Short- and long-term responses of riparian cottonwoods (Populus spp.) to flow diversion: Analysis of tree-ring radial growth and stable carbon isotopes

Schook, Derek M.; Friedman, Jonathan M.; Stricker, Craig A.; Csank, A. Z.; Cooper, David J.

doi:10.1016/j.scitotenv.2020.139523

Cited by 23 publications

(19 citation statements)

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“…In addition, stable carbon isotope discrimination (∆ 13 C) in tree‐rings records the canopy‐integrated ratio of photosynthetic assimilation to stomatal conductance (Ehleringer et al, 1993; Farquhar et al, 1989; McCarroll & Loader, 2004), making it a promising EWS candidate. In forests of the western United States, ∆ 13 C has been used extensively to understand various aspects of past drought stress due to the dominant impact of stomatal closure on this signal (Keen et al, 2020; Leavitt et al, 2011; Roden & Ehleringer, 2007; Schook et al, 2020; Szejner et al, 2016; Voelker et al, 2019). Both ring width and ∆ 13 C records offer insight into differing dimensions of drought stress that may be important for recognizing novel EWS.…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

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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“…The initial DW decline beginning in the 1960s is interpreted as being due to drought stress, while at RU, competition for light associated with a successional transition to white fir‐dominated forest is a likely cause (Table 1). Higher drought stress at DW compared to RU has been demonstrated by higher stable carbon isotope ratios beginning abruptly in 1961, stronger correlation between BAI and stable carbon isotope ratios, stronger correlations relating tree‐ring metrics to precipitation and flow, higher branch mortality and lower canopy vigour (Schook et al, 2020). Here, we add that the DW reach also had higher tree mortality (Figure 10) and fragmentation of the forest canopy (Figure 8).…”

Section: Discussionmentioning

confidence: 99%

“…Historical forest management practices appear to have caused the tree‐ring narrowing at RU. Nearly all of the RU cottonwoods established from 1876 to 1899 (Schook et al, 2020) after timber harvests opened the forest canopy. Conifers have since regrown and now shade out cottonwoods, providing an alternate mechanism for tree‐ring narrowing (Cailleret et al, 2017).…”

Section: Discussionmentioning

confidence: 99%

“…Tree‐ring chronologies were developed using standard dendrochronological techniques for each study reach using cores collected at 1.3 m above ground from randomly selected living cottonwoods >20‐cm diameter (elaborated in Schook et al, 2020; Stokes & Smiley, 1968). We used basal area increment (BAI), derived from ring width and distance to the pith, to characterize the cross‐sectional growth of each annual ring (Biondi, 1999).…”

Section: Methodsmentioning

confidence: 99%

“…Tree-ring chronologies were developed using standard dendrochronological techniques for each study reach using cores collected at 1.3 m above ground from randomly selected living cottonwoods >20-cm diameter (elaborated in Schook et al, 2020;Stokes & Smiley, 1968).…”

Section: Tree-level Cottonwood Productivitymentioning

confidence: 99%

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Riparian forest productivity decline initiated by streamflow diversion then amplified by atmospheric drought 40 years later

et al. 2022

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Riparian trees and their annual growth rings can be used to reconstruct drought histories related to streamflow. Because the death of individual trees reduces competition for survivors, however, tree-ring chronologies based only on surviving trees may underestimate drought impacts. This problem can be addressed by calculating productivity at the stand scale to account for tree mortality and establishment. In the semi-arid Great Basin in the western United States, we calculated riparian wood production from 1946 to 2016 along a stream where most flow has been removed by a diversion pipeline since 1961. The water table was found to be generally below the root zone of cottonwoods (Populus angustifolia and P. angustifolia Â trichocarpa) in the pipeline-dewatered reach but within it in reference reaches. To reconstruct forest productivity through time, we separately combined measurements of tree-ring basal area increment with either changing forest area from aerial photos or a census of cross-dated living and dead cottonwoods. Both approaches revealed productivity declines in the dewatered reach relative to adjacent reference reaches, and the decline accelerated in the 2000s. Tree-ring narrowing resulted in divergence between the dewatered reach and one reference reach within 5 years after diversion. However, the dewatered reach did not diverge from the other reference reach until 40 years later, when an unprecedented early 2000s atmospheric drought coupled with diversion to cause extensive cottonwood mortality. We conclude that dendrochronological investigations of forest response to environmental stress should incorporate stand dynamics and that the full impacts of flow diversion can be delayed for decades.

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Riparian cottonwood mortality following compound impacts from river water withdrawal and hydroclimatic variation

Rood

Mahoney

2023

Ecohydrology

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Originating in Glacier Park, Montana, the transboundary St. Mary River has provided a focus for international water sharing for a century. It was dammed and diverted in the USA, and more extensively in Alberta, where it supports Canada's centre for agricultural irrigation. Following water withdrawals, the riparian cottonwoods (Populus angustifolia) collapsed, and we assessed the woodland decline downstream from the St. Mary Dam, through eight sets of aerial photographs over seven decades. These revealed 88% woodland loss from 1951 to 1999 (R2 = 0.984), including a steeper decline with the 1980s drought. Following the implementation of an environmental flow regime that increased minimum flows after 1993, the remnant woodlands were stabilized, with a slight recovery by 2022. Analyses of the historical hydrology revealed compound contributions to the woodland mortality. (1) Annual river flows declined with increasing water diversion, and (2) late summer flows were particularly depleted. (3) Dam operations resulted in abrupt stage recessions and irregular spikes. (4) Accompanying climate warming, the spring snowmelt advanced and late summer flows declined. (5) The greatest climatic influence involved multiple‐year clusters with high versus low flows, corresponding with the Pacific decadal oscillation (PDO) from 1920 to 1990 (R2 = 0.365), but less coupled thereafter. This long‐term study demonstrates the coordination between hydroclimatic variation, water management and the fate of riparian woodlands, which reveal ecosystem health. An environmental flow regime provided benefit, and for other regulated rivers in dry ecoregions, we recommend functional flow regimes that provide sufficient minimum flows and avoid abrupt flow recession or irregular spikes.

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Short- and long-term responses of riparian cottonwoods (Populus spp.) to flow diversion: Analysis of tree-ring radial growth and stable carbon isotopes

Cited by 23 publications

References 75 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

Riparian forest productivity decline initiated by streamflow diversion then amplified by atmospheric drought 40 years later

Riparian cottonwood mortality following compound impacts from river water withdrawal and hydroclimatic variation

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