Tree mortality from a short-duration freezing event and global-change-type drought in a Southwestern piñon-juniper woodland, USA

Poulos, Helen M.

doi:10.7717/peerj.404

Cited by 14 publications

(10 citation statements)

References 48 publications

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“…). It is also consistent with patterns of mortality associated with long‐term drought interacting with sporadic freeze–thaw events to increase mortality rates in Pinus cembroides and Juniperus deppeana (Polous ) and multiple co‐existing Juniperus species due to xylem embolism (Willson and Jackson ). Because of this interaction between a background stressor (gradual loss of snow or occasional drought) and a sporadic weather event (in the examples, thaw and freezing events), this mortality is not expected every year.…”

Section: Discussionsupporting

confidence: 73%

Transitional climate mortality: slower warming may result in increased climate‐induced mortality in some systems

Buma

2018

Ecosphere

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The potential for climate change to cause mass tree mortality in forested systems by pushing environmental conditions past physiological tolerance thresholds is well documented. Less well studied is damage and mortality associated with climatic transitions, where mortality is less on either side of the transition; the shift from freezing winter conditions to thawed winter conditions in temperate and high latitudes is a clear example. “Transitional climate mortality” is sporadic, but widespread, associated with exposure to mortality during these climatic transitions, and triggered by proximal weather events like a hard freeze after a period of above freezing temperatures. Interestingly, this suggests that slower warming could result in more intensive mortality because of extended exposure to potential mortality events. The concept is tested using a well‐studied species (Callitropsis nootkatensis) on the US/Canadian Pacific coast. To identify the transitional mortality zone, statistical modeling combined with a current mortality map and bioclimatic variables was used. This process identified the −5° to 0°C zone (mean temperature of the coldest month) as particularly associated with transitional mortality. Weather station data from multiple locations were used to validate observations. Four GCMs (General Circulation Model) and two future warming scenarios (representative concentration pathway 2.6 and 8.5) were used to estimate time and spatial extent of exposure at broad scales; slower warming results in more intensive cumulative exposure than faster warming. Finally, by combining the observed mortality zone with weather station data a generalizable binomial model was tested as a means to estimate potential future mortality. This model is applicable to any system where the transitional mortality zone (e.g., temperature range) and the frequency of proximal mortality triggers are known. This type of mortality phenomena has been understudied but may be a large driver of future forest change, given the frequency of mortality events and the ubiquity of the freeze–thaw transition across temperate systems globally.

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Section: Discussionsupporting

confidence: 73%

Transitional climate mortality: slower warming may result in increased climate‐induced mortality in some systems

Buma

2018

Ecosphere

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“…Q. emoryi may still be pushed downslope from its optimal elevation zone. It was found to be more vulnerable to drought‐induced mortality than either Q. grisea or Q. arizonica in a long‐term drought in Texas (Poulos ). Among the white oaks, Q. rugosa has been found to be a relatively shade‐tolerant species (Poulos et al.…”

Section: Discussionmentioning

confidence: 99%

“…Q. emoryi may still be pushed downslope from its optimal elevation zone. It was found to be more vulnerable to drought-induced mortality than either Q. grisea or Q. arizonica in a long-term drought in Texas (Poulos 2014). Among the white oaks, Q. rugosa has been found to be a relatively shade-tolerant species (Poulos et al 2008), which may allow it to live a similarly conservative evergreen lifestyle at the middle elevations of the white oak gradient, while its relatives demonstrate different timing of deciduousness.…”

Section: Species Coexistence and Niche Partitioning Within Subgeneramentioning

confidence: 99%

Leaf‐level trade‐offs between drought avoidance and desiccation recovery drive elevation stratification in arid oaks

