For months, motorists on the East-West Tollway have been intrigued with the mounds of dirt and clay up to 40 feet high going up along the Morton Arboretum`s border with the toll road in Lisle.
These are berms, and they are part of an unusual, three-pronged experiment.
They will serve as barriers to noise from traffic on the adjacent tollway and to salt spray and airborne vehicle pollutants. They also will become test plots for trees and shrubs and methods of seeding that the arboretum hopes will generate trees tolerant to urban stress and inexpensive shortcuts to planting trees along expressways in urban areas.
More than a million cubic yards of fill from suburban construction jobs has been used to form berms designed by Anthony Tyznik, arboretum landscape architect.
A West Chicago contracting company, A.A. Conte & Son Inc., is donating the fill from work it is doing on other projects in the area, the arboretum said.
The related landscaping and planting is funded by the $2.5 million trust fund eastablished by the Illinois State Toll Highway Authority as part of its agreement with the arboretum over the taking of more than 16 acres from the arboretum to build the Du Page Tollway.
While the berm construction has been going on, arboretum Research Director George Ware has been raising seedlings in greenhouses and nursery plots to be planted on the berms next year. These included hybrid poplars, elms and maples; shining (winged) sumac; and other species.
The effects of salt spray from vehicles on various types of trees are being studied by the arboretum`s Urban Vegetation Lab, funded by the tollway trust.
Onto the berms will go trees and shrubs known to be salt tolerant and those whose tolerance is uncertain.
Some portions of the berms will be planted in prairie vegetation, others in certain grasses to test their survival on clay fill.
Among the new trees to be evaluated are two from Asia and one from the United States. One is the Chinese white poplar, which Ware said is rare in North America.
Another is a Japanese aspen, grown at the arboretum from seed received from Japan. And the third is a slender ``Tower`` poplar from an Idaho nursery that gives the windbreak effect of the Lombardy poplar but is much longer lived.