How Prescribed Burns Are Saving the World's Largest Trees

A NASA-funded study with lidar and high-resolution mapping has put a number on what foresters have long suspected: controlled burns genuinely save giant sequoias.

Giant sequoias grow nowhere else on Earth. Restricted to the western slopes of California's Sierra Nevada, they can exceed 300 feet in height, stand more than 30 feet wide, and live for over 3,000 years. They are keystone species: deep carbon sinks, water filters, and living shelters for birds, insects and small mammals.

They evolved alongside fire. Their thick, tannin-rich bark resists flame, and their high-placed cones often need heat to release seed. The problem is the modern fire regime. Decades of suppression removed the small, cool "cultural fires" once set by Indigenous stewardship, leaving thick underbrush, standing dead wood and a carpet of dry fuel. When wildfires returned, they burned hotter and deeper than the trees were adapted for.

The bottom line: During the 2020–2021 fire seasons, which scorched a record 6.8 million acres across California, 19% of the total mature giant sequoia population was destroyed. But in forests treated with prescribed burns just years earlier, the trees were nearly four times more likely to survive extreme wildfires.

Putting a Number on a Long Suspect

Researchers analyzed 26,403 individual giant sequoias across 19 groves in Sequoia and Kings Canyon National Parks, combining lidar scans, stem maps, high-resolution aerial imagery and computer modelling. The paper, published in Nature Communications, estimated that prescribed burns saved roughly 1,800 giant sequoias.

Until this study, the case for prescribed fire was largely anecdotal — strong observational support, but little hard evidence. By pairing satellite-era remote sensing with species-specific ground maps, the team turned a plausible theory into a measurable conservation tool.

Why Low, Cool Fire Is Not the Enemy

A prescribed burn is deliberately low in intensity. A technician with a drip torch sets fire to thin underbrush while fire conditions are controlled. The flames consume the fuel ladder — the small sticks and leaf litter that would otherwise carry fire up into the tree canopy — and leave the sequoias largely unscathed.

The lesson extends beyond sequoias. Old-growth forests worldwide face the same imbalance: fire excluded for decades, then returning at catastrophic intensity. This work shows that high-resolution remote sensing can guide species-specific fire management, a capability that old-growth conservation everywhere can use.