Studies Show Alarming Decline in Giant Sequoia Seedlings Post Mega-Fires

Recent studies conducted by the Giant Sequoia Lands Coalition and the U.S. Geological Survey (USGS) have unveiled a concerning decline in giant sequoia seedlings in areas affected by recent mega-fires. According to the studies, some regions may lack sufficient seedlings to sustain the next generation of these millennia-old trees. Since 2015, extreme wildfires have resulted in the death of up to 20% of the world’s mature giant sequoias, with the bulk of these losses occurring during three wildfires in 2020 and 2021.

The unprecedented scale and severity of these fires have raised alarms among researchers. Nathan Stephenson, Ph.D., a scientist emeritus at the USGS’s Western Ecological Research Center, emphasized the gravity of the situation. “Giant sequoias are the largest trees in the world. They’re fire-adapted and rely on fire to reproduce. But recent fires have killed thousands of mature trees and, in some cases, their seeds too,” he said. The USGS has been instrumental in providing data-driven models to aid the Giant Sequoia Lands Coalition in land management and restoration decisions.

Adding to the challenge, the seedlings that have emerged post-2020 and 2021 wildfires face new climate conditions, including higher average temperatures and the most severe drought conditions recorded in the past 121 years. These adversities are likely to diminish the survival rates of giant sequoia seedlings. In areas where mature seed trees have perished, the prospects for natural recovery are bleak.

David Soderberg, Ph.D., an ecologist at the USGS’s Western Ecological Research Center, noted the variability in sequoia regeneration across different areas. “Some areas are doing well, but in other sites where the seeds and seed trees burned, or where young seedlings have died from high heat and drought, natural long-term recovery appears to be unlikely,” he said. This suggests that severely impacted sequoia grove areas may not have enough reproduction to replace the trees lost.

Giant sequoias, known for their immense size and age, are crucial in capturing carbon and thus play a significant role in combating climate change. The loss of these trees not only affects biodiversity but also undermines efforts to mitigate global warming. Joanna Nelson, Ph.D., director of science and conservation planning for Save the Redwoods League, highlighted the importance of these findings. “Working from the best science available, we can better understand when and where sequoia reproduction may be too low for future success—and be equipped to take action,” she said.

The Giant Sequoia Lands Coalition has been proactive in addressing this issue. To date, the coalition has completed wildfire resilience work across half of California’s giant sequoia acres and has planted more than 500,000 native seedlings in severely burned areas. These efforts are guided by ongoing scientific research and monitoring to ensure evidence-based restoration techniques.

The new research presents critical data for land managers. One study, published in the June 2024 issue of Forest Ecology and Management, offers conservative estimates of the natural amount of sequoia seedlings per area necessary for forest regeneration. This data will help land managers interpret the effects of wildfires on sequoia reproduction and decide whether replanting is necessary to maintain current populations.

Another study, published in the March 2024 issue of Ecosphere, assesses the likelihood of natural recovery in areas affected by the 2020 and 2021 mega-fires. The findings indicate that without intervention, there may be a long-term or permanent loss of sequoia grove areas, especially where mature seed trees have died and seedling numbers are below historic norms.

In summary, these studies underscore the urgent need for intervention and informed management to ensure the survival and regeneration of giant sequoias, which are not only ecological treasures but also vital allies in the fight against climate change.