Forest for the Trees

"Tree mortalityā€¯ and fire management in the Sierra Nevada

by Julia Rock

Illustration by Franco Zacharzewski

published September 28, 2018

In March of 2017, the National Academy of Sciences, Engineering, and Medicine hosted a workshop in Washington D.C. titled “A Century Of Wildland Fire Research: Contributions To Long-term Approaches For Wildland Fire Management,” which was sponsored by the US Department of Agriculture (USDA) Forest Service. Dr. Scott Stephens, a fire ecologist from the University of California, Berkeley, and one of the most prominent fire ecologists in the country, gave a presentation entitled “Fire and Fuels Management: What works where?” in which he discussed the distinct fire regimes that different types of ecosystems require to stay healthy.

Dr. Stephens uses Wood Buffalo National Park, an area in the Northwest Territories of Canada, as an example. He explains that the ecosystem is adapted to “infrequent high severity fires,” characterized by severe fires that burn every 70 to 150 years. However, this is changing: the region experienced a large fire in 2004 and then again in 2014. Stephens shows a slide with a picture from the forest: “You can see those skeletons of the Jack pine there in the foreground. We found one seedling in an area of almost fifty square meters. Here you see a place where fire regimes are changing abruptly because of climate warming, and we are seeing major changes in vegetation.” The picture shows a grassy area, with the thin, skeletal remains of what used to be Jack pines.

Dr. Stephens pulls up his next slide, which contains three pictures from the Sierra Nevada region in California. He gives the audience some data which was taken from an area of the Stanislaus National Forest in the Sierra Nevada: in 1911, there were 19 trees per acre. A century later, in 2013, there were 224 trees per acre. Six months later, the Rim Fire came through the forest, which was the largest fire to ever take place in the Sierra Nevada and the fifth-largest fire in California history. Why did the density of trees in the region increase by an order of magnitude between 1911 and 2013? Over the past century, the US Forest Service has adhered to a policy of fire prevention and suppression in national forests (think: Smokey Bear), in which smaller fires are quelled before they can burn naturally. Even in the 1960s, as scientific research in the United States pointed to the need to allow fires to burn in order to promote healthy forests, fire suppression continued, in part due to the timber industry’s vested interest in preventing burns. The consequence was the high density of trees that Dr. Stephens points to in 2013. These trees serve as the fuel that allows massive fires such as the Rim Fire to burn on a scale previously unseen in these forests.

In the months following the workshop, California saw its most destructive fire season in state history: 1.2 million acres of land burned, at least 46 people were killed, and nearly $12 billion in damage was caused. This year’s season is on track to surpass the 2017 season by almost all measures. The Los Angeles Times reported on September 8 that wildfires had burned 1.2 million acres of land, destroyed more than 1,200 homes, and killed at least a dozen people so far this year in California. September and October are expected to be the peak of the fire season.




“This is a different type of fire,” Carmen Tubbesing, a Ph.D candidate studying wildfires at the University of California, Berkeley, told the Independent. Tubbesing is a researcher in the Stephens Lab at Berkeley, where she studies the effects of extreme fire behavior in the Sierra Nevada. In an interview with the Independent, Tubbesing explained that the Sierra landscape is changing rapidly, as pine trees die and chaparral—a family of shrub-like plants which thrive in drought and post-fire landscapes—takes over. When a high-severity fire kills all of the trees in the area, chaparral proliferates due to the availability of sunlight, whereas it takes a much longer time for pines to regrow. This disrupts the natural process in which burning pine trees spread their seeds for future generations of trees to grow.

Tubbesing explains that this new breed of fires has accelerated the anticipated impacts of climate change on the region. One of the most alarming consequences of these high-severity fires is their impact on the ongoing “tree mortality crisis,” in California, in which 129 million trees have died in the state since 2010. The crisis has been caused by a number of factors, including drought and a bark beetle infestation, and the devastating impacts of large fires that have wiped out entire forests. The crisis has hit the Sierra Nevada especially hard: in some parts of the region, over 90 percent of pine trees are gone. The Sierra Nevada is California’s largest carbon sink––meaning its trees capture carbon dioxide from the atmosphere––and retains about 60 percent of the state’s water. An estimated 85 percent of the dead trees are in the Sierra.

The US Department of Agriculture (USDA) Forest Service webpage about the tree mortality crisis warns: “Millions of trees in the Sierras and Central Coast forests are stressed from higher temperatures, competition for water resources during this historic drought, and multiplying bark beetles. They simply can’t withstand this deadly combination of stressors and are rapidly turning orange and dying. Even with the increased rainfall this past year, stressed trees will continue to die because while green, they have been invaded by bark beetles and just don’t know they’re dying yet.” This language coming from a federal government website is notably stark and desperate, especially considering that the current administration is tirelessly rolling back environmental regulations and ignoring the impacts of climate change. Fires, though, are impossible to ignore. Hillsides covered in dead trees, which comprise the state’s largest carbon sink and play a crucial role in maintaining the state’s water resources, undeniably beg for swift government action.




