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Thesis Abstract – Halsey (2018)

Title:

Post-Fire Seedling Emergence in a California Sage Scrub Community

Author and college:

Jack Halsey, Pitzer College

Date:

April 2018

Degree:

Bachelor of Arts in Environmental Analysis: Science

Advisors:

Diane Thomson, Keck Science Department of Claremont McKenna, Pitzer, and Scripps Colleges

Abstract:

California Coastal Sage Scrub (CSS) is a fire-adapted community rich in floral diversity, but historic fire frequencies are changing due to climate warming, invasive species, and other anthropogenic impacts. Few studies have characterized seedling emergence in CSS after fire. This gap limits our understanding of how CSS recovers from fire and ability to predict the consequences of changes in fire frequency. The goal of this study was to better understand how native and non-native plant species common in CSS germinate or resprout in the first year after a fire. In spring of 2017, fire partially burned a patch of CSS habitat where plant communities were being monitored, creating burned and unburned areas with pre-fire data. In the first growing season after fire, I measured seedling emergence in both burned and unburned areas along 12 transects where pre-fire data were available from 2012-17. I then compared abundances of non-native grasses, native shrubs, native forbs, and non-native forbs between burned and unburned areas, for both pre and post-fire data. I observed shrub seedling germination only for Artemisia californica, and shrub resprouting was limited to just four species. Burned areas showed increased native forb abundance and decreased non-native grass abundance, relative to both unburned areas and pre-fire conditions. Given the importance of shrub cover to CSS communities, the weak recruitment of native shrubs in the first year after fire could slow habitat recovery. Low winter precipitation in 2017-18 may explain this lack of shrub recovery; if so, future climate warming could reduce the potential for CSS to rebound after fire. At the same time, my results support previous work showing that fire can kill invasive grass seeds and promote germination of native forbs. This pattern may be short-lived, though, as grasses can recolonize from neighboring unburned areas. Further research should investigate grass and shrub abundances in additional years post-fire, and long-term recovery from fire in general.

For more information:

Contact Diane Thomson – dthomson@kecksci.claremont.edu