Just like pipes and sidewalks, I believe trees should be treated like invaluable infrastructure. They don’t get the credit they deserve—they’re typically put in the “nice to have but can do without” category when it comes to budgeting decisions. However, they provide a number of environmental benefits, including reducing carbon dioxide, filtering and absorbing stormwater runoff and moderating temperatures. When used in an urban setting in conjunction with complete streets programs, they offer all of these benefits and then some.
The findings released in the latest National Climate Assessment are clear: our climate is changing and the effects are already being felt in communities across the country. More frequent and intense weather-related events continue to impact our infrastructure and increase the urban heat island effect. What does this mean for typical multimodal roadway users? Less comfort, lower air quality and, ultimately, less use. The report states that global action to significantly cut greenhouse gas emissions can substantially reduce climate-related risks. By investing in infrastructure to improve local air quality and reduce heat islands in urban areas, we can mitigate the risks in our local communities.
Tree canopies over greenways and complete streets help create a safer, more sensible and more equitable transportation system. In addition to their environmental benefits, trees create a barrier between sidewalks and the road and help to passively managing vehicle speed by influencing the context of our corridors. These vertical visual cues help to reinforce that motorists are no longer on a high-speed roadway and most drivers will respond by reducing their speed, helping to lower the speed differential between vehicles and multimodal users and drastically improve safety. Trees also promote walking by creating a more aesthetically appealing environment and add to the area’s placemaking.
However, according to American Forests Magazine, the average life span of a street tree is seven years. There’s no denying that the urban environment is harsh and a number of factors can contribute to a healthy street tree’s demise, including air pollution, lack of drainage and damage from vehicles. However, poor soil condition is the leading cause of poor tree growth.
By taking a context sensitive design approach, understanding the surrounding environment and the native plant materials, as well as the transportation needs of multimodal users, landscape architects, engineers and planners can work hand-in-hand to create corridors that are as enjoyable to use as they are effective. Keep reading to learn how we’re making trees – arboreal infrastructure – a priority on some of our projects and the design considerations we’re taking to help trees be an investment worth making.
Start with the Right Species
The first step in a tree’s success is selecting the correct species. It’s imperative to be familiar with the soil and climate type in the area so you can select hearty varieties that will withstand climate and environmental threats. It’s also important to plant an assortment of species throughout the community. A diverse tree population spreads the risk of damage during storms as well as creates a more aesthetically appealing space. Additionally, select species that don’t drop fruit, nuts or other debris. Loose droppings can lead to twisted ankles and bike wrecks.
Select the Best Site
Clearly, we can’t simply drop trees anywhere. Often a site’s location can offer clues on potential stresses that may impact tree health. It’s imperative to consider both above-ground and below-ground site attributes during the site assessment, a step that is often skipped and leads to tree failure. Variables such as light exposure, slope, wind, the presence of other trees and the location of overhead wires and lights can have a huge impact, as well as underground conditions like root area, soil pH, depth and compaction, and the presence of underground utilities.
A few strategies to overcome site challenges include continuous planting, or planting trees in areas with shared soil space so the roots can spread out between themselves, and structural soil, a material that can go underneath pavement to create space for roots.
When selecting placement, it’s also key to adhere to established zones in the right-of-way. While zones normally vary depending on the context and available width, there should be clear areas dedicated to pedestrian traffic, bike traffic or a combination of both, along with dedicated space for street furniture, amenities and landscaping. By incorporating a variety of elements, we can keep users connected to the corridor and taking advantage of all the street has to offer.
In areas where growing conditions might not be ideal, start with smaller trees. While big trees bring big benefits, they are more likely to be damaged. Smaller trees have an easier time adapting to the surrounding conditions. Our team is using this technique on the Town Branch Commons project, a multimodal trail, greenway and park system in downtown Lexington, Kentucky.
To maximize the budget for a project, look for opportunities to combine landscape architecture installations with stormwater management features such as bioswales and innovative drainage patterns. Not only do low impact approaches lessen the burden on our closed drainage systems, but they can also help to extend the life of budding street trees and potentially minimize maintenance with early investment in appropriate infiltration basins.
Make Streets for People
Ultimately, completing our streets is about creating an environment for all users, no matter their ability, and providing the spaces necessary for people to navigate safely and comfortably. While creating complete streets can be a challenge, we owe it to the communities we serve to develop flexible designs and work across professional barriers that sometimes exist between landscape architects and engineers. Just as bike racks and pedestrian lighting are considered integral parts of complete streets, trees should be considered vital to the success of a multi-modal transportation experience. Join us in treating trees as the valuable infrastructure they are.