Creating urban forests: Don’t wait 20 years for twigs to grow into trees
April 30, 2021
April 30, 2021
Investing in robust mature canopy from day one needs to be the new standard for all urban development projects
When we think of urban environments, the first images that often come to mind are of concrete, steel, glass, and brick. From buildings and sidewalks to roads and infrastructure, the built environment is generally short on greenery and long on man-made materials. While many of us live in cities, the reality is that humans are not made to survive in the built environment alone. Mature tree canopy plays a vital role in the urban environment.
Strategic tree placement has tremendous benefits. Trees can help cool the air between 5- and 14-degrees Fahrenheit, mitigating urban heat island effect. They also absorb pollutant gases (such as carbon monoxide and nitrogen oxides), filter particulates (dust, dirt, smoke), increase biodiversity, support pollinators, regulate and filter stormwater flow, reduce erosion caused by falling rain, create soil conditions that promote infiltration, reduce energy needs, and improve mental and physical health.
In both public and private new developments and redevelopments, trees and landscape are often an afterthought. They are left to the edges, maximizing interior spaces and minimizing conflict with the architecture.
Typically, trees used for these developments are young, two-inch caliper—not much more than tall twigs—and viewed as somewhat expendable. While their replacement costs less than larger mature trees, the reality is that in their infancy, they’re not providing much benefit. It can take 10 to 20 years for these little trees—if they make it that long—to begin providing any real shade or environmental benefits.
Despite growing awareness—at both the public and private level—of the importance of a robust urban tree canopy, mature trees are still consistently viewed as a nice-to-have option, rather than what they are: An indispensable utility of a modern city, a tool for public health, and a critical investment in the fight against climate change.
What if we valued urban canopy the same way we value running water and electricity? Would you accept being told it will take 10 years before you have electricity? Think of the outcry if we tried to fix a broken traffic light with a pole that would take 20 years to grow in and becomes useful.
Communities have long underestimated and undervalued the impacts of a mature tree canopy in a neighborhood. Overall, trees can bring as much as five times their cost in return on investment, according to the Arbor Day Foundation. Mature trees add about $10,000 in value for residential development and $15,000 for commercial development, and retail located near mature tree canopies brings in about 12% higher tax revenue, according to a study from Washington State University.
Mature trees add about $10,000 in value for residential development and $15,000 for commercial development.
Studies have also repeatedly shown that tree-covered commercial shopping districts are more successful than those without canopy. According to Urban Canopy Works, consumers showed a willingness to pay 11% more for goods and shopped for longer periods of time in shaded and landscaped business districts.
In areas with a mature tree canopy, studies consistently show people are healthier, happier, and safer. As we’re looking for ways to address historic inequities in the urban environment, the lack of mature, non-invasive trees are a dead giveaway of an underserved neighborhood. A study in Baltimore found that as the tree canopy increases, crime goes down—a 10% increase in tree canopy was associated with a 12% drop in crime.
In the fight against climate change, the importance of a mature tree canopy is even more stark. In addition to the other essential benefits, studies show that each mature tree can offset up to 48 pounds of carbon per year and even improve adjacent indoor air quality. A robust canopy can lower the need for air conditioning by 30% and decrease winter heating bills by 20-50%. A single mature tree can absorb 20 gallons of water per day, significantly mitigating stormwater runoff. Their infant counterparts accomplish a small fraction of that.
The urgency of climate change does not afford us the luxury of time. So why do we keep expecting two-inch caliper trees to address shade, air quality, placemaking, habitat, health, and equity challenges? It’s unrealistic, and it isn’t helping us meet the immediate challenges we are facing. Unfortunately, most developers don’t even know installing mature trees is an option and municipalities generally only use small trees.
Cities need a true urban canopy now—not 20 years from now. By reframing our view of the urban tree canopy as a vital public service, and sourcing trees that are up to the task, cities can realize benefits at installation.
Broadly positioning the idea of mature tree canopies as a basic public utility is the big-picture goal. So, what does that look like on a project basis? As urban designers and landscape architects, we know one of the biggest hurdles is justifying the extra up-front cost. The solution is planning ahead—way ahead —and keeping sight of the return on investment in the process.
