by T.W. Budig
ECM Capitol Reporter
Blazing autumn colors lend matchless evidence to the strength of the urban forest. The Metropolitan Regional Parks System, with 96 parks and trails overall in the seven-county metro area, includes about 59,000 acres and logged an estimated 45 million visits in 2012, testimony to the value placed on leafy spaces.
Urban trees are valuable in reducing storm runoff and cooling otherwise sizzling pavement. Just as well-placed trees can keep homes cooler by blocking sunlight from shining through windows and heating floors, the same is true with sidewalks, bridges and other outdoor hard surfaces.
Experts are getting away from counting trees to determine the robustness of the urban forest, said Gary Johnson, University of Minnesota Extension Service professor. Instead, they’re thinking in terms of canopy cover.
An emphasis on sheer numbers has resulted in the methodical planting of trees in the hard, dry soils along street curbs. The mortality rates for these trees is extremely high, Johnson said.
An ideal canopy, at the minimum, is perhaps 40-45 percent coverage, Johnson said. Downtown Minneapolis, with single-digit percent canopy cover, isn’t close.
“Pretty pitiful,” Johnson said.
Johnson, a specialist in urban and community forestry, mentions Eagan and Minnetonka as suburban cities with top-notch forestry programs.
Gregg Hove, Eagan supervisor of forestry, is something of an apologist when it comes to suburban trees. With an empathy that explains 20 years on the job, Hove cited the loss of topsoil, compaction and other suburban realities that trees, meant for loamy and moist forest soils, confront along cul de sacs.
“If you could ask a tree, they’d want nothing to do with living in the city,” Hove said, smiling. “Everybody wants the maple and birch, but neither one of those trees should be planted in an urban yard. They’re forest trees.”
Still, examining aerial photos of Eagan, one dating from the 1950s and the other recent, Hove noted the city is leafier than 60 years ago. Tree-lined neighborhoods have replaced farm fields.
Development and healthy urban forests are not mutually exclusive, Hove said.
“They’ve done a pretty good job on this down here (in Eagan),” he said.
One hallmark of a good forestry program, Johnson believes, is community buy-in. In Eagan, buy-in took herculean form in 2001 when the community rallied around saving a 27-inch diameter bur oak, perhaps 150 years old, threatened by the saw as a result of city improvements.
Some $50,000 in private donations was raised to have the Grandfather Tree, as it was dubbed, dug out and moved. Its root ball was 25 feet across, 6 feet deep.
“It was either one of those deals where we pulled it off, I kept my job, or got fired,” Hove quipped.
Eagan’s forestry program strives for thriftiness. Downed or dead trees are mulched — 3,000 yards of mulch came out of a recent bad storm.
Another innovation had the city using lumber milled from city trees for paneling at a public safety center.
The arrival of Dutch elm in the 1970s spurred development of a forestry program in Eagan, Hove said. That’s true with many cities, he said.
“Is it expensive to have a (forestry) program? I think it’s more expensive not to have a program,” Hove said.
“I tell my boss the tree inspector talks to more people and shakes more hands than the mayor does,” he said, smiling.
Although giant root balls are not common in Minnetonka, Jo Colleran, the city natural resources manager, senses a deep appreciation for nature among residents.
“They love their trees, they love their wetlands, they love the natural features of the community,” Colleran said.
One task for Colleran and Emily Ball, Minnetonka forester, in part is community outreach. A comprehensive forestry section was created on the city’s website. The city sponsors an annual tree sale, with some 1,300 to 1,500 trees sold last time to about 700 households.
According to Ball, not everyone knows how deep to plant a tree or how to prepare a root ball.
“But we’re always working to improve that,” she said.
Urban forestry practices that make sense in one city may not in another. While some cities use vibratory plows to sever the shared root systems between oaks to combat the spread of oak wilt, sloping ground, garden walls and other unique factors can limit the use of trenching, Ball noted.
Human emotions also play a role in urban forestry.
“I think people (are) much less excited about protecting their elms than their oaks,” Ball said. “I think people get more attached to oaks.”
One lesson the Minnetonka city staff tries to teach is plant diversity. Insect pests tend to go for specific trees, Ball said.
“We don’t know what will be on our doorstep next. But if you have diversity of tree species, you have some resiliency,” she said.
One insect pest at the door is emerald ash borer, or EAB, an nonnative insect that kills ash trees.
Quarantines for Ramsey, Hennepin, Houston and Winona counties exist, making it illegal to move ash firewood or other ash materials, which could spread the infestation, out of these counties.
EAB hasn’t been found yet in Minnetonka, Ball said.
“We’ve been actively looking for it,” she said.
Hove noted that EAB has been spotted at Fort Snelling, and he isn’t hopeful.
“We assume it’s here,” he said.
Illinois is getting “slammed” by EAB, Johnson said. Still, he considers EAB a “wimpy” bug, one that, without human assistance, will advance slowly.
The tree experts urge landowners to select trees appropriate in size and to the climate for their properties. Hove warned against “volcano mulching,” or piling mulch high on tree trunks. Mulching is good, but volcano mulching is an invitation to disease.
Remember where trees like to grow, Hove suggested.
“Try to imitate what’s happening out in the woods.”
Tim Budig can be reached at [email protected].