Tree-planting update: what's going in the ground this year?

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Forestry

This year's models: MPRB's top tree species for 2018 plantings

serviceberry blossoms
Serviceberry trees are both good-looking and notoriously hardy.

Chestnut blight fungus. Dutch elm disease. Emerald ash borer infestations. These successive disasters have wiped out billions of trees throughout the U.S. over the past century, reminding us that however stalwart they seem, trees are also vulnerable. By targeting single species of trees, these diseases helped to prove that diversity is the key to a healthy urban forest. 


The Minneapolis Park and Recreation Board (MPRB) has been expanding the range of public tree species in the city for the past half-century. But before a species is widely introduced, it undergoes an experimental trial as part of MPRB's ongoing collaboration with the University of Minnesota’s (U of M) Department of Forest Resources. 


The partners coordinate trial plantings, sharing information on species that are growing in U of M research environments as well as "in the field": that is, along streets and on parkland in Minneapolis. Thanks to U of M research, MPRB has been able to plant hundreds of disease-resistant cultivars of elm trees and an array of other options, as it works to develop a diverse, healthy and resilient urban forest. 

 

What makes a top tree?

Beauty alone won't cut it. Trees at the top of MPRB's planting list must also stand up to a host of challenges, including:

  • Restricted growing space due to buildings, utility lines, curbs, sidewalks
  • Drought
  • Salt from road maintenance
  • Compacted soil
  • Air pollution 
  • High winds
  • Damage from vehicles, lawn maintenance, snow removal


The species below have proven their mettle and make up more than half of the 8,000 trees that are getting planted this spring. 


river birch

River Birch 

Long a mainstay of floodplains along the Mississippi River, this species has become common throughout southern Minnesota. It is noted for its striking curled bark, tolerance for compacted soils and resistance to a pest that attacks many other birch species.

Buckeye - various cultivars

This tree provides dense shade and spectacular fall color; the autumn splendor' cultivar, among those being planted by MPRB, was developed at the U of M. It has an unusual palmately compound leaf structure (five leaves radiate from a single stem) and yellow spring flowers that are currently in bloom  

buckeye tree
Kentucky Coffeetree

Kentucky Coffeetree

As its name indicates, this tree grows in the upper South of the U.S. but has also long been a part of the Minnesota River prairie. The female trees of this notably tough species are distinguished by seed pods that persist through winter - but only seedless cultivars will be planted along Minneapolis streets.

 

Oak - various cultivars

This mighty and long-lived species was the focal point of the once-common oak savannas that spread across the Midwest. Today it's also esteemed for the benefits it provides as a habitat for an amazing array of insects and wildlife. 

 

Quercus robur
serviceberry tree

Serviceberry
A tried-and-true Minnesota favorite, this is among the smaller species MPRB is planting. It boasts white springtime flowers (in bloom right now), dark blue summer berries prized by birds and humans alike, and gorgeous red autumn leaves. 

Catalpa

Common throughout the Midwest, the catalpa readily adapts to adverse growing conditions. Its glossy, heart-shaped leaves provide maximum shade, and large clusters of fragrant white flowers in mid-June are an ornamental bonus.

 

Catalpa
London plane tree

London Plane
First noted in their eponymous city in the mid-1600s, the plane tree is remarkably long-lived, thriving amid pollution and enduring drought. Those qualities, plus its dense shade, beautiful mottled bark and impressive size, have made it a popular urban tree around the world.

Gingko Biloba
MPRB is planting fruit-free gingko cultivars, to the relief of anyone who's smelled its fruit ripening in the fall. The gingko is famed as a living fossil, meaning it has existed virtually unchanged for hundreds of millions of years - or ever since dinosaurs may have been munching on that odiferous fruit. 

gingko

2018 trial plantings 

MPRB is also testing several species that are more common to warmer climates, but gaining ground farther north, thanks to innovations and newer cultivars: the hardy rubber tree, whose thick leaves resemble those of the elm; the bald cypress, a swamp native developing a new reputation as a tough and adaptable street tree; and the American sweetgum, another southern species once used for soaps, adhesives and pharmaceuticals.  


Next update: Which trees get planted where?

MPRB's science-based approach to "prescribed diversity" within the urban forest will be covered in a couple of weeks


In the meantime: