YOSEMITE NATIONAL PARK – After exploration by millions of visitors over the past 100 years, it's hard to imagine anything left to discover amid the majesty of Yosemite's glacier-cut granite cliffs and giant Sequoia groves.

But, by thinking small, scientists have discovered new species of lichen clinging like microscopic starfish to Yosemite icons such as El Capitan, Half Dome and Vernal Falls, and countless slabs of less famous rock. And they are trying to determine whether the species exist anywhere else.

The chance to collect and study the lichen that give the Yosemite's granite faces their distinctive black and rust-colored striping enticed world-class climbers to the park last week. Dangling from ropes with chisels in hand, they gave earthbound scientists access to the microcosms that exist at their fingertips.

“We hear about new species of life being discovered in the remote Amazon, but here in Yosemite?” said extreme mountaineer Carlos Buhler, a member of the only team to ascend Mt. Everest's 29,000-foot east face. “This world of lichen is something that climbers see up close every day without knowing very much about it, so it's a chance for me to learn more about the world in which I live. I doubt I'll ever look at lichen the same way again.”

National Park Service scientists look at lichen – a combination of fungus and algae – as one of nature's best harbingers of air pollution and climate change, so they are in a race to determine exactly what species are growing in the 1,169-square-mile park.

“It's important to know what our baseline flora and fauna are before we lose it, and lichen are a good baseline,” said Martin Hutten, a Yosemite lichenologist who entered the field after discovering that air pollution had destroyed all but the most hardy lichen in his native Netherlands.

Hundreds of species of slow-growing lichen in the Sierra Nevada cling to everything from trees and shrubs to metal handrails over Merced River tributaries. Like tiny sponges, they suck from the atmosphere both the water and nutrients that feed them – and the pollutants that kill. Yosemite scientists are beginning to use the lichen as an indicator species for the amount of polluting nitrogen and sulfur in the forests.

“There is a tremendous amount of biodiversity that hasn't been discovered here in Yosemite,” said Niki Nicholas, the park's chief of resources management and science. “People probably think that Yosemite has been around forever so everything must have been discovered.”

Last year, scientists cataloged a new orchid unique to Yosemite, and two years before that found three new species of bees.

“If we have it now, we can see if we still have it 15 years from now,” said Linda McMillan, the chairman of the American Alpine Club's Yosemite Committee who has been recruiting members to work on similar projects in parks and nature preserves around the world. “No one group in the world can understand something as complex as an ecosystem.”

The lichen study is part of an ongoing public-private effort funded by the federal government and the nonprofit Yosemite Fund to take a biological inventory of the park's resources in a rapidly changing environment.

“I can think of worse ways for my tax dollars to be spent,” said Steve Mackison, visiting from Maryland, as he watched Hutten rappel down Vernal Falls, a 317-foot waterfall.

Already the research has led to new discoveries in Yosemite, where scientists had assumed the vivid black, gray and rust-colored bands that run down the face of Vernal Falls were oxidized minerals washed there over centuries by falling water. “One thing we have definitely established since getting close is that a lot of these streaks are different things that are alive,” Hutten said.

The search for new lichen species in Yosemite paid off when scientists found one pollution-intolerant species, Altectoria sarmentosa, which was thought to exist in only one place in California. They say some of the approximately 100 unfamiliar species they are sending to Oregon State University for further testing could turn out to be unique to the park and, perhaps, the world.

“Already we have doubled the number of species known to be here,” Nicholas said, “but we know we have lots more.”

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