Planting for the future: Enhancing communities with a thriving tree canopy
February 16, 2017
Trees are an essential component of community design, and need to be considered from the outset
The best neighborhoods in our cities have thick tree canopies. Street trees and front yard trees are an essential component of high quality urban design. Some of the most ardent criticisms of some new development is that they are barren of trees. But designing a strategy to create a successful tree canopy is much more complex than most people imagine: it takes a careful integration between planning, landscape architecture and the engineering infrastructure, predominantly transportation and utilities, to make it work.
Why trees?
Trees add beauty to neighborhoods. They add color and variety, and they create the sense of enclosure that comforts people. Ample evidence shows that a healthy tree canopy contributes to improved physical and mental health. As if all that weren’t enough, trees improve microclimatic conditions and, if placed correctly, they can help reduce urban heat island effects and improve the energy efficiency of our homes.
Mature neighborhoods, mature trees
New neighborhoods created in the post war era appear today to have lush tree coverage in along the streets and in front yards. There are a number of reasons why this is the case. As inefficient as some of these neighborhoods are from the perspective of land consumption, the large lots with houses set well back from the street create ample room for trees to grow and thrive. There was a concerted effort by many municipalities to introduce new tree plantings in the 1970s and 1980s, and the trees planted then are now mature, majestic, and fully grown. In addition, it was typical to string electricity and utility cables on overhead lines at rear lot lines in this era, so there are far fewer utility conflicts. With communities predominately dependent on cars, sidewalks and multiuse pathways were less common, which allowed for more boulevard space for the trees.
Design challenge: Smaller lots
In contemporary new developments, planning renderings often show a lush regular rows of street trees regardless of the development type. But the reality is that there is considerable competition for space in the public realm, and trees become hard to place.
Our emphasis on more efficient land consumption means that lots are narrower. If a lot has a front yard parking pad, then the total proportion of the site that is free to plant trees is much smaller. In many neighborhoods, for certain compact dwellings, we have dramatically reduced or eliminated front yard setbacks and the requirements for outdoor amenity areas. The result? We reduce the amount of space available for tree planting in the boulevard. And depending on soil type and conditions, we also limit the size and type of trees that can be planted, because some tree roots could affect the structural integrity of nearby dwellings.
So we see more large, single family with ample floor space, but placed on narrower lots. For townhomes and terrace suite buildings, soft surfaces outside the dwellings—surfaces such as grass—give way to hard surfaces, such as concrete. One solution may be to move parking away from the street in rear lanes or to parking areas, but that is not always a welcome strategy in some communities due to maintenance questions and the concerns of long term owners. The multi-modal transportation requirements for the community puts added pressure to install wider sidewalks and paved pathways, taking away green space available for the trees.
Design challenge: Utility conflicts
The second design challenge is the conflict with utilities. As we have moved to buried utilities for aesthetic and resiliency against weather damage, the land below a street right-of-way is in high demand. Most utilities have strict requirements for setback from each other, and from trees. In some cases, setbacks are required for safety while, in others, setbacks help prevent construction damage by above-grade equipment to tree roots or buried lines.
Design challenge: Picking the right tree
The third design challenge to creating a successful tree canopy, is using appropriate species of trees, species that are both sufficiently mature to survive, and which have an appropriate growing medium and soil volume. Communities lose many street trees due to invasive species, storm damage, diseases, and infestations. On the other hand, not all trees can survive urban conditions: these trees suffer from poor soil conditions and drainage due to compaction, contamination from de-icing salt, or they are planted in small pits, limiting their growth.
If we want healthy tree canopies, then we must ask key questions when planning these new contemporary developments, questions like: How close to the street should we plant trees? What visual character do we want to develop? Is the goal to create a continuous green canopy along the street edge or over the roadway? In cold climates that require de-icing salt, trees need a minimum setback from the street edge which, combined with sidewalks, reduce more significantly the effect of the overhanging canopy over a roadway. All these questions may lead planners to rethink the arrangement and use of the public realm portions of roadways.
A thriving tree canopy
A successful strategy for incorporating street and front yard trees involves:
- Committing to a tree strategy early in the design process
- Using integrated design teams involving landscape architects, engineers and planners
- Carefully choosing species of trees while taking into account biodiversity, soil conditions, available size of the growing area and potential conflicts
- Understanding that local soil conditions affect the approach. If soil conditions are poor or there are problems with clay, houses may need to be set back further in order to create enough area for trees to thrive
- Consulting with utilities early in the design process, and developing careful strategies for utilities placement that take into account the competition for space
- Developing more flexible standards for clearances between the municipal and utility infrastructure and the trees, and for ‘clustering’ the utilities together or under sidewalks to allow for more unencumbered boulevard space
- Developing drainage strategies that consider tree health, which may include constructed tree pits, bioswales, or soakaway areas that provide irrigation into the soil medium
- Giving developers credit for trees planted outside of the right of way if the space within the right of way is insufficient or inappropriate
- Developing clear maintenance plans for trees in first years after planting, including educating the new residents about what they can do to promote the success of their trees
Thick tree canopies add enormous value to our cities and bring residents an improved sense of well-being. If we are to achieve these canopies in today’s more compact communities, we must ensure the design process is highly integrated. By implementing these successful design strategies, in time, new communities will enjoy the same thriving tree canopies found in mature neighborhoods.