By Save the Redwoods League
Cover photo by Johnathan Irish
Late in the summer of 2020 . . .
Wildfire spread across California. The record-breaking fire season would eventually burn well over 4 million acres. This footage is of the SQF Complex/Castle Fire burning in September 2020.
Learn about the giant sequoia’s unique relationship with fire, and what makes modern fires so different from what the trees have experienced in the past.
Fire in the giant sequoia ranges of the Sierra Nevada is not new, and is in fact a necessary ecological feature.
What is new is that this level of severity poses a unique challenge to these ancient trees, which have thrived for millennia alongside fire.
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Sequoia National Forest
25 miles north of Kernville
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Unprecedented loss?
The Castle Fire, also known as the SQF Complex Fire, would eventually burn through roughly a third of the entire giant sequoia range, or about 16,000 acres.
About 40% of those acres burned severely, and since severe fire kills monarchs, this potentially means huge losses of ancient trees. At the League’s Alder Creek property, of the 65 acres of grove area that burned severely, at least 80 monarchs were killed.
After the fire
Dozens of giant sequoia burned at Alder Creek, owned by Save the Redwoods League.
As the Los Angeles Times noted:
”The towering trees had grown on this Sierra Nevada ridge top for well over 500 years. They had lived through many wildfires and droughts. But they could not survive the Castle fire…”
Researchers have to go back over 700 years to find another fire that did anywhere near as much damage to the giant sequoia range, and even that fire event may have had less extensive impacts than this one.
Fire Impacts at Alder Creek Grove
A League-held property
How did this happen, and why now?
To understand how modern wildfires are taking down some of the oldest, largest and most fire-adapted species on the planet, we need to understand their fire history, adaptations and recent changes to the ecosystem.
From the tiniest seeds grow giants
Giant sequoia cones are generally one to three inches long, and the seeds are the size of an oat flake.
The sealed green cones can remain on the tree for up to 20 years, until they dry out, creating openings that release their seeds.
Fire unlocks life
Giant sequoia cones are serotinous, which means that fire on the forest floor causes them to dry out, open and release their seeds.
This adaptation ensures that the tree times the release of most of its seeds to coincide with fire, which creates ideal conditions for regeneration success.
Fire burns off woody debris and exposes the soil, it creates an ash layer that returns nutrients to the soil and increases sunlight by killing some of the competing pines and firs.
Thriving with fire
Giant sequoia can thrive in a world of frequent fires.
The bark of a monarch can be up to two feet thick, insulating them from fire damage. It’s rich with tannins that help the trees resist pests and disease, making giant sequoia resilient and long lived—the oldest known giant sequoia lived to be 3,200 years old.
The thick bark also insulates living tissue from the low- to moderate-severity fires that burned frequently in the past.
Caring for giants
These fires were started by lightning or by Native tribes that used fire as a means of managing and caring for the forest.
These fires regularly reduced fuels—the pine needles, fallen branches and other woody debris on the forest floor—and cleared out some of the smaller trees and brush, making extreme fires less likely.
Long-term survival
Sequoia did sometimes sustain fire damage, torching out parts of their crowns or creating large “catfaces”—large triangular burned areas at the base of many monarchs, formed over time by successive fires.
The larger issue is fire severity
Fire-resilient giant sequoia are likely to survive a low-to moderate-severity fire, which could really be largely restorative by reducing fuels and tree density. In contrast, high-severity fire that consumes nearly everything in its path is too hot for giant sequoia to survive.
Although significant seedling regeneration may still occur—since the cones need heat to open—the ancient trees that are killed in this type of fire are irreplaceable.
But how do we know what we know about the history of fire in giant sequoia?
And what can that tell us about why giant sequoia are now being killed at alarming rates, rather than thriving, in wildfires?
Of tree rings and fire
To understand how frequent fires were in the past, scientists use dendrochronology, the study of tree rings.
A tree’s annual growth rings can be used to age a tree, and they can also store a record of wildfire.
Studying tree rings
In the 1990s, Dr. Tom Swetnam and colleagues collected cross sections—flat slabs cut from already dead and downed giant sequoia trees.
