Now showing items 10447-10466 of 11162

    • Transverse momentum and process dependent azimuthal anisotropies in root S-NN=8.16 TeV p plus Pb collisions with the ATLAS detector

      ATLUS Collaboration; Univ Arizona, Dept Phys (SPRINGER, 2020)
      The azimuthal anisotropy of charged particles produced in sNN=8.16TeV p+Pb collisions is measured with the ATLAS detector at the LHC. The data correspond to an integrated luminosity of 165 nb-1 that was collected in 2016. Azimuthal anisotropy coefficients, elliptic v2 and triangular v3\, extracted using two-particle correlations with a non-flow template fit procedure, are presented as a function of particle transverse momentum (pT) between 0.5 and 50 GeV. The v2 results are also reported as a function of centrality in three different particle pTintervals. The results are reported from minimum-bias events and jet-triggered events, where two jet pT thresholds are used. The anisotropies for particles with pT less than about 2 GeV are consistent with hydrodynamic flow expectations, while the significant non-zero anisotropies for pT in the range 9-50 GeV are not explained within current theoretical frameworks. In the pTrange 2-9 GeV, the anisotropies are larger in minimum-bias than in jet-triggered events. Possible origins of these effects, such as the changing admixture of particles from hard scattering and the underlying event, are discussed.
    • Trapping set ontology

      Vasic, Bane; Chilappagari, Shashi Kiran; Nguyen, Dung Viet; Planjery, Shiva Kumar; Univ Arizona, Dept Elect & Comp Engn (IEEE, 2009-09)
      The failures of iterative decoders for low-density parity-check (LDPC) codes on the additive white Gaussian noise channel (AWGNC) and the binary symmetric channel (BSC) can be understood in terms of combinatorial objects known as trapping sets. In this paper, we derive a systematic method to identify the most relevant trapping sets for decoding over the BSC in the error floor region. We elaborate on the notion of the critical number of a trapping set and derive a classification of trapping sets. We then develop the trapping set ontology, a database of trapping sets that summarizes the topological relations among trapping sets. We elucidate the usefulness of the trapping set ontology in predicting the error floor as well as in designing better codes.
    • Trash reconsidered: A relational approach to deposition in the Pueblo Southwest

      Fladd, Samantha G.; Hedquist, Saul L.; Adams, E. Charles; School of Anthropology, University of Arizona; Arizona State Museum, University of Arizona (Elsevier BV, 2021-03)
      Deposition creates the archaeological record; however, the social implications of depositional practices are often overlooked, particularly when considering domestic materials found in upper room fill. In this paper, we argue that the term “trash” and its connotations mischaracterize the thought and meaning that motivate decisions about deposition, as exemplified by ethnohistoric and modern accounts of disposal within Pueblo society. Understanding the context and content of deposition can reveal important aspects of the identities, beliefs, and relationships of the individuals and groups who created them. We explore the social role of deposits at Homol'ovi I, an ancestral Hopi pueblo in northeastern Arizona, through detailed analyses of excavation data. Drawing on contemporary Hopi insights, rooms and objects are found to assume distinct social identities, specifically gender, that influence the placement of materials throughout the pueblo. We conclude that patterns of cultural deposition from all contexts have the potential to provide significant insights about the life histories, reuse, and commemoration of spaces and objects when considering archaeological contexts worldwide. © 2021 Elsevier Inc.
    • Trauma resuscitation requiring massive transfusion: a descriptive analysis of the role of ratio and time

