How do trees die? A test of the hydraulic failure and carbon starvation hypotheses

Sevanto, Sanna; McDowell, Nate G.; Dickman, L. Turin; Pangle, Robert E.; Pockman, William T.

doi:10.1111/pce.12141

Cited by 707 publications

(652 citation statements)

References 41 publications

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“…In our dendrochronological survey, a majority of spruce stopped growing by 2008 (Figure 1) but the canopy retained a similar green shade during epidemic I (Figures 2a versus 2b and 2c) while the slope of the NEE to g c relationship did not change (Table 2 and Figure 8). Where the trees store carbon during this time is unknown, because bark beetles consume the cambium and effectively girdle the tree while the blue stain fungi block water flow which will also reduce sugar utilization and phloem transport [Sevanto et al, 2014]. We thus speculate that carbon remains in and near the needles.…”

Section: Changes In Neementioning

confidence: 94%

Ecosystem CO₂/H₂O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles

et al. 2014

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Disturbances are increasing globally due to anthropogenic changes in land use and climate. This study determines whether a disturbance that affects the physiology of individual trees can be used to predict the response of the ecosystem by weighing two competing hypothesis at annual time scales: (a) changes in ecosystem fluxes are proportional to observable patterns of mortality or (b) to explain ecosystem fluxes the physiology of dying trees must also be incorporated. We evaluate these hypotheses by analyzing 6 years of eddy covariance flux data collected throughout the progression of a spruce beetle (Dendroctonus rufipennis) epidemic in a Wyoming Engelmann spruce (Picea engelmannii)-subalpine fir (Abies lasiocarpa) forest and testing for changes in canopy conductance (g c ), evapotranspiration (ET), and net ecosystem exchange (NEE) of CO 2 . We predict from these hypotheses that (a) g c , ET, and NEE all diminish (decrease in absolute magnitude) as trees die or (b) that (1) g c and ET decline as trees are attacked (hydraulic failure from beetle-associated blue-stain fungi) and (2) NEE diminishes both as trees are attacked (restricted gas exchange) and when they die. Ecosystem fluxes declined as the outbreak progressed and the epidemic was best described as two phases: (I) hydraulic failure caused restricted g c , ET (28 ± 4% decline, Bayesian posterior mean ± standard deviation), and gas exchange (NEE diminished 13 ± 6%) and (II) trees died (NEE diminished 51 ± 3% with minimal further change in ET to 36 ± 4%). These results support hypothesis b and suggest that model predictions of ecosystem fluxes following massive disturbances must be modified to account for changes in tree physiological controls and not simply observed mortality.

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Section: Changes In Neementioning

confidence: 94%

Ecosystem CO₂/H₂O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles

et al. 2014

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“…The mechanism of forest decay could be xylem embolism, carbon starvation, or both [16][17][18]. Xylem embolism can occur more quickly under very severe drought [16]; however, carbon starvation seems to be the most important factor in determining EVI decrease under long-term climate conditions [16].…”

Section: Differences In Response Due To Differences In Stock Volume Dmentioning

confidence: 99%

“…Meanwhile, root growth is accelerated to increase the uptake of soil moisture [13,14]. When the intensity of drought stress exceeds the tree's ability to adapt and resist the stress, other physiological responses set in, manifesting in the yellowing of leaves and leaf shedding [14,15], and the tree eventually dies from xylem embolism, carbon starvation, or both [16][17][18]. The question of how to use methods such as remote sensing, meteorological drought index, ground surveys, and various other ways to recognize the onset of drought and assess its impact in different intensities of drought is one of the key areas of research today.…”

