SANTA CRUZ — The hardest part of tree-sitting at UC Santa Cruz isn't the cold, the rain, or the fierce winds that rattle your perch.

What's tough is what's happening on the ground: Threatened suspensions. Arrests. And the challenge of communicating — from 70 feet up, while wearing a ski mask to hide your identity — to students who are largely unaware of your mission to squelch campus growth.

It's no sylvan sanctuary. Protesters awake to the roar of buses climbing Science Hill, carrying students to overcrowded classrooms and too few labs — the soundtrack of a campus bursting at the seams.

"It's noisy," said a protester who would identify himself only as "Owl," speaking from a small redwood in a parking lot that is the future site of a new Biomedical Sciences Building, part of the university's overall expansion plan.

"It feels much more like a forest at night," he said.

The protest represents the latest collision of eco-idealism with the ambitions of a major research university, which hopes to add 4,500 students and 3.8 million square feet of new construction by 2020.

Like other UCs, the university is mandated to provide education for California's skyrocketing number of eligible high school graduates. But elected officials in the quirky, left-leaning city say such growth will tax resources and forever change their tiny Utopia by the Sea.

Like their treetop brethren at UC Berkeley, who for a year have been sitting in the way of a $125 million sports training center, the UC Santa Cruz protesters have put down roots.

It has been 92 days since they hoisted up platforms in the dark and climbed out onto limbs, wrapped in layers of wool, fleece and what they assert is their right to free speech. The university says they are not students.

Early on in the campaign, incidents of graffiti, vandalism and false fire alarms angered some would-be supporters.

But a recent crackdown by school officials may sway popular opinion again. Seven protesters face criminal charges for disobeying police officers. As many as 30 face civil sanctions — including a popular professor who was sued by the university after delivering warm Miso soup.

A 19-year-old freshman who did not climb a tree but supported the demonstrators has been threatened with a two-month suspension.

But most students on this protest-proud campus seem largely unmindful, scurrying to class past signs reading "Pedestrian Warning!"

"The vast majority of people have no idea why they're in the trees," said campus lecturer and longtime city Councilman Mike Rotkin. "They haven't been successful in getting their message out."

Meanwhile, representatives of the university, the city of Santa Cruz and the county are in mediation, attempting to resolve their differences over three impacts identified in the long-range plan: housing, water and transportation.

Jennifer Charles, a spokeswoman for the sitters, says that construction of the Biomedical Sciences Building is the first step in a plan that imperils both the quality of the education and the environment. "We're here until the university changes its plans," Charles said.

Each sturdy treehouse is equipped with a cargo line, so that ground crews can send up supplies. Sitters wear harnesses to prevent a fall. They urinate in bottles and defecate in buckets, using a hand sanitizer to keep clean. Every several days, the sitters change shifts, descending and ascending in darkness, to escape notice.

A social crowd, protesters visit by traversing to each other's trees. They've been serenaded by the Raging Grannies and fed warm squash and rice casseroles.

"I've been pretty busy," Owl said. "I lost a game of backgammon this morning."

Across the street, at the Physical Sciences Building, professors grow increasingly angry. One has posted a huge sign across his windows reading: "Protesters Go Home."

The university will go to court Feb. 21 to ask for an order to get the sitters out of the trees, arguing that the protest constitutes illegal camping and has created dangerous, unsanitary conditions.

But extricating the unwilling could pose its own problem. If pulled, they could fall and get hurt.

"It might," Rotkin said, "be best to just wait them out."