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Open Access Publications from the University of California

Scholarly Works (50 results)

  • Article
  • Peer Reviewed
UC Berkeley Previously Published Works (2016)
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2008)
    Eusocial bee (Apidae) foragers are able to mark food sources with olfactory attractant or repellent signals. Because these bees also have an excellent ability to learn associatively, they may be able to associate forager-deposited marks either positively or negatively with food depending on reward quality. We provide the first field experiments showing such a context-based interpretation of field information (odour marks and visual local enhancement) in stingless bees. We sequentially exposed individual foragers of the stingless bee Scaptotrigona mexicana to three situations in which one feeder was marked with either the visual presence of nestmates (sealed inside clear containers to prevent odour release) or odour marks alone. In the first situation, we offered two equally rewarding sucrose feeders (unscented 2.5 M sucrose solution). In this case, experienced foragers showed no preference on their subsequent visits to any of the feeders, even though the marked feeder was made more conspicuous with odour marks or the visual presence of nestmates. In the second situation, experienced foragers significantly preferred the marked feeder when it offered a sucrose reward. In the third situation, when the marked feeder offered no carbohydrate reward (only water) and the unmarked feeder offered sucrose, the experienced foragers avoided the marked feeder and significantly preferred the unmarked one. Thus, foragers learned to associate food quality positively or negatively with chemical or visual marks at the food source. © 2008 The Association for the Study of Animal Behaviour.
      Creative Commons 'BY' version 4.0 license
      • Thesis
      • Peer Reviewed
      UC Berkeley Electronic Theses and Dissertations (2024)

      The increasing frequency and severity of wildfire in California, exacerbated by climate change and historical forest management practices, underscore a critical need for increased forest management which reduces the risk of high severity fire. Currently, over $100 billion is needed to meet federal forest management goals outlined in the U.S. Forest Service Wildfire Crisis Strategy, but total, nonrecurring public funding is approximately $5 billion. To help fill this gap, state and federal agencies explicitly call for public-private partnerships to increase the diversity of funding sources. In this dissertation I evaluate the potential of carbon finance to fund forest management via the carbon benefits from utilizing low-value biomass and by monetizing increased forest carbon stocks from treatments which restore forest resilience. This dissertation helps to advance the field of biomass utilization by exploring ways to increase investment in biomass-based products and exploring the carbon benefits of a fire resilient forest structure, both novel contributions to the literature.

      I employ a comprehensive set of methodological frameworks that integrate ecological, economic, and policy analyses to understand how carbon finance can support forest restoration goals in California. The methods used here include discounted cash flow analysis, life cycle assessment, and forest growth models. I reveal how forest management aimed at restoring fire resilience and biomass utilization can contribute to climate objectives. I further show that carbon revenue from biomass utilization and avoided wildfire emissions can contribute significant funding to forest restoration in the Sierra Nevada Mountains.

      Themes emerging from this dissertation include: 1) The clear carbon benefits of biomass utilization and the pivotal role it can play in scaling forest restoration and closing funding gaps while generating profitable returns to investors. Fuels made from biomass have an Internal Rate of Return (IRR) of 19% and nonfuel products have an IRR of 13% in the baseline scenario, showing the potential for profitable investment in products utilizing low-value forest biomass. 2) Biochar production could turn low-value biomass into approximately 70 million carbon credits annually, provide IRRs as high as 10 – 30% to investors, and eliminate costs associated with pile-burning. While biochar has lower carbon benefits than other biomass-based products like hydrogen, biochar production is technologically mature and requires low capital expenditures, which can help to build biomass supply chains to unlock higher carbon benefit biomass utilization options. 3) The carbon benefits of restoring resilience and biomass utilization can pay for forest restoration in many instances, providing up to $4,000 per acre. However, to fully unlock markets for low-carbon intensity biomass-based commodities from low-value forest biomass, policy support for low carbon fuels and carbon markets will be crucial. Similarly, private investment will need rigorous predictive tools to forecast revenue from carbon markets, tolls which will need to be iteratively developed as the market evolves. This dissertation explores the predictive tools necessary to estimate the impact of various policy and market scenarios on financial returns. Through this work, I hope to advance our ability to predict, and generate revenue from, the carbon benefits of forest restoration.