These cross sections were then brought back to the Laboratory of Tree-Ring Research at the University of Arizona for study.
Sampling sequoia groves
There are about 73 distinct groves of giant sequoia on the western slope of the Sierra Nevada mountains in California. Giant sequoia co-occur with common mixed-conifer tree species, including sugar pine, ponderosa pine, white fir, incense cedar, and occasionally red fir.
A Slice of History
Dr. Swetnam and his team collected samples in five of the largest giant sequoia groves in Sequoia and Kings Canyon National Parks, Mountain Home State Demonstration Forest, Yosemite National Park and Giant Sequoia National Monument.
Dating Historical Wildfire
Sixteen to forty-six fire-scarred stumps or logs were sampled in each grove, yielding a detailed history of fire spanning the past 1,400 years.
Because giant sequoia live so long, these are some of the longest precisely dated time series of fire events in existence.
Although some fire events were dated as early as 1,123 BC, Dr. Swetnam’s study focuses on fire activity beginning in 500 AD, which is when there were enough samples to confidently interpret the fire history. His research shows fires were far more frequent in these ranges before settlers exploring America's western frontiers began actively suppressing fire at the turn of the 20th century, soon after the American Civil War.
1850s – Present: UPSETTING THE BALANCE
European American arrival in California brought dramatic changes to giant sequoia forests. People cut some of the big trees and shipped them across the globe to showcase their magnificence and to make a profit. Over time, roughly one-third of the giant sequoia groves were logged.
Fire Suppression on the Rise
The most dramatic change related to Euro-American settlement was the cessation of fire. By the 1870s settlers began to suppress fires where they could, and the forcible removal of Native peoples from their ancestral territories ended their traditional use of fire. By the early 1900s it became a national policy and a mission of the U.S. Forest Service and National Park Service to extinguish all fires as quickly as possible.
Euro-American settlers were also concerned for the giant sequoia, but because they did not seek out indigenous knowledge, they did not grasp the critical role that fire plays in these ecosystems.
Without regular fires to help clear out the underbrush, there has been a large increase in both surface fuels (woody debris and litter on the forest floor) and ladder fuels (small trees that can enable a fire to transition from the understory into the treetops).
A changing forest
These dramatic changes increase the risk of severe fire. If a fire burns through a forest that has over 100 years of fuels accumulation, fire behavior will be much more intense, resulting in larger pockets of high severity than observed historically when fire burned roughly every 10 to 20 years.
Without fire to release seeds and to clear the woody debris and competing vegetation, new giant sequoia seedlings cannot establish.
These repeated photos of the Confederate Group in Yosemite’s Mariposa Grove show dramatic forest changes after over 70 years of fire exclusion.
Climate change adds another layer
The warming climate further exacerbates wildfire activity.
Climate has always been an important driver of wildfire activity; fire history in giant sequoia shows how fires become more frequent with warmer and drier conditions.
During the Medieval period (circa 900 to 1300) in what is now the western United States, temperatures were elevated and droughts were frequent and extreme.
As expected, fire activity increased during this time period; as fires became more frequent, each individual fire likely got smaller because fuel did not have as much time to build up in between.
In the 20th century, the relationship between fire and climate became temporarily decoupled—even though lightning would strike and conditions were warm enough, effective fire exclusion resulted in most of the groves having no fire at all during this time.
Now, the combination of the build-up of fuels and rapidly warming climate is overwhelming our best firefighting efforts, and the effects are increasingly severe.
Portions of Alder Creek were damaged in the Castle Fire by Kyle Cooper/Save the Redwoods LeagueSave the Redwoods League
Modern high-severity fires are killing monarchs
The 2020 Castle Fire (aka SQF Complex) is the fourth wildfire in the last five years that burned severely into giant sequoia groves, suggesting an alarming new trend.
Climate change is having other indirect effects on giant sequoia ecosystems, including increased drought stress and potential drought and beetle interactions, which we are only beginning to investigate and understand.