Fallon

Cavender‐Bares

2018

Ecosphere

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Citation: Fallon, B., and J. Cavender-Bares. 2018. Leaf-level trade-offs between drought avoidance and desiccation recovery drive elevation stratification in arid oaks. Ecosphere 9(3):e02149. 10. 1002/ecs2.2149 Abstract. Understanding the extent to which climate limitations drive elevation stratification among species is integral to predicting the impacts of climate change. Zonation patterns of species within mountains have been well documented, and shifts in these patterns have been correlated with recent warming. However, the physiological mechanisms that explain these zonation patterns are not well understood. We used a system of broadly sympatric oak species within semi-arid mountains to (1) investigate the extent to which species elevation ranges correlate with climate, (2) test for associations of cold and drought resistances with upper and lower elevation limits, and for trade-offs between resistance mechanisms with elevation, and (3) examine the extent to which species-wide climatic ranges predict traits that drive local community assembly along an elevation gradient. We found that aridity gradients but not winter minimum temperatures predict oak stratification. Species differed in drought resistance, demonstrating a tradeoff between drought avoidance and drought recovery. At lower elevations, species avoided drought stress during the dry season through leaf abscission; at upper elevations, they maintained transpiration but recovered from daily desiccation via higher leaf water storage capacity, rather than tolerating desiccation via lower turgor loss points. Freezing resistance, measured as stem electrolyte leakage, was not correlated with elevation differences. Taken together, these results indicate that elevation stratification is linked to drought resistance rather than freezing resistance. We also found evidence of niche partitioning among closely related oaks linked to contrasting leaf phenology. The functional, phenological, and physiological traits important for elevation stratification were correlated with species' range-wide mean annual precipitation and precipitation seasonality, but not aridity. Our findings indicate that drought resistance along a leaf avoidance-recovery trade-off is integral to species stratification within this semi-arid montane system. Additionally, the mechanism of stratification acts upon traits and strategies conserved at the species level. Species within this system are likely vulnerable to range retraction under increased drought as a consequence of this phenological avoidance-physiological tolerance trade-off.

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“…A study of the pinyon-juniper stands in Big Bend National Park, found that P. cembroides had the highest tree mortality followed by J. deppeana, and Q. emoryi, resulting from a combined stress of a severe winter freeze event and the 2011 drought (Poulos, 2014). A study of the pinyon-juniper stands in Big Bend National Park, found that P. cembroides had the highest tree mortality followed by J. deppeana, and Q. emoryi, resulting from a combined stress of a severe winter freeze event and the 2011 drought (Poulos, 2014).…”

Section: Discussionmentioning

confidence: 99%

Measuring canopy loss and climatic thresholds from an extreme drought along a fivefold precipitation gradient across Texas

Schwantes

Swenson

González‐Roglich

et al. 2017

Global Change Biology

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Globally, trees are increasingly dying from extreme drought, a trend that is expected to increase with climate change. Loss of trees has significant ecological, biophysical, and biogeochemical consequences. In 2011, a record drought caused widespread tree mortality in Texas. Using remotely sensed imagery, we quantified canopy loss during and after the drought across the state at 30-m spatial resolution, from the eastern pine/hardwood forests to the western shrublands, a region that includes the boundaries of many species ranges. Canopy loss observations in ~200 multitemporal fine-scale orthophotos (1-m) were used to train coarser Landsat imagery (30-m) to create 30-m binary statewide canopy loss maps. We found that canopy loss occurred across all major ecoregions of Texas, with an average loss of 9.5%. The drought had the highest impact in post oak woodlands, pinyon-juniper shrublands and Ashe juniper woodlands. Focusing on a 100-km by ~1,000-km transect spanning the State's fivefold east-west precipitation gradient (~1,500 to ~300 mm), we compared spatially explicit 2011 climatic anomalies to our canopy loss maps. Much of the canopy loss occurred in areas that passed specific climatic thresholds: warm season anomalies in mean temperature (+1.6°C) and vapor pressure deficit (VPD, +0.66 kPa), annual percent deviation in precipitation (-38%), and 2011 difference between precipitation and potential evapotranspiration (-1,206 mm). Although similarly low precipitation occurred during the landmark 1950s drought, the VPD and temperature anomalies observed in 2011 were even greater. Furthermore, future climate data under the representative concentration pathway 8.5 trajectory project that average values will surpass the 2011 VPD anomaly during the 2070-2099 period and the temperature anomaly during the 2040-2099 period. Identifying vulnerable ecological systems to drought stress and climate thresholds associated with canopy loss will aid in predicting how forests will respond to a changing climate and how ecological landscapes will change in the near term.

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Tree mortality from a short-duration freezing event and global-change-type drought in a Southwestern piñon-juniper woodland, USA

Cited by 14 publications

References 48 publications

Transitional climate mortality: slower warming may result in increased climate‐induced mortality in some systems

Transitional climate mortality: slower warming may result in increased climate‐induced mortality in some systems

Leaf‐level trade‐offs between drought avoidance and desiccation recovery drive elevation stratification in arid oaks

Measuring canopy loss and climatic thresholds from an extreme drought along a fivefold precipitation gradient across Texas

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