The planning and design phase of a development can take years, sometimes a decade or more on big urban redevelopment projects. But trees and landscaping are often the last thing to be considered, arriving after all other work is complete. Honestly, they are often shoehorned into urban areas to meet the minimum municipal requirements. It’s a race to the bottom, where no one really wins. By training everyone in the development process to think about, and in some cases acquire, mature trees during the planning stages of a project, we can help mitigate cost and handpick trees that are best suited for the application. This represents a shift in mindset, but the reality is, the change is not all that complicated.
By using a process called “contract growing” to acquire mature trees, landscape architects work with contractors to track down, tag, and relocate medium-sized trees two to six years before the intended installation, rather than purchasing mature trees near the end of construction for nearly twice the cost—if you can even find them. On average, you’re looking at about $1,000 per inch of caliper between 5-10 inches (though once you get 17 inches and up, you’ll pay more of a premium). Contract growing offers substantial savings, but the larger benefit is increasing the odds of finding the specific trees you’re looking for and maximizing their long-term success once installed.
Right now, our team is using contract growing for a major project in Denver, which has less than 4% canopy coverage—the lowest of any major city in the US. For the redevelopment of Denver’s iconic 16th Street Mall, we aim to improve that figure. This project will bring 244, 7- to 10-inch caliper trees to one of Denver’s best-known pedestrian and transit thoroughfares. It’s a meaningful step forward into this new way of looking at growing canopy in urban areas.
We’ve been working for four years with the City and County of Denver, along with a tree procurement contractor, to achieve the forthcoming 16th Street Mall canopy. Our team scouted more than 5,000 trees at 10 nurseries in four states to find the best options for the mall that address historic character, transportation specifications, and canopy resilience goals. In all, 300 trees were selected and relocated to a dedicated contract growing facility just north of Denver in 2020. Our team will oversee the contract growing facility through the completion of the project.
Proper maintenance is another crucial aspect of creating a thriving urban tree canopy. Young trees are cheap relative to other development costs at about $600 to $800 per tree. For comparison, a single park bench usually costs twice that.
Property owners and cities expect to lose and replace several trees within the first few years of development, which resets the growing process all over again. Ensuring robust and complete tree care will save money in the long run and lead to better immediate outcomes.
When we consider mature trees at a project’s onset, we are better able to plan for soil volume and maintenance. So, more care goes into the tree from the start. Basically, we put them in the best position to survive.
Not only is a mature tree better protected as an investment, but there are also immediate benefits that don’t come with planting a younger tree. Starting at day one, there is true landscape, real shade, and meaningful environmental and social benefits. Not in 20 years, but from the first day.
We worked on a private mixed-use development recently that is a great example of the value mature trees deliver from the start. It took some convincing to get the client to sign off on purchasing a mature tree. The tree itself was just under $5,000 to purchase, transport, and install. It was a 5.5-inch caliper honey locust and was tagged, delivered, and installed within just five days. Luckily, they only needed one, so it wasn’t too difficult to find on shorter notice.
Yes, it was several times the cost of a standard tree—but when put in context of the $2 million, 18,000-square-foot plaza, the return on investment was crystal clear. We have shared this example with other clients. Their first comment? “We had no idea this was even possible. Why would we do it any other way?”
Mature urban canopies provide a sense of place and establishment in the public realm that is often lost in the redevelopment process. Generally, the public places a higher value on tree canopy than cities and developers. When we go into the public input phase of a project, trees are almost always the single most requested item.
People are drawn to places with great trees. No one wants to picnic under a two-inch caliper tree on a hot day. From a placemaking perspective, they create immeasurable value. Trees are critical for building vibrant communities and are often cited by the public as the most important community improvement. They go a long way toward creating equitable urban spaces and giving new projects a sense of establishment and place.
So, what are we waiting for?
With looming health, equity, and environmental challenges in the US, those of us driving the built environment are responsible for ensuring that we’re doing so in a way that is beneficial to the generations that come after us. That means planting more—and bigger—trees now.