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Open Access Publications from the University of California

Scholarly Works (32 results)

  • Article
  • Peer Reviewed
UC Irvine Previously Published Works (2021)
Journaling of consumed foods through digital devices is a popular self-tracking strategy for weight loss and eating mindfulness. Research has explored modalities, like photos and open-ended text and voice descriptions, to make journaling less burdensome and more descriptive than traditional barcode and database searches. However, less is known about how people prefer to journal foods when less constrained by limitations of databases, natural language processing, and image recognition. We deployed a food journal prototype supporting varied devices and input modalities, which 15 participants used to journal 1008 food logs over two weeks. Participants had diverse strategies for indicating what and how much they ate, varying from ambiguous foods to specifying varieties and using different measurements for clarifying amount. Some strategies were interpretable by natural language food identification and image classification services, while others point to open research questions. We finally discuss opportunities for accounting for variance in food journaling.
    Cover page: Investigating Preferred Food Description Practices in Digital Food Journaling
    • Article
    • Peer Reviewed
    UC Santa Cruz Previously Published Works (2021)
    Globally, cold-limited trees and forests are expected to experience growth acceleration as a direct response to warming temperatures. However, thresholds of temperature limitation may vary substantially with local environmental conditions, leading to heterogeneous responses in tree ecophysiology. We used dendroecological and isotopic methods to quantify shifting tree growth and resource use over the past 143 years across topographic aspects in a high-elevation forest of central Mexico. Trees on south-facing slopes (SFS) grew faster than those on north-facing slopes (NFS) until the mid-20th century, when this pattern reversed notably with marked growth rate declines on SFS and increases on NFS. Stable isotopes of carbon, oxygen, and carbon-to-nitrogen ratios suggest that this reversal is linked to interactions between CO2 stimulation of photosynthesis and water or nitrogen limitation. Our findings highlight the importance of incorporating landscape processes and habitat heterogeneity in predictions of tree growth responses to global environmental change.
      Cover page: Climate-induced reversal of tree growth patterns at a tropical treeline
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2013)

      Background

      The analysis of tree-ring carbon isotope composition (δ(13)C) has been widely used to estimate spatio-temporal variations in intrinsic water use efficiency (iWUE) of tree species. Numerous studies have reported widespread increases in iWUE coinciding with rising atmospheric CO(2) over the past century. While this could represent a coherent global response, the fact that increases of similar magnitude were observed across biomes with no apparent effect on tree growth raises the question of whether iWUE calculations reflect actual physiological responses to elevated CO(2) levels.

      Methodology/results

      Here we use Monte Carlo simulations to test if an artifact of calculation could explain observed increases in iWUE. We show that highly significant positive relationships between iWUE and CO(2) occur even when simulated data (randomized δ(13)C values spanning the observed range) are used in place of actual tree-ring δ(13)C measurements. From simulated data sets we calculated non-physiological changes in iWUE from 1900 to present and across a 4000 m altitudinal range. This generated results strikingly similar to those reported in recent studies encompassing 22 species from tropical, subtropical, temperate, boreal and mediterranean ecosystems. Only 6 of 49 surveyed case studies showed increases in iWUE significantly higher than predicted from random values.

