Burned trees in Sequoia National Park
Credit: USFS
November 19, 2021 - SEQUOIA AND KINGS CANYON NATIONAL PARKS, Calif. – Land managers in the Southern Sierra Nevada are reckoning with the effects of large wildfires ignited by a significant lightning event in early September, including the KNP Complex, which burned mostly within Sequoia and Kings Canyon National Parks, and the Windy Fire, which burned mostly on the Sequoia National Forest.
Findings from a recently compiled fire response plan estimate that across the footprints of the two fires, between 2,261 and 3,637 large giant sequoias (four feet or more in diameter) have either already been killed by fire or have been so severely burned that they are expected to die within the next three to five years. These losses make up approximately 3-5% of the world’s population of large giant sequoias.
This assessment of impacts to giant sequoias comes from a report compiled by a Burned Area Emergency Response (BAER) team and are drawn from analysis conducted by scientists from the Nature Conservancy and the National Park Service. These giant sequoia groves are located across lands administered by Sequoia and Kings Canyon National Parks, Sequoia National Forest, Tule River Tribe, UC Berkeley, and Save the Redwoods League, all partners in the Giant Sequoia Lands Coalition, established earlier this year to collaborate on strategies to protect these threatened trees.
These 2021 losses are being quantified in the wake of 2020’s highly destructive Castle Fire in the same region, which resulted in the mortality of 10-14% of the world’s native population of large giant sequoias. After such devastating losses last year, there has been significant concern about the impacts of the 2021 fires.
These estimates include 1,330 – 2,380 trees within the KNP Complex footprint and 931 – 1,257 trees within the Windy Fire footprint. In total, 27 giant sequoia groves fall fully or partially within the perimeters of the fires. These estimates were calculated by comparing pre- and post-fire satellite imagery classified by fire severity, aerial reconnaissance, and on-the-ground assessments where possible.
While giant sequoias require periodic low-to-moderate intensity fire to maintain healthy ecology, a history of fire suppression across the American West has resulted in denser forests with high levels of fuel loading. In combination with hotter droughts driven by climate change, these conditions have changed how wildfire burns in the southern Sierra Nevada, resulting in large areas of high severity fire effects and massive fire events.
“The sobering reality is that we have seen another huge loss within a finite population of these iconic trees that are irreplaceable in many lifetimes,” says Sequoia and Kings Canyon National Parks Superintendent Clay Jordan. “As we navigate the complex process of restoring access to the parks, we will continue to work diligently with our partners in the Giant Sequoia Lands Coalition to become ever-better stewards of these incredibly special places, despite the enormous challenges we face.”
Some key areas, such as the Giant Forest in Sequoia National Park, experienced reduced fire severity, due in large part to a history of prescribed burning. As this year’s wildfires approached sequoia groves, firefighters deployed new tactics that reduced losses to these trees from high severity fire. Many areas within the fire footprints burned at low to moderate severity, and some areas did not burn at all.
To view the executive summary of the impacts of the 2021 fire season on giant sequoias, read the full report of these findings as extracted from the response plan, or find more information and resources about emerging threats to giant sequoias, visit www.nps.gov/seki/learn/gslc.htm. A media kit with contacts for all Giant Sequoia Lands Coalition partners, photo galleries, fact sheets, and more is also provided on this site.
Executive Summary
The 2021 fire season included two large wildfires (both started by the same lightning storm in early September) that burned into a large number of giant sequoia groves. This species has a limited distribution, covering just ~28,000 acres in ~70 groves on the western slopes of the Sierra Nevada mountains. Given the impacts of the 2020 Castle Fire to sequoia groves, where losses were estimated at 10-14% of the entire Sierra Nevada population of sequoia trees over 4 feet in diameter, there is significant concern by sequoia managers and the public regarding the impacts of these new fires. This report summarizes potential impacts to groves that were burned in the 2021 fire season, in the KNP Complex Fire and Windy Fire, including number of groves burned, amount of grove area burned at differing vegetation severity (RAVG-composite burn index), estimated number of large sequoias killed based on a preliminary analysis, the percentage of the entire population this loss represents, potential for regeneration failure, and potential for loss of seed source due to erosion (for KNP only). All of the data, data analysis, maps and modeling contained in this report are excerpted from the Burned Area Emergency Response Plan for the KNP Complex produced by an interagency team and submitted by the National Park Service. Some additional explanatory text and structure has been added to make this a standalone report. Because of this emphasis, there is more detail and analysis for KNP Complex sequoia groves than those burned in the Windy Fire.