        Cover page: Investing in Resilience: Monetizing Carbon to Support Forest Restoration in California
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2022)
        Bioenergy with carbon capture and sequestration (BECCS) is critical for stringent climate change mitigation but is commercially and technologically immature and resource intensive. State and federal fuel and climate policies can drive first markets for BECCS in California. We develop a spatially explicit optimization model to assess niche markets for renewable natural gas (RNG) production with carbon capture and sequestration (CCS) from waste biomass in California. Existing biomass residues produce biogas and RNG and enable low-cost CCS through the upgrading process and CO2 truck transport. Under current state and federal policy incentives, RNG-CCS can avoid 12.4 mmtCO2e/year (3% of California's 2018 CO2 emissions), of which 2.9 mmtCO2/year are captured and sequestered. It simultaneously produces 93 PJ RNG/year (4% of California's 2018 natural gas demand) with a profit maximizing objective, resulting in profits of $11/GJ. Distributed RNG production with CCS can potentially catalyze markets and technologies for CO2 capture, transport, and storage in California.
          Cover page: Market Potential for CO2 Removal and Sequestration from Renewable Natural Gas Production in CaliforniaCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC Santa Barbara Previously Published Works (2022)
          Abstract: The evolution of obligate kleptoparasitism, the theft of food, has led to remarkable innovations, including physical weapons and chemical signals that can evolve into chemical weapons. Stingless bees in the genus Lestrimelitta are excellent examples of this phenomenon because they are obligate kleptoparasites that no longer collect floral resources and instead steal brood resources from other bees. Their ability to raid successfully is thus essential to their fitness even when they fight species that are physically bigger, have larger defense forces, or both. We conducted morphometric analyses, quantified Lestrimelitta niitkib mandibular gland pheromone (MGP) components, and carried out individual fighting trials between L. niitkib and the stingless bee Scaptotrigona mexicana, a common victim species, to shed light on the detailed reasons for their success at robbing. Measurements showed that L. niitkib mandibles have thicker exoskeleton cuticles and overall greater width, particularly in the medial and proximal sections, than S. mexicana, which is quite similar in body size. In all fights, L. niitkib bit victims and released MGP, as it does during raids. Scaptotrigona mexicana victims exhibited significantly increased uncoordinated behaviors and showed partial or complete paralysis. We analyzed and quantified the major components of MGP, which consisted of large quantities of geranial (mean of 253 μg) and neral (48 μg) per bee. Microinjections of 1 bee equivalent (BE) of natural or synthetic MGP and ≥ 0.1 BE of geranial significantly increased deleterious behaviors and paralysis as compared to control injections. We suggest that the large quantities of MGP used during raiding have led to an unexpected outcome, a semiochemical evolving the additional function of a toxin, and contribute to the ability of Lestrimelitta to rob its victims. Significance statement: Kleptoparasites, organisms that steal food resources, employ multiple physical and chemical tools to survive. The success of kleptoparasitism requires a balance between honesty and coercion in interspecific communication. The genus Lestrimellita consists of a group of kleptoparasitic stingless bee species that raid other bee colonies for food and therefore depend upon winning these raids. However, why they succeed remains not fully understood. We studied differences in morphology between L. niitkib and its victims, the pheromones they release during raids, and ran individual fight trials between L. niitkib and a common victim to identify why they are successful. We suggest that the release of pheromones at the beginning of raids, in concert with the pheromone’s toxicity, has been combined to improve L. niitkib’s ability to successfully rob.
            Cover page: Fighting ability and the toxicity of raiding pheromone in an obligate kleptoparasite, the stingless bee Lestrimelitta niitkib
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2023)
            Low carbon fuel and waste management policies at the federal and state levels have catalyzed the construction of Californias wet anaerobic digestion (AD) facilities. Wet ADs can digest food waste and dairy manure to produce compressed natural gas (CNG) for natural gas vehicles or electricity for electric vehicles (EVs). Carbon capture and sequestration (CCS) of CO2 generated from AD reduces the fuel carbon intensity by carbon removal in addition to avoided methane emissions. Using a combined lifecycle and techno-economic analysis, we determine the most cost-effective design under current and forthcoming federal and state low carbon fuel policies. Under many scenarios, designs that convert biogas to electricity for EVs (Biogas to EV) are favored; however, CCS is only cost-effective in these systems with policy incentives that exceed $200/tonne of CO2 captured. Adding CCS to CNG-producing systems (Biogas to CNG) only requires a single unit operation to prepare the CO2 for sequestration, with a sequestration cost of $34/tonne. When maximizing negative emissions is the goal, incentives are needed to either (1) fund CCS with Biogas to EV designs or (2) favor CNG over electricity production from wet AD facilities.
              Cover page: Policy Analysis of CO2 Capture and Sequestration with Anaerobic Digestion for Transportation Fuel Production.
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2018)
              Capture and permanent geologic sequestration of biogenic CO2 emissions may provide critical flexibility in ambitious climate change mitigation. However, most bioenergy with carbon capture and sequestration (BECCS) technologies are technically immature or commercially unavailable. Here, we evaluate low-cost, commercially ready CO2 capture opportunities for existing ethanol biorefineries in the United States. The analysis combines process engineering, spatial optimization, and lifecycle assessment to consider the technical, economic, and institutional feasibility of near-term carbon capture and sequestration (CCS). Our modeling framework evaluates least cost source-sink relationships and aggregation opportunities for pipeline transport, which can cost-effectively transport small CO2 volumes to suitable sequestration sites; 216 existing US biorefineries emit 45 Mt CO2 annually from fermentation, of which 60% could be captured and compressed for pipeline transport for under $25/tCO2 A sequestration credit, analogous to existing CCS tax credits, of $60/tCO2 could incent 30 Mt of sequestration and 6,900 km of pipeline infrastructure across the United States. Similarly, a carbon abatement credit, analogous to existing tradeable CO2 credits, of $90/tCO2 can incent 38 Mt of abatement. Aggregation of CO2 sources enables cost-effective long-distance pipeline transport to distant sequestration sites. Financial incentives under the low-carbon fuel standard in California and recent revisions to existing federal tax credits suggest a substantial near-term opportunity to permanently sequester biogenic CO2 This financial opportunity could catalyze the growth of carbon capture, transport, and sequestration; improve the lifecycle impacts of conventional biofuels; support development of carbon-negative fuels; and help fulfill the mandates of low-carbon fuel policies across the United States.
                Cover page: Near-term deployment of carbon capture and sequestration from biorefineries in the United States.
                • Article
                California Agriculture, Volume 73, Issue 2 (2019)
                Through technology demonstration and policy engagement, UC ANR specialists, advisors and AES faculty can support California's ambitions to remove CO2 from the atmosphere.
                  Cover page: UC experts can lead on carbon dioxide removal
                  • Thesis
                  • Peer Reviewed
                  UC Berkeley Electronic Theses and Dissertations (2015)