      Conclusions/significance

      Our results reveal that increases in iWUE estimated from tree-ring δ(13)C occur independently of changes in (13)C discrimination that characterize physiological responses to elevated CO(2). Due to a correlation with CO(2) concentration, which is used as an independent factor in the iWUE calculation, any tree-ring δ(13)C data set would inevitably generate increasing iWUE over time. Therefore, although consistent, previously reported trends in iWUE do not necessarily reflect a coherent global response to rising atmospheric CO(2). We discuss the significance of these findings and suggest ways to distinguish real from artificial responses in future studies.
        Cover page: Explaining Global Increases in Water Use Efficiency: Why Have We Overestimated Responses to Rising Atmospheric CO2 in Natural Forest Ecosystems?
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2016)
        Nitrogen (N) deposition is a key global change factor that is increasing and affecting the structure and function of many ecosystems. To determine the influence of N deposition on specific systems, however, it is crucial to understand the temporal and spatial patterns of deposition as well as the response to that deposition. Response of the receiving plant communities may depend on the life stage-specific performance of individual species. We focus on the California oak savanna because N deposition to this system is complex-characterized by hotspots on the landscape and seasonal pulses. In a greenhouse experiment, we investigated the relative influence of N deposition on plant performance during early growth, peak biomass, and senescent life stages across different soil types, light, and community compositions. To represent the community we used three grass species-a native, naturalized exotic, and invasive exotic. At early growth and peak biomass stages performance was measured as height, and shoot and root biomass, and at the senescent stage as seed production. Simulated N deposition 1) increased shoot biomass and height of the native and, even more so, the naturalized exotic during early growth, 2) positively affected root biomass in all species during peak biomass, and 3) had no influence on seed production at the senescent stage. Alone, N deposition was not a strong driver of plant performance; however, small differences in performance among species in response to N deposition could affect community composition in future years. In particular, if there is a pulse of N deposition during the early growth stage, the naturalized exotic may have a competitive advantage that could result in its spread. Including spatial and temporal heterogeneity in a complex, manipulative experiment provides a clearer picture of not only where N management efforts should be targeted on the landscape, but also when.
          Cover page: The Effect of Nitrogen Deposition on Plant Performance and Community Structure: Is It Life Stage Specific?
          • Article
          • Peer Reviewed
          California Agriculture, Volume 76, Issue 2-3 (2022)

          Maintaining and enhancing soil organic carbon storage can mitigate climate change while promoting forage growth. California has adopted incentive programs to promote rangeland practices that build soil organic carbon. However, there is no standard framework for assessing the baseline level of soil organic carbon at the ranch scale. Here, we use the Ecological Site Description — a land-type classification system — to help ranch managers set priorities about where to implement practices to increase soil organic carbon. We measured baseline carbon stocks at 0 to 15 and 15 to 30 centimeters' depth across three ecological sites and two vegetation states (shrubland and grassland) at Tejon Ranch, California. We discovered increased levels of soil carbon at ecological sites in higher elevations, and more soil carbon in shrublands as compared to grasslands. Slope, elevation, and soil texture, as well as plant litter and shrub cover, were significant predictors of soil carbon. The Ecological Site Description framework can serve as an important tool to help range managers keep carbon in the soil and out of the atmosphere.

