Abstract Detail


Hernandez, Mayra [1], Regier, Jordyn [4], Sicangco, Camille Kilayko [2], Smith, Karagan [3], Davis, Stephen [4], Holmlund, Helen [4].

Dynamic stressors altering southern California shrublands.

Anthropogenic stressors are changing California’s vegetation. Plants in the Santa Monica Mountains, such as the shrublands made up of chaparral and coastal sage scrub (CSS), have adapted to thrive under specific fire and drought regimes. Chaparral and CSS communities are made up of a variety of species that have developed traits to mitigate drought stress and repopulate after fire. However, with increasing human activity fire frequency has also increased, thus decreasing the length of time between fires (fire-return interval). Fire and invasive species interact to play significant roles in native community degradation. For example, invasive species introduced by humans fill gaps where native species have been removed by disturbances, such as wildfire. These invasive species may outcompete native species, resulting in a positive-feedback loop and potentially converting the vegetation-type. In an environment with such drastic changes, plants may struggle to fill their niches, allowing the pervasive nature of invasive species to proliferate. Using empirical methods, our lab has analyzed chaparral composition and cover sampled between 1985-2021 for one site using permanent points. Beginning in 2021, CSS data was collected for the same permanent-point site and three additional sites with varying conditions and fire frequencies were included; sites added in 2021 were sampled using randomized, transient points. Sampling of the permanent-point site occurred at several intervals, documenting post-fire recovery after each of five fires experienced. Using a two-way ANOVA (p < 0.05), results for 2021 data showed a significant difference for basal dominance between chaparral and CSS at two sites, between chaparral populations at one site and no significant difference for basal dominance between all CSS populations. A two-way ANOVA (p < 0.05) for crown dominance provided a significant difference between chaparral and CSS at one site, chaparral populations were significantly different across sites, however, two sites with equal fire frequencies were not significantly different from each other, and there was no significant difference for crown dominance between all CSS populations. Using a one-way ANOVA (p < 0.05), chaparral total density was found to be significantly different across sites. Similar to crown dominance, chaparral total density at two sites with equal fire frequencies were not significantly different from each other. A one-way ANOVA (p < 0.05) on CSS total density showed no significant difference between any populations. Using our complete 1985-2021 data, we have found that a previously dominant chaparral species, Ceanothus megacarpus, which is unable to resprout in post-fire conditions, has disappeared from our permanent-point site. Additionally, chaparral species capable of seeding and resprouting are struggling to maintain their densities – relative to their densities prior to fire-frequency increasing. If these patterns continue, chaparral species, including those which can resprout, may become locally extirpated as new individuals are not able to establish and legacies die off. Detrimental effects from climate change and human influence will only continue to break down our ecosystems. If we are to preserve our native shrublands, conservation efforts must be planned and action must be taken to restore sites where species have already disappeared.

1 - CSU Dominguez Hills
2 - University of Florida
3 - UC San Diego
4 - Pepperdine University

coastal sage scrub
vegetation-type conversion

Presentation Type: Poster
Number: PEC009
Abstract ID:393
Candidate for Awards:None

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