Hydro Lines and Corridors

Hydro lines and hydro corridors are energy infrastructures within urban areas and Canadian urban forests. The location of hydro lines in Canada, above or below ground, depends on when the urban areas were developed and built. Aboveground hydro lines are found along city streets, sidewalks, and laneways in older subdivisions or neighbourhoods in Canada. One of the most common fixtures on Canadian streets is utility poles with hydro lines attached. Due to maintenance standards, this energy infrastructure interferes with trees and constrains tree canopy development, growth, and height (Appleton, 2006). In newer developments and subdivisions, hydro lines are buried underground, where they have the potential to restrict root growth and tree planting. In both cases, urban trees share limited growing space with these utility fixtures, restricting how many trees and which species can be planted under hydro wires. The design, planting, and maintenance of trees within or near hydro wires always requires careful considerations of factors such as available growing space, proximity to hydro wires, future risk of tree interference with electrical infrastructure, compliance with local regulations or utility guidelines, tree species selection, tree height and canopy spread at maturity, growth habit, long-term maintenance requirements, tree trimming or pruning, accessibility for maintenance crews, the potential for breakage during storms or high winds, visual aesthetics, and community impact  (Dupras et al., 2016; Appleton, 2006; Bloniarz, 1992; Browning & Wiant, 1997). 

Hydro Lines

In the planning and design phase, landscape and tree planting plans in areas under or close to hydro lines should consider tree height and canopy spread at maturity. It is crucial to carefully plan tree planting based on tree size at maturity, growing conditions (soil, nutrients), and distance from hydro lines to determine which species are suitable to plant under hydro wires. Choosing the right tree species can reduce pruning and maintenance intensity, leading to healthier, more aesthetically pleasing trees along streets and under hydro lines. More importantly, the right tree species can significantly reduce the risk of power outages and accidental fires, resulting in economic savings (Bloniarz, 1992). Power companies and many Canadian municipalities (see Canadian Online Resources section) have a list of recommended tree species that are suitable to plant adjacent to power lines (Appleton, 2006).

It is standard practice for utility companies across Canada to perform routine tree maintenance along power lines and corridors (Parent et al., 2019; Perrette et al., 2021). Utility companies also maintain street trees and park trees that are within range of hydro lines. To ensure safety and hydro wire clearance, trees under or near hydro lines are managed on an individual basis. Maintenance around power lines can only be done by trained and certified professional arborists. Canadian utility companies often develop and provide various tree resources, including tree pruning maintenance standards, hazards to watch for, and a list of certified arborists in the area on their websites (see Canadian Online Resources section). Trees along power lines are usually pruned at 5-6 years intervals, but some can be as frequent as 3 years (Perrette, Delagrange, & Messier, 2020; Browning & Wiant, 1997; Millet & Bouchard, 2003; Millet, 2012; Lecigne et al., 2018). A good understanding of tree species biology can help improve pruning practices, lessen its impact on trees, and reduce pruning costs (Perrette, Delagrange, & Messier, 2020; Millet, 2012). Additionally, consistently assessing the overall health of a tree can help determine the frequency of pruning and its suitability for extensive pruning (Perrette et al., 2021). This, in turn, can inform maintenance planning to optimize the allocation of time, human resources, and funding. 

Hydro Corridors

In addition to hydro lines, urban areas are often intersected by transmission corridors, commonly called hydro corridors. Hydro corridors are long and narrow linear spaces, covered by shrubs and grasses, used by hydro companies for high-voltage hydro transmission, which requires very tall transmission towers. These areas have strict regulations regarding the type of vegetation growing under transmission lines due to safety concerns. Trees are prohibited under and within a certain distance from the transmission lines because their height can pose safety risks. Electricity can easily arc out of transmission lines and jump into the taller tree branches. As a result, vegetation directly under hydro lines in hydro corridors should be low. Different hydro companies and municipalities may have different rules, but most guidelines indicate that woody vegetation over 6 meters is not permitted in these areas (Hydro Ottawa, 2025).

The hydro corridors themselves can support native plants and provide habitats for wildlife, insects, and birds. They often act as ecological corridors and serve as a landscape linkage between urban centers, rural communities, and beyond (Hydro Ottawa, 2010). There has also been a repurposing of how land under hydro corridors is used in urban areas, from providing recreational spaces and supporting urban gardening to strategically enhancing urban biodiversity and improving ecological connectivity in Canadian cities. For example, the Meadoway 16-kilometre-long hydro corridor in Toronto has been gradually transformed into a native meadow and will become a linear urban park when finished (TRCA, 2022). Hydro corridor lands have been incorporated into the urban green system to support recreation in Winnipeg (Sage Creek, 2023) and urban biodiversity restoration in Calgary (City of Calgary, n.d.). Similar efforts towards restoring hydro corridors and converting them to native plant communities and wildlife habitats are happening across many Canadian cities, such as Montreal, Guelph, and Ottawa, to name a few (Hydro Quebec, 2024; Milkweed Journal, 2016; OSC, 2024).