            Cover page: Using Ecological Site Descriptions to make ranch-level decisions about where to manage for soil organic carbon
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2018)
            This study was designed to address a major source of uncertainty pertaining to coupled carbon-water cycles in montane forest ecosystems. The Sierra Nevada of California was used as a model system to investigate connections between the physiological performance of trees and landscape patterns of forest carbon and water use. The intrinsic water-use efficiency (iWUE)-an index of CO2 fixed per unit of potential water lost via transpiration-of nine dominant species was determined in replicated transects along an ∼1,500-m elevation gradient, spanning a broad range of climatic conditions and soils derived from three different parent materials. Stable isotope ratios of carbon and oxygen measured at the leaf level were combined with field-based and remotely sensed metrics of stand productivity, revealing that variation in iWUE depends primarily on leaf traits (∼24% of the variability), followed by stand productivity (∼16% of the variability), climatic regime (∼13% of the variability), and soil development (∼12% of the variability). Significant interactions between species composition and soil properties proved useful to predict changes in forest carbon-water relations. On the basis of observed shifts in tree species composition, ongoing since the 1950s and intensified in recent years, an increase in water loss through transpiration (ranging from 10 to 60% depending on parent material) is now expected in mixed conifer forests throughout the region.
              Cover page: Integrating effects of species composition and soil properties to predict shifts in montane forest carbon–water relations
              • Article
              • Peer Reviewed
              UC Irvine Previously Published Works (2023)
              The persistence of organic carbon (C) in soil is most often considered at timescales ranging from tens to thousands of years, but the study of organic C in paleosols (i.e., ancient, buried soils) suggests that paleosols may have the capacity to preserve organic compounds for tens of millions of years. However, a quantitative assessment of C sources and sinks from these ancient terrestrial landscapes is complicated by additions of geologically modern (~ 10 Ka) C, primarily due to the infiltration of dissolved organic carbon. In this study, we quantified total organic C and radiocarbon activity in samples collected from 28- to 33-million-year-old paleosols that are naturally exposed as unvegetated badlands near eastern Oregon's "Painted Hills". We also used thermal and evolved gas analysis to examine the thermodynamic stability of different pools of C in bulk samples. The study site is part of a ~ 400-m-thick sequence of Eocene-Oligocene (45-28 Ma) paleosols, and thus we expected to find radiocarbon-free samples preserved in deep layers of the lithified, brick-like exposed outcrops. Total organic C, measured in three individual profiles spanning depth transects from the outcrop surface to a 1-m depth, ranged from 0.01 to 0.2 wt% with no clear C-concentration or age-depth profile. Ten radiocarbon dates from the same profiles reveal radiocarbon ages of ~ 11,000-30,000 years BP that unexpectedly indicate additions of potentially modern organic C. A two-endmember mixing model for radiocarbon activity suggests that modern C may compose ~ 0.5-2.4% of the total organic C pool. Thermal and evolved gas analysis showed the presence of two distinct pools of organic C, but there was no direct evidence that C compounds were associated with clay minerals. These results challenge the assumption that ancient badland landscapes are inert and "frozen in time" and instead suggest they readily interact with the modern C cycle.
                Cover page: Accumulation of radiocarbon in ancient landscapes: A small but significant input of unknown origin
                • Thesis
                • Peer Reviewed
                UC Irvine Electronic Theses and Dissertations (2024)

                The increasing ubiquity of personal devices and technologies, such as home displays, smart-speakers, and wearables, has created new opportunities for individuals and families to monitor and manage their health and wellbeing. However, personal and family informatics systems have not kept up with such increased ubiquity, leading to a missed opportunity in making health informatics more convenient, connected, and meaningful. Many continue to struggle to effectively incorporate tracking into their daily lives and leverage the multiple technologies they have contact with. In my dissertation, I investigate how the design of multi-device health informatics systems can better support individuals in their self-tracking practices and facilitate collaboration within families for collective wellbeing. By leveraging the diverse capabilities of smartphones, smartwatches, smart-speakers, and more, I demonstrate how informatics tools can be designed to accommodate the varied needs and contexts of everyday life, both for individual use and for family collaboration.

                Towards self-tracking, I demonstrate how multi-device, multimodal systems can provide flexibility and redundancy of options for rich data capture and help individuals overcome situational barriers to tracking. Through the design and evaluation of the ModEat system, I show how supporting food journaling across smartphones, computers, and voice assistants with various input modalities can accommodate people's goals, preferences, and contexts.

                Examining how to help families collaborate towards health and wellbeing management, I explore the design of multi-device systems to facilitate family co-regulation practices. My evaluation of the CoolTaco deployment demonstrates that a smartwatch-based system can mediate shared awareness and remote collaboration between parents and children with ADHD around behavioral regulation. Through a co-design study, I reveal opportunities for in-home displays to integrate family data and guide productive discussions around each member's regulation needs relating to moods, exercise, and goals. Building on these insights, my design and evaluation of FamilyBloom showcases how integrating personal and shared devices can support diverse co-regulation practices, enabling reflection and mutual care in the face of varied routines and individual preferences within families.

