In 2021, an 88,307-acre wildfire reached California's sequoias; decades of fuel-clearing burns helped limit damage in Giant Forest to 1.2%, versus 40% nearby

Some of the oldest trees on the planet nearly burned, and their survival came down in part to decisions made decades earlier. The National Park Service published a detailed comparison of the 2021 wildfire's impact, titled Two Sequoia Groves and a Wildfire, explaining how the 88,307-acre KNP Complex Fire burned portions of 16 giant sequoia groves. When park researchers set two of the biggest groves side by side, Redwood Mountain Grove and Giant Forest, the outcomes were nowhere near the same. Only 1.2 per cent of Giant Forest burned at moderate or high severity, compared with 40 per cent of Redwood Mountain Grove. Across the KNP Complex Fire, scientists estimated that between 1,330 and 2,380 large sequoias had already been killed or would die within three to five years.

Giant sequoias are relatively fire-adapted. They carry thick, fire-resistant bark and have evolved alongside frequent fire for thousands of years. Low-severity fires can clear smaller trees and accumulated fuels while creating gaps where young sequoias can grow. The problem comes when fire burns with much greater severity, something that has become more common as fuel accumulates and drought and warming affect fire conditions. The comparison points to geography, access and differences in fire history as important factors in the two groves' contrasting outcomes.

Why the two groves told such different stories


Location played a major role in the fire's different impacts. Redwood Mountain Grove sits across steep canyon slopes and ridgelines in Kings Canyon National Park, terrain where fire can spread faster uphill because flames preheat and dry fuels above them. Canyons, ridges, and saddles can also alter wind patterns, increasing wind speeds and intensifying fire behaviour. Giant Forest, by contrast, sits on a rolling plateau between the Marble and Middle Forks of the Kaweah River, where much of the terrain tends to favour more moderate fire spread that is easier to manage. Access followed a similar pattern. Giant Forest has roads and trails closer to the grove, giving firefighters safer and easier access for prescribed burns and protective actions when severe wildfire approached.

The comparison also points to each grove's history of prescribed burning as an important factor. Giant Forest has had prescribed burns distributed throughout most of the grove, while Redwood Mountain Grove's burns have been concentrated mainly in its more accessible northern portion. Redwood Mountain had an earlier start, with small burns beginning in the mid-1960s for fire-effects research, but Giant Forest subsequently had many more prescribed burns across a larger area.

The decades of prescribed burns that shaped the outcome

That difference became clear once the wildfire hit. In the northern part of Redwood Mountain Grove, recent prescribed burns had already reduced ground fuels, small trees and undergrowth, and some areas had been burned two or three times. The KNP Complex Fire moved through this treated area with less severe effects, killing some small trees and shrubs while most sequoias survived. In the southern portion, which lacked recent fire history, the effects were far more severe, leaving groups of charred, dead sequoias.

Giant Forest had an added layer of protection. A 2019 prescribed burn unit near the Generals Highway helped stop the fire's growth below the General Sherman Tree, illustrating how reduced fuels can slow wildfire spread.

Firefighters also worked ahead of the flames in both groves, clearing fuels from the bases of large sequoias and using backburning and other burning operations to reduce the fuel available to the approaching fire. In Redwood Mountain, crews cleared fuels around 45 large sequoias and conducted backfiring operations along the Generals Highway, Big Baldy Trail and Redwood Ridge. In Giant Forest, firefighters began burning operations on September 19, 2021, using hand ignitions to reduce woody material, pine needles, and younger trees that could carry fire into larger trees.

The broader lesson is that these emergency measures were not working in isolation. Areas that already had a history of prescribed burning had less accumulated fuel when the wildfire arrived, giving firefighters a stronger foundation for slowing its spread and reducing its intensity. The NPS also notes that previous prescribed fire work appears to have reduced fire severity in some areas affected by recent high-severity fires.

What this shows about getting ahead of trouble

Giant Forest was spared in part because repeated prescribed burns had reduced fuels over time. Redwood Mountain Grove was not doomed; it simply had less of that groundwork in place across much of the grove when severe conditions arrived. The difference between the two landscapes shows why maintaining a history of prescribed fire can matter before a major wildfire arrives.

Since the fire, managers have continued planning and conducting prescribed burns, selective thinning and pile burning, as well as replanting some severely burned areas. They are also studying how giant sequoias are responding to hotter droughts and more severe wildfires. The takeaway from the two groves is clear: preparation made a measurable difference.