Grove-level Estimates
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In total 27 sequoia groves are fully or partially within the fire perimeters of the KNP Complex Fire and the Windy Fire.
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16 groves burned in the KNP Complex Fire.
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11 groves burned in the Windy Fire.
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For both fires combined, 6,109 acres of giant sequoia groves were burned. This estimate is based on updated grove boundaries provided by the NPS and the USFS Region 5 Remote Sensing Laboratory.
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KNP: 4,374 acres
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Windy: at least 1,735 acres (Note: this estimate does not include two groves on the Tule River Reservation for which there is not publicly available spatial data)
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Sequoia Grove Vegetation Burn Severity Analysis Using Composite Burn Index (CBI)
Fire severity was assessed using the USFS Rapid Assessment of Vegetation Condition after Wildfire (RAVG) four class Composite Burn Index product (CBI4) (details on the severity maps can be found on the RAVG website https://fsapps.nwcg.gov/ravg/). This analysis contains four categories of vegetation change: undetected change, low, moderate, and high, where high severity has been associated with 95% tree mortality (Miller et al., 2009). The acreage burned by severity class for each fire is:
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KNP Complex (all ownerships):
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Undetected change: 1,169 acres
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Low: 1,849 acres
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Moderate: 740 acres
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High: 616 acres
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Windy Fire (all ownerships):
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Undetected change: 228 acres
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Low: 659 acres
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Moderate: 437 acres
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High: 411 acres
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Large Sequoia Mortality Estimates
For the KNP Complex we estimate that between 1,330-2,380 sequoias over four feet in diameter have already been killed or will die within the next three to five years. This estimate is based on RAVG satellite analysis combined with mortality rates from surveys in other sequoia groves that burned in three previous fires (similar methodology to Stephenson and Brigham 2021).
For the Windy Fire, we estimate that between 931-1,257 sequoias over four feet in diameter have already been killed or will die within the next three to five years.
The combined impact of these two fires is estimated to be 2,261-3,637 sequoias over four feet in diameter that have already been killed or will die within the next three to five years. These losses make up an estimated 3-5% of the entire Sierra Nevada sequoia population over four feet in diameter. On top of the 10-14% of large sequoias lost in the 2020 Castle fire, these fire impacts represent a significant threat to large sequoia persistence.
Potential for Regeneration Failure
The least understood impacts of these wildfires are impacts to sequoia regeneration in high severity areas. Sequoias generally regenerate well after wildfire, though reports of inadequate regeneration in high severity areas are raising concerns. Regeneration failures could potentially occur if the cones and/or seeds were incinerated during crown fire, seeds did not survive the smoldering fire, or seeds washed away due to surface erosion. In these cases, regeneration would be dependent on proximity to live tree seed sources.
For the KNP complex we analyzed high severity areas within sequoia groves that were over 100 meters from an intact sequoia grove area with live sequoia trees (represented by areas of undetected change, low or moderate severity). In total 436 acres were identified that may be vulnerable to total sequoia loss if regeneration from seeds that survived the fire is inadequate. Of the 436 acres >100m from live sequoia forests, 335 acres are on NPS lands. The Burned Area Rehabilitation Plan recommends reforesting these 350 acres with giant sequoias if adequate regeneration is not present based on subsequent field surveys.
Erosion modeling suggests that the high severity areas identified for potential restoration are also at high risk of losing any seeds that did survive the fire due to surface erosion.
Other Key Points
In several places that burned during this event, previous prescribed fire work appears to have reduced fire severity (portions of Redwood Mountain Grove, Giant Forest). In other areas previous prescribed fire and mechanical thinning treatments, as well as preparation for upcoming burn units, allowed fire crews opportunities to safely fight fire more effectively (prescribed burn preparations at Lost Grove and Park Ridge Fire Lookout area were used during suppression operations on the KNP complex).
Although we are seeing some significant high and moderate severity areas in sequoia groves where we expect impacts to large giant sequoias to be detrimental, much of the grove area in the KNP Complex burned at low severity and we expect beneficial results for giant sequoias in these areas. These beneficial effects include fuel reduction, small canopy openings ideal for regeneration, and removal of litter and generation of ash – also ideal conditions for giant sequoia seedlings.
Other areas not classified as high severity may have also had beneficial effects, but the effects will likely be more mixed. In areas classified as “undetected change,” there will likely be a mix of completely unburned areas and areas that had a light surface fire that is similar to low severity fire effects. The fire effects in moderate severity will be the most variable, with some areas having beneficial effects and others being more severe.
Read the Report
Source: NPS
