Despite these impressive statistics, the fact that redwoods are home to so many additional species intrigued Dr. Næsborg and her husband, Cameron Williams, a doctoral candidate at the University of California, Berkeley, who met Dr. Næsborg over a decade ago at a lichen conference in Estonia. The researchers had suspected that the redwoods’ rosy colored namesake tannins would deter communities from forming in the trees, because many organisms do find those chemicals unpalatable.

Mr. Williams was the first to try to identify all the players involved in those communities. He focused on epiphytes (literally “on plant”), or species that grow on trees without harming them, like mosses, lichens and other vegetation. Ascending redwoods in northwestern California, he found trunks wrapped in blankets of fuzzy, grass-green moss; twigs covered by whimsical chartreuse lichen wisps; and in places where they could eke out a precarious roothold, a variety of saplings and bushes — currant, huckleberry, hemlock and more — some of which had epiphytic communities of their own. All told, the survey found that redwoods contain more diversity — 282 epiphytes in and directly beneath the trees — than other tree species that researchers had previously sampled, including the Douglas fir and the Sitka spruce. This study also uncovered a species new to science — a lichen as diminutive as its redwood host is towering. Sprouting from the tree bark like a minuscule hair, Mr. Williams bestowed it with a fitting name: redwood stubble.

The research would most likely have ended there if not for Save the Redwoods League, a nonprofit group that promotes protection of redwoods. The league asked the researchers to conduct an epiphyte survey of redwood communities at the southern end of the tree range. Preliminary results of that study reveal patterns of diversity — 237 species so far — similar to those found in the north.

In both the north and south, from Jedediah Smith Redwoods State Park to Pfeiffer Big Sur State Park, lichens — science-fiction-like organisms that exist as symbiotic assemblies of fungi and algae or cyanobacteria — make up most of the species identified. About 17,000 lichen species are known worldwide, although much about them remains unknown — for example, the potential uses for the more than 600 unique compounds that lichens are known to produce. Some of them are already being used today as antibiotics in soaps and deodorants, and others as ingredients in traditional treatments for constipation, arthritis and kidney diseases; others still are being investigated as cancer-fighting agents.

“Potentially, we could find some compounds that could be beneficial to humans,” Dr. Næsborg said. “We really don’t know what we’d be missing if we don’t climb the trees.”