Eucalyptus trees were introduced into California in the 1850s for their potential as lumber and have since become one of the most common invasive arboreal plants. However, the essential oils stored in eucalyptus leaves which have antifungal and antibacterial properties, have been documented to negatively affect soil health. This study investigated the impacts of these essential oils on soil microbial activity and macronutrient levels in comparison to native oak species. We sampled 3 locations in the LA Zoo’s Oak Woodland area. We used Solvita soil respiration kits to assess microbial activity and we also measured pH, nitrogen, and phosphorus levels. Results indicated that soils beneath eucalyptus trees were more acidic and had lower macronutrient levels compared to those beneath oak trees. The soil respiration analysis also showed reduced CO2 levels in areas where eucalyptus leaves were most abundant, suggesting lower microbial activity. In combination with the acidification, reduced macronutrient levels, and diminished microbial activity, this study supports previous findings that eucalyptus essential oils negatively impact soil health. However, from a conservation perspective, prior to removal of these trees, adequate replacements must be found to provide critical habitat for avian species, particularly nesting raptors, and to prevent erosion.

Paola Suarez is a recent graduate of California State University, Northridge, where she earned her Bachelor’s degree in Ecology & Evolutionary Biology with a minor in Anthropology. She is interested in plant ecology and mycology, with an emphasis on habitat restoration and bioremediation. Paola has had the privilege of working with organizations such as the Los Angeles Zoo, the Santa Monica Mountains Fund, and various non-profits, which have nurtured both her scientific interests and her passion for cultural ecology.