Save the Redwoods League has been working with the US Forest Service to study two 2017 wildfires: the Pier Fire in Black Mountain Grove in Giant Sequoia National Monument and the Railroad Fire in Nelder Grove in the Sierra National Forest.
Many were killed outright by those fires, and a few sustained enough injury that they have slowly succumbed over the last few years.
Linnea Hardlund, Save the Redwoods League's former Giant Sequoia Forest Fellow and Fire Ecologist, studies a map on preliminary burn severity while monitoring damage on the League's Alder Creek property.
In Nelder Grove, of the 104 monarchs greater than four feet in diameter, 29 were killed. In Black Mountain Grove, of the approximately 180 trees surveyed (a subsample of this very large grove), over 50 were killed.
Many of these were over 10 feet in diameter, and many had likely been alive for millennia.
These results were shocking even to giant sequoia scientists, and now we already know that the 2020 Castle Fire killed significantly more.
Time is running out to restore fire resilience to giant sequoia forests.
Restoring resilience: BRINGING FIRE BACK TO GIANT SEQUOIA
The primary solution to save ancient monarchs from fire may seem counterintuitive—we actually need more low severity fire on the landscape. Forest managers and firefighters use prescribed fire to safely bring fire back to the groves under very specific conditions.
Prescribing Burns
To safely burn and reduce fire severity in these fuel-loaded groves and allow fire to do its good work, fire managers conduct prescribed burns in the spring or fall, when the temperatures are lower and relative humidities are higher.
2019 Sherman Prescribed Burn in Sequoia National Park. Video courtesy NPS/Linnea Hardlund.
Fire managers also ensure that wind speeds are low and blowing in a favorable direction. Extensive safety and contingency plans are in place any time a burn is implemented.
Restoring resilience: RESTORATION THINNING
Although restoration of fire is the most critical restoration tool because it promotes the next generation of sequoia and burns up the dead woody debris on the forest floor, restoration thinning also plays an important role.
Restoration thinning targets the smaller trees that can act as ladder fuels
The small trees are then either piled and burned in place, or removed and used for biofuel. Thinning is best done along with prescribed fire, because only fire will consume the dead fuel on the ground.
Giant sequoia are not only fire resilient, they are fire dependent for their regeneration — but fire exclusion has dramatically reduced their fire resilience
Although giant sequoia need fire, these groves were generally in a heavily fuel-loaded state prior to these recent fires, leading to high severity and loss of ancient monarchs.
Both Yosemite and Sequoia-Kings Canyon National Parks have restored several groves using prescribed fire and some mechanical thinning, but most of the groves in the range still need restoration to be fire resilient in the warming climate.
2020 was a record fire year not only for California, but also for its impacts on giant sequoia
With heavy fuel loads as a result of fire exclusion and the warming climate, severe fires that kill giant sequoia have dramatically increased in the last five years.
According to CalFire data, roughly 25% of the range burned in wildfires between 1910-2015. In the last five years, 65% of the range has burned — 33% of it in 2020 alone.
Preliminary fire severity as of October 14th, showing roughly 40% of the grove area burned at high severity (shown in red), where most of the monarchs were likely killed. The League will re-measure these plots in 2021 to better understand the fire’s impacts. Preliminary fire severity map created by Spatial Informatics Group, using Landsat data and thresholds described in Miller & Quayle 2015.
These fires are raising an alarm bell
But even as this is a story of loss, we still feel hope for the sequoia, because we know what we need to do to ensure that these ancient giants persist on the landscape.
Giant Forest by Anthony AmbroseSave the Redwoods League
How the League is taking action
Save the Redwoods League views wildfire as a top priority in our larger effort to protect and restore California’s redwood forests.
We need to restore more “good fire” so that the ancient trees—the oldest of which had survived hundreds of wildfires prior to fire exclusion—survive into the future.
Bringing Back Indigenous Cultural Burns
First cultural burn on League land revives tribal traditions and forest resilience.
California banned cultural burning back in 1850, as part of legislation to forcibly remove Indigenous people from their ancestral lands.
