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Open Access Publications from the University of California

Scholarly Works (5 results)

  • Thesis
  • Peer Reviewed
UC Santa Cruz Electronic Theses and Dissertations (2020)

This work examines plant response to human alteration in deserts and coastal salt marshes, two systems in which abiotic stress is assumed to limit plants more strongly than biotic factors.

In the desert, I used experimental panels to simulate the effect of solar energy infrastructure on two habitat types. I measured plant diversity and abundance, finding that panels interacted with rainfall and physical features of each habitat type to drive different outcomes. Under panels, diversity and abundance tended to be higher in one habitat type, but lower in the other. I also examined panel effects on the demography of a closely related rare-common species pair. Panel effects on individual demographic rates were rarely strong, but matrix models integrating these effects across the life cycle revealed a negative impact on the rare species, mediated by increased competition under panels. This result highlights the risk of using a common relative to predict impacts on a rare species.

In the coastal salt marsh, I tested whether the Stress Gradient Hypothesis (SGH) can be applied to improve restoration outcomes. The SGH framework predicts that interactions between plants should shift from competition to facilitation as stress increases. I found that soil conditions were more stressful (more negative water potential) at higher marsh elevations, so I expected clustered plantings to do better upslope. I planted two natives in loose and clustered patterns and tracked their performance across elevation for two years. Surprisingly, performance did not vary with elevation during the first year, while clustering had a negative effect on growth. After two years both species showed clear but inverse patterns of cover across elevation – yet across the entire elevation gradient, clustering strongly inhibited cover in both species.

My work demonstrates that even in “stressful” systems, abiotic stress is not always the dominant constraint on plants. To develop effective conservation and restoration strategies in these systems will require a deep understanding of how human disturbance interacts with the biotic and abiotic drivers that govern plant performance.

    Cover page: Plant Response to Land Use Change in Two Iconically Stressful Habitats: California’s Desert Solar Fields and Restored Coastal Salt Marshes
    • Article
    • Peer Reviewed
    UC Santa Cruz Previously Published Works (2023)
    The Stress Gradient Hypothesis predicts facilitation will become more important than competition where abiotic stress is high, and the framework successfully predicts positive interactions between species in many systems. Fewer studies have focused on intraspecific facilitation, and to our knowledge none examine intraspecific interactions in Pacific Coast salt marshes of North America. We used two species that tend to occur in large, monospecific patches to test for intraspecific facilitation in a restored California marsh, where tides and evaporation during summer create moisture and salinity gradients across elevation. We tested performance of Frankenia salina or Jaumea carnosa in restoration plots using two treatments: clustered plantings to promote facilitation, and widely spaced plantings to limit interaction between individuals. We characterized the soil water potential gradient and measured plant survival, cover, physiology, and susceptibility to herbivory across elevation and planting treatments. Soil water potential declined sharply with elevation, suggesting plant stress should be higher upslope. However, tissue water potential was unaffected by elevation, and survival was high—suggesting growing conditions remained benign. A seawater addition treatment did not alter the response of plants or plant interactions to the abiotic gradient. At 19 months, intraspecific competition prevailed across the entire elevation gradient for both species, with less transplant cover in clustered plantings. However, clustered Frankenia fared better during a transient period of heavy rabbit herbivory. Aside from this temporary benefit, clustering did not reduce stress and strongly suppressed growth—suggesting that restoration designs for the high marsh should minimize competition.
      Creative Commons 'BY' version 4.0 license
      • Article
      Research Publications (2018)
      Due to global loss and degradation of salt marshes, restoration and conservation havebecome necessary to protect and preserve salt marsh systems. Restoration can exacerbate the common environmental stressors – salinity and drought – present in Mediterranean salt marsh ecosystems. Grading and clearing of land to restore tidal influence and remove non-native weeds creates large expanses of bare soil, increasing evaporation rates. As moisture is lost, salts are concentrated in the soil, making growing conditions more difficult for transplants. Multiple species are usually planted during revegetation efforts, but different species are likely to vary in tolerance to moisture and salinity stress; yet, the relative effect of these stressors on manyCalifornia salt marsh natives are unknown. To address this knowledge gap, we appliedgreenhouse watering treatments to five perennials common in central California coast salt marshes. We evaluated response to water volume and salinity by measuring survival, growth, and tissue water potential. As predicted, drought significantly reduced tissue water potential for all five species; however, only three species showed a significant decline in water potential with increasing of salinity treatments. Contrary to expectations, growth was unaffected by drought or salinity treatments. Our results suggest these species have broad tolerance to drought and salinitystress they may encounter in the salt marsh ecotone.
        Cover page: Halophyte Response to Drought and Salinity Stress and Implications for RestorationCreative Commons 'BY-SA' version 4.0 license
        • Article
        • Peer Reviewed
        UC Santa Cruz Previously Published Works (2021)
        Political and economic initiatives intended to increase energy production while reducing carbon emissions are driving demand for solar energy. Consequently, desert regions are now targeted for development of large-scale photovoltaic solar energy facilities. Where vegetation communities are left intact or restored within facilities, ground-mounted infrastructure may have negative impacts on desert-adapted plants because it creates novel rainfall runoff and shade conditions. We used experimental solar arrays in the Mojave Desert to test how these altered conditions affect population dynamics for a closely related pair of native annual plants: rare Eriophyllum mohavense and common E. wallacei. We estimated aboveground demographic rates (seedling emergence, survivorship, and fecundity) over 7 yr and used seed bank survival rates from a concurrent study to build matrix models of population growth in three experimental microhabitats. In drier years, shade tended to reduce survival of the common species, but increase survival of the rare species. In a wet year, runoff from panels tended to increase seed output for both species. Population growth projections from microhabitat-specific matrix models showed stronger effects of microhabitat under wetter conditions, and relatively little effect under dry conditions (lack of rainfall was an overwhelming constraint). Performance patterns across microhabitats in the wettest year differed between rare and common species. Projected growth of E. mohavense was substantially reduced in shade, mediated by negative effects on aboveground demographic rates. Hence, the rare species were more susceptible to negative effects of panel infrastructure in wet years that are critical to seed bank replenishment. Our results suggest that altered shade and water runoff regimes associated with energy infrastructure will have differential effects on demographic transitions across annual species and drive population-level processes that determine local abundance, resilience, and persistence.
          Cover page: Microhabitats associated with solar energy development alter demography of two desert annuals.
          • Article
          • Peer Reviewed
          UC Santa Cruz Previously Published Works (2020)
          Seed bank survival underpins plant population persistence but studies on seed bank trait-environment interactions are few. Changes in environmental conditions relevant to seed banks occur in desert ecosystems owing to solar energy development. We developed a conceptual model of seed bank survival to complement methodologies using in-situ seed bank packets. Using this framework, we quantified the seed bank survival of two closely related annual desert plant species, one rare (Eriophyllum mohavense) and one common (Eriophyllum wallacei), and the seed bank-environment interactions of these two species in the Mojave Desert within a system that emulates microhabitat variation associated with solar energy development. We tracked 4860 seeds buried across 540 seed packets and found, averaged across both species, that seed bank survival was 21% and 6% for the first and second growing seasons, respectively. After two growing seasons, the rare annual had a significantly greater seed bank survival (10%) than the common annual (2%). Seed bank survival across both species was significantly greater in shade (10%) microhabitats compared to runoff (5%) and control microhabitats (3%). Our study proffers insight into this early life-stage across rare and common congeners and their environmental interactions using a novel conceptual framework for seed bank survival.
            Cover page: Simulated Photovoltaic Solar Panels Alter the Seed Bank Survival of Two Desert Annual Plant Species.
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