Tree Mortality in Blue Oak Woodland During Extreme Drought in Sequoia National Park, California

Das, Adrian J.; Ampersee, Nicholas J.; Pfaff, Anne Hopkins; Stephenson, Nathan L.; Swiecki, Tedmund J.; Bernhardt, Elizabeth A.; Haggerty, Patricia K.; Nydick, Koren R.

doi:10.3120/0024-9637-66.4.164

Cited by 11 publications

(15 citation statements)

References 20 publications

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“…Consistent with our results, others have reported that blue oak mortality is concentrated in the driest, southern part of the Sierra Nevada Range (Brown et al 2018, Jacobsen and Pratt 2018, Das et al 2019, Fettig et al 2019a) and southernmost interior Coast Ranges (Brown et al 2018, McLaughlin et al 2020. We show that blue oaks on south-facing aspects are more susceptible to drought stress, while the potential for soil moisture to drain into a pixel is correlated with less drought stress.…”

Section: Climate Changesupporting

confidence: 92%

Detection of drought‐induced blue oak mortality in the Sierra Nevada Mountains, California

et al. 2021

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From 2011 to 2016, California experienced a millennial-intensity drought, generating high levels of tree mortality. Remote sensing has been used to monitor the long-term impacts of drought; however, discriminating dead from live trees in arid and semiarid deciduous woodlands is challenging. The goals of this study were to assess and map the spatial patterns of drought-induced tree mortality in a blue oak (Quercus douglasii) woodland, a highly drought-tolerant species forming savannas along the lower foothills surrounding California's Central Valley. Airborne hyperspectral imagery was used to identify the most important wavelength regions predicting drought-induced blue oak mortality. The best metric to predict canopy stress was a normalized ratio using the spectral bands 937.53 and 1100.08 nm with a correlation with tree mortality of R 2 = 0.83. The image prediction of mortality for nine field plots found that 16 of 98 trees died (17.9%) during the drought. We further evaluated tree mortality in 82 independent plots, and we found the greatest image predictive accuracy for tree mortality between 1% and 10%. When applied at the landscape level, the regression-based index found mortality ranged from 1% to more than 51% in oak stands with an average mortality of 10% over the entire study region. In addition, tree mortality at landscape level showed higher tree mortality in blue oaks on south-facing aspects probably because of higher insolation rates and in sites with low potential for accumulated drainage.

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Section: Climate Changesupporting

confidence: 92%

Detection of drought‐induced blue oak mortality in the Sierra Nevada Mountains, California

et al. 2021

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“…Relationships that are non-significant are colored in white. Das et al (2020) reported that about 19% of standing blue oak trees and 14% of all trees were killed during that drought. In blue oak species, mortality was high across all tree size classes, with a higher mortality rate in trees over 40 cm at breast height (Das et al, 2020).…”

Section: Discussionmentioning

confidence: 99%

“…Das et al (2020) reported that about 19% of standing blue oak trees and 14% of all trees were killed during that drought. In blue oak species, mortality was high across all tree size classes, with a higher mortality rate in trees over 40 cm at breast height (Das et al, 2020). In the Klamath Mountains of northern California, Bost et al (2019) found a three-fold increase in the area of canopy decline during the drought.…”

Section: Discussionmentioning

confidence: 99%

“…Despite the importance of this unique ecosystem, there is a lack of information on the negative consequences of the recent drought on tree cover as well as the long-term patterns of tree cover change in the area. A more recent study on the drought's effect on tree mortality was limited to a small subset of blue oak woodlands (Das et al, 2020). In a 2017 post-drought survey in the Sequoia National Park, Das et al (2020) estimated that 19% of standing blue oak and 14% of all trees were killed during that drought, with blue oak basal area dropping by 26%.…”