      Peralta, Ruben; Vijay, Adarsh; El-Menyar, Ayman; Consunji, Rafael; Abdelrahman, Husham; Parchani, Ashok; Afifi, Ibrahim; Zarour, Ahmad; Al-Thani, Hassan; Latifi, Rifat; et al. (Springer, 2015)
      OBJECTIVE: We aimed to evaluate whether early administration of high plasma to red blood cells ratios influences outcomes in injured patients who received massive transfusion protocol (MTP). METHODS: A retrospective analysis was conducted at the only level 1 national trauma center in Qatar for all adult patients(≥18 years old) who received MTP (≥10 units) of packed red blood cell (PRBC) during the initial 24 h post traumatic injury. Data were analyzed with respect to FFB:PRBC ratio [(high ≥ 1:1.5) (HMTP) vs. (low < 1:1.5) (LMTP)] given at the first 4 h post-injury and also between (>4 and 24 h). Mortality, multiorgan failure (MOF) and infectious complications were studied as well. RESULTS: During the study period, a total of 4864 trauma patients were admitted to the hospital, 1.6 % (n = 77) of them met the inclusion criteria. Both groups were comparable with respect to initial pH, international normalized ratio, injury severity score, revised trauma score and development of infectious complications. However, HMTP was associated with lower crude mortality (41.9 vs. 78.3 %, p = 0.001) and lower rate of MOF (48.4 vs. 87.0 %, p = 0.001). The number of deaths was 3 times higher in LMTP in comparison to HMTP within the first 30 days (36 vs. 13 cases). The majority of deaths occurred within the first 24 h (80.5 % in LMTP and 69 % in HMTP) and particularly within the first 6 h (55 vs. 46 %). CONCLUSIONS: Aggressive attainment of high FFP/PRBC ratios as early as 4 h post-injury can substantially improve outcomes in trauma patients.
    • Trauma surgery associations and societies: which organizations match your goals?

      Ball, Chad; Grondin, Sean; Schieman, Colin; Feliciano, David; Dixon, Elijah; Kirkpatrick, Andrew; Ivatury, Rao; Salomone, Jeffrey; Reed, Lawrence; From the Departments of Surgery, University of Calgary, Foothills Medical Center, Calgary, Alberta, Canada; et al. (BioMed Central, 2014)
      This focused summary is a multi-institutional, multi-national, and multi-generational project designed to briefly summarize current academic trauma societies for both trainees and faculty alike. The co-authorship is composed of former and/or current presidents from most major trauma organizations. It has particular relevance to trainees and/or recent graduates attempting to navigate the multitude of available trauma organizations.
    • Traumatic brain injury induced temperature dysregulation: What is the role of β blockers?

      Asmar, Samer; Bible, Letitia; Chehab, Mohamad; Tang, Andrew; Khurrum, Muhammad; Castanon, Lourdes; Ditillo, Michael; Douglas, Molly; Joseph, Bellal; Division of Trauma, Critical Care, Emergency Surgery, and Burns, Department of Surgery, College of Medicine, University of Arizona (Lippincott Williams & Wilkins, 2021-01)
      BACKGROUND: Traumatic brain injury (TBI) is associated with sympathetic discharge that leads to posttraumatic hyperthermia (PTH). Beta blockers (ββ) are known to counteract overactive sympathetic discharge. The aim of our study was to evaluate the effect of ββ on PTH in critically-ill TBI patients. METHODS: We performed retrospective cohort analysis of the Medical Information Mart for Intensive Care database. We included all critically ill TBI patients with head Abbreviated Injury Scale (AIS) score of 3 or greater and other body region AIS score less than 2 who developed PTH (at least one febrile episode [T > 38.3°C] with negative microbiological cultures (blood, urine, and bronchoalveolar lavage). Patients on preinjury ββ were excluded. Patients were stratified into (ββ+) and (ββ-) groups. Propensity score matching was performed (1:1 ratio) controlling for patient demographics, injury parameters and other medications that influence temperature. Outcomes were the number of febrile episodes, maximum temperature, and the time interval between febrile episodes. Multivariate linear regression was performed. RESULTS: We analyzed 4,286 critically ill TBI patients. A matched cohort of 1,544 patients was obtained: 772 ββ + (metoprolol, 60%; propranolol, 25%; and atenolol, 15%) and 772 ββ-. Mean age was 63.4 ± 15.4 years, median head AIS score of 3 (3-4), and median Injury Severity Score of 10 (9-16). Patients in the ββ+ group had a lower number of febrile episodes (8 episodes vs. 12 episodes; p = 0.003), lower median maximum temperature (38.0°C vs. 38.5°C; p = 0.025), and a longer median time between febrile episodes (3 hours vs. 1 hour; p = 0.013). On linear regression, propranolol was found to be superior in terms of reducing the number of febrile episodes and the maximum temperature. However, there was no significant difference between the three ββ in terms of reducing the time interval between febrile episodes (p = 0.582). CONCLUSION: Beta blockers attenuate PTH by decreasing the frequency of febrile episodes, increasing the time interval between febrile episodes, and reducing the maximum rise in temperature. ββ may be a potential therapeutic modality in PTH. LEVEL OF EVIDENCE: Therapeutic, level IV. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.
    • Traumatic Brain Injury-Induced Sex-Dependent Changes in Late-Onset Sensory Hypersensitivity and Glutamate Neurotransmission

