Practicum Project | 2008

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

Students: David Kunugi and Aya Satoh

Final Report

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.