Drought and fire work together to alter California shrub systems

Two biology professors at California State University, Bakersfield (CSUB), husband and wife team Drs. Brandon Pratt and Anna Jacobsen, have been studying drought tolerance of shrublands and forests for most of their careers. The couple met at Pepperdine University in 2002 where their mutual interests brought them together in the lab of noted teacher and scholar Dr. Stephen Davis. In 2005, the couple married and moved to CSUB to continue their research and teach in the Department of Biology.

For the last 7 years at CSUB, Drs. Pratt and Jacobsen have been studying a range of topics including the physiology and structure of plant vascular systems, the processes by which plants turn sunlight into chemical energy (photosynthesis), work with local farmers on improving table grape production, and international work in South Africa studying shrub systems that are analogous to those in California. Their work has been widely published in international journals and they have received nearly $1.8 million dollars in funding for their research from the National Science Foundation, the Andrew Mellon Foundation, and the National Park Service.

“Most of the funding goes to pay undergraduate and master’s students to help in research projects and to purchase state-of-the-art equipment to use in our labs at CSUB,” explains Jacobsen. “By design, all of our work involves students, which is a win-win relationship because our students help us to collect data, and we use our research as a platform to teach them about biology, advanced research methods, and how to conduct scientific research, including statistical analysis and writing research papers. These skills are invaluable and help students to reach their career goals after leaving CSUB,” says Pratt. “Having these undergraduate student research opportunities is not universal at colleges and universities, and is part of what makes CSUB unique,” according to Jacobsen.

Their most recent study, published in the international journal Global Change Biology, examined how California’s shrublands respond to drought after a fire. “This is an important topic because droughts and fires appear to be occurring more often together. Thus, examining how ecosystems recover after fire and during a drought is a timely topic. When we really looked into it, we were surprised at how little information was available on this topic,” explains Pratt. A fire in the Santa Monica Mountains of southern California burned an area just south of the city of Westlake Village in July 2007. This fire was followed by the lowest rainfall ever recorded in much of southern California. “The fire followed by the intense drought created a unique opportunity to study how these two stressors may combine to affect this ecosystem,” said Pratt.

Published in the journal on December 26, 2013, this study finds that some species suffer high levels of mortality after a fire if it is followed by a drought year. This finding may seem obvious; however, it was actually a big surprise. The findings were unexpected because many shrubs in southern California resprout after their aboveground branches are killed by the fire. Belowground the situation is different where the large root system survives the fire because it is insulated from heat by the surrounding soil. It is generally assumed that resprouting plants, with their large intact root systems, are less sensitive to drought than smaller and more fragile seedlings. Pratt and co-authors found that populations of species that produce seedlings after fire were better at coping with the drought than some of the other species that rely exclusively on resprouting. This was because the seedlings did not suffer unusually high mortality during the drought as was the case for some of the resprouts. This study demonstrates that species abundances and distributions can rapidly change after fires if they are followed by drought. This is a concern for the health, resilience, and diversity of California’s unique ecosystems because many of these species are very rare and only occur in small areas, and only in California.

The study was a joint effort between CSUB and Pepperdine University. Co-authors included numerous undergraduate students from both CSUB and Pepperdine who made significant contributions to the project, and many additional undergraduate and graduate students were acknowledged for their efforts in helping to survey populations in the field. One former CSUB undergraduate student and study co-author, Aaron Ramirez, is now a Ph.D candidate at UC Berkeley. Mr. Ramirez is studying how island ecosystems respond to drought. “It is exciting to be a part of research that gets published and to have the opportunity to make significant contributions to issues so important to the ecosystems of southern California,” said Mr. Ramirez. “Both fire and drought continue to be very important components of southern California ecosystems and our study helps to shed light on how these components may interact to drive change in the future,” explains Mr. Ramirez.   

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