Trivia quiz: What’s a baseball bat made from?
The answer is air, with a little water and just a few minerals from the ground.
“It’s true. Trees are 96 percent air and water,” said Kirk Johnson, a paleobotanist and chief curator of the Denver Museum of Nature & Science. “The body of a plant is carbohydrates, which is nothing more than carbon dioxide and water mixed through photosynthesis.
“Most people believe that trees are made from the soil. If that was true, the ground around trees would sink. It doesn’t, because they’re made from the air.”
It was a chat like that between Johnson and Mayor John Hickenlooper that gave rise to the mayor’s push to plant 1 million trees in Denver over the next 20 years.
“The whole idea came while we were attending a climate- change meeting,” Hickenlooper said Thursday. “I started thinking about it, that trees clean the air of carbon dioxide, which comes from burning gas in automobiles and air conditioners.
“Trees provide the shade that cools down neighborhoods. If we started planting trees in low-income neighborhoods that don’t have them, or if we planted trees on the south side of houses, everything would cool down.
“We could have schoolkids plant trees every year. We could require that two or three trees be planted at new homes. We could have a huge impact on our energy usage while spending very little money.”
The city of Denver has roughly 1 million trees now, or an average of 25 trees per city block, according to a survey by American Forests. Tree canopies in thickly treed neighborhoods like Country Club or Washington Park cover 6 percent of the city’s area. The city forester estimates that the mayor’s plan could triple the canopy coverage to 18 percent of the city.
“Trees make urban landscapes much more pleasant, much cooler,” Johnson said.
Commercial tree experts like the plan.
“It takes water to plant a tree. But once they’re established, they save on water usage because of their shade,” said Dave Paricio, district manager of Davey Tree Experts. “They definitely reduce the air temperature around them and the need for moisture. I think it’s a good idea.”
Paricio said many of Denver’s trees are toward the end of their life expectancy, which is generally 70 to 80 years. “I get called to look at 15 to 20 city-owned trees a week that are being condemned because of their age or for safety reasons. It would be great if the city replaced all of them.”
Staff writer Mike McPhee can be reached at 303-820-1409 or mmcphee@denverpost.com.