Before then, tribes had used fire to help manage the ancient sequoia and other forests for millennia. The practice typically involved lighting small, controlled fires to clear overgrown shrubs, small trees, and dead leaves.
In the Sierras, these low-intensity fires promoted the growth of plants for food, materials, or medicinal purposes, helped manage habitat for wildlife, and maintained the health of the giant sequoias, which were adapted to thrive in a fire-prone environment.
I'll Go If You Go podcast host Emily Harwitz delves into the world of fire adaptation and resilience across California with a double feature: Katie Low, fire ecologist and Statewide Coordinator for UC Agriculture and Natural Resources Fire Network, and Saul Tejeda, an Assistant Captain on the Yosemite Wildland Fire Module with over a decade of experience on the fireline.
This episode goes broad and deep, so if you’re hankering to learn about California’s state of fire preparedness, how a prescribed burn happens, how technology is advancing wildland firefighting, or the technical nitty-gritty of what it’s like to work with fire, you’re in luck.
Read more about our guests.
Giant Forest by Anthony AmbroseSave the Redwoods League
Future-proofing our forests
We’re moving quickly to ensure that the properties we manage are prepared for a future with more extreme wildfire, and we’re encouraging state and federal land managers to ramp up efforts to make their coast redwood and giant sequoia landscapes more fire resilient.
How you can help
You can support these important efforts by learning about the League’s work.
Keep up with the latest news on redwoods and fire on Save the Redwood League's website.
Follow these links to learn more specifics on the impacts of the 2020 wildfire on giant sequoia, our Wildfire Effects in Giant Sequoia Study and our Giant Sequoia Beetle Study.
The Giant Sequoia Lands Coalition is a coordinated call to action of the 11 land management stewards, supported by other agencies and non-government organizations, to accelerate the protection of giant sequoias and their ecosystems, in a new era of emerging threats associated with climate change and human interference of natural wildfire processes on the landscape.
Together, we hold the key to the future of these forests.
References & Sources
Below are references that were used to create this data visualization story.
Publication on fire history that supplied the data visualized above:
Swetnam, T.W. (1993). Fire History and Climate Change in Giant Sequoia Groves. Science 262, 885–889.
History of the National Parks and giant sequoias:
Dilsaver, L.M., and W.C. Tweed. 1990. Challenge of the big trees: a resource history of Sequoia and Kings Canyon national parks. Sequoia Natural History Association, Three Rivers, California, USA.
Giant sequoia fire and forest ecology:
Dodd, R.S., and DeSilva, R. (2016). Long-term demographic decline and late glacial divergence in a Californian paleoendemic: Sequoiadendron giganteum (giant sequoia). Ecology and Evolution 6, 3342–3355.
Hartesveldt, R.J. 1964. Fire ecology of the giant sequoias: controlled fires may be one solution to survival of the species. Natural History 73: 12-19.
Harvey, H.T., H.S. Shellhammer, and R.E. Stecker. 1980. Giant sequoia ecology: fire and reproduction. National Park Service Scientific Monograph Series 12, Washington, D.C., USA.
Kilgore, B.M., and D. Taylor. 1979. Fire history of a sequoia mixed-conifer forest. Ecology 60: 129-142.
Parsons, D.J. 1978. Fire and fuel accumulation in a giant sequoia forest. Journal of Forestry 76: 104-105.
Parsons, D. J., and S.H. DeBennedetti. 1979. Impact of fire suppression on a mixed-conifer forest. Forest Ecology and Management 2: 21-33.
Piirto, D.D., and Rogers, R.R. (2002). An Ecological Basis for Managing Giant Sequoia Ecosystems. Environmental Management 30, 110–128.
Rundel, P.W. (1971). Community structure and stability in the giant sequoia groves of the Sierra Nevada, California. American Midland Naturalist 85, 478–492.
Rundel, P.W. (1972). Habitat restriction in giant sequoia: the environmental control of grove boundaries. American Midland Naturalist 87, 81–99.
