Stable isotopes of tree rings reveal seasonal-to-decadal patterns during the emergence of a megadrought in the Southwestern US

Szejner, Paul; Belmecheri, Soumaya; Babst, Flurin; Wright, William E.; Frank, David; Hu, Jia; Monson, Russell K.

doi:10.1007/s00442-021-04916-9

Cited by 18 publications

(11 citation statements)

References 51 publications

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“…At SOS, increased California hydroclimate variability (Black et al, 2018; Swain et al, 2018; Yoon et al, 2015) was likely the main driver of the increasing sensitivity of RWI and Δ 13 C to PDSI, similar to the findings of Szejner et al (2020) in the southwestern United States. However, unlike the range‐edge populations studied by Szejner et al (2021), trees at SOS displayed increasing growth (Keen et al, 2020) and no declines in un‐detrended Δ 13 C of individual trees ( data not shown ) in the decades preceding the mortality event. It seems likely that increasing competition was a contributing factor in recently greater drought sensitivity since basal area at SOS averaged 33 m 2 ha −1 , which is above the 25 m 2 ha −1 threshold identified by Voelker et al (2019) as the point at which competition‐induced drought stress is initiated in mature to old ponderosa pine forests of central Oregon.…”

Section: Discussioncontrasting

confidence: 54%

“…However, unlike the range-edge populations studied by Szejner et al (2021), trees at SOS displayed increasing growth (Keen et al, 2020) and no declines in un-detrended Δ 13 C of individual trees (data Table 1) at SOS.…”

Section: Increasing Hydroclimate Sensitivity As An Ews For Drought-related Forest Mortalitymentioning

confidence: 75%

“…As would be expected, sites where forest dieback was most extensive were located near the southwestern range edge of ponderosa pine. Similarly, southwestern US ponderosa pines have been characterized by shifts in mean tree-ring carbon isotope composition prior to the ongoing Megadrought, but only when sampled very near the southern range limit for the species (Szejner et al, 2021). However, as climate warming continues, EWS will become increasingly important in areas further from species trailing range edges.…”

Section: Increasing Hydroclimate Sensitivity As An Ews For Drought-re...mentioning

confidence: 99%

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Changes in tree drought sensitivity provided early warning signals to the California drought and forest mortality event

Keen

Voelker

Wang

et al. 2021

Global Change Biology

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Climate warming in recent decades has negatively impacted forest health in the western United States. Here, we report on potential early warning signals (EWS) for drought-related mortality derived from measurements of tree-ring growth (ring width index; RWI) and carbon isotope discrimination (∆ 13 C), primarily focused on ponderosa pine (Pinus ponderosa). Sampling was conducted in the southern Sierra Nevada Mountains, near the epicenter of drought severity and mortality associated with the 2012-2015 California drought and concurrent outbreak of western pine beetle (Dendroctonus brevicomis). At this site, we found that widespread mortality was presaged by five decades of increasing sensitivity (i.e., increased explained variation) of both tree growth and ∆ 13 C to Palmer Drought Severity Index (PDSI). We hypothesized that increasing sensitivity of tree growth and ∆ 13 C to hydroclimate constitute EWS that indicate an increased likelihood of widespread forest mortality caused by direct and indirect effects of drought. We then tested these EWS in additional ponderosa pine-dominated forests that experienced varying mortality rates associated with the same California drought event. In general, drier sites showed increasing sensitivity of RWI to PDSI over the last century, as well as higher mortality following the California drought event compared to wetter sites. Two sites displayed evidence that thinning or fire events that reduced stand basal area effectively reversed the trend of increasing hydroclimate sensitivity. These comparisons indicate that reducing competition for soil water and/or decreasing bark beetle host tree density via forest managementparticularly in drier regions-may buffer these forests against drought stress and associated mortality risk. EWS such as these could provide land managers more time to mitigate the extent or severity of forest mortality in advance of droughts. Substantial efforts at deploying additional dendrochronological research in concert with remote sensing and forest modeling will aid in forecasting of forest responses to continued climate warming.

