August 15, 2014
Vineland Research and Innovation Centre is continuing the Greening the Highways study project, in conjunction with Landscape Ontario and the Canadian Nursery Landscape Association.

The project is a five-year study of tree growth at five highway sites in Niagara. The trees were planted as would normally be done by a Ministry of Transportation contractor.

Darby McGrath, research scientist, nursery and landscape at Vineland, is conducting the study.

She says when she began the research, she really wanted to determine what actually is driving tree mortality. McGrath said speculation included road salt, high winds and pollution as causes of tree deaths along highways.

She points to soil compaction and the quality of soil at the Niagara highway sites as a factor. In a newspaper interview, McGrath is quoted, “We’re not saying that road salt doesn’t influence certain plantings, and that pollution can’t be damaging, but most of the time it won’t matter because the trees won’t survive long enough for those things to actually have an influence.”

The soil at the test sites is heavy clay that is re-used as fill. Once that heavy soil is compacted, the roots of trees have a difficult time fanning out to reach water and nutrients.

“The soil conditions are not unique to these plantings,” says McGrath. She says that it’s not unusual to see similar soil conditions at road construction sites, housing developments, etc.
The researcher says that when the trees are planted at the highway sites, holes are dug, trees put in and everyone walks away.

At two test sites, four species of trees were planted: honey locust, eastern red bud, Freeman maple and common hackberry. McGrath says the best growing tree was the maple, and the worst was the hackberry.

McGrath is quoted in the article, “We want to see now what the difference is for those species, along with the difference between them in the prepared and non-prepared soil.”
The trees at the five sites, once planted, are left to live or die on their own. They are not watered or fertilized.

Results of the study will be turned over to the MTO to guide it in future plantings.

The final report on the Greening the Highways project on sites along the 401 in Toronto came in 2012. Data for that report was gathered over a two-year period.

The project began in September 2009, when the Minister of Transportation at the time, Jim Bradley, announced that $1-million was being allocated to the project. Planting began in the late spring of 2010.

The partnership also included Landscape Ontario, Vineland Research and Innovation Centre and the Ontario Ministry of Transportation.

About 2,000 trees were grown at Vineland, as well as Braun, Willowbrook and Sheridan Nurseries. Trees chosen for the project were those resistant to winter highway salt and summer dry spells.

The first long-term data was collected in July 2011 and September 2011. The planting sites were along the 401 at the junction with the 427 and three sites next to the Allen Expressway.
The final report on the first study was written by Dr. Hannah Mathers. Mathers concluded that in future studies with MTO, the planting of experimental trees should be supervised by a researcher responsible for the project.