Stephens, S.L., and Finney, M.A. (2002). Prescribed fire mortality of Sierra Nevada mixed conifer tree species: effects of crown damage and forest floor combustion. Forest Ecology and Management 162, 261–271.
Stephenson, N.L., D.J. Parsons, and T.W. Swetnam. 1991. Restoring natural fire to the sequoia-mixed conifer forest: should intense fire play a role? Proceedings of the 17th Tall Timbers Fire Ecology Conference 17: 321-337.
Giant sequoia dendrochronology:
Brown, P.M., M.K. Hughes, C.H. Baisan, T.W. Swetnam, and A.C. Caprio. 1992. Giant sequoia ring-width chronologies from the central Sierra Nevada, California. Tree-Ring Bulletin 52: 1-14.
Caprio, A. 2004. Temporal and spatial dynamics of pre-Euroamerican fire at a watershed scale, Sequoia and Kings Canyon national parks. Pages 107-125 in: N.G. Sugihara, M.E. Morales, and T.J. Morales, editors. Proceedings of the conference on fire management: emerging policies and new paradigms. Association for Fire Ecology Miscellaneous Publication 2, Davis, California, USA.
Caprio, A.C., and T.W. Swetnam. 1995. Historic fire regimes along an elevational gradient on the west slope of the Sierra Nevada, California. Pages 173-179 in: J.K. Brown, R.W. Mutch, C.W. Spoon, and R.H. Wakimoto, technical coordinators. Proceedings: Symposium on fire in wilderness and park management. USDA Forest Service General Technical Report INT-GTR-320, Ogden, Utah, USA.
Carroll, A.L., Sillett, S.C., and Kramer, R.D. (2014). Millennium-Scale Crossdating and Inter-Annual Climate Sensitivities of Standing California Redwoods. PLoS ONE 9, e102545.
Douglass, A.E. 1949. A superior sequoia ring record. Tree-Ring Bulletin 16(1): 2-6.
Hughes, M.K., R. Touchan, and P.M. Brown. 1996. A multi-millennial network of giant sequoia chronologies for dendroclimatology. Pages 225-234 in: J.S. Dean, D.M. Meko, and T.W Swetnam, editors. Tree rings, environment and humanity. Radiocarbon, Tucson, Arizona, USA.
Sillett, S.C., Van Pelt, R., Carroll, A.L., Campbell-Spickler, J., and Antoine, M.E. (2019). Structure and dynamics of forests dominated by Sequoiadendron giganteum. Forest Ecology and Management 448, 218–239.
Climate history, climate change and impacts:
Abatzoglou, J.T., and A.P. Williams. 2016. Climate change has added to western US forest fire. Proceedings of the National Academy of Sciences 113 (42) 11770-11775.
Martin, R.E., Asner, G.P., Francis, E., Ambrose, A., Baxter, W., Das, A.J., Vaughn, N.R., Paz-Kagan, T., Dawson, T., Nydick, K., et al. (2018). Remote measurement of canopy water content in giant sequoias (Sequoiadendron giganteum) during drought. Forest Ecology and Management 419–420, 279–290.
Paz-Kagan, T., Vaughn, N.R., Martin, R.E., Brodrick, P.G., Stephenson, N.L., Das, A.J., Nydick, K.R., and Asner, G.P. (2018). Landscape-scale variation in canopy water content of giant sequoias during drought. Forest Ecology and Management 419–420, 291–304.
Stephenson, N.L., Das, A.J., Ampersee, N.J., Cahill, K.G., Caprio, A.C., Sanders, J.E., and Williams, A.P. (2018). Patterns and correlates of giant sequoia foliage dieback during California’s 2012–2016 hotter drought. Forest Ecology and Management 419–420, 268–278.
Su, Y., Bales, R.C., Ma, Q., Nydick, K., Ray, R.L., Li, W., and Guo, Q. (2017). Emerging Stress and Relative Resiliency of Giant Sequoia Groves Experiencing Multiyear Dry Periods in a Warming Climate: Emerging Stress of Giant Sequoia Groves. Journal of Geophysical Research: Biogeosciences 122, 3063–3075.
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