TULARE COUNTY – Extreme heat in California has killed more ancient sequoia trees in the last 10 years than the last two millennia.
That’s according to research conducted by the National Park Service which has undertaken a massive replanting effort to replace one quarter of the oldest trees despite arguments from environmental groups who say humans should not intervene as the forest will naturally restore itself following large scale wildfires.
The KNP Complex Fire in 2021 wiped out about 500 giant Sequoia trees which had stood for more than one thousand years in the Redwood Mountain Grove in Kings Canyon. Redwood Mountain has the greatest number of these massive millennial trees in the two national parks (about 2,000) followed closely by the Giant Forest.
Sequoias worldwide grow only in a few locations on the western slope of the Sierra, notably just a few miles east of Visalia and the area’s claim to fame. Redwood Mountain is the world’s second-largest sequoia grove (after Mountain Home Grove) and represents 10% of all native grove areas in existence.
Four conservationist groups tried to halt the NPS effort arguing that wilderness protection means the land should remain untouched, even if that leads to losing sequoias there. But today, the replanting of a Redwood Mountain continues.
KNP was the killer
The KNP Complex fire in October 2021 was not your run-of-the-mill wildfire but rather an extreme case.
The KNP Complex Fire burned 88,307 acres in Sequoia and Kings Canyon National Parks, and cost $170 million to fight. The fire was declared 100% contained on Dec. 16, 2021, after more than three months of firefighting. Redwood Mountain Grove lost between 974 and 1,574 large sequoias to the fire, while Giant Forest only had low to moderate fire effects along its west and northwest edges.
In the decades preceding the fire, average temperatures in the Sierra increased measurably but precipitation did not. This trend was driven partly by climate change. Climate change and consequent warming in California has helped produce hotter and more severe droughts, such as the one California endured between 2012 and 2016. Acute stress from that drought killed many trees in the Sierra Nevada, particularly at middle elevations. Extreme heat weakened trees leading to an estimate in 2021 that Sequoia and Kings Canyon National Parks held over one million beetle-killed trees that were helping drive the KNP Complex Fire.
Fire officials attributed the mega-fire to a massive lightning storm that caused dozens of fires up and down the state. The KNP fire burned hot in the canyon, putting up 40,000-foot convective pyrocumulus or pyrocumulonimbus clouds visible from the far side of the Sierra Nevada. In the sequoia grove itself, the fire generated winds strong enough to strip bark and foliage from the sequoia trees, and flames likely climbed into the canopies of the sequoias, leaping from tree top to tree top. Flames were said to reach 150 feet.
The dramatic effect of extreme heat on the crown of these Sequoia trees greatly reduced any chance that any seeds would survive even as these ancient trees died, according to NPS scientist Nathan Stephenson.
Stephenson and others have penned a response to research that suggested intervention was not necessary, pointing out that recent post-wildfire regeneration has often been well below historical levels.
The intensity of recent wildfires burned cones out of the sequoias’ crowns and killed much of the local seed source. Simultaneously, the historical drought and temperatures almost certainly reduced germination and survival of post-fire sequoia seedlings. Consequently, sequoia seedling densities following recent wildfires often were significantly—and sometimes dramatically—lower than historical reference densities. Large scale wildfires in recent years have reduced the mature sequoia population by 13-19 percent.
Sequoias are used to surface fires. Research shows that the life cycle of sequoia groves was dominated by frequent surface fires. On average, at least one fire burned somewhere within a large sequoia grove every two years, and a fire burned at the base of any individual sequoia every 15 to 17 years. Thus, a typical 1,000-year-old sequoia will have lived through more than 60 fires, and a 3,000-year-old sequoia may have lived through as many as 200 fires.
Wildfires are a part of the germination cycle for these giant trees. It is not unusual that local patches of higher-intensity surface fire would scorch portions of sequoia crowns—causing the scorched cones to open and release their abundant seeds—while nearly always leaving the tree alive.
