The area burned by wildfire in the Sierra Nevada has increased by 274% over the last 40 years and the area impacted by stand-replacing fire has also increased. The forests in the Sierra Nevada are important for provision of clean water and are also part of the state’s climate action plan. As a result, figuring out how to reduce the chances of large, hot fires presents a large challenge.
We know that the current pace and scale of forest treatments to reduce the risk of large, hot fires is inadequate given the scale of the problem and the area burned by wildfire is projected to increase with on-going climate change. In a recent study led by Shuang Liang, we set out to determine how the pace of large-scale treatment implementation would alter carbon storage across the Sierra Nevada. We ran simulations under projected climate and wildfire and two management scenarios. Both management scenarios included applying thinning and prescribed burning treatments to low and mid-elevation forests. These are forests that have been most impacted by fire suppression. In the distributed scenario, we simulated an equal portion of the area treated at each time-step and with full treatment implementation by the end of this century. In the accelerated scenario, we simulated the same treatments over the same area, but schedule the treatments so they were complete by 2050. We included a control scenario that assumed no active management for comparison.
The area burned between all three scenarios was fairly consistent because we used the same fire size distributions in our simulations (black line in Figure 1). However, the proportion of burned area that was burned by stand-replacing fire (severity 4 and 5) decreased substantially. The faster pace of treatment under the accelerated scenario increased the proportion of area burned by surface fire (severity 1 and 2) and decreased the area burned by stand-replacing fire at a much faster rate than the distributed scenario.
Both the accelerated and distributed treatments ended up storing more carbon than the control by 2100 (Shown by the difference in Figure 2).
However, what was most striking was how these treatments influence the carbon balance of Sierra Nevada forests as a percentage of California’s 2020 emissions limit from the Governor’s Climate Action Plan. Initially, total carbon losses are higher in the treatment scenarios, with the accelerated treatment having the largest loss (Figure 3). However by 2030, carbon loss is similar amongst all three scenarios and by 2050 the accelerated scenario has lower emissions than the wildfire emissions under the control.
As we demonstrated in a previous study, changing climate and the increase in area burned has the potential to increase wildfire emissions by 19-101% by later this century. The results from this study demonstrate that restoring surface fires to the low and mid-elevation forests in the Sierra Nevada can reduce the magnitude of future emissions and maintain a larger amount of carbon stored in these forests.
Humans have extended the fire season and are responsible for 84% of all wildfires that occurred from 1992-2012 by providing unnatural ignition sources. The Albuquerque Journal recently published an article - Hotter, Faster Burns Expected - which stated, this is likely to be a significant fire season in the southwest. While absolutely true, what the article missed is that humans are entirely responsible for the predicament we face this year. While drought and dense forests create conditions that allow large, hot wildfires to burn, there is no wildfire without a source of ignition. Unattended campfires, cigarettes tossed out the window, and downed powerlines are the causes of many wildfires. There are no natural ignition sources until the lightning strikes that accompany monsoon season begin in the southwest. We have the ability to prevent this from being a significant fire season by eliminating human-caused ignitions.
Beyond this year, the wildfire problem is considerably larger than one dry winter. Regular fires burning on the forest floor historically maintained more open conditions and large, hot, fast-moving wildfires were rare. The large, tree-killing wildfires that occur now like the Cerro Grande, Las Conchas, and many others, are completely of our own making. By suppressing fires for a century, we have created dense forests that are loaded with fuel. In addition to the fuel we’ve added to the forest, we’re also cranking up the temperature by continuing to burn fossil fuels.
There is a strong link between temperature and area burned by wildfire. As temperature has increased, the length of the fire season in the southwest has increased by 110 days since the 1970s. When snow melts earlier in the season, forests dry out and are more flammable. In the southwest, the area burned by wildfire is 1200% larger than it was in the 1970s. The link between flammability and temperature is how wet the fuels (logs, branches, etc) in the forest are. Higher temperatures dry out forest fuels faster. Since 1984, human-caused warming has accounted for a doubling in the forest area burned in the western US. The drying and increasingly large wildfires are creating treeless landscapes that are dominated by shrubs. With on-going drought, higher temperatures, and larger, tree-killing wildfires large portions of our landscape may not grow forests again.
We need to learn to live with fire in the southwest. We need to eliminate the carelessness that provides the ignition source for wildfire. We also need to accept that fire is an important part of our forests and be tolerant when managers use fire to restore our forests. We have to accept that managed fires will sometimes cause smoke where we live. We have to accept that when there is a managed fire, we won’t be able to access the area for recreation for a short period of time. We have to accept that if we live in a flammable environment it is our personal responsibility to make our homes fire safe. If we learn to live with fire, forest managers will have the latitude to restore this important ecological process and help slow how quickly we lose our forests to climate change.
Imagine a career where a high success rate means you fail more than 50% of the time and you can never prove you are correct. That is being a scientist.
I live in a world where the majority of my friends are also scientists and I often forget that most people have relatively limited formal exposure to science. Sure, you take biology and chemistry in high school and if you’re not a science major in college, you take a few science classes. What gets lost in this level of education is how messy the scientific process is and how often you fail to accomplish your objective. What also gets lost is how the excitement of unexpected results is really what drives most of us. We teach science as a linear process in introductory science classes – researcher develops hypothesis, designs experiment to test hypothesis, experiment supports hypothesis, new knowledge acquired and added to text book. But, that isn’t how it really works.
A more accurate representation of this bland description is that – researcher develops hypothesis, designs experiment to test hypothesis, experiment fails for any number of reasons, researcher develops new experiment to test hypothesis, experiment inconclusive, new knowledge acquired, researcher reevaluates hypothesis and starts over. Of course, that doesn’t do the process justice. In my experience as a forest ecologist it usually goes something like this:
If you’re not a scientist (which I hope) and reading this (the whole reason I write this blog), you’re probably thinking – This poor science geek can only make friends with other scientists. and It must be pretty demoralizing to fail most of the time. I certainly can’t speak for everyone in science, but I’m pretty obsessive when it comes to thinking about forests and most of my friends are pretty obsessive about thinking about their study systems too. It’s not a curse; nature is a fascinatingly complex puzzle. I absolutely love forests and I strive to do meaningful work that helps us understand and better manage our forests. As for the failure part, sure sometimes it’s disheartening. But the unexpected is what motivates me. When I get unexpected results and it challenges me to think about the forest in a new way, that is what wakes me up in the middle of the night. That is what allows me to let the grant proposal and paper rejections roll off my back. When I teach introductory ecology, I try and communicate to students that this process is not linear like their textbook would have them believe. The information that makes it into a book has lots of failure and reevaluation behind it. The individuals that discovered those things in their textbook were driven by curiosity and the desire to more completely understand whatever system they were working in. While this career certainly doesn’t appeal to most, I just hope that people who aren’t scientists can appreciate the process the way I appreciate the process an artist or business person or engineer goes through.