The importance of urban trees

Major research project looks at role of trees in intercepting rain

Cam Fortems / Kamloops Daily News
June 22, 2013 01:00 AM

Environmental science student Julie Schooling and assistant professor Darryl Carlyle-Moses evaluates the rain being collected by the American beech tree at McArthur Island.

Parents of soccer or baseball players - soccer mom Julie Taylor is one of them - spend plenty of time at McArthur Island Park in springtime.

In addition to her duties as a fan, however, Taylor roamed through the park for an estimated 1,000 hours over the past year, running tree-to-tree fixing damage to equipment, measuring rainfall, patching up her rainfall collection system and answering questions from the curious: just what are you doing with the silicone and tubing on that tree?

On Wednesday this week, she stood under the shelter of an American beech tree on Kamloops' emerald island, along with Darryl Carlyle-Moses, a TRU assistant professor in geography and project supervisor.

The increasingly wet professor ran every five minutes to a nearby rain gauge, part of the extensive labour involved in the project.

Getting wet and answering questions is part of the job when you're conducting research on the role urban trees play in interceptingand, in some cases, funnelling rain.

This week's weather brought a steady stream of rain to assist with further measurements in the long-term project slated to end this fall.

Taylor set out last spring as part of her master's of science program to determine the role of trees with interception of storm water - the kind of event for which Kamloops is famous in spring.

The original plan was to use buckets and volunteers to measure the amount of rain that gets through leaves, called throughfall, as well as that which comes down the trunk, known as stemflow.

Volunteers were dispatched to the park with rain buckets in advance of storms, something that quickly proved impractical.

"By the time we did our first rain event, we realized how much work that would be."

So Taylor focused her research on stemflow over a longer period. There are 40 trees representing 22 species in the park bearing the signature open black hose wrapped on the trunk feeding into a blue tote box.

The trees and the "research in progress" notices are a familiar site on the island.

Obstacles have included early vandalism, city sprinklers and storms that can quickly overflow buckets enclosed in the blue totes.

Despite those challenges, some clear trends have emerged. (The study only looked at leaf-bearing trees).

In general, trees with smooth bark and a narrow shape quickly transfer rainfall to the ground - ideal for self-watering, but not desirable in a harsh rainstorm.

With its smooth, waxy bark, the American beech is the perfect example. Once a steady rainfall starts, the hose wrapped around the trunk collecting rain that trickles down the trunk starts to pump out a steady stream into the bucket, enough water to resemble a swiftly running garden hose.

"We're trying to find out what it is about this tree that makes it the perfect storm," Taylor said.

On the other hand, Taylor said trees with rough bark are able to store considerable amounts of water.

"Some rough-barked trees can take up to six millimetres of rain (before transferring to the soil)," Carlyle-Moses said.

"It's like a sponge - lots of places for water to get caught up in."

By contrast, the American beech starts pumping water down its trunk with as little as one millimetre of rainfall.

Rough-barked trees are ideal to intercept large storms. Species include green ash and red oak.

Taylor has already presented her study to the Association of American Geographers in Los Angeles as well as to a conference in Saskatoon. There are also plans to present at a conference in San Francisco this winter.

But the master's student, who is also trained as a landscape architect, doesn't plan to keep her findings locked up in an ivory tower. Instead, she hopes to make them available to the City of Kamloops (a sponsor) as well as to landscape professionals and homeowners alike, both through a website and brochures available at nurseries and garden centres.

"It will give them tools to make better decisions."

Information for the general public should be ready this spring.

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