Assessment Notes

Justification

Calicium sequoiae is narrowly endemic to old-growth Coast Redwood forests in California where it grows on the bark of redwood trees. Its extent of occurrence is 5,083 km² and its area of occupancy is 32 km². There are estimated, ongoing declines in the extent and quality of habitat and inferred ongoing declines in the extent of occurrence, area of occupancy, and number of mature individuals due to logging, climate change, and large, high-intensity wildfires. Its subpopulations have been severely fragmented by large-scale timber harvesting that has resulted in only ca. 5% of old-growth coast redwood forests remaining intact today. Therefore, it is assessed as Endangered: B2ab(i,ii,iii,v).

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Taxonomic notes

The species was described by Williams and Tibell (2008) and the type specimen was collected in Prairie Creek Redwoods State Park, Humboldt County, CA.

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Geographic range

Calicium sequoiae is endemic to old-growth Coast Redwood forest in Northern California. The species has been found in Jedediah Smith Redwoods State Park, Six Rivers National Forest, Prairie Creek Redwoods State Park, Redwood National Park, Humboldt Redwoods State Park, and Armstrong Redwoods State National Reserve.  It could be present in the few other old-growth parks between Humboldt Redwoods SP and Armstrong SNR, but this has not been verified.

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Population and Trends

Calicium sequoiae has so far only been found on old-growth Coast Redwood (Sequoia sempervirens) trees, which were historically impacted by widespread logging, leaving only about 5% of the original forests intact. The remaining old-growth redwood forests are severely fragmented. Because Calicium sequoiae only lives on old-growth Coast Redwoods, impacts to the tree likely caused equivalent impacts to the population of the lichen species. Climate change impacts, including drought, and large-scale wildfires that occur as a result of fire suppression are projected to further reduce the population size of this species. Indeed, one of the few remaining occurrences of Calicium sequoiae, at Armstrong Redwoods State Natural Preserve experienced a low intensity fire in 2020. If the occurrence at Armstrong was extirpated by the fire it would result in a 92% reduction of EOO and a 12.5% reduction in AOO. The impacts of the fire remain to be confirmed.

Population Trend: Decreasing

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Habitat and Ecology

This species appears to be restricted to thick, fibrous bark between 20 and 80 m above ground level on trunks of large coast redwood (Sequoia sempervirens) trees in low elevation, old-growth redwood forests.

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Threats

Historically, logging was the greatest threat to Calicium sequoiae. Only c.5% of old-growth Coast Redwood forest is left after decades of timber harvesting, so the lichen populations are likely severely fragmented. However, most old Coast Redwood trees are currently protected in State and National Parks. Wildfires, which are projected to increase in frequency and severity, are probably the most imminent threat. The southernmost location, Armstrong Redwoods State Natural Preserve experienced a low intensity fire in 2020, but as conditions get warmer and drier, even parks in the north may experience hot, devastating fires in the future.

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Conservation Actions

Calicium sequoiae occurs in multiple protected areas, including State and National Parks. It is not currently protected at the state or federal level in California or the United States. 
This species is difficult to gather accurate knowledge about since it requires climbing of the trees to access where it grows. The species is too tiny to see from the ground and anatomical and chemical tests need to be performed to confidently identify it. Climbing without a research permit is strictly prohibited in all State and National Parks. In addition to Coast Redwoods, other possible hosts could be other members of Cupressaceae that share similar bark textural characteristics to Coast Redwood, and these should be explored. Actions to stop climate change from getting worse are needed for the protection of this species.

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Use and Trade

This species could be impacted by collecting of specimens, but this is almost certainly not a major threat to this species because it lives high up in the trees and people are not allowed to climb them.

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Source and Citation

Reese Næsborg, R. 2021. Calicium sequoiae. The IUCN Red List of Threatened Species 2021: e.T180412795A184974492. Accessed on 22 November 2025.

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