CSUB faculty members part of international team researching drought-related tree death

Dr. Anna Jacobsen and Dr. Brandon Pratt join international team of 37 co-authors

By California State University, Bakersfield

November 9^th, 2020

You don’t have to live in California long to notice the effects of climate change: the warming summers, devastating fires, and regular drought. What those phenomena mean for the environment they leave behind is something scientists are still learning.

Dr. Anna Jacobsen and Dr. Brandon Pratt, both professors in the biology department of California State University, Bakersfield’s School of Natural Sciences, Mathematics, and Engineering, are part of an international team researching tree replacement patterns after drought-related tree death.

“This study compiled data from researchers around the globe who have studied, documented, and/or observed massive tree mortality events,” Dr. Jacobsen said. “We wanted to examine what would happen to these forests in the years after tree die-offs.”

Dr. Jacobsen and Dr. Pratt are two of 37 co-authors of a study on their research that was recently published in Proceedings of the National Academy of Sciences of the United States of America, a prestigious and high-profile scientific journal.

“The record droughts observed in California in the last decade are not unique to California,” Dr. Pratt said. “Extreme droughts have been happening in many areas of the globe and this is one of the most important aspects of climate change in the context of the implications for ecological, agricultural, and socioeconomic systems.”

Possible outcomes of massive tree deaths that the two looked at included the chance of seedlings of the same species to emerge, a sign of recovery; if other tree species would become dominant instead, signaling a shift in the forest; or if non-tree species like shrubs and grasses would take over where the trees had died.

“We found evidence for all of these patterns, but the most common pattern was for different tree species and shrubs to become more dominant,” Dr. Jacobsen said, noting that occurred in 69 percent of sites. “This indicates that the composition and structure of our forests are changing to something new and different than they were before.”

CSUB faculty members part of international team researching drought-related tree death

While the published report includes data from all over the world, the Bakersfield team contributed their findings of a study on an oak woodland in the foothills of the Tehachapi Mountains, just off Highway 58.

“During the peak of the drought, in 2014, there was substantial mortality in some of the blue oak (Quercus douglasii) that naturally occur in that region,” Dr. Pratt said. “This is a California endemic oak species that occurs almost exclusively in the foothills around the Central Valley and in the coast ranges. We found that the dead trees were not being replaced by new trees but were being replaced by weeds (mainly grasses) that are native to the Mediterranean Basin.”

Working on a large research team with members in different countries is not always easy but Dr. Jacobsen and Dr. Pratt aren’t new to working with colleagues on different continents. For years, they have worked with other scientists who study the five mediterranean-type ecosystems around the world: the Mediterranean Basin, South Africa, western Australia, central Chile and right here in California.

“This group has a meeting every three to four years (it’s the ‘Olympics’ for mediterranean-type climate region researchers) and we know the organizers of this research project from these meetings that we have been attending for the last 20 years,” Dr. Pratt said. “It has been fascinating to go visit these places and study them, and to be able to compare them to California.”

Getting the team’s paper published took time, but Dr. Jacobsen and Dr. Pratt are happy to now be able to share their work with the science community. By working with scientists in different parts of the world, they observed emerging patterns that would be hard to track in a narrower study.

“It also is a potent reminder that the things that we are seeing ‘in our own backyard’ are not isolated — the extensive death of trees in our forests, including pine, fir, and oak, are also consistent with what is happening in many places,” Dr. Jacobsen said. “These are large losses! And the cascading effects of these losses are only becoming more apparent: increased fire risk, altered watersheds and debris flow, changes in how we use our forests for recreation, impacts to industries that utilize forests as a resource, etc.”

To read the article, Dr. Jacobsen and Dr. Pratt’s first to be published in PNAS, please go to www.pnas.org/content/early/2020/10/27/2002314117.

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Footnotes

Story by Kelly Ardis, communications specialist for the School of Natural Sciences, Mathematics, and Engineering

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FootNotes

Story by Kelly Ardis, communications specialist for the School of Natural Sciences, Mathematics, and Engineering

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CSUB faculty members part of international team researching drought-related tree death

Dr. Anna Jacobsen and Dr. Brandon Pratt join international team of 37 co-authors

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