                Through these studies, my dissertation demonstrates that multi-device, multimodal health informatics can support the needs of individuals and families in their everyday practices surrounding tracking, reflecting, and acting for self and co-regulation of health and wellbeing needs. I suggest that leveraging device ecosystems and designing for varied levels of engagement and collaboration can result in more available and useful tools. Through empirical findings and novel systems, my dissertation contributes to understanding of how to create effective tools for personal and family health tracking in everyday life.

                  Cover page: Towards Multi-Device Ecosystems for Personal and Family Health TrackingCreative Commons 'BY' version 4.0 license
                  • Article
                  • Peer Reviewed
                  Climate & Ecosystems (2020)
                  One-fourth of Brazilian Amazonia is managed for timber production, but only a small portion of active logging sites follow sustainable forest management plans (SFMPs). Amazon forests without SFMPs are susceptible to deforestation because such plans integrate the use of forest products and conservation goals by allowing selective wood extraction following regulations aimed at reducing the long-term impact of logging. However, it remains uncertain whether reduced-impact selective logging typical of SFMPs (17-20 m3 ha-1 yr-1 of 38-70 species) changes forest regeneration, carbon (C) stocks, and nutrient cycling. Here, we tested the hypothesis that litter and soil biogeochemical parameters serve as indicators of sustainable logging as forest regeneration, C stocks, and C-to-nutrient ratios in soil and litter become progressively similar to those of primary forests as time elapses after logging. We used a chronosequence spanning nine years since logging to relate litter and soil (at 0-10, 10-30, 30-50 cm depth) C stocks and 12 and 15 biogeochemical parameters, respectively, as well as canopy cover and tree seedling density (10-150 cm tall) in upland evergreen Amazon forests. In one unlogged and four logged stands sampled three, five, seven, and nine years after logging, we compared 15 permanent plots (three replicated 0.5 ha plots per time-since-logging category). We found that five parameters explained >80% of the variation in soil and litter properties among logged and unlogged stands. Litter parameters were more sensitive to logging than soil parameters, as litter C stocks and C-to-nutrient ratios increased systematically after logging. Canopy cover decreased over time and was ~14% lower nine years after logging. Total seedling density did not change consistently over time but was ~54% higher seven years after logging. Our data suggest that the SFMP guidelines have served the purpose of maintaining soil quality and forest regeneration. Litter and soil parameters can be useful indicators of sustainable forest management in upland evergreen forests in Central Amazonia.
                    Cover page: Litter and soil biogeochemical parameters as indicators of sustainable logging in Central Amazonia
                    • Article
                    • Peer Reviewed
                    UC Davis Previously Published Works (2015)
                    Cellular respiration depletes stored carbohydrates during extended periods of limited photosynthesis, e.g. winter dormancy or drought. As respiration rate is largely a function of temperature, the thermal conditions during such periods may affect non-structural carbohydrate (NSC) availability and, ultimately, recovery. Here, we surveyed stem responses to temperature changes in 15 woody species. For two species with divergent respirational response to frost, P. integerrima and P. trichocarpa, we also examined corresponding changes in NSC levels. Finally, we simulated respiration-induced NSC depletion using historical temperature data for the western US. We report a novel finding that tree stems significantly increase respiration in response to near freezing temperatures. We observed this excess respiration in 13 of 15 species, deviating 10% to 170% over values predicted by the Arrhenius equation. Excess respiration persisted at temperatures above 0 °C during warming and reoccurred over multiple frost-warming cycles. A large adjustment of NSCs accompanied excess respiration in P. integerrima, whereas P. trichocarpa neither excessively respired nor adjusted NSCs. Over the course of the years included in our model, frost-induced respiration accelerated stem NSC consumption by 8.4 mg (glucose eq.) cm(-3) yr(-1) on average in the western US, a level of depletion that may continue to significantly affect spring NSC availability. This novel finding revises the current paradigm of low temperature respiration kinetics.
                      Cover page: Frost Induces Respiration and Accelerates Carbon Depletion in Trees
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