“I like that metaphor a lot,” biologist Zane Moore said, as he grasps a branch of the unusual conifer and holds it up to the light.

Brilliant October sunshine filters through the high forest canopy, where the silver-green needles of healthy trees soak up rays and turn them into fuel. But the albino tree lacks chlorophyll, the green pigment that allows plants to make food from light via photosynthesis. It is incapable of the one thing that all trees must do to live.

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“It shouldn't be here. It should be dead, but it's not,” Moore said. “Just like a ghost.”

The mystery of the albino redwood has stumped researchers for more than a century. The trees are so improbable that those who haven't seen them up close sometimes question whether they can exist at all.

But Moore is convinced that this ghost story has a scientific solution — one that should change how we view not just the albino trees, but also the entire forest.

Moore is a doctoral student at the University of California in Davis with a professorial manner and an easy smile. He's been visiting Henry Cowell Redwoods State Park, an old-growth redwood grove near Santa Cruz, since he was a small child, and spotted his first albino redwood here at 16.

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For the trees' own protection, staff at the park typically don't tell visitors how to find them.

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“Trees can be loved to death,” docent Dave Kuty said. “They're not like animals. They can't run away.”

Kuty is the unofficial caretaker of Henry Cowell's 11 albinos; he alone knows where each one hides. Some look like haphazardly spray-painted bushes, while others resemble the artificial white trees sold around Christmas. Still others are little more than single, luminous branches high up in the canopy, barely discernible in the shifting morning sun.

As a teenager in 2010, Moore heard Kuty give an interview to a local radio station about the redwoods, and he set out to track one down for himself.

That quest won Moore membership into the loose group of botanists, park rangers and enthusiasts devoted to understanding the enigmatic trees. Now he is among the foremost experts on the albino redwoods of the Santa Cruz mountains. And he's only 22.

It helps that hardly anyone else has studied them. Albinos are exceedingly rare — there are only 406 in existence, by Moore's latest count. And redwoods as a species are notoriously complex. The trees' genomes have 32 billion base pairs to humans' 3.2 billion, and they carry six copies of each chromosome instead of two. No one has successfully sequenced the redwood genome, making it impossible to pinpoint the mutation that causes their albinism.

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Redwoods can also clone themselves, further complicating scientists' understanding of them. Vast rings of related plants communicate via their roots, and during the hard months of winter and early spring, they'll distribute nutrients evenly among themselves. Scientists have spilled dye onto trees at one end of a grove and traced it through the root network all the way to the other side.

“Most people, when they come to the redwood, they look up at the canopy,” Kuty says. “But down is where the action is.”

This collaboration lasts only until summer comes. Then every tree, sprout and branch must fend for itself. Those that can't photosynthesize enough sugar are cut off from the shared root system and discarded during what's known as the autumn “needle drop.”

That shedding process is taking place now at Henry Cowell. Bits of branches drift hundreds of feet down from the canopy, buffeted by a soft breeze. The air carries the scent of wood smoke and the spicy aroma of crushed leaves. The redwoods' great age and immense height — coast redwoods, Sequoia sempervirens, are the tallest organisms on the planet and live as long as 2,500 years — give the forest a cathedral-like quality.

But Moore looks down as he explains how albino redwoods take advantage of their shared root system by siphoning off sugars produced by their healthy neighbors. “A lot of people thought they were parasites,” he said. “They even called them 'vampire trees.' "

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That interpretation never made sense to Moore. If redwoods are so ruthless about sloughing off unproductive branches, it seems unlikely that they would tolerate a parasite year after year.

“Redwood trees are smarter than that,” he said. He looks around at the towering green trees that surround — and presumably, sustain — the small albino. “Why, why, why?”

Moore and a colleague, arborist Tom Stapleton, set out to document the locations of every known albino redwood. Their map revealed that white trees tended grow where the conditions become less favorable — a hint that environmental pressure might allow the mutants to thrive.

Next, Moore sought help from his fellow redwood fans up and down the California coast, soliciting clippings from both albino trees and their healthy hosts.

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He found that the albino needles were saturated with what should have been a deadly cocktail of cadmium, copper and nickel. On average, white needles contained twice as many parts per million of these noxious heavy metals as their green counterparts; some had enough metals to kill them ten times over. Moore thinks faulty stomata — the pores through which plants exhale water — are responsible: plants that lose liquid faster must also drink more, meaning that the albino trees have twice as much metal-laden water running through their systems.

“It seems like the albino trees are just sucking these heavy metals up out of the soil,” Moore said. “They're basically poisoning themselves.”

Moore's theory — which he presented at a redwood conference last month and hopes to publish next year — is that albino redwoods are in a symbiotic relationship with their healthy brethren. They may act as a reservoir for poison in exchange for the sugar they need to survive.

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“It’s really interesting work, and I’m so glad he’s doing it,” said Jarmila Pittermann, a plant ecophysiologist at the University of California in Santa Cruz who studies redwood water transport systems. She agreed that poor stomata control is probably responsible for the build up of heavy metals in the albino plants.

“As far as conferring advantage to the healthy trees,” she added, “I think that more work needs to be done.”

Moore acknowledged that he needs to study the phenomenon further. His next experiment will involve dousing lab-grown green and white redwoods with nickel to see whether the plants with an albino partner stay healthier. He also wants to test whether the heavy metals in albino trees stay bound up in the plants or eventually leak back into the soil.

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If his theory does turn out to be valid, Moore can envision a day when albino redwoods are planted in polluted areas to help make the soil safer for other trees.

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But first the albinos themselves must be kept safe. Moore runs through the rare trees' lengthy list of threats: Overzealous visitors may trample the roots and damage their ability to pump water. Some profiteer might see an opportunity to sell naturally white Christmas trees. Years of unrelenting drought have already taken their toll on California's redwood forests. And even if each albino could be guarded and preserved, what about the green trees they depend on?

“When you're looking at redwoods, you need to take into account more than just one tree,” he says. “It's the interactions of the community as a whole that makes the forest. That interconnection from root to root to root.”

As his younger colleague talks, Kuty glances toward the trail, where two women have been listening to Moore's every word.

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“Can we help you find something?”

“We're looking at the phantom redwood,” one of them replies. She introduces herself as Hisun Rim, and her friend is Gerry Fabella. They drove 90 minutes from Oakland to search for the albino.

“Are you Zane?” Rim asks. She'd just heard a radio story about Moore's research — that's what prompted her visit.

He nods, and her face lights up. “We feel so special that we’re here, that we bumped into you,” Rim gushes. “It’s like it’s meant to be.”

Moore looks bashful; Kuty, proud. Moore hands Rim a business card and points to the address of an albino redwood website that he and Stapleton set up. They're always looking for help finding more trees, he explains, and preserving the ones that are already known.

“It's like a Redwood League,” Rim said later — a chain of tree-lovers working up and down the California coast, collaborative in much the same way as the forest network they aim to protect.

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In a fit of unabashed enthusiasm, Rim asks Moore for a hug, and he obliges. Then he and Kuty walk back toward the trail to give Rim and Fabella a moment by themselves with the tree.

From a short distance, the two women are still visible through the foliage. They gaze upward and chat in hushed, awed tones. But it's impossible to discern the albino right in front of them. Like a ghost, it has already vanished.