Litter removal increases native plant diversity in coastal sage scrub

Link To Share This Poster: https://cdmcd.co/E3vG8L
Live Discussion Link: https://cdmcd.co/A9PGww

Advyth Ramachandran, Rhea Amatya, Michael Fugate, Jared D. Huxley, Caryn Iwanaga, Tesa Madsen-McQueen, Annika Rose-Person and Marko Spasojevic, Department of Evolution, Ecology, and Organismal Biology, University of California Riverside, Riverside, CA, Thuy-Tien Bui, Department of Environmental Sciences, University of California Riverside, Riverside, CA

Background/Question/Methods
The highly diverse coastal sage scrub of the California Floristic Province is one of the most endangered ecosystems in the U.S. Multiple waves of invasion by exotic annuals, and subsequent type conversion to exotic annual grassland dominated by Bromus diandrus, has reduced the cover of native subshrubs and forbs. To address this conservation challenge, an experiment was established in 2008 to test whether thatch accumulation may be a mechanism by which exotic annuals reduce native species success. Students in introductory biology courses helped establish 180 1.5 x 3 m plots on a north-facing slope on the University of California, Riverside campus composed of coastal sage scrub invaded by exotic annuals. Plots were installed using a paired design, where one plot received litter and thatch removal in fall, while the other was left as unmanipulated control (90 pairs total). Overall species richness, native species richness, and the dominance of the invasive annual grass Bromus diandrus were then recorded annually in spring over 7 years to ask: what is the effect of litter removal on plant diversity in invaded coastal sage scrub ecosystems?

Results/Conclusions
We found that the raking treatment had a significant positive effect on both native species richness and overall species richness, and in reducing the dominance of the invasive grass Bromus diandrus. This suggests that litter removal has the potential to be a simple, non-toxic method for increasing native plant diversity in degraded coastal sage scrub. The UCR SEEDS chapter will reinitiate this experiment, collecting baseline data on species composition in Spring 2021 and by renewing raking treatments in Fall 2021, to examine the long-term impacts of raking and provide further insight into the efficacy of litter removal as a management strategy. Controlling non-native annual invasion in coastal sage scrub is expected to increase the cover of native subshrubs and forbs associated with many animal species, including several endangered species, while also having implications for wildfire fuels management, as exotic annuals have reduced the fire interval in this ecosystem.