Practicum 2007-2008

The following are the final reports prepared by IoES students for the 2007-2008 Practicum.

Effects of Hydromulch on Post-Fire Seed Germination

Student(s): Caroline Evans, Angel Kwok, and Sarah Maquindang

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One of Southern California’s latest fires occurred on May 8, 2007 at Griffith Park, the largest municipal park in the United States located in Los Angeles. In order to increase slope stability and protect homes, the city aerially applied hydromulch to over half of the burned area. However, the effectiveness of hydromulch as a slope stabilizer and its potential effects on post-fire vegetation are not well known. We used two experiments, one in the field and one in plant containers, to determine whether or not hydromulch had any significant negative effects on post-fire chaparral vegetation recovery. In the field experiment, there were no significant differences in plant density between our study areas with hydromulch compared to areas without hydromulch. The second seeding experiment showed growth underneath the hydromulch, from which can be concluded that enough sunlight is available underneath hydromulch to support plant growth. Thus, the insignificant differences between vegetation growth and density in hydomulched and non-hydromulched for both experiments indicated that the application of hydromulch might not be as detrimental towards vegetation germination as previously hypothesized.

Fire-Induced Water-Repellent Soil Layers in Non-Hydromulched Areas of Griffith Park, Los Angeles, California

Student(s): David Kunugi and Aya Satoh

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Questions: Have water-repellent soil layers discouraged pioneer species from successfully revegetating Griffith Park? How do the levels of water repellency vary among minimally burned, partially burned, and severely burned sites?
Location: United States, California, Los Angeles, Griffith Park (Latitude: 34.125°; Longitude: 118.302°)

Methods: Sites were classified as severely burned, partially burned, and minimally burned, based on both present and remnant plant matter found on location. GPS coordinates of all sites were recorded, and the water-drop test was performed on soil surface and five centimeters below ground. Three different levels of water repellency (hydrophilic, hydrophobic, and strongly hydrophobic) were determined based on how long it took for each drop of water to absorb into the soil.

Results: Ten sites were selected to be studied over a period of two months. Categorizing hydrophobic properties of soil with their respective burn severity level remained challenging, as there was variance within the timed results. Mode analysis was performed to clean up the nominal data, and a strong correlation was observed between minimally burned locales and their hydrophilic tendency.
Conclusion: The duration of time required for each drop of water to absorb into a soil profile can be used as an indicator of a soil’s water repellency level. Minimally burned sites demonstrate superior vegetative rebounds following a fire and tend to consist of more hydrophilic soils compared to partially burned and severely burned sites.

The Effects of Hydromulch and Fire Intensity on Post-Fire Chaparral: A Griffith Park Case Study

Student(s): Stephanie Debats, Deidre Pilotte, and Rashmi Sahai

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Question: Does hydromulch as a post-fire erosion mitigation treatment affect vegetation recovery in a chaparral ecosystem?

Location: Griffith Park, Los Angeles, California.

Methods: Vegetation sample transect plots were marked at two separate locations within the park, one to which hydromulch was applied, and one to which it was not. At the two locations, we selected one transect plot each of high and low burn severity, and species and number of individuals were sampled. The heights and widths of several indicator species were also sampled. Paired t-tests were used to test our hypothesis.

Results: Species diversity was found to statistically insignificant when comparing hydromulched to non-hydromulched areas. Plant density was found to be statistically significant with greater plant density found in non-hydromulched area. Plant growth, in terms of height and width, was found to have no conclusive trends or differences between hydromulched and non-hydromulched areas.
Conclusions: While species diversity was not statistically significant, the p-value was very close to being significant, signifying that a larger sample might have yielded a statistically significant result. The species diversity seemed to converge over time, as the number of herbaceous annuals reduced in the low fire intensity/non-hydromulched transect. The statistically significant higher plant density in non-hydromulched area signifies that hydromulch acts as a physical barrier, impeding vegetation recovery. Therefore, policymakers should be aware that hydromulch will reduce initial plant density. The plant growth data was inconclusive, because a random sampling of individuals does not account for individual growing conditions and varying germination times.

The Impact of Hydromulch on Native and Non-native Species in a Post-Fire Recovery Period within Los Angeles’ Griffith Park

Student(s): Bailey Blosser and Joelle Jahng

Advisor: Hartmut Walter

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Non-native plant growth after a fire is often a common characteristic associated with a fire-adapted plant community. The relationship between native and non-native plant growth after a fire and the application of erosion-control measures such as hydromulch is not well understood. In this paper, we explore the relationship between diversity, richness, and abundant growth rates in an urban wilderness park setting of native and non-native California chaparral. In the spring of 2008, we studied Los Angeles’ largest urban park, Griffith Park, that experienced an 800-acre fire in May of 2007 and an application of hydromulch to 500 acres of the park. We used the Shannon diversity index and the Student t test to find diversity levels and to measure variation among samples in order to determine if there is a relationship between native and non-native species diversity, richness, and growth rates and the application of hydromulch. We found that plots with no or partial application of hydromulch had slightly higher indices of diversity and richness than plots without hydromulch. No relationship was apparent between hydromulch application and non-native growth dominating over native growth, however there was an overall higher frequency of non-native plant counts, specifically Brassica nigra (Black Mustard) and Daucus carota (Queen Anne’s Lace) over native species plant counts regardless of hydromulch coverage.