Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (5 results)

  • Article
  • Peer Reviewed
UC Davis Previously Published Works (2018)
Invasive species fundamentally change the bio-physical and ecological characteristics of the ecosystems they invade. Rapidly expanding invasive species may facilitate the spread of other invasive species, and successive invasion events may lead to novel species interactions that may push the system beyond its equilibrium state and change successional pathways. Knowing the direction of the invasion front may be useful to predict impacts of invasive species. Water primrose (Ludwigia spp.), one of the invasive floating macrophytes in the Sacramento-San Joaquin River Delta (hereafter, Delta), has increased in cover rapidly over the past three decades likely outcompeting native and non-native species, changing their functional relationships, with cascading effects in the macrophyte communities of the aquatic ecosystem. In this study, we analyze the directionality of water primrose invasion and assess which spaces it occupies, whether it has overcrowded or outcompeted other vegetation communities, and its implications for succession in the Delta. We used imaging spectroscopy data acquired in June of 2004, June of 2008, November of 2014, and October of 2016 for the 2500 km2 of the Delta to map the communities of submerged macrophytes, floating macrophytes, and emergent marsh. We found that water primrose cover increased fourfold in the Delta over the past 13 yr, changing significantly in the central Delta and Liberty Island region from 122 ha in 2004 to 471 ha in 2016. Water primrose expanded first by spreading over open water and submerged macrophytes and, when that habitat was exhausted, primrose invasion switched direction and encroached into emergent marsh. This bilateral expansion to both open water and the marsh is likely to change rates of succession and affect the restoration of the native Delta marshes. Understanding the mechanisms behind the expansion dynamics of this invasive will allow managers to counter its impact on newly established vulnerable marshes.
    Cover page: Water primrose invasion changes successional pathways in an estuarine ecosystem
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2017)
    Coastal ecosystems are greatly endangered due to anthropogenic development and climate change. Multiple disturbances may erode the ability of a system to recover from stress if there is little time between disturbance events. We evaluated the ability of the saltmarshes in Barataria Bay, Louisiana, USA, to recover from two successive disturbances, the DeepWater Horizon oil spill in 2010 and Hurricane Isaac in 2012. We measured recovery using vegetation indices and land cover change metrics. We found that after the hurricane, land loss along oiled shorelines was 17.8%, while along oil-free shorelines, it was 13.6% within the first 7 m. At a distance of 7-14 m, land loss from oiled regions was 11.6%, but only 6.3% in oil-free regions. We found no differences in vulnerability to land loss between narrow and wide shorelines; however, vegetation in narrow sites was significantly more stressed, potentially leading to future land loss. Treated oiled regions also lost more land due to the hurricane than untreated regions. These results suggest that ecosystem recovery after the two disturbances is compromised, as the observed high rates of land loss may prevent salt marsh from establishing in the same areas where it existed prior to the oil spill.
      Cover page: Marsh Loss Due to Cumulative Impacts of Hurricane Isaac and the Deepwater Horizon Oil Spill in Louisiana
      • Article
      Research Reports (2021)

      Catastrophic wildfires over the past five years (2015-2020) have caused damage to the Caltrans road network in 81 separate wildfire events, leading to expenditures of over $590,000,000 to repair highway assets. To reduce the risk of further wildfire damage and to improve public safety, particularly for disadvantaged communities, Caltrans has engaged in assessing the priority locations for vegetation treatment within the lands it owns called the Right of Way (ROW). A 2019 analysis provided a map showing the top 17% of vulnerabilities in the road network, representing both the risk of wildfire and to disadvantaged communities that might need to use the transportation network as means of evacuation. This UC Davis research project was designed to support efforts within Caltrans in conducting a wildfire vulnerability risk assessment for fuels reduction in the ROW to protect Caltrans’ infrastructure and travelers. The project involved four components: 1) conducting a rigorous peer review of the 2019 GIS-based study commissioned by Caltrans; 2) collecting and assessing the outputs of several climate change, fire, and other models currently developed or under development for California, as well as future climate projections; 3) developing a framework for the use of the prioritized segment model with other data further identify priority areas for fuels and risk reduction; and 4) interviews with Caltrans staff on opportunities and obstacles to increasing the pace and scale of vegetation treatments. The results contribute to infrastructure risk assessments, can be used to prioritize areas for treatment, to create a tracking system of areas treated and risk lowered over multiple years, and to engage local governments and wildfire fighting units to coordinate landscape fire risk reductions.

      View the NCST Project Webpage

        Cover page: 2020 Critical Update to Caltrans Wildfire Vulnerability Analysis
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2021)
        From 2011 to 2016, California experienced a millennial-intensity drought, generating high levels of tree mortality. Remote sensing has been used to monitor the long-term impacts of drought; however, discriminating dead from live trees in arid and semiarid deciduous woodlands is challenging. The goals of this study were to assess and map the spatial patterns of drought-induced tree mortality in a blue oak (Quercus douglasii) woodland, a highly drought-tolerant species forming savannas along the lower foothills surrounding California's Central Valley. Airborne hyperspectral imagery was used to identify the most important wavelength regions predicting drought-induced blue oak mortality. The best metric to predict canopy stress was a normalized ratio using the spectral bands 937.53 and 1100.08 nm with a correlation with tree mortality of R2 = 0.83. The image prediction of mortality for nine field plots found that 16 of 98 trees died (17.9%) during the drought. We further evaluated tree mortality in 82 independent plots, and we found the greatest image predictive accuracy for tree mortality between 1% and 10%. When applied at the landscape level, the regression-based index found mortality ranged from 1% to more than 51% in oak stands with an average mortality of 10% over the entire study region. In addition, tree mortality at landscape level showed higher tree mortality in blue oaks on south-facing aspects probably because of higher insolation rates and in sites with low potential for accumulated drainage.
          Creative Commons 'BY-SA' version 4.0 license
          • Article
          Policy Briefs (2022)

          A key function of a highway network is to maintain access during normal and emergency operations. During wildfire evacuations, first-responders and firefighters depend on highways and local roads for transporting heavy equipment to communities in need. The California Department of Transportation (Caltrans) is expanding vegetation management to begin establishing defensible space zones along California’s nearly 16,000 miles of state highways and in about 230,000 acres of highway right-ofway. However, extended drought, a longer fire season, and higher temperatures brought on by climate change, along with the spread of invasive weeds and dense, dry vegetation, have created new challenges.

          The California Department of Forestry and Fire Protection produced a Community Wildfire Prevention and Mitigation Report in 2019 with a methodology to assess wildfire risk. Caltrans and researchers at the University of California, Davis applied these methods to develop a highway-segment-specific prioritization model for vegetation management within highway rights-of-way. The researchers also interviewed Caltrans staff about opportunities for and obstacles to increasing the pace and scale of vegetation treatments. This policy brief summarizes the findings from that research and provides policy implications.

          View the NCST Project Webpage

            Cover page: A Model for Efficiently Allocating Resources to Mitigate Wildfire Risk along California Roadways
            Top