Street trees add green features and design value to cityscapes
What are street trees?
Green landscaping adds color and texture into urban communities by using organic elements, providing relief from an otherwise built-out city environment. Street trees and other softscape elements are value-adding community features that increase greenspace, reduce air pollution, provide shade, and maintain ecological balance.
From an aesthetic standpoint, trees along sidewalks are used to enhance streetscape character and should be designed in harmony with pre-existing infrastructure. Consider street lighting and buildings, as well as benches and existing trees, before planting new street trees. The tree’s texture, bark and leaf characteristics, and density should fit the climate and look of the surrounding area.
Street trees also positively affect neighborhood walk appeal. A higher walk appeal means people in the area enjoy their walk more, encouraging them to walk further and more frequently. As a neighborhood increases its walk appeal, the economy benefits as property values in surrounding areas often improve as well.
Tree grates protect urban trees
Street trees are subject to more abuse than trees in a quiet park or forest. Urban trees that live in demanding cityscapes need protection. Tree grates are particularly useful in rigorously-travelled sidewalks, or when sidewalk widths limit pedestrian traffic flow—where some pedestrians will be forced to step on or around the base of the trees.
A tree grate is a type of metal grating that is installed to be flush with the pavement around a tree. Grate slots allow for air, sunlight, and water to reach the tree roots while the surrounding soil is protected from pedestrian traffic and remains uncompacted. Tree grates create a protective barrier, providing more loose soil and space for tree root development. They also provide a decorative element along ceremonial streets, matching a street’s design style.
What to consider when selecting street trees
Before selecting and planting street trees, the planner must always account for how demanding the urban environment can be. City trees typically have high drought tolerance with the ability to stay hardy regardless of the climate. They should be carefully selected and adapted to soil and microclimate conditions and designed to be durable and long-lasting.
Tree selection for commercial and residential streets
Selection of street trees also depends on the street type, as well as the goals for the particular street. Ceremonial streets, which are streets that serve as celebrated civic spaces for various events and parades, are designed with consistency and formality in mind. This is also true for major commercial streets, where street trees follow the city’s pattern of formal and consistent planting styles that facilitate place recognition. For these wider streets, larger trees with overarching canopies and medium density foliage will work well.
For residential and smaller streets, street tree planting can be more diverse and less formal. Try medium-sized trees with light- to medium-density foliage. For narrower streets and alleys, trees with columnar forms are appropriate. The planting style can reflect the neighborhood preference and interesting variety exists from neighborhood to neighborhood. However, it is still important to use consistent plantings overall.
General guidelines when selecting the right tree for commercial and residential streets:
- The mature size, texture, and color of the tree should reflect the street design goals.
- The mature canopy should not interfere with street lighting, signage, or building fronts.
- The crown of the tree at maturity should not affect surrounding infrastructure or overhead high-voltage power lines.
- The root systems should not affect utilities, sidewalks, or curbs.
Tree root considerations
Equally important in tree selection is the tree’s rooting system. Trees typically have either deep taproots, or shallow lateral roots. Deep-rooted trees have roots that reach deep within the earth and this is how they seek out water and nutrients. Contrastingly, shallow-rooted trees spread their roots laterally. This means that their roots are spread out near the soil surface and they seek out rainwater from the tree’s canopy. Lateral roots run the risk of growing too large, disturbing and heaving up cement sidewalks. For urban streets and sidewalk trees, deep-rooting trees are ideal as their rooting system helps them to survive. They will also not interfere with cement surfaces and tree grates.
When it comes to planting street trees, the distance between the tree and sidewalk differs depending on the expected mature height of the tree.
How far to plant a tree from the sidewalk based on tree height:
- Trees reaching up to 30 feet high should be planted a minimum of 3–4 feet from sidewalks.
- Trees reaching up to 30–50 feet high should be planted a minimum of 5–6 feet from sidewalks.
- Trees reaching up to 50 feet high should be planted a minimum of 8 feet from sidewalks.
The best tree species for sidewalk planting
The best trees for sidewalk planting are those that are deep rooted and find nutrients from deep within the soil. They do not have rooting near the surface, minimizing the chances of roots pushing through tree grates or pavement.
Top 10 sidewalk trees for North American climates
- Cherry tree
- Japanese lilac tree
- Pear tree (ornamental pear trees)
- White oak
The environmental climate and aesthetics will also influence the type of tree that is most suitable for planting. Sidewalk trees are meant to add charm to the street while appreciating pre-existing design palettes and neighborhood character.
Ensuring a healthy lifespan for urban trees
The likelihood of urban trees flourishing and staying healthy depends greatly on proper tree selection. Careful planning is required in order to find trees that are compatible with the climate and environment in which they will be planted. Long-term street design considerations and infrastructure changes should be kept in mind, as well as all above- and below-ground utilities. The mature height and spread of trees, as well as drought and insect resistance are all key considerations to ensure that sidewalk trees have a promising future in enhancing any bustling cityscape.