Your high school science teacher was right – trees are the lungs of our cities.  

They enhance air quality by removing pollutants, help regulate local climate by allowing water to evaporate into the atmosphere, reduce soil erosion, and provide shade for other vegetation.

As part of GO Expansion – the largest transit expansion program in Canadian history -Metrolinx has been coordinating planting of trees since last year to offset and surpass the loss of the ones that have to be removed to build and operate expanded GO service. 

Of the approximately 22,000 new native trees and shrubs Metrolinx funded across the region in 2020 as compensation, the majority were coordinated through Toronto and Region Conservation Authority (TRCA).

Here is a sneak peak at how work like this comes together.

The Why: making way for a better and cleaner transit system

By moving away from diesel trains, GO Expansion will bring better air quality to the entire region. In order to accommodate overhead wires and other electrification infrastructure and to support the faster, more efficient and greener transit system, trees and vegetation within GO-owned rail corridors will have to be protected, trimmed, and removed.  

Metrolinx has been leaning on the expertise of local conservation authorities across its service area to determine and implement the proper tree compensation strategy for these changes to rail corridors. The guiding principles for Metrolinx projects going forward resulting from this collaboration were laid out in the 2020 Metrolinx Vegetation Guideline.

When it’s all said and done, everyone in the Greater Toronto and Hamilton area will benefit from modernized and clean GO service as well as increased tree cover.

The Who: TRCA is instrumental to compensation planning and implementation

Conservation authorities’ jurisdictions are based around watersheds, which can span across numerous municipalities. TRCA’s authority in particular covers six upper-tier and 15 lower-tier municipalities. Some of Canada’s largest and fastest growing municipalities, including Toronto, Markham, and Vaughan, are located entirely within the TRCA watershed jurisdiction.

Because the majority of trees that will have to be removed to accommodate GO Expansion are located within the City of Toronto, Metrolinx has been relying heavily on TRCA’s expertise and aligning with their goal of sustaining and improving the ecological health of the region.

”TRCA leads and supports numerous ecological restoration and compensation projects while keeping the larger lens of the overall health of each watershed in mind,” explains Kelly Jamieson, TRCA’s senior project manager of restoration projects.

Jamieson has been leading the planning and application of TRCA’s planting projects related to the GO Expansion program.

“In cases such as GO Expansion, we provide the strategic direction as far as selecting and planning with our municipal partners for the benefit of local ecosystems, while also ensuring that proper municipal compensation requirements are followed,” Jamieson says.

The Where: prioritizing planting sites

In most cases, replacement trees cannot be planted in the same area they are removed from, as clearance is needed for new infrastructure. That’s why Metrolinx works with corresponding conservation agencies where the removals are taking place to replace trees within the same municipality and watershed.

“TRCA maintains a database of over 10,000 restoration opportunities,” Jamieson says.

“They are classified by type, size, ease of implementation, and their ability to improve the larger surrounding habitat. Healthy, functioning, ecosystems are needed to produce ecosystem services.”

The What: choosing the right palette of vegetation to plant

Experts at TRCA say that specific planting plans are developed for each individual site.

 “We look for appropriate reference sites in the immediate area and the native species which make up that natural community and target to replicate its makeup, so that it fits like a puzzle,” says Jamieson.

For example, last year at Rouge National Urban Park, as part of the GO Expansion compensation program, TRCA planted among others, Silver Maple, Balsam Poplar, White Pine, and Red Osier Dogwood. 

Only native species are included in these plans and invasive species are strategically controlled during initial pre-planting site preparation. TRCA officials say invasive species were largely introduced into the area by people for culinary, aesthetic, or gardening reasons (garlic mustard is an example), although there are accidental introductions as well. Because they do not have natural predators here, they dominate native species and force them out.

The When: ensuring the long-term health of newly planted trees

TRCA hires seasonal staff and engages volunteers to plant new trees in addition to its own full-time complement. Planting season typically starts in mid April through to early June – once the ground thaws and then resumes in the fall. Between September and December trees begin to go dormant and can be transplanted.  

TRCA says they try to limit planting new trees in the summer because the higher temperatures and less rain makes it much harder for them to establish themselves in a new environment.

Each planting sites carries a five-year assessment term with check-ins, typically at years one, three, and five. Following each assessment adaptive management can be implemented to offset the possible effects of hot summers, animals foraging in the area and invasive species.

Metrolinx is also working with other conservation authorities across the region including Conservation Halton, Lake Simcoe Region Conservation Authority (LSRCA), Credit Valley Conservation (CVC) and Central Lake Ontario Conservation (CLOCA) where changes to rail corridors will occur in preparation for GO Expansion.

Planting season is already in full swing so stay tuned for more stories from compensation planting sites throughout the region. 

To receive detailed updates about work within rail corridors related to GO Expansion and about other Metrolinx projects near you, please sign up for regional newsletters at Metrolinx.com/newsletter.