By Jeff McMahon, Opinion, Forbes
People who want to know what trees to plant for a changing climate sometimes have trouble getting a clear answer, in part because the answer varies by region, in part because the effects of climate change are uncertain, and in part because the best answer scientists can offer is: lots.
Plant lots of trees. Plant lots of kinds of trees.
“I often get asked by people, ‘What species of trees do you recommend?'” said Lydia Scott, director of the Chicago Region Trees Initiative. “And I say I recommend that you plant broad species diversity. I never get sucked into this issue of identifying for them what exact species they should be planting.”
Institutions like the CRTI and the Morton Arboretum do have tree-selection tools to help individuals choose species, and the USDA’s regional vulnerability assessments identify species expected to thrive or struggle. But scientists emphasize that they can’t be certain which trees will thrive, so it’s going to be important to plant a variety.
“I think the answer is to just try as many trees as we can,” said Matt Lobdell, the curator for the Morton Arboretum, a tree museum and science center outside of Chicago. “What we’re looking at is trying to get as many as we can to kind of hedge our bets so that we have these healthy trees for future generations.”
In recent years arborists have learned the perils of a lack of diversity.
“In a lot of our urban areas what we have done in the past is plant a lot of monocultures along our streets,” said Leslie Bryant, a climate change specialist with the U.S. Forest Service. “We had a row of elm trees, and Dutch elm disease came through and what did we do? We planted a bunch of ash trees. So what we ended up with is the emerald ash borer coming through, wiping out almost all of our ash trees.”
In Riverside Illinois, near Chicago, the village forester is planting more trees from southern Illinois that may survive better in a warmer climate, Bryant said, and he’s planting a greater diversity of trees on each street. Among the newcomers: accolade elm, buckeye, pecan.
“This doesn’t mean we can’t continue—and we shouldn’t stop—planting our native trees, but we’re going to have to start diversifying our portfolio, if you will, to make sure that we’re resilient into the future.”
Sometimes trees surprise their keepers. Lobdell has a critically endangered Georgia oak thriving at the arboretum, serving as a gene bank should the small wild population perish in Georgia. And he’s seen a southern magnolia survive a harsh Chicago winter with no damage.
“Despite growing in East Texas, the Gulf Area, Florida panhandle, it’s fully hardy here in our collection,” he said. “So some of these plants can be a lot more resilient than we might think they are at first. Even though it might seem like these plants might require very specific conditions, sometimes they don’t. Sometimes they can perform well outside of their native range.”
So the ultimate way to find out which kinds of trees will perform well in the changing climate is to plant many kinds.
“When you’re asking your landscaper or you’re thinking what trees you want to plant on your property, you want to be thinking about diversity,” Lydia Scott said. “Instead of saying ‘I love that tree on my neighbor’s property, I want one just like that,’ you say, ‘I want to find a tree that has similar qualities as that tree but that is different than that tree.'”
If you like the fall colors of a neighbor’s sugar maple, consider the sweet gum or frontier elm, she said. The Arboretum’s tree selector, geared to Northern Illinois, allows users to filter trees for fall color and other attributes, including height, shape, blossoms, fruit, flowers, bark.
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