Hydroclimate whiplash damages California's tallest redwoods after years of drought
Tall trees are generally associated with high-biomass forests. This is particularly true for forests dominated by Sequoia sempervirens (hereafter redwood), the world's tallest tree species. Extreme decay resistance, the ability to survive high-severity fires, shade tolerance and prolific trunk reiteration (resprouting) make the species unique, allowing tall redwood forests to accumulate more…
California's tallest redwoods, found in Sequoia sempervirens forests, are renowned for their high-biomass and carbon storage capabilities. California's Redwood National and State Parks (RNSP) safeguard nearly half of the world's population of these ancient trees. However, extreme weather events threaten the conservation of these reserves.
In 2022-2023, California experienced hydroclimate whiplash, characterized by a series of atmospheric rivers, high winds, and rare canopy snow load. This weather pattern severely impacted the tallest redwoods, causing substantial damage to the forest canopy, particularly in Northwestern California.
Ground-based measurements and repeated airborne laser scanning (ALS) were employed to inventory the tallest redwoods and assess the impact of the storms. The study revealed a significant decrease in the number of redwoods over 100 meters tall from 950 in 2022 to 825 after the storms. While most damages resulted from crown loss rather than treefall, this loss amounted to 2-8 years of biomass accumulation. The damage was particularly severe in Humboldt County, a region considered high-biomass elsewhere.
The biomass distribution differs significantly between primary and secondary forests within RNSP. Primary forests, which cover less than a third of the park, contribute more than two-thirds of the total live-tree biomass and hold four to seven times as much biomass per hectare as secondary forests. Despite the higher biomass, secondary forests have more trees per hectare.
The relationship between tree count and biomass is inverse in high-biomass primary forests, where a few massive trees hold most of the biomass. This suggests that selective logging in secondary forests could promote the growth of dominant trees, accelerating secondary forest development. However, the precise monitoring of ongoing forest restoration through additional fieldwork and ALS is necessary to maximize height growth and carbon storage in redwood forests within RNSP.
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