Section: Introductionmentioning

confidence: 99%

Stock Volume Dependency of Forest Drought Responses in Yunnan, China

Luo

Zhou

et al. 2018

Forests

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Abstract:Revealing forest drought response characteristics and the potential impact factors is quite an important scientific issue against the background of global climate change, which is the foundation to reliably evaluate and predict the effects of future drought. Due to the high spatial heterogeneity of forest properties such as biomass, forest age, and height, and the distinct differences in drought stress in terms of frequency, intensity, and duration, current studies still contain many uncertainties. In this research, we used the forests in Yunnan Province in Southwest China as an example and aimed to reveal the potential impacts of forest properties (i.e., stock volume) on drought response characteristics. Specifically, we divided the forest into five groups of stock volume density values and then analyzed their drought response differences. To depict forest response to drought intensity, the standardized precipitation evapotranspiration index (SPEI) was chosen as the explanatory variable, and the change in remote sensing-based enhanced vegetation index (deficit of MODIS-EVI, dEVI) was chosen as the response variable of drought stress. Given that the SPEI has different time scales, we first analyzed the statistical dependency of SPEIs with different time scales (1 to 36 months) to the response variable (i.e., dEVI). The optimal time scale of SPEI (SPEI opt ) to interpret the maximum variation of dEVI (R-square) was then chosen to build the ultimate statistical models for the five groups of stock volume density. The main findings were as follows: (1) the impacts of drought showed hysteresis and cumulative effects, and the length of the hysteresis increased with stock volume densities; (2) forests with high stock volume densities required more soil water and were therefore more sensitive to the changes in water deficit; (3) compared with the optimal time scale of SPEI (SPEI opt ), the SPEI with the commonly used time scale (e.g., 1, 6, and 12 months) could not well reflect the impacts of drought on forests and the simulation error of dEVI increased with stock volume densities; and (4) forests with higher stock volume densities were likely to experience a greater risk of degradation following higher atmospheric concentrations of greenhouse gases (Representative Concentration Pathway (RCP) 8.5). As a result, both the time scale of the meteorological drought index and the spatial difference in forest stock volumes should be considered when evaluating forest drought responses at regional and global scales.

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“…2008), and the two mechanisms likely interact (McDowell 2011; Sevanto et al. 2014). Species differences in adaptation to shade also may affect the role of NSC in shade tolerance.…”

Section: Introductionmentioning

confidence: 99%

Drought and shade deplete nonstructural carbohydrate reserves in seedlings of five temperate tree species

Maguire

Kobe

2015

Ecology and Evolution

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Plants that store nonstructural carbohydrates (NSC) may rely on carbon reserves to survive carbon‐limiting stress, assuming that reserves can be mobilized. We asked whether carbon reserves decrease in resource stressed seedlings, and if NSC allocation is related to species' relative stress tolerances. We tested the effects of stress (shade, drought, and defoliation) on NSC in seedlings of five temperate tree species (Acer rubrum Marsh., Betula papyrifera Marsh., Fraxinus americana L ., Quercus rubra L., and Quercus velutina Lam.). In a greenhouse experiment, seedlings were subjected to combinations of shade, drought, and defoliation. We harvested seedlings over 32–97 days and measured biomass and NSC concentrations in stems and roots to estimate depletion rates. For all species and treatments, except for defoliation, seedling growth and NSC accumulation ceased. Shade and drought combined caused total NSC decreases in all species. For shade or drought alone, only some species experienced decreases. Starch followed similar patterns as total NSC, but soluble sugars increased under drought for drought‐tolerant species. These results provide evidence that species deplete stored carbon in response to carbon limiting stress and that species differences in NSC response may be important for understanding carbon depletion as a buffer against shade‐ and drought‐induced mortality.

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How do trees die? A test of the hydraulic failure and carbon starvation hypotheses

Cited by 707 publications

References 41 publications

Ecosystem CO₂/H₂O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles

Ecosystem CO₂/H₂O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles

Stock Volume Dependency of Forest Drought Responses in Yunnan, China

Drought and shade deplete nonstructural carbohydrate reserves in seedlings of five temperate tree species

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How do trees die? A test of the hydraulic failure and carbon starvation hypotheses

Cited by 707 publications

References 41 publications

Ecosystem CO2/H2O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles

Ecosystem CO2/H2O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles

Stock Volume Dependency of Forest Drought Responses in Yunnan, China

Drought and shade deplete nonstructural carbohydrate reserves in seedlings of five temperate tree species

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Ecosystem CO₂/H₂O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles

Ecosystem CO₂/H₂O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles