By Jared Flesher

One hundred million years ago there was a tree. It grew fast and tall and flourished in many places, including North America. Then 20 million years ago it vanished—globally extinct—save for the fossil record it left behind. Or so we humans thought. 

In the 1940s, Chinese botanists rediscovered the tree in a remote valley. Local villagers already knew the tree and revered it. Seeds were collected and propagated. In 1948 one of those saplings was planted on Princeton University’s campus, next to the art museum. 

That’s a short history of the dawn redwood. 

— — —

The dawn redwood was a favorite of someone I liked very much, the late Princeton ecologist Henry Horn, who passed away three years ago this March. Henry had a knack for paying close attention to birds and bugs and other phenomena most people generally ignored. On walks across campus he would pause often to observe and explain small natural wonders—and big ones—such as the redwood. 

I recently took a newcomer on campus to meet the redwood, as he was someone I surmised would appreciate a good tree. He did. And I told him, “This is the tallest tree on campus.” 

I thought I was right—surely Henry had told me. But that night in bed my internal fact-checkers started to worry. Maybe Henry had said one of the tallest. Had the legend of this tree grown, like a great fish caught long ago? 

 

 

The next morning I consulted the Internet and my confidence wavered. The latest published report appears to be a 2014 article in Princeton Alumni Weekly, declaring the “largest tree on campus” to be a huge tulip poplar, next to Prospect House, towering at 135-feet. The same article put the dawn redwood at a mere 115 feet. 

But something seemed odd. An earlier Internet article from 2005 also estimated the dawn redwood at 115 feet. Dawn redwoods are famous for growing fast—up to two feet per year. It seemed unlikely our dawn redwood had ceased growing for a decade. 

I sent an inquiry to the Office of the University Architect, supposing there might be a special division devoted to tree height. There isn’t. But I did receive in response a tantalizing observation from architect Dan Casey, who was atop the Nassau Hall cupola three years ago while it was under renovation. Dan had taken the time to look southeast from the cupola toward the tall trees and noted that the dawn redwood looked “just a bit taller” than the champion poplar. 

Clearly, new measurements were needed.

 

I consulted briefly with a researcher in Ecology & Evolutionary Biology and learned that a laser rangefinder is what’s needed for accurate tree measurement. This I promptly acquired from an online retailer started by a Princeton alum. Further reading informed me I would also need some trigonometry (at last!). Here’s the technique: 

Stand about 150 feet away from your tree. Using your rangefinder, measure the distance to the tallest point on the tree. Also note the angle from your eye level to the treetop, which is a data point available on modern rangefinders. Next measure the distance and angle to the base of the tree’s trunk. Finally, take your measurements and do some math, as described in the graphic below:

I journeyed to the lawn between the art museum and Prospect House to find my answers. The dawn redwood and the tulip poplar are merely 200 feet apart; you can stand between these two giants and wonder. Looking up, it’s impossible to tell which is taller.

I’m a rookie in tree measurement, so I took multiple measurements of each tree from different spots to make sure the results I was getting were consistent. (They were, within the rangefinder’s margin of error of plus/minus 3 feet.) Here are the results:

The dawn redwood is… 123 feet tall.

I did this calculation first and was a little sad, because I was hoping Henry’s favorite tree would win.

Next up, the tulip poplar. It is… 118 feet tall.

Wait, what?

This is significantly less than the 135 feet cited in Princeton Alumni Weekly. I can’t say for sure what’s amiss, but I have a suspicion.  

During my deep dive into the science of champion tree height measurement, I learned that a measuring technique called the “tangent method” held sway for decades. But then a huge problem was discovered. Even forestry professionals, according to a University of Illinois expert, “were overestimating tree heights by as much as 40 percent!” This was particularly an issue among trees that are leaning, or, like our sprawling tulip poplar, in which the tallest branches are not directly over the trunk. Only recently did a new equation rise to prominence, the “sine method,” which corrects for these problems. I suspect the tulip poplar’s historical height record may be skewed by inaccuracies inherent to the tangent method. Or maybe not.

 

 

Is absolute truth obtainable? Back when I was studying journalism, a wise professor warned how the careless use of superlative has embarrassed many an otherwise-diligent journalist. So let’s be circumspect. I’m a novice tree measurer using new tools for the first time. I haven’t measured every tree on campus, just the two most likely candidates. But I think it’s reasonable to say this: The best available data points to the dawn redwood as the tallest tree on campus. And it’s only going to get taller.

There’s one more thing you should know. Around 1948, when a dawn redwood sapling was planted next to the Princeton University Art Museum, several more were planted along Broadmead Street, near Lake Carnegie. I wouldn’t call them “on campus,” as the grove feels remote, but it’s University property. Those trees look just as tall as the art museum’s dawn redwood—and maybe taller.

So what’s the meaning of a grove full of tall trees stretching gracefully toward the sky? I recently scrawled in my notebook a thought by the master woodworker George Nakashima, who believed trees have souls of a sort. “It matters not which is the oldest or largest,” he wrote. “The wonder is in their being.”

 

 

Learn More:

“Dawn Redwood, in the Forest of the Living Gods”
A history of the dawn redwood from arborist Max Paschall

“Trees of Princeton University”
A handy and beautiful PDF guide to some of the University’s most notable trees

“The Sine Method: A Better Tree Height Measuring Technique”
Good advice for measuring the height of a tree, from forester Jay C. Hayek

“Nature Walks with Henry Horn”
An Office of Sustainability web-series featuring ecologist Henry Horn