      Krishna, Gokul; Bromberg, Caitlin; Connell, Emily Charlotte; Mian, Erum; Hu, Chengcheng; Lifshitz, Jonathan; Adelson, P. David; Thomas, Theresa Currier; Univ Arizona, Coll Med Phoenix, Dept Child Hlth; Univ Arizona, Dept Epidemiol & Biostat (FRONTIERS MEDIA SA, 2020-08)
      Women approximate one-third of the annual 2.8 million people in the United States who sustain traumatic brain injury (TBI). Several clinical reports support or refute that menstrual cycle-dependent fluctuations in sex hormones are associated with severity of persisting post-TBI symptoms. Previously, we reported late-onset sensory hypersensitivity to whisker stimulation that corresponded with changes in glutamate neurotransmission at 1-month following diffuse TBI in male rats. Here, we incorporated intact age-matched naturally cycling females into the experimental design while monitoring daily estrous cycle. We hypothesized that sex would not influence late-onset sensory hypersensitivity and associatedin vivoamperometric extracellular recordings of glutamate neurotransmission within the behaviorally relevant thalamocortical circuit. At 28 days following midline fluid percussion injury (FPI) or sham surgery, young adult Sprague-Dawley rats were tested for hypersensitivity to whisker stimulation using the whisker nuisance task (WNT). As predicted, both male and female rats showed significantly increased sensory hypersensitivity to whisker stimulation after FPI, with females having an overall decrease in whisker nuisance scores (sex effect), but no injury and sex interaction. In males, FPI increased potassium chloride (KCl)-evoked glutamate overflow in primary somatosensory barrel cortex (S1BF) and ventral posteromedial nucleus of the thalamus (VPM), while in females the FPI effect was discernible only within the VPM. Similar to our previous report, we found the glutamate clearance parameters were not influenced by FPI, while a sex-specific effect was evident with female rats showing a lower uptake rate constant both in S1BF and VPM and longer clearance time (in S1BF) in comparison to male rats. Fluctuations in estrous cycle were evident among brain-injured females with longer diestrus (low circulating hormone) phase of the cycle over 28 days post-TBI. Together, these findings add to growing evidence indicating both similarities and differences between sexes in a chronic response to TBI. A better understanding of the influence of gonadal hormones on behavior, neurotransmission, secondary injury and repair processes after TBI is needed both clinically and translationally, with potential impact on acute treatment, rehabilitation, and symptom management.
    • Traumatic injury among females: does gender matter?

      El-Menyar, Ayman; El-Hennawy, Hany; Al-Thani, Hassan; Asim, Mohammad; Abdelrahman, Husham; Zarour, Ahmad; Parchani, Ashok; Peralta, Ruben; Latifi, Rifat; Clinical Research, Trauma Surgery Section, Hamad General Hospital, PO Box 3050, Doha, Qatar; et al. (BioMed Central, 2014)
      BACKGROUND:Trauma remains one of the leading causes of morbidity and mortality worldwide. Generally, the incidence of traumatic injuries is disproportionately high in males. However, trauma in females is underreported.AIM:To study the epidemiology and outcome of different mechanisms and types of traumatic injuries in women.METHODS:We conducted a traditional narrative review using PubMed, MEDLINE and EMBASE, searching for English-language publications for gender-specific trauma between January 1993 and January 2013 using key words "trauma", "gender", "female" and "women".RESULTS:Among 1150 retrieved articles, 71 articles were relevant over 20 years. Although it is an important public health problem, traumatic injuries among females remain under-reported.CONCLUSION:There is a need for further research and evaluation of the exact burden of traumatic injuries among females together with the implementation of effective community based preventive programs.
    • Traumatic injury compromises nucleocytoplasmic transport and leads to TDP-43 pathology

