Will shifting climate change Salt Lake's urban forest?
Weather • Some trees struggle through rapid cooling, warming.
Published: May 21, 2012 02:52PM
Updated: September 6, 2012 02:53PM
image
Paul Fraughton | The Salt Lake Tribune Forester with USU extension, Mike Kuhns checks the awl shaped evergreen leaves of a giant sequoia on the state capitol grounds which showed some signs of stress due to an early cold snap last season Wednesday, October 5, 2011

Editor's Note: This story originally appeared in The Salt Lake Tribune on November 27, 2011.

Three giant sequoias that have loomed ominously brown over the northwest corner of the Utah Capitol complex for most of this year raised questions in Mike Kuhns' mind.

Is climate change hitting Utahns where they live? Is it time to rethink the urban forest?

It's clear to Kuhns, a Utah State University Extension forester, what stripped the green from those manicured California imports before they recovered this fall, and it's the same thing that happened to select breeds of trees and shrubs across the Salt Lake Valley on a November night last year.

It's unclear that climate change caused the event that damaged or killed greenery on Utah lawns. It could be a freak occurrence. But it is in line with predictions for a phenomenon scientists expect to increase with climate change this century: weather variability.

What happened was a rapid cold snap on Nov. 24 after an unusually warm month. At Kuhns' home in the Cache Valley,where trees died, daily highs that had been reaching the 50s and 60s suddenly plunged to 15. The next day's low fell to 9 below. A similar drop occurred statewide.

Trees such as the Capitol sequoias hadn't had time to respond to autumn and shut down their growing season. Instant winter shocked their system.

"They didn't know what was coming," Kuhns said.

It wasn't just Kuhns noting the damage. At Salt Lake City's Western Garden Center, Joel Pickelner fielded calls and comforted customers who came in seeking help.

"A lot of fruit trees got zapped," he said. Same for laurels, hollies and a locally popular hedge called euonymus, all "normally very tolerant of our winters. They just weren't ready."

"We had people come in crying, saying, 'Oh my gosh, this thing's been here 30 years,' " Pickelner said.

For Kuhns, it seemed a wake-up call that Utah gardeners should heed. If in position to plant new trees, he said, they might consider passing up some formerly popular trees that are already on the edge in this area's traditional weather patterns.

True cedars probably aren't a good bet if climate variability increases rapid cooling and warming, he said. Many were badly damaged last year, and there are a few thousand in theSalt Lake Valley.

Sequoias also are susceptible, though the valley sports only a few hundred of them.

Flowering pears may struggle as well, Kuhns said. They are hurt by late spring frosts as well as quirky falls.

Salt Lake City's urban forester, Bill Rutherford, said he's not sweating the climate-change question. He has seen sequoias suffer before, because they're a bit out of their range here anyway. It's not that some climate scenarios aren't startling for urban landscapes, he said, but it's hard to know how to respond appropriately.

Some scientists believe Arizona's climate will gradually overtake Utah, he said, but he's not recommending that people plant desert palo verdes here. For one thing, they don't shade well, and home energy bills would rise.

Because most Utahns water their lawns, Rutherford explained, urban trees have a little easier time adapting to change than their wild counterparts on the national forests.

"I'm wrapping my arms around every one of the trees that we've got," he said. "We're encouraging people to be good stewards of what we have, and we'll enjoy them as long as we can."

Many residents want to plant drought-tolerant trees, either out of a conservation ethic or fear about a drying climate. The U.S. Interior Department released a report this year predicting that the Colorado River Basin, which supplies some of the Wasatch Front's municipal water, will yield 9 percent less annual runoff by mid-century.

Rutherford advises people to consult an expert before choosing a drought-tolerant species, though, because some are known to worsen air pollution with the organic compounds they emit in times of heat stress. Honey locusts and Kentucky coffees, he said, are among the trees gaining popularity for low water demands and relatively little pollution contribution.

Xeriscape for a desert landscape? Pump more water to keep things green? Wait and see?

If climate change throws more weird weather at Utah while lengthening the growing season and water requirements as predicted, urban landscapers face an evolving set of these calculations.

bloomis@sltrib.com

Twitter: @brandonloomis