Before white settlers arrived, the people who lived in the Willamette Valley set such regular fires that the only trees left in any numbers were cottonwoods and Douglas firs along riverbanks.

EUGENE — There is a tree outside John Witte's window on the University of Oregon's campus: a wispy, wiry contraption that the instructor has been curious about since he switched offices a year ago. It is a tree wedged in among a row of stately Norway maples lining the Memorial Quad.

Witte looked it up recently and learned the tree's name: Caucasian wingnut, planted the year he first arrived in Oregon in 1976.

Funny, he thought: "I've been known as something of a wingnut."

It's that kind of curiosity about the campus' spectacular de facto arboretum that brought Witte and a trove of other arboreal enthusiasts to the Pioneer woman statue outside Gerlinger Hall recently for a two-hour walk with tree expert Dennis "Whitey" Lueck.

To call Lueck a tree expert is akin to saying Einstein knew a thing or two about particle physics, which is why not a soul in the group successfully stumped the wry instructor during his session, and why Lueck couldn't possibly impart everything he knows about the campus specimens in a single autumn afternoon.

Or, as Lueck put it, "We're walking past trees where I just have to say, 'No, I can't talk about you today.'"

Still, as he speed-walked through red and yellow fallen leaves, Lueck blasted through a far-reaching orientation spread across the university's grounds.

Perhaps the most interesting fact came at the walk's start, with Lueck's revelation that all but one of the tree species weren't here at the University of Oregon's 1876 founding.

Before white settlers arrived, the people who lived in the Willamette Valley set such regular fires that the only trees left in any numbers were cottonwoods and Douglas firs along riverbanks, Lueck said.

At the university's opening, only two trees were on campus, both of them Oregon white oaks. Everything that forms the impressive canopy that exists now, with hundreds of varieties, was planted.

That includes the eastern black walnut tree, planted in 1920, that reaches out and above Gerlinger Hall and drops bombs on those who walk beneath it this time of year, bombs containing a delicious nut too time-consuming to harvest to be worth most people's time.

There's the beloved European beech tree to the west, its bark resembling the skin of an elephant.

There's the Harlequin glorybower, near the HEDCO Education building complex, with its tiny red leaves, plump berries and leaves that smell of peanut butter.

"Wow," exclaimed at least three different people who needed to find out with their own noses. They do smell like peanut butter.

There are the trees that aren't there but maybe still should be, as far as Lueck is concerned — the grove of giant sequoias cut down to make room for an extension of the Knight Library, when they could have been built around, anchoring a courtyard. Then there's the missed opportunity to build trees that grow bigger than the Katsura, crab apple and Japanese maples planted at HEDCO, Lueck said.

"What is this part of campus going to look like in 50 years?" he asked.

There are the widely revered gingko trees with their green and yellow leaves, the oldest tree still growing on the planet, a species that reportedly has been around for 200 million years.

And, of course, there is the "moon tree," an otherwise unassuming Douglas fir whose seeds rode with the astronauts of Apollo 14 on their 1971 mission to the moon.

Lueck teaches a "Trees of Oregon" course and has been giving tree tours since 2003 to teach people about "the world around you."

"A lot of people come here, and they know there are all kinds of trees," he said. "But they have no idea what they are."

From now on, perhaps the Caucasian wingnuts on campus will be a bit less anonymous.