      Anderson, E.N.; Morera, A.A.; Kour, S.; Cherry, J.D.; Ramesh, N.; Gleixner, A.; Schwartz, J.C.; Ebmeier, C.; Old, W.; Donnelly, C.J.; et al. (eLife Sciences Publications Ltd, 2021)
      Traumatic brain injury (TBI) is a predisposing factor for many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), Parkinson's disease (PD), and chronic traumatic encephalopathy (CTE). Although defects in nucleocytoplasmic transport (NCT) is reported ALS and other neurodegenerative diseases, whether defects in NCT occur in TBI remains unknown. We performed proteomic analysis on Drosophila exposed to repeated TBI and identified resultant alterations in several novel molecular pathways. TBI upregulated nuclear pore complex (NPC) and nucleocytoplasmic transport (NCT) proteins as well as alter nucleoporin stability. Traumatic injury disrupted RanGAP1 and NPC protein distribution in flies and a rat model and led to coaggregation of NPC components and TDP-43. In addition, trauma-mediated NCT defects and lethality are rescued by nuclear export inhibitors. Importantly, genetic upregulation of nucleoporins in vivo and in vitro triggered TDP-43 cytoplasmic mislocalization, aggregation, and altered solubility and reduced motor function and lifespan of animals. We also found NUP62 pathology and elevated NUP62 concentrations in postmortem brain tissues of patients with mild or severe CTE as well as co-localization of NUP62 and TDP-43 in CTE. These findings indicate that TBI leads to NCT defects, which potentially mediate the TDP-43 pathology in CTE. © 2021, Anderson et al.
    • Travel Nurse Onboarding: Current Trends and Identified Needs

      Bethel, Claire; Olson, Susan; Bay, Curt; Uyeda, Tami; Johnson, Karen; Univ Arizona, Coll Nursing (LIPPINCOTT WILLIAMS & WILKINS, 2019-09-01)
      OBJECTIVE The purpose of this study was to describe current practices for onboarding travel nurses (TRNs) and identify TRNs' specific onboarding needs. BACKGROUND Onboarding must be streamlined and organized for TRNs to provide safe patient care. METHODS Cross-sectional descriptive survey was used with 306 TRNs throughout United States who were recruited electronically from a closed social media group page. RESULTS The TRNs identified critical information, including unit patient ratios, onboarding schedule 7 to 14 days before travel assignment start, and login IDs/accesses on day 1. Travel nurse onboarding and competency assessment checklists should be specific to the unit/facility where they will work. CONCLUSION Findings from this study have the potential to support hospitals in the development of streamlined and tailored TRN onboarding to support regulatory compliance and patient safety as well as realize significant cost savings for TRN onboarding.
    • Traveling Waves of a Go-or-Grow Model of Glioma Growth

      Stepien, Tracy L.; Rutter, Erica M.; Kuang, Yang; Univ Arizona, Dept Math (SIAM PUBLICATIONS, 2018)
      Glioblastoma multiforme is a deadly brain cancer in which tumor cells excessively proliferate and migrate. The first mathematical models of the spread of gliomas featured reactiondiffusion equations, and later an idea emerged through experimental study called the "Go or Grow" hypothesis in which glioma cells have a dichotomous behavior: a cell either primarily proliferates or primarily migrates. We analytically investigate an extreme form of the "Go or Grow" hypothesis where tumor cell motility and cell proliferation are considered as separate processes. Different solution types are examined via approximate solution of traveling wave equations, and we determine conditions for various wave front forms.
    • Treatment for Early, Uncomplicated Coccidioidomycosis: What Is Success?

      Galgiani, John N; Blair, Janis E; Ampel, Neil M; Thompson, George R; Univ Arizona, Coll Med, Valley Fever Ctr Excellence; Univ Arizona, Coll Med, Dept Med (OXFORD UNIV PRESS INC, 2019-09-23)
      The care of primary pulmonary coccidioidomycosis remains challenging. Such infections produce a variety of signs, symptoms, and serologic responses that cause morbidity in patients and concern in treating clinicians for the possibility of extrapulmonary dissemination. Illness may be due to ongoing fungal growth that produces acute inflammatory responses, resulting in tissue damage and necrosis, and for this, administering an antifungal drug may be of benefit. In contrast, convalescence may be prolonged by other immunologic reactions to infection, even after fungal replication has been arrested, and in those situations, antifungal therapy is unlikely to yield clinical improvement. In this presentation, we discuss what findings are clinical indicators of fungal growth and what other sequelae are not. Understanding these differences provides a rational management strategy for deciding when to continue, discontinue, or reinstitute antifungal treatments.
    • Treatment impacts on temporal microbial community dynamics during phytostabilization of acid-generating mine tailings in semiarid regions