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Section: Discussioncontrasting

confidence: 54%

Section: Increasing Hydroclimate Sensitivity As An Ews For Drought-related Forest Mortalitymentioning

confidence: 75%

Section: Increasing Hydroclimate Sensitivity As An Ews For Drought-re...mentioning

confidence: 99%

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Changes in tree drought sensitivity provided early warning signals to the California drought and forest mortality event

Keen

Voelker

Wang

et al. 2021

Global Change Biology

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“…It has long been known that vegetation response to environmental variability is revealed by tree rings (e.g., Monson et al 2018) and that a careful study of their anatomy provides critical insight into plant physiological responses to climate. Szejner et al (2021) assess stable isotopes in tree rings to reveal that trees near the arid range limit herald recent megadroughts in the southwestern U.S. Heilman et al (2021) use tree rings to find that plant water use efficiency has increased across the savanna-forest ecotone in the Midwestern U.S., but also show that growth has not and is now less sensitive to precipitation variability, especially in trees growing in open canopy microclimates. All these dynamics play out across large regions, and Fang et al (2021) note that Mediterranean Europe and North Africa have become shrubbier over the satellite record in part because shrubs are more resilient against recent extreme droughts than forests.…”

Section: Tree-ring Researchmentioning

confidence: 99%

Preface: honoring the career of Russell K. Monson

2021

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“…Nowadays, various studies demonstrated strong species-specific sensitivity to environmental drivers evaluated through tree ring stable isotopes [21,22]. The tree rings stable carbon isotopes are widely used to retrospect trees response to climate change due to carbon dioxide increase.…”

Section: Introductionmentioning

confidence: 99%

A Tree Ring Proxy Evaluation of Declining Causes in Pinus sylvestris L. and Pinus nigra J.F. Arnold in Northeastern Romania

Nechita

Iordache

Costinel

et al. 2022

Forests

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Drought-induced dieback has been extensively studied in various forests habitats. We used a retrospective tree ring width (TRW), basal area increment (BAI), oxygen isotope ratios in tree ring cellulose (δ18OTR) and carbon isotope ratios in tree ring cellulose (δ13CTR) to assess causes in declining Pinus sylvestris L. and Pinus nigra J.F. Arnold. The climate data analysis indicates a significant increased trend occurred after 1980 in minimum, mean and maximum temperature and a reduced amount of precipitation compared to the 1920–1980-time scale. According to the Palmer Drought Severity Index, we found two extreme drought years (1946 and 2000) and three years with severe drought (1990, 2003 and 2012). One-way ANOVA indicated no significant difference between P. nigra and P sylvestris tree ring width, basal area increment, but a considerable difference between δ13CTR and δ18OTR. Basal area increment evaluated the climate-growth relationship most accurately, comparing to δ18OTR and δ13CTR, which explained the influences of environmental factors in tree rings formation. The δ13CTR was mainly negatively correlated with high temperatures from April-August current growing seasons. The negative correlation between δ13CTR and NDVI indices (June, August) shows a decreased carbon uptake induced by drought from summer to early autumn. The low δ18OTR signal was associated with a complex of factors, including the strong influence of heavy precipitation occurring in the growing season and a weak reaction of declined trees to resources. Species-specific responses to drought in 1990, 2003 and 2012 indicated P. sylvestris as more sensitive to drought whit higher demand for water supply in the optimal compared with P. nigra. Weak and unstable correlations in time with increasing/decreasing values in drought periods were obtained more accurately using δ18OTR compared to δ13CTR. The species-specific resilience response to drought years showed a weak resilience and resistance in P. sylvestris occurred more evident after the 2012 event compared to less sensitive P. nigra trees. Decision-makers can use presented results to reinforce specific management plans capable of protecting and changing local compositions where is the case with species more resistant to drouth.

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Stable isotopes of tree rings reveal seasonal-to-decadal patterns during the emergence of a megadrought in the Southwestern US

Cited by 18 publications

References 51 publications

Changes in tree drought sensitivity provided early warning signals to the California drought and forest mortality event

Changes in tree drought sensitivity provided early warning signals to the California drought and forest mortality event

Preface: honoring the career of Russell K. Monson

A Tree Ring Proxy Evaluation of Declining Causes in Pinus sylvestris L. and Pinus nigra J.F. Arnold in Northeastern Romania

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