Minneapolis, St. Paul try simple tubes to help grow young trees

Losing trees faster than they can be replaced, Minneapolis is looking to a simple but innovative device for help in restoring the urban canopy.

Seedlings encased in "tree tubes" will be planted this fall along Dean Parkway, as the city grapples with the loss of thousands of trees from June storms and invasive beetles known as emerald ash borer.

If the pilot project goes well, it could be replicated in other parts of the city.

The inexpensive plastic tubes, made by Eagan-based Plantra Inc., act as miniature greenhouses that shield young plants from wind, weeds and animals. Anchored in the ground with a fiberglass stake, they filter light through 1,084 vents and are designed to help trees grow straight and strong.

Currently, the 5,000 trees planted yearly by the Minneapolis park system tend to come from commercial nurseries and are often many feet tall and several years old by the time they're planted into the city's soil. That's because it is often difficult to grow seedlings in an urban setting, where their development can be thwarted by the missteps of people and the trampling and gnawing of rabbits and woodchucks.

Working with researchers at the University of Minnesota, the Minneapolis Park and Recreation Board hopes the tubes can foster the growth of more and longer-lasting trees by nurturing seedlings as they mature in place.

Establishing trees when they are smaller and younger gives them a better chance of becoming resilient to stresses in their environment and living longer, according to Chad Giblin, a university horticultural scientist working on the project.

Lais developed the 4-foot tubes to ensure that they offer just the right amount of light and support after finding that previous versions gave the plants too much shade that caused them to end up weak and spindly.

The technology, already used on Minnesota highways, also has gained traction in St. Paul. University researchers and volunteers planted 40 oak seedlings in tubes in the city's Newell Park in June, and they are expected to plant another 100 to 150 trees encased in tubes in the High Bridge Dog Park next month.

In Minneapolis, the trees purchased by the Park Board have trunks that are typically 1¾ inches in diameter and can be up to 12 feet tall.

Planting young trees is less expensive, but it can be more challenging, according to Ralph Sievert, the Park Board's forestry director. They are vulnerable to getting hit by, say, a lawn mower in urban parks. Even in more natural parks, such as Theodore Wirth, seedlings can be "out-competed" by surrounding vegetation.

Giblin, a self-described tree geek, said the goal is to get more healthy trees in urban and community forests, "and tubes are presenting themselves as being one way that cash-strapped communities can have another option.

Cities nationwide are grappling with how to replace a dwindling supply of trees. The U.S. Forest Service found last year in a study of aerial photographs that urban areas are losing 4 million trees a year, while paved surfaces are expanding.

More widespread, comprehensive programs may be needed to stem that decline, researchers concluded.

The urban forest must constantly be renewed, just like the human population, said Don Willeke, a lawyer living on Dean Parkway who is working with Giblin on the project.

"I tell people, 'While all children should be adopted, if you had your choice, would you adopt a 6-month-old, a 6-year-old or a 16-year-old? Which one would adapt better to your family?' " he said. "And it's the same with trees — a tree that grows from a seedling in place, or at least a small tree in place, is going to adapt better to its new home."

Maya Rao • 612-673-4210