      Valentín-Vargas, Alexis; Neilson, Julia W; Root, Robert A; Chorover, Jon; Maier, Raina M; Univ Arizona, Dept Soil Water & Environm Sci (ELSEVIER SCIENCE BV, 2018-03-15)
      Direct revegetation, or phytostabilization, is a containment strategy for contaminant metals associated with mine tailings in semiarid regions. The weathering of sulfide ore-derived tailings frequently drives acidification that inhibits plant establishment resulting in materials prone to wind and water dispersal. The specific objective of this study was to associate pyritic mine waste acidification, characterized through pore-water chemistry analysis, with dynamic changes in microbial community diversity and phylogenetic composition, and to evaluate the influence of different treatment strategies on the control of acidification dynamics. Samples were collected from a highly instrumented one-year mesocosm study that included the following treatments: 1) unamended tailings control; 2) tailings amended with 15% compost; and 3) the 15% compost-amended tailings planted with Atriplex lentiformis. Tailings samples were collected at 0, 3, 6 and 12months and pore water chemistry was monitored as an indicator of acidification and weathering processes. Results confirmed that the acidification process for pyritic mine tailings is associated with a temporal progression of bacterial and archaeal phylotypes from pH sensitive Thiobacillus and Thiomonas to communities dominated by Leptospirillum and Ferroplasma. Pore-water chemistry indicated that weathering rates were highest when Leptospirillum was most abundant. The planted treatment was most successful in disrupting the successional evolution of the Fe/S-oxidizing community. Plant establishment stimulated growth of plant-growth-promoting heterotrophic phylotypes and controlled the proliferation of lithoautotrophic Fe/S-oxidizers. The results suggest the potential for eco-engineering a microbial inoculum to stimulate plant establishment and inhibit proliferation of the most efficient Fe/S-oxidizing phylotypes.
    • Treatment of COVID-19: Perspective on Convalescent Plasma Transfusion

      Farhat, Ryan M.; Mousa, Mohammad A.; Daas, Eshaan J.; Glassberg, Marilyn K.; Univ Arizona, Coll Med Phoenix; Univ Arizona, Coll Med Phoenix, Dept Med, Div Pulm Crit Care & Sleep Med (FRONTIERS MEDIA SA, 2020-07)
      The novel coronavirus (COVID-19) has continued its global spread since the first documented case in late 2019 in Wuhan, China. With over 10 million cases and 500 thousand deaths reported worldwide, the need for an effective treatment regimen is evident. Historically, convalescent plasma (CP) has been utilized in the treatment of viral respiratory pathogens. Critically ill patients with COVID-19 in China and South Korea have been treated with CP given the ineffectiveness of experimental therapies with antivirals alone. This commentary explores the importance of published experience and the pending establishment of efficacy to facilitate an informed decision regarding the therapeutic use of CP. With increasing mortality around the world from COVID-19 infection, the need for alternative, effective treatment regimens is critical.
    • Tree growth and vegetation activity at the ecosystem-scale in the eastern Mediterranean

      Coulthard, Bethany L; Touchan, Ramzi; Anchukaitis, Kevin J; Meko, David M; Sivrikaya, Fatih; Univ Arizona, Lab Tree Ring Res; Univ Arizona, Sch Geog & Dev (IOP PUBLISHING LTD, 2017-08-01)
      Linking annual tree growth with remotely-sensed terrestrial vegetation indices provides a basis for using tree rings as proxies for ecosystem primary productivity over large spatial and long temporal scales. In contrast with most previous tree ring/remote sensing studies that have focused on temperature-limited boreal and taiga environments, here we compare the normalized difference vegetation index (NDVI) with a network of Pinus brutia tree ring width chronologies collected along ecological gradients in semiarid Cyprus, where both radial tree growth and broader vegetation activity are controlled by drought. We find that the interaction between precipitation, elevation, and land-cover type generate a relationship between radial tree growth and NDVI. While tree ring chronologies at higher-elevation forested sites do not exhibit climatedriven linkages with NDVI, chronologies at lower-elevation dry sites are strongly correlated with NDVI during the winter precipitation season. At lower-elevation sites, land cover is dominated by grasslands and shrublands and tree ring widths operate as a proxy for ecosystem-scale vegetation activity. Tree rings can therefore be used to reconstruct productivity in water-limited grasslands and shrublands, where future drought stress is expected to alter the global carbon cycle, biodiversity, and ecosystem functioning in the 21st century.
    • Tree growth in Switzerland is increasingly constrained by rising evaporative demand

      Trotsiuk, Volodymyr; Babst, Flurin; Grossiord, Charlotte; Gessler, Arthur; Forrester, David I.; Buchmann, Nina; Schaub, Marcus; Eugster, Werner; Laboratory of Tree-Ring Research, University of Arizona; School of Natural Resources and the Environment, University of Arizona (Wiley, 2021-06-13)
      The response of trees to intra-annual environmental constraints varies temporally throughout a growing season and spatially across landscapes. A better understanding of these dynamics will help us anticipate the impacts of short-term climate variability and medium-term climate change on forests. Using the process-based 3-PG forest ecosystem model, we assessed the spatial manifestation and seasonal variation in environmental constraints [vapour pressure deficit (VPD), air temperature and soil water availability] on tree growth for the potential distribution range of seven widespread Central European tree species. We focused our analyses on Switzerland, where large climatic gradients occur within a comparatively small geographic area. On average, over the last 60 years, simulated forest growth during the May–August growing season was limited by high VPD (67% of the forested area), low air temperature (29%) or low soil water availability (4%). But this response varied among species and across elevations. When comparing the period 1961–1990 with 1991–2018, we observed major shifts from former temperature limitation to recent VPD limitation across 12% of the area (3%–25%, depending on species), mainly at mid-elevations (700–1,200 m a.s.l.). At the same time, forest growth at lower elevations (i.e. below 700 m a.s.l.) became more limited by available soil water at the end of the growing season. Synthesis. Our results highlight how the relative impact of environmental growth constraints has shifted in the last three decades, and show that the importance of VPD as a dominant environmental growth constraint has increased for tree species in Swiss and Central European forests. Understanding the spatial and temporal variability in environmental growth constraints will help to generate accurate species-specific risk maps for forest managers to identify areas with elevated drought and heat stress in the near future.
    • Tree growth response to recent warming of two endemic species in Northeast Asia

      Altman, Jan; Treydte, Kerstin; Pejcha, Vit; Cerny, Tomas; Petrik, Petr; Srutek, Miroslav; Song, Jong-Suk; Trouet, Valerie; Dolezal, Jiri; Univ Arizona, Lab Tree Ring Res (SPRINGER, 2020-04-27)
      The impact of climatic change on forest ecosystems has received considerable attention, but our understanding of the modulation of this impact by elevational differences and by species interaction is still limited. Here, we analyse tree-ring-based growth-climate relationships for two dominant tree species along an 800-m elevational gradient on Jeju Island, South Korea. Both species, broadleaf Quercus mongolica (QUMO) and coniferous Abies koreana (ABKO), grow at the southern end of their distributional range and they have adjacent altitudinal ranges. We use static and moving bootstrapped correlation analysis to identify the effect of recent warming on their growth. QUMO is primarily positively influenced by moisture during the previous autumn at its upper elevational distribution. Recent warming, however, has diminished this relationship, while the enhancing impact of warm and dry summer conditions on QUMO growth has increased. These recent shifts in growth-climate relationship suggest an upward migration potential for QUMO due to warming-enhanced growth at higher elevations. ABKO growth, on the contrary, is primarily reduced by high winter and summer temperatures. This negative relationship has become more explicit in recent decades, particularly at lower elevations. At the highest elevation, however, ABKO growth-temperature relationship has consistently become more positive in the most recent decades. In the elevational zone where ABKO and QUMO co-exist, warming plays a primary role in ABKO growth reduction, while QUMO growth increases and thus induces a potential upward migration of QUMO. This combined effect can lead to population decline of ABKO. Our results significantly enhance our understanding of the impact of climate warming on two interacting species and provide information necessary for adaptation strategies to preserve declining ABKO populations.
    • Tree Morphologic Plasticity Explains Deviation from Metabolic Scaling Theory in Semi-Arid Conifer Forests, Southwestern USA

      Swetnam, Tyson L.; O’Connor, Christopher D.; Lynch, Ann M.; Univ Arizona, Sch Nat Resources & Environm; Univ Arizona, Tree Ring Res Lab (Public Library of Science, 2016-07-08)
      A significant concern about Metabolic Scaling Theory (MST) in real forests relates to consistent differences between the values of power law scaling exponents of tree primary size measures used to estimate mass and those predicted by MST. Here we consider why observed scaling exponents for diameter and height relationships deviate from MST predictions across three semi-arid conifer forests in relation to: (1) tree condition and physical form, (2) the level of inter-tree competition (e.g. open vs closed stand structure), (3) increasing tree age, and (4) differences in site productivity. Scaling exponent values derived from non-linear least-squares regression for trees in excellent condition (n = 381) were above the MST prediction at the 95% confidence level, while the exponent for trees in good condition were no different than MST (n = 926). Trees that were in fair or poor condition, characterized as diseased, leaning, or sparsely crowned had exponent values below MST predictions (n = 2,058), as did recently dead standing trees (n = 375). Exponent value of the mean-tree model that disregarded tree condition (n = 3,740) was consistent with other studies that reject MST scaling. Ostensibly, as stand density and competition increase trees exhibited greater morphological plasticity whereby the majority had characteristically fair or poor growth forms. Fitting by least-squares regression biases the mean-tree model scaling exponent toward values that are below MST idealized predictions. For 368 trees from Arizona with known establishment dates, increasing age had no significant impact on expected scaling. We further suggest height to diameter ratios below MST relate to vertical truncation caused by limitation in plant water availability. Even with environmentally imposed height limitation, proportionality between height and diameter scaling exponents were consistent with the predictions of MST.
    • Tree Mortality Decreases Water Availability and Ecosystem Resilience to Drought in Piñon-Juniper Woodlands in the Southwestern U.S.

      Morillas, L.; Pangle, R. E.; Maurer, G. E.; Pockman, W. T.; McDowell, N.; Huang, C.-W.; Krofcheck, D. J.; Fox, Andrew; Sinsabaugh, R. L.; Rahn, T. A.; et al. (AMER GEOPHYSICAL UNION, 2017-12)
      Climate-driven tree mortality has increased globally in response to warmer temperature and more severe drought. To examine how tree mortality in semiarid biomes impacts surface water balance, we experimentally manipulated a pinon-juniper (PJ) woodland by girdling all adult pinon trees in a 4 ha area, decreasing pinon basal area by similar to 65%. Over 3.5 years (2009-2013), we compared water flux measurements from this girdled site with those from a nearby intact PJ woodland. Before and after girdling, the ratio of evapotranspiration (ET) to incoming precipitation was similar between the two sites. Girdling altered the partitioning of ET such that the contribution of canopy transpiration to ET decreased 9-14% over the study period, relative to the intact control, while noncanopy ET increased. We attributed the elevated noncanopy ET in the girdled site each year to winter increases in sublimation and summer increases in both soil evaporation and below-canopy transpiration. Although we expected that mortality of a canopy dominant would increase the availability of water and other resources to surviving vegetation, we observed a decrease in both soil volumetric water content and sap flow rates in the remaining trees at the girdled site, relative to the control. This postgirdling decrease in the performance of the remaining trees occurred during the severe 2011-2012 drought, suggesting that pinon mortality may trigger feedback mechanisms that leave PJ woodlands drier relative to undisturbed sites and potentially more vulnerable to drought.
    • Tree Ring-Based Historic Hydroclimatic Variability of the Baja California Peninsula

      Gutierrez-Garcia, G.; Leavitt, S.W.; Trouet, V.; Carriquiry, J.D.; Laboratory of Tree-Ring Research, University of Arizona (Blackwell Publishing Ltd, 2020)
      The Baja California Peninsula is one of the most arid regions in Mexico, receiving an average of only 168 mm of precipitation annually. Climate change scenarios project drier and warmer conditions in the region at the end of this century driven by anthropogenic emissions of greenhouse gases. The growing demand for limited water supplies and the impacts of climate change pose a challenge to manage the already scarce water resources in the Peninsula. Analysis of historical hydroclimatic variability in the Peninsula is limited because most of the early instrumental climate data collection started only in the 1950s. In this study, we reconstruct past precipitation variability for the Peninsula using two tree ring chronologies from northern (Pinus monophylla) and southern (Pinus lagunae) Baja California. Our two reconstructions document multicentury hydroclimatic variability in the Peninsula, including events that turned out to be more extreme than those captured by modern instrumental records. Drought episodes are longer, more frequent, and more intense in the northern peninsula compared to the southern region. Multiyear dry and wet events in our two reconstructions exhibit broad spatial extent, affecting most of northwest Mexico and the western United States, which are mainly caused by broad-scale atmospheric circulation patterns such as El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). The results of this study allow framing current and projected droughts in a longer-term context, thus providing a better understanding of past climate variability and a basis for robust water resource management in the region. ©2020. American Geophysical Union. All Rights Reserved.