Large wildfires require many different levels of government response. Getting to zero emissions as quickly as possible will be necessary to prevent the worst of the damage caused by severe fires and tree mortality, because temperature rise and drought only increase the probability of large, high severity fires. However, in the short term, more scientifically informed fire management policies are crucial to create more resilient forests. As Dr. Stephens explained in the 2017 workshop, different forest ecosystems require different fire regimes, and the process of managing a fire regime is ongoing: “This is a conversation with the land that goes on forever. This idea that you’re going to do prescribed burning and management—it’s something that’s going to go on for eternity. You can’t somehow think you’ve got it done.”

Bob Kingman is the Assistant Executive Direcor at the Sierra Nevada Conservancy (SNC), a state agency created in 2004 to provide “strategic direction” for policy in the region. The SNC is tasked with allocating billions of dollars in state bonding funds to local communities, non-profit organizations, and tribes who submit grant applications to fund local projects related to forest health. Kingman oversees the competitive grant process, and says that one of the main goals of the funds is to “bring people together to discuss forest health and bring resources to communities in need.” Kingman says the state is concerned about the impact of forest health on watersheds in California (which in turn impacts drought patterns), but it is nearly impossible to make effective policy decisions at a state level when the needs of different communities are so distinct.

Kingman said that the role of the SNC in allocating resources for projects related to forest health and fires has increased in recent years, due to the increasingly obvious fact that the state’s forests are at risk, and the implications that this has for water access in the region. Dr. Gabrielle Boisramé is also an affiliate of the Stephens lab, where she researches the relationship between wildfires and water resources in the Sierra Nevada, and has studied the impact of tree mortality and fires on water retention in forests. “We know that really big, high-severity fires can cause a lot of water quality and erosion problems –– that’s what most people have been able to study in the past,” Dr. Boisramé told the Independent. Dr. Boisramé’s research has instead emphasized the impact that forest density and tree cover has on the Sierra’s ability to provide water for the rest of the state. It’s a precarious balance: if forests are too dense, due to fire suppression practices, the trees use up all of the moisture in the region. Additionally, when forests are too dense, less snow reaches the forest floor, which prevents the buildup of snow pack that is necessary to provide water for the rest of the state.

Dr. Boisramé hopes that her research, and that of other hydrologists and ecologists, will serve as the basis for better fire management policy. “The goal is that our work is used as evidence when people are trying to make decisions based on the best science available. I do try and write things that are very scientifically rigorous, but also accessible, with figures and maps that are very clear.” The California Fire Science Consortium (CFSC) is a non-profit organization with the goal of ensuring a “free flow of fire science information,” according to its website. Dr. Boisramé says that organizations like the CFSC are crucial because they help policymakers and fire managers make informed decisions based on the best research available.




The other aspect of the policy approach towards wildfires is mitigating the causes of climate change—most importantly the state’s reliance on fossil fuels. On August 27, the State of California released its fourth Climate Change Assessment, which outlines how climate change has already affected California, and what changes the state expects to see in the future. The purpose of the Climate Change Assessments, the first of which was conducted in 2006 by three state agencies, is to provide scientific foundations for the state to turn to when writing policy. The most recent study wastes no time in explaining the stakes of this assessment: “Since its Third Climate Change Assessment in 2012, California has experienced several of the most extreme natural events in its recorded history: a severe drought from 2012-2016, an almost non-existent Sierra Nevada winter snowpack in 2014-2015, increasingly large and severe wildfires, and back-to-back years of the warmest average temperatures.” These visible impacts of climate change are perhaps more compelling than warnings about burning fossil fuels, because of their visibility and proximity to people in California.

The Fourth Climate Change Assessment warns that future fires will only be worse if carbon emissions continue at their current rates. “One Fourth Assessment model suggests large wildfires (greater than 25,000 acres) could become 50 percent more frequent by the end of century if emissions are not reduced.” Just two weeks after the Assessment was released, on September 10, Governor Jerry Brown signed a bill into law mandating that the State meet a target for 100 percent  of energy sources in the state to be zero-emission by 2045.

However, a comprehensive climate policy that addresses the health of the state’s forests is necessary to complement action on fossil fuel infrastructure. The Los Angeles Times Editorial Board wrote on September 1, “The challenge will be ensuring that environmental and public safety interests, not commercial interests, drive the state’s policies on forest management. Regardless, the era of benign neglect of the state’s forests has to come to an end.”

Recent legislation signed by the Governor indicates that the state government is already moving away from historic fire suppression practices towards prescribed burns and management policies more closely matched to the needs of different forest ecosystems. Prescribed burn policies can be politically tenuous, because many homes and businesses located on the edges of forests will inevitably be touched by burns. Additionally, the forests damaged by the fires of the past few years and the tree mortality crisis are in need of tree removal and reforestation. A more comprehensive state policy towards its forests are needed. “We have the Clean Water Act, the Endangered Species Act, the Clean Air Act, we do not have a ‘Forest Resiliency’ or ‘Forest Act,’” Dr. Stephens told the audience at the 2017 workshop. Perhaps its time has come.


JULIA ROCK B’19 is looking for a job as a fire ecologist.