Yosemite’s Merced Grove of giant sequoias: critical restoration continues despite legal challenges

Abstract Background Giant sequoias are the most massive individual trees on earth, and among the longest-lived. They also have a limited distribution, covering ~10,000 ha across ~70 distinct groves. Severe wildfires in 2020 and 2021 impacted 82% of the range, killing roughly 13-19% of the entire population of these irreplaceable trees. Within the giant sequoia range, the Merced Grove is one of the most at risk of burning at high severity. Located in Yosemite National Park, it has no recorded wildfire history and has received minimal restoration treatment, most of which occurred decades ago. From 2008 to 2018, six wildfires burned towards the grove, but were stopped by aggressive fire suppression and favorable weather conditions. The grove is in complex terrain, adjacent to the park’s boundary, and surrounded by long-unburned mixed-conifer forests, which has challenged the park’s attempts to implement prescribed fire for decades. Park managers determined that restoration thinning could help reduce prescribed fire implementation complexity and increase forest resilience to drought and wildfire and began implementation in 2022. Litigation attempted to halt this work. Among the plaintiff’s claims were that the park did not follow appropriate procedures during their environmental impact analysis as required under the National Environmental Policy Act (NEPA), and that there was considerable scientific controversy around mechanical thinning. Results The U.S. District Court ruled in favor of Yosemite National Park, finding that they followed appropriate NEPA procedure and that the plaintiffs failed to prove that the work was “highly controversial.” On appeal, the U.S. Ninth Circuit Court affirmed the District Court’s decision, noting that the plaintiffs had mischaracterized the project and the relevant science. Conclusions From high-value sequoia groves that are relatively rare on the landscape, to the extensive frequent fire forests across the western U.S., fire’s return is inevitable. There is strong evidence that active management, such as thinning and prescribed fire treatments to reduce fuels, can create forests that are more resilient to wildfire and other stressors. This restoration project and its associated court case demonstrate that when agencies follow the appropriate procedures for their circumstances, plan projects based on the best available science, and use that science to defend their work, they can prevail in the face of litigation. With the staggering losses of large, ancient giant sequoias to severe wildfires in recent years, this restoration work is both urgent and essential.