New Studies Show Mega-Fires Threaten Giant Sequoia Regeneration in Northern California

Two comprehensive studies on giant sequoia regeneration, announced by the Giant Sequoia Lands Coalition, reveal that recent mega-fires have caused unprecedented damage to these iconic trees.

Researchers from the U.S. Geological Survey’s Western Ecological Research Center found that the extreme wildfires since 2015 have killed up to 20% of the world’s mature giant sequoias, with the majority perishing in the 2020 and 2021 wildfires.

Unprecedented Wildfires

These recent fires have burned with an intensity far beyond the historical norm, raising concerns about the long-term survival of giant sequoia groves. The studies indicate that without intervention, some groves may suffer a permanent loss of acreage due to the death of seed trees and the exceptionally low number of new seedlings.

“What we used to call high-severity fire does not compare to the unprecedented scale and severity of the wildfires we’ve experienced in recent years in the Sierra Nevada,” said Nathan Stephenson, Ph.D., scientist emeritus at the U.S. Geological Survey’s Western Ecological Research Center. “Giant sequoias are fire-adapted and rely on fire to reproduce. But recent fires have killed thousands of mature trees and, in some cases, their seeds too.”

Challenging Climate Conditions

The new seedlings that have germinated face additional challenges. They are growing under new climate conditions, including higher average temperatures and severe droughts, which significantly reduce their chances of survival. In areas where mature seed trees have died, the likelihood of natural recovery is greatly diminished.

“Sequoia regeneration has varied widely across the range since the recent mega-fires,” said David Soderberg, Ph.D., ecologist at the U.S. Geological Survey’s Western Ecological Research Center. “Some areas are doing well, but in other sites, where seeds and seed trees burned or young seedlings have died from high heat and drought, natural long-term recovery appears to be unlikely.”

The Importance of Restoration

Giant sequoias are not only the world’s largest trees but also among the oldest, playing a crucial role in carbon storage. The old-growth sequoia groves, second only to old-growth coast redwood forests, store massive amounts of carbon per area, making them vital climate allies.

“These are important findings that identify the density of seedlings—the number per area—that is enough for the tiny, young trees to survive and become majestic sequoia adults,” said Joanna Nelson, Ph.D., director of science and conservation planning for Save the Redwoods League. This research will help land managers determine how to best care for the giant sequoia groves, particularly in emergency-response windows post-fire.

Ongoing Research and Efforts

The Giant Sequoia Lands Coalition continues to support research and restoration programs across the sequoia range. To date, they have completed wildfire resilience work across half of California’s giant sequoia acres, planted over 500,000 native seedlings in severely burned areas, and conducted scientific research to support evidence-based restoration techniques. Their efforts are detailed in the GSLC’s recently published Progress Report for Saving the Sequoias.

About the Studies

The studies, published in the journals Forest Ecology and Management and Ecosphere, provide vital data on the natural amount of sequoia seedlings per area needed for forest regeneration and the number required for sufficient tree survival to adulthood. They document the post-fire burst of seedlings followed by a significant decline due to high seedling mortality rates and low establishment of new seedlings in subsequent years. The research offers a statistical tool to inform restoration and management decisions following large, severe wildfires.

As the battle against extreme wildfires continues, these findings underscore the urgent need for proactive measures to preserve the future of giant sequoias, ensuring that these ancient giants can thrive for generations to come.