In its June 25 issue, Time magazine re-ran that goofy picture of Mayor John Hickenlooper riding a scooter, the one it used in 2005 when it named him one of the country’s best big-city mayors.
The recent article was about how state and local government leaders were “doing things that Washington has failed to do,” such as trying to reduce greenhouse gases. Our very own Hick, the article said, “created the first 10-year plan to end homelessness … and introduced Greenprint Denver to reduce greenhouse gas emissions.”
It was only a brief mention in a news illustration, as was the mention the following week showing that Denver has a tree canopy of only about 10.4 percent, which is less than half of what it should be for cities in the West. It suggests that the city needs to plant more trees, as Greenprint Denver plans to do.
But all this tree-planting is not as simple as it seems, notes Carol Lyons of The Tree Project. Trees also can produce ozone, and they need water, which can be a problem in the arid West.
Trees overall are good, and that’s why cities are planting them. Trees absorb carbon dioxide, collect particulates, prevent erosion and floods and provide cooling shade. Los Angeles has a campaign to plant 1 million trees over the next 30 years; Hickenlooper wants to reach that goal in 20 years.
According to Time, an Eastern city needs at least 40 percent tree cover; cities in the West need 25 percent. Asked where that figure might have come from, a CSU forestry expert said someone probably just pulled it out of the air, so to speak.
City life is tough on trees, and Dutch elm disease wiped out a lot of Denver’s shade 20 or so years ago. Climate change seems to be making life easier for tree pests, at the same time it makes healthy trees more desirable as one way to fight back.
When lots are scraped to build sidewalk-to-alley McMansions, the big old trees go, too. A big tree is 60 to 70 times better at fighting pollution than a freshly planted sapling. More asphalt also means higher temperatures, and helps explain why cities are getting warmer. It’s not just climate change; it’s trading green and leafy for flat, black and sticky.
But planting a tree is “only a first small step if one wishes to increase the tree population,” Lyons points out. Species must be carefully selected, appropriately placed and watered, especially when they’re young. The goal of The Tree Project, part of the Denver-based Institute for Environmental Solutions, “is to identify how trees can be used to optimize energy and water conservation, and air quality,” she said.
The trouble with trees is that, while they can improve air quality, they also can increase air pollution – especially ozone. When Lyons mentions this, people are reminded of Ronald Reagan’s “killer trees,” and they scoff. But it’s ozone from vegetation that makes the Smoky Mountains smoky, Lyons notes. She said the worst trees, mostly younger, fast-growing ones, can emit 10,000 times more ozone than the best ones.
Planners also need to consider whether trees will save water or waste it. “There is anecdotal evidence that trees may help conserve water with increased shade, but this has not been adequately demonstrated,” Lyons said. “Will Mayor Hickenlooper’s tree-planting proposal result in a net increase in water consumption that this area cannot support?”
This failure to fully embrace tree-hugging without raising a few questions has raised doubts about The Tree Project. “We’ve been called anti-tree,” Lyons said. “We’re not; we’re extremely pro-tree.” They’re just looking for the optimal tree, or trees, whose side effects don’t overshadow the good, so to speak.
Fred Brown (punditfwb@aol.com), retired Capitol Bureau chief for The Denver Post, is also a political analyst for 9News.
