September 15, 2012
Final report notes Green Highways study an important first
An inspection of the 401 sites in 2011 showed some species were doing well, while others had not survived the year.
The final report on the Greening the Highways project states that data gathered over the two-year period is extremely useful, but further study is required.

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

The partnership 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 were chosen for resistance to winter highway salt and summer dry spells.
The report begins, “Trees are the most effective systems for carbon sequestration, however, lack of data regarding tree survival and means of promoting survival in highway right-of-ways (ROWs) have limited the conversion of highway ROWs from carbon sources to immense carbon sinks.”

There have been no previous studies of tree survival in highway right-of-ways. The planting sites were along the 401 at the junction with the 427 and three sites next to the Allen Expressway.  

The first long-term data collected in July 2011 and September 2011 indicated survival is dependent on species, site and production environment used before out-planting. Following winter of 2010-11, the survival range was 100 per cent for trees grown under retractable roof greenhouses (RRG), to five per cent for field-produced trees. The report says the RRG trees in Sept. 2011 had the highest survival (without trees being replaced) with 100 per cent survival for Acer ‘Autumn Blaze’ (site 5 and 6), Betula jacquemontii (site 6), Celtis occidentalis (site 5) and Gleditsia triacanthos (site 4, 5 and 6).

With millions of miles of roads and acres of ROW land, the study states that opportunities for increasing Ontario nursery production to meet future planting needs are substantial.  
“We have identified species that are doing well in the 401 ROW sites such as Gleditisia triacanthos, Celtis occidentalis, and Acer freemanii. Species that have poor survival include Acer pseudoplatanus, Betula lenta, Betula papyrifera, and Ginkgo biloba. Generally, these poor species were below grade at planting and were produced in a polyhouse environment,” says the report.

The study concludes that the polyhouse environment provided the lowest survival rate at 39.8 per cent, compared to 57.5 per cent for field-grown trees, 68.2 per cent for the RRG and 66.1 per cent for VRG (vented-roof greenhouses).

The report states, “This project also involved growing a tree liner crop at the Vineland Research and Innovation Centre RRG (for out plant spring 2012). The three container substrates used had significant impact on caliper, especially height growth for Cercis canadensis.   

“Comparisons of out-plant survival of other unknown source bare-root liners of Acer freemannii ‘Jeffersred’ and Celtis occidentalis versus RRG or vented-roof liners out-planted at the 401/Allen Expressway and 401/427 intersections were conducted and indicated the RRG provided the highest survival of both species.”

The report concludes that the RRG production method promoted better than expected tree survival. “The poor survival shown by the polyhouse environment trees was unexpected.” There was also concern expressed about some of the trees being planted too deep. “In future studies with MTO, the planting of experimental trees should be supervised by a researcher responsible for the project,” states the report.

The trees for the 401 sites were planted by a contractor who successfully obtained the planting and two year maintenance contract. The report reveals that this added an additional level of complexity to the study. “Several trees have been inadvertently ‘weed whipped’ at the base and some completely cut off. Many trees, especially of field grown oak, have been replanted making survival on the sites seem higher than if no replant was conducted. It has also inflated the survival percentages of certain production methods and species over other methods and species that have not been replaced and have survived since the June 2010 planting.”  

As a result of the Ontario project, Ohio State University researchers have initiated a cross-border (Canada/U.S.) initiative with the sites in Canada (2010), two in central Ohio (2011) and two more this year.

Dr. Hannah Mathers was senior research fellow at Vineland and helped  coordinate the highway project, before ending her contract and moving back to Ohio State University. She hopes to continue evaluations of these trees for many more years at Ohio State. “Results obtained after the 2012 spring replant will be most valuable to provide actual survival data of trees along highways,” says Mathers.

The report concludes with a wish list:
  • That MTO starts specifying species found in this project to be of higher survival for roadside plantings.
  • That MTO advocates the use of trees grown in Ontario for Ontario highway sites.
  • That MTO advocates the use of tree whips produced in RRG greenhouses planted densely (6X6), versus larger caliper trees planted on large spacing.
  • That Ontario nursery growers adopt the RRG production methods for increased survival of trees after planting into landscapes or roadside sites.

“We’re excited about what these trials could mean for Ontario. The more trees we can plant successfully along our highways, the better it is for our environment and it can help us create a more viable farm sector,” says LO executive director Tony DiGiovanni. “Being able to grow liners in Ontario means that $30 million in sales will stay in our province rather than going out west — and a tremendous reduction in transportation.”