also show that plant VWC integrates the mechanisms involved in individual tree death: hydraulic failure (PLC), carbon depletion across organs and their interaction. Our results are promising for landscape-level monitoring of DIM risk.

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