                  Climate change mitigation requires gigaton-scale carbon dioxide removal technologies, yet few examples exist beyond niche markets. This dissertation informs large-scale implementation of bioenergy with carbon capture and sequestration (BECCS), a carbon-negative energy technology. It builds on existing literature with a novel focus on deployment, design, commercialization, and communication of BECCS.

                  BECCS, combined with aggressive renewable deployment and fossil emission reductions, can enable a carbon-negative power system in Western North America by 2050, with up to 145% emissions reduction from 1990 levels. BECCS complements other sources of renewable energy, and can be deployed in a manner consistent with regional policies and design considerations. The amount of biomass resource available limits the level of fossil CO2 emissions that can still satisfy carbon emissions caps. Offsets produced by BECCS are more valuable to the power system than the electricity it provides. Implied costs of carbon for BECCS are relatively low (~$75/ton CO2 at scale) for a capital-intensive technology.

                  Optimal scales for BECCS are an order of magnitude larger than proposed scales found in existing literature. Deviations from optimal scaled size have little effect on overall systems costs – suggesting that other factors, including regulatory, political, or logistical considerations, may ultimately have a greater influence on plant size than the techno-economic factors considered.

                  The flexibility of thermochemical conversion enables a viable transition pathway for firms, utilities and governments to achieve net-negative CO2 emissions in production of electricity and fuels given increasingly stringent climate policy. Primary research, development (R&D), and deployment needs are in large-scale biomass logistics, gasification, gas cleaning, and geological CO2 storage. R&D programs, subsidies, and policy that recognize co-conversion processes can support this pathway to commercialization. Here, firms can embrace a gradual transition pathway to deep decarbonization, limiting economic dislocation and increasing transfer of knowledge between the fossil and renewable sectors.

                  Global cumulative capital investment needs for BECCS through 2050 are over $1.9 trillion (2015$, 4% real interest rate) for scenarios likely to limit global warming to 2 °C. This scenario envisions deployment of as much as 24 GW/yr of BECCS by 2040 in the electricity sector. To achieve theses rates of deployment within 15-20 years, governments and firms must commit to research, development, and deployment on an unprecedented scale.

                  Three primary issues complicate emissions accounting for BECCS: cross-sector CO2 accounting, regrowth, and timing. Switchgrass integration decreases lifecycle greenhouse gas impacts of co-conversion systems with CCS, across a wide range of land-use change scenarios. Risks at commercial scale include adverse effects on food security, land conservation, social equity, and biodiversity, as well as competition for water resources. This dissertation argues for an iterative risk management approach to BECCS sustainability, with standards being updated as more knowledge is gained through deployment. Sustainability impacts and public opposition to BECCS may be reduced with transparent measurement and communication.

                  Commercial-scale deployment is dependent on the coordination of a wide range of actors, many with different incentives and worldviews. Despite this problem, this dissertation challenges governments, industry incumbents, and emerging players to research, support, and deploy BECCS.

                    Cover page: Deployment, Design, and Commercialization of Carbon-­Negative Energy Systems
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (2009)
                    Within a rewarding floral patch, eusocial bee foragers frequently switch sites, going from one flower to another. However, site switching between patches tends to occur with low frequency while a given patch is still rewarding, thus reducing pollen dispersal and gene flow between patches. In principle, forager switching and gene flow between patches could be higher when close patches offer similar rewards. We investigated site switching during food recruitment in the stingless bee Scaptotrigona mexicana. Thus, we trained three groups of foragers to three feeders in different locations, one group per location. These groups did not interact each other during the training phase. Next, interaction among trained foragers was allowed. We found that roughly half of the foragers switched sites, the other half remaining faithful to its training feeder. Switching is influenced by the presence of recruitment information. In the absence of recruitment information (bees visiting and recruiting for feeders), employed foragers were site specific. Foragers only switched among feeders that were being visited and recruited to. Switching was not caused by learned aversion to experimental handling. Switching in response to recruitment could provide a fitness benefit to the colony by facilitating rapid switching among exploited patches and provide a benefit of increasing plant gene flow between patches. © 2009 El Colegio de la Frontera Sur.
                      Creative Commons 'BY' version 4.0 license
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