Thanks to the Aug. 19 tornado, Minneapolis will soon be getting a head start on planting the urban forest of the future -- one that's long on diversity but maybe a little shorter overall.

Residents who might recall living in a virtual elm forest, and more recently an ash grove, are about to see their streets and parks lined instead with the likes of Kentucky coffee, buckeye, river birch, pear, alder and even hop hornbeam.

The replanting will start next spring in south Minneapolis, where a tornado, weak by most standards, nevertheless uprooted or toppled nearly 300 trees, including a 5-foot-diameter cottonwood and a 170-year-old green ash. Over time, the tree cover citywide will be transformed as ash trees -- widely used for decades to replace diseased elms -- fall themselves to an expected infestation of the emerald ash borer.

"A lot of cities had almost all elm. They were nearly the perfect urban tree," said Minneapolis Park and Recreation Board forester Ralph Sievert. "Now the idea is to have a mix so we don't have all our eggs in one basket. We'll get a variety out there so we're not going to lose so many trees all at once."

Several generations ago, nearly 90 percent of the trees on public land in Minneapolis were American elms, Sievert said. Though ash were a favored replacement and now stand in towering, blocks-long ranks in parts of the city, ash now make up 19 percent of the city's boulevard trees.

Diversity of tree species is growing in importance with the easy international spread of invasive species, said David Nowak, a research project leader for the U.S. Forest Service, who has studied trees in Minneapolis. But while some cities are pursuing both, some aren't. In many new developments around the Twin Cities, for example, the Autumn Blaze maple has been planted almost exclusively because it grows well where new sod is being watered, and is readily available, said Rock Kelly, production manager at Bachmann's wholesale nursery, which grows trees for cities across the Upper Midwest.

Minneapolis has a lot of maple and linden right now, Sievert said. Minneapolis foresters have been planting some disease-resistant varieties of American elm in recent years, but only sparingly.

A Minnesota buckeye is born

Replanting in the storm's wake will involve species that might seem unfamiliar but are known to grow in the Upper Midwest. One though, literally has Minnesota roots.

The Autumn Splendor buckeye actually originated nearly 40 years ago at the Minnesota Landscape Arboretum, apparently the result of an accidental genetic mix in a collection of painted buckeye at the Morton Arboretum outside of Chicago, from which the Minnesota arboretum bought seedlings. Unlike most buckeyes, which go drab and drop their leaves at the end of summer, the Autumn Splendor variety turns red and holds its leaves into the fall.

Sievert also offered some reassurance to those who associate Kentucky coffee trees with a mess of large, brown seed pods. The city will be planting a seedless variety, he said, with a name that evokes a clean, urban style: Espresso.

It's unlikely that any of the new trees will grow as tall as American elms, which sometimes reached 100 feet. But they're also not as likely to pry up sidewalks with large roots or need continual trimming to stay clear of wires, Sievert noted.

Some landscape designs -- at entrances, for example -- will continue to call for uniformity, but residents today may be more accepting of a mix of trees on their block than in the past, said Katie Himanga, president of the Minnesota Shade Tree Advisory Committee.

People who actually lived with the cathedral-like effect of towering elms on urban streets are now in the minority, she said.

Sievert said he believes most residents aren't looking for massive trees, but will be happy with trees that shade their homes and cars.

Bill McAuliffe • 612-673-7646