A million trees here, a million trees there, and pretty soon we’re talking about some real shade.

Or is it real money we’re talking about?

For years, a local consensus has been building about trees in Tucson: We need to plant them — lots of them — to improve the quality of life in the metro area. To cool neighborhoods, to ward off the worst possible effects of a hotter climate and to lessen the urban heat-island effect. Overall, trees improve our well-being.

On the global scale, planting 1.2 trillion trees could also offset one decade’s worth of carbon emissions, a study found this year. Scotland planted 22 million trees just last year.

In Tucson, our efforts have been on a smaller scale. In 2013, Mayor Jonathan Rothschild started an initiative he called “10,000 Trees,” which has so far led to the planting of more than 50,000.

That might sound substantial, but Rothschild says the pace of planting is not keeping up with tree deaths. The new expert opinion is that the scale of planting needs to be much greater, the pace much faster, if we are to make much of a difference in our tree cover in the Tucson metro area as the climate warms.

An informal group formed called Shade Tucson, representing groups with an interest in environmental sustainability, has started trying to figure out how to improve the city’s tree cover from the current 8%, as well as expanding the canopy around the metro area. Mead Mier of the Pima Association of Governments calculated the actions needed to increase the local canopy, in the city or in the broader metro area.

“When we looked at 20%, it was not even fathomable,” Katie Gannon, the executive director of Tucson Clean and Beautiful, told me.

Their conclusion: It’s more realistic to try to go from 8% tree canopy to 15%, and to try to do it by 2030. But to accomplish that, Tucsonans will need to plant more than 300,000 trees per year. Yes, per year.

It will require a massive effort, even if we push off the goal to a later date, maybe another decade down the road.

“It might take 20 years, it might take 30,” Gannon said. “All the more reason we need to get started now.”

Another member of the Shade Tucson group, Tanya Quist, addressed the Tucson City Council on Tuesday. Quist is a UA plant scientist who directs the university’s arboretum, which in the UA’s case is actually the campus itself.

She went through the multitudinous benefits of trees, but importantly explained what it takes to ensure a planted tree thrives — planting the right tree in the right place, planting it correctly, getting it established, maintaining it gently. Most trees that die prematurely fail because they weren’t planted properly, she said.

Her point, though, and the growing consensus among people who care about these things, is that to make a difference, the scale of the effort has to be massive. Therefore, it has to have a leader, a plan and guidelines for how to carry it out.

“What we’re interested in ultimately is having a system. You can’t plant a tree, especially not millions of trees, without having a system,” she said.

The drawbacks and difficulties are easy to imagine.

For one, Tucson is not naturally a forest. In much of the metro area, the biggest plant that would grow without our help would be a creosote bush, although native trees such as mesquites, palo verdes and acacias don’t have much trouble growing throughout the city.

Another challenge: The trees require water, especially when they are getting established. If native trees are planted, that won’t be as much of a problem, but it’s still a requirement, especially if the climate continues warming. On the other hand, trees can help retain water filtration into the ground rather than letting it flow into the sewer system.

* I understand and agree that registration on or use of this site constitutes agreement to its user agreement and privacy policy.

Another difficulty: To essentially double the tree canopy requires massive planting on private land because there simply aren’t enough good, publicly owned places. Property owners will have to agree to take part, and they’ll have to do the job well.

Finally, of course, there’s the question of money. Planting one tree is not expensive. But when you’re buying and planting and maintaining them by the hundreds of thousand per year, that could add up.

Benjamin Ruddell, a Northern Arizona University professor and engineer who studies sustainability, recognizes all the benefits that trees have in a city, but he has some warnings about a big tree-planting campaign.

“Trees are kind of expensive. This isn’t like New England, where the tree will grow by itself if you plant it” Ruddell said. “They take a lot of work, especially in desert cities.”

If the main concern is shade, it might be better in many urban sites to build shade structures, he said. Playgrounds, bus stops and roadsides are the kind of places where tree-planting may not end up being the best option, he said.

“Trees are great, but you’ve got to put them in the right places (to have an impact), and some of those places don’t work very well,” Ruddell said.

Challenges aside, the enthusiasm among council members was clear after Quist’s presentation Tuesday. And all three Democratic candidates for mayor — Randi Dorman, Steve Farley and Regina Romero — have made tree-planting a part of their environmental and sustainability platforms.

The one candidate who is also a council member, Romero, told me “I’ve been saying we need to plant a million by 2030. It’s actually 2 million we need by 2030. We have to be sure we push the envelope in terms of goals, but not make it sound like it’s impossible.”

The idea of a Tucson with twice as many trees is an exciting possibility, actually. But it’s going to take deliberation, a realistic plan, public buy-in and, yes, some money.

Contact: tsteller@tucson.com or 807-7789. On Twitter: @senyorreporter

Columnist

Tim Steller is the Star’s metro columnist. A 20-plus year veteran of reporting and editing, he digs into issues and stories that matter in the Tucson area, reports the results and tells you his opinion on it all.