AURORA | On a sunny summer morning, Mamie D. Eisenhower Park in southeast Denver is lively.
There’s a constant tap-tapping of pickleballs meeting rackets just across from the pool where children are laughing and splashing. Cicadas buzz in the trees and cyclists whirl by a group of research students measuring newly-planted trees on the High Line Canal, which is in the process of transitioning from a water delivery system to a massive urban greenspace — larger than Manhattan’s Central Park — spanning multiple cities and counties.
The students, a group of women from the University of Colorado-Denver, are outfitted with tools that will help them determine how well the baby trees are doing and whether the High Line Canal Conservancy along with its municipal partners should continue to plant those same species of trees along the 71-mile-long canal, which only sometimes holds water these days.
The High Line Canal was built in the 1880s as a way to get water out to farm land on the high plains. While water rights disputes kept the project from being completed, it did help irrigate nearly 20,000 acres. By the 1920s, Denver Water had acquired the canal, and in 2011, Fairmount Cemetery remained the only customer along the stretch of the canal.
Depending on where a tree is planted along the canal, it might have access to more water, have better soil and even get better light.
“Some of the things you look at for the environmental factors are like, what is the slope here? What’s the distance from the tree to the canal? What’s the distance from the tree to the trail? And then we also look at what direction the slope is facing, because that can affect the amount of sun and amount of moisture it gets,” CU Denver graduate student Alissa Iverson said, reaching for a daubenmire frame, which helps researchers look at the other plants growing around the new tree.
She’s taking note of life around the small Western Catalpa, so that if it ends up thriving — or not — future researchers might be able to figure out why and plant more trees accordingly. Meanwhile, Kristina Pisarenko and Summer Merrell, both on the soil team, take moisture readings of the surrounding earth and determine whether the dirt is more sandy or contains more clay.
This summer, the group of undergraduate and graduate students, working with the Denver Botanic Gardens, measured the health and surrounding environment of about 225 trees along the trail. Over the next several years, it’s expected that more than 3,500 trees — an estimated 50 trees per half mile — will be planted along the canal. Some of them are species native to Colorado waterways, and some of them you’re more likely to see lining busy urban streets than growing on a river.
“The big picture of planting a variety of trees together rather than one or two allows for more resilience against different kinds of conditions,” Denver Botanic Gardens research scientist Christina Alba said. “The native trees require a lot of water. That’s their natural habitat — they’re riparian. They occur along the waterways. So if you’re going to plant some of the native trees, they need more water over their lifespan, whereas these guys, the non-natives that are street trees, and more drought tolerant. Once you get them established in the first few years, you should be able to lay off irrigation and they should be able to do OK.”
A little less than half of the trees along the canal are cottonwoods, the Denver Botanic Gardens estimates, and many are toward the end of their lifespan. The new trees will help the canal continue to be a space hundreds of thousands of residents across the metroplex can utilize for recreational purposes.
The High Line Canal Conservancy, a non-profit organization dedicated to preserving the canal, reports that more than 350,000 people live within a mile of the canal and nearly a half-million people use the canal regularly. Some of them, the group of researchers said, know their stretch of the canal well and have been curious about the tree study.
“You get these people who walk past the same spot every day,” said Laurel Hartley, who teaches biology at CU Denver and helps oversee the research. “This is where they do their daily walk, so they tell you a lot.”
The intrigued regulars also gave the students a chance to practice their citizen outreach skills. Alba said being public ambassadors is an important part of the research process, especially for students who may end up finding work in education.
“I’ve worked on a lot of different research projects throughout my undergraduate and graduate career, so whenever I’m on a research project I want to have a three minute or less pitch,” Iverson said. “So what I usually say is that we’re with the Denver Botanic Gardens — because I want people to know that the Botanic Gardens does research — and CU Denver, and we’re looking at tree health, the health of the saplings that were planted last year and relating them to environmental variables.”
Studying the trees just a year after being planted only gives the Conservancy and its partners a little slice of information. Alba, Hartley and the students aren’t ready to say they’ve made any definitive findings, but they hope to be back in future years to record more data as the saplings grow and the canal blossoms into its new life.