Complete crown scorch from surface fires—such as in this portion of Redwood Mountain Grove that burned at high severity in the 2021 KNP Complex wildfire—kills sequoias while typically still triggering abundant seed release.
In contrast, crown fire, which is the recent and historically unprecedented extreme of high-severity fire in sequoia groves, has burned many cones out of the sequoias’ crowns, killing much of the seed source and contributing to low seedling densities.
With no seed source the Park Service realized that a huge swath of the treasured Sequoia forest would be lost forever. without lending a hand.
Before the historically unprecedented wildfires of 2015, 2017, 2020, and 2021, researchers reported a positive relationship between local fire severity and sequoia reproduction.
Crown fires have been absent for at least a millennium. Research concluded that the grove had not experienced a crown fire of any meaningful size for at least the preceding 2000 years – until now. Evidence is clear that this was the first time such a cataclysmic fire event has carried out mass murder of the big trees in two thousand years.
Starting Life Over
Christy Brigham Ph.D, Chief of Resources Management and Science Sequoia and Kings Canyon National Parks, is in charge of the replanting effort.
“In October and November of 2023 we planted approximately 65,000 giant sequoia seedlings in the southern third of Redwood Mountain Grove and approximately 6000 sequoia seedlings in Board Camp Grove,” Brigham said. “Overall survivorship of planted seedlings in the Redwood Mountain planting area was approximately 70 percent approximately one year after planting. Some areas within the planting area had low survivorship and if weather allows, will be replanted this November. “
For Board Camp grove, hot weather at the time of planting and a significant delay at the beginning of the project resulted in low survivorship of approximately 10 percent. NPS is also hoping to replant this area using modified methods, such as waiting for cool weather following a set amount of precipitation and storing seedlings in coolers, to improve survival this year.
“In my view, the restoration projects are a success and we are learning and modifying as we go,” Brigham said. “I will also say that researchers that I have taken into the field could not tell that seedlings were planted which I think shows that the project was done in a sensitive manner and mimicked conditions seen in areas that had natural sequoia regeneration (where seedlings are spaced and arranged in such a manner as to resemble natural regeneration).”
Redwood Mountain Grove lost between 974 to 1,574 large sequoias to the fire while Giant Forest only had low to moderate fire effects along its west and northwest edges.
Scars of Survival
Looking back, NPS said Redwood Mountain Grove had an earlier start to prescribed burning, beginning with small burns conducted for fire effects research projects in the mid-1960s, while Giant Forest has since had many more prescribed burns over a larger area.
Between 1980 and 2022, park staff conducted 62 prescribed burns in Giant Forest. By contrast, between 1964 and 2016, a total of 18 prescribed burns were done in Redwood Mountain, and the 1964 and 1965 burns were small and centered around areas where scientists did research projects on fire effects and giant sequoia seedling establishment. The prescribed burns in Giant Forest are distributed throughout most of the grove area. Prescribed burns in Redwood Mountain are primarily in the northern portion of the grove, which is more accessible, and therefore, safer for fire staff to work in, and less complex to prepare and burn.
The fire also burned north through Redwood Canyon until reaching the areas burned out by fire crews at the upper part of the grove. Recent prescribed burns conducted in 2004, 2006, 2009, 2011, 2012, and 2016 moderated the fire’s severity in this area because ground fuels and small trees and undergrowth had already been reduced. Some areas had been burned in prescribed fires 2-3 times.
The difference in fire effects between the north portion of the grove, which had been treated with prescribed burning in recent history, and south portions of the grove, which lacked recent fire history, is stark. In the south, the groups of charred, dead sequoias are heart wrenching to see. In the north, the fire killed some small trees and shrubs, but sequoias and most other trees still stand remaining a green haven of forest.
During the state’s 2021 wildfire season nearly 2.6 million acres burned, the second largest area on record after 2020.