Section: Introductionmentioning

confidence: 99%

“…A more recent study on the drought's effect on tree mortality was limited to a small subset of blue oak woodlands (Das et al, 2020). In a 2017 post-drought survey in the Sequoia National Park, Das et al (2020) estimated that 19% of standing blue oak and 14% of all trees were killed during that drought, with blue oak basal area dropping by 26%. Meanwhile, landscape-wide studies using bioclimate modeling to project the vulnerability of blue oak distribution relied on climate and hydrologic factors, precluding important factors such as wildfire disturbance (Kueppers et al, 2005;Brown et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Hotter Drought Escalates Tree Cover Declines in Blue Oak Woodlands of California

et al. 2021

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California has, in recent years, become a hotspot of interannual climatic variability, recording devastating climate-related disturbances with severe effects on tree resources. Understanding the patterns of tree cover change associated with these events is vital for developing strategies to sustain critical habitats of endemic and threatened vegetation communities. We assessed patterns of tree cover change, especially the effects of the 2012–2016 drought within the distribution range of blue oak (Quercus douglasii), an endemic tree species to California with a narrow geographic extent. We utilized multiple, annual land-cover and land-surface change products from the U.S. Geological Survey (USGS) Land Change Monitoring, Assessment and Projection (LCMAP) project along with climate and wildfire datasets to monitor changes in tree cover state and condition and examine their relationships with interannual climate variability between 1985 and 2016. Here, we refer to a change in tree cover class without a land-cover change to another class as “conditional change.” The unusual drought of 2012–2016, accompanied by anomalously high temperatures and vapor pressure deficit, was associated with exceptional spikes in the amount of both fire and non-fire induced tree cover loss and tree cover conditional change, especially in 2015 and 2016. Approximately 1,266 km2 of tree cover loss and 617 km2 of tree cover conditional change were recorded during that drought. Tree cover loss through medium to high severity fires was especially large in exceptionally dry and hot years. Our study demonstrates the usefulness of the LCMAP products for monitoring the effects of climatic extremes and disturbance events on both thematic and conditional land-cover change over a multi-decadal period. Our results signify that blue oak woodlands may be vulnerable to extreme climate events and changing wildfire regimes. Here, we present early evidence that frequent droughts associated with climate warming may continue to affect tree cover in this region, while drought interaction with wildfires and the resulting feedbacks may have substantial influence as well. Consequently, efforts to conserve the blue oak woodlands, and potentially other vegetation communities in the Western United States, may benefit from consideration of climate risks as well as the potential for climate-fire and vegetation feedbacks.

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Downed wood removal effects on survival and site fidelity of woodrats in a California oak woodland

Smyser,

Hardy,

Davis

et al. 2024

J Wildl Manag

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Owing to the increasing intensity and frequency of wildfires in the western United States, the removal of woody debris (downed dead wood and snags) from fire‐prone landscapes is being evaluated for wildfire mitigation. Consequently, the study of the ecological value of coarse woody debris to sustain dependent species has become of foremost importance. From 2004–2009, we used a before‐after control‐impact (BACI) study design to assess the effects of downed wood removal on a population of big‐eared woodrats (Neotoma macrotis) in an oak woodland (Quercus spp.) in coastal‐central California, USA. Using Pollock's robust design mark‐recapture analyses (with 12 primary capture occasions represented by trapping each spring and fall, and secondary occasions composed of 3 trap nights), we estimated survival and emigration rates. Further, applying mixed‐effects models, we evaluated the effects of 7 habitat attributes on woodrat abundance and reproduction. Following the experimental removal of downed wood from the 11 randomly selected treatment plots, woodrat survival was higher (P = 0.013), and emigration was lower (P = 0.007) among 11 control plots on which downed wood was retained. Woodrat abundance within plots was best predicted by stem density, demonstrating positive demographic associations with habitat complexity. Plot‐level reproductive success (i.e., the presence of juveniles within a plot during spring) was more likely with increasing snag density. These findings indicate that snags and downed dead wood are key components of high‐quality habitat for big‐eared woodrats. Management of woody debris to mitigate wildfire risk should consider the ecological value of this habitat attribute for big‐eared woodrats and other dependent species.

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Tree Mortality in Blue Oak Woodland During Extreme Drought in Sequoia National Park, California

Cited by 11 publications

References 20 publications

Detection of drought‐induced blue oak mortality in the Sierra Nevada Mountains, California

Detection of drought‐induced blue oak mortality in the Sierra Nevada Mountains, California

Hotter Drought Escalates Tree Cover Declines in Blue Oak Woodlands of California

Downed wood removal effects on survival and site fidelity of woodrats in a California oak woodland

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