Name: Steven Crum  
Role: Graduate Student Researcher – University of California, Riverside

Project Title:   Scaling soil respiration dynamics across regional land-use and climate gradients in southern California, USA

The exchange of carbon dioxide between the soil and the atmosphere, known as CO2 flux, is a major process affecting ecosystem function and climate change. Different types of land uses (agriculture, urban, natural open space, etc.) have differential impacts on CO2 flux. By taking gas measurements underneath vegetation and at the soil surface, this project aims to understand how soil temperature and soil moisture influence CO2 flux over three land-cover types (urban residential, citrus agriculture, and natural lands).

Photos provided by Steven Crum

Name: Margaret Simon
Role: Graduate Student Researcher – University of California, Los Angeles – Ecology and Evolutionary Biology
Project Title: The effect of biotic and abiotic factors on invasive pest spread.


This project examined factors that may influence the spread of an invasive insect pest in southern California, the bagrada bug (Bagrada hilaris). Specifically, the research focused on competition between the invasive bagrada bug and a native insect, the harlequin bug (Murgantia histrionica), and also on how temperature affects the outcome of this competition. Bagrada may benefit from having a broader diet than the native harlequin bug, while the harlequin bug may be better adapted to southern California’s Mediterranean climate. Ultimately, the project goal is to determine if temperature and competition are sufficient to predict abundances of bagrada and how those abundances may change seasonally and annually.

Name: Barry S. Nerhus, Jr.
Role: Graduate Student Researcher – California State University, Long Beach

Project Title: The movements, habitat use, and population assessment of Western Pond Turtles (Actinemys marmorata) in a southern California seasonal wetland.


An estimated 90% of natural wetlands in California have been converted to urban or agricultural uses, and this habitat loss has had a negative impact on many aquatic species. The western pond turtle was previously proposed for listing under the Federal Endangered Species Act, but listing was declined due to a lack of information about abundance and distribution of this species. This project used mark-recapture methods and radio tracking techniques to study population size, habitat use, and reproductive potential of western pond turtles in the San Joaquin Marsh Reserve. 20 nesting sites were identified and the population size was estimated at 306 individuals, which is the largest reported estimate in southern California.

Name:  Michael Goulden, et. al.
Role: Faculty – University of California, Irvine – Earth System Science

Project Title:  Factors that control Typha marsh evapotranspiration


The researchers examine the physical and biological factors affecting the rate of evaporative water loss from Typha-dominated marshes, and contrast the results with evaporation rates from other vegetation types. Key conclusions are that (1) evaporation from plants represents 80% of total evaporation in the marsh, (2) a thick accumulation of organic matter covering surface water keeps water temperatures low, resulting in a very low rate of surface water evaporation, (3) the evapotranspiration rate of the marsh ecosystem is similar to the rates that have been reported for upland grasslands.

Inventory and Monitoring of Invasive Shot-Hole Borers in Riparian Tree Communities at UC Irvine

Initiated spring 2017, ongoing.

Invasive Shot-Hole Borers (ISHB) are beetles in the genus Euwallacea that have been vectoring a disease known as Fusarium Dieback across a wide variety of tree species throughout southern California since the early 2000s. Infestation up to the landscape scale has occurred within urban, agricultural, and natural environments, and rates of tree mortality have been high in many areas. Although cultivated areas around UC Irvine have been well surveyed for ISHB, little information is available regarding the status of ISHB in natural and restored vegetation around the campus.

The purpose of this project is to examine Platanus racemosa, Populus fremontii, and Salix trees in riparian and wetland habitats for the presence and density of ISHB holes. Individual trees have been categorized according to their infection level and physically tagged to allow recurrent monitoring. Results from the surveys will be used for land management planning at UC Irvine and shared with regional academic and public agency partners to further understand the broader ecology of the ISHB epidemic in California.

Bibliography of Research at the San Joaquin Marsh 2017