Editor’s Note: This is the second article in a four-part series that examines the complex relationship between green spaces, public policy and the urban heat island effect, while highlighting citizen-led strategies to mitigate the sweltering heat. Part 3 will tackle the problem with power lines.
In 1857, the people of New York City decided they wanted a park. The famed landscape architect Frederick Law Olmsted won the city’s design competition to develop a green space in the middle of Manhattan, between what are now 59th and 106th streets, resulting in the creation of Central Park.
About 40 years later, Olmsted was commissioned to design another Central Park, this time in Louisville, Kentucky. Both parks have successfully anchored their respective communities to a pristine space for the public. A natural refuge in what was otherwise a dense, noisy, and often polluted environment.
What’s frequently overlooked is the fact that Central Park in New York was originally a network of small villages inhabited by Irish immigrants and freed slaves who purchased the land approximately 50 years before the park’s construction.
Similarly, Louisville’s Central Park was the former site of the Southern Exposition building and had the unique distinction of being the largest wooden structure in the world when it opened to the public in the summer of 1833.
The thing to remember is that the central parks of New York and Louisville did not evolve from an “undeveloped” parcel of wilderness. Urban green spaces are a choice. They exist only as a result of human intervention.
In the first installment of Green Space, we discussed how car-centric policies have effectively transformed downtown into a giant parking lot and increased the city’s urban heat island (UHI) effect. Here, we focus on Louisville’s green infrastructure, trees, and the administrative inattention that led to the demise of both.
We should begin in 2015 when Louisville officials commissioned the Ohio-based Davey Institute to assess the condition of the municipal ecosystem. Their objective: to find ways to mitigate the UHI effect and repair the city’s ailing tree canopy.
The research reaffirmed some of the long-standing data that showed the connection between tree coverage and urban heat. Direct sunlight can raise surface temperatures well above ambient air temperatures, but under the shade of a healthy canopy, temperatures can drop 10 to 15 degrees lower when compared to non-shaded areas. In fact, trees can block 70 percent to 90 percent of solar radiation from ever reaching the earth’s surface.
Tree-lined sidewalks are also excellent at providing immediate protection from the sun. A concern worth noting, however, is that some sidewalk tree containers have insufficient soil volume for their root systems, which are designed to quickly shed water from the topsoil and into the combined sewer system. These individual pits can cause lateral root growth that pushes up against the sidewalk, producing cracks and “stub-toe” spots along the sidewalk.
Fortunately, there are some newfound solutions on this front. Soil channels can be constructed to connect individual tree containers beneath the pavement to help boost water retention and give the root networks some much-needed breathing room (the Virginia Cooperative Extension has a great introductory manual on this technique).
Trees also increase property values, reduce sewer overflows, and can even save an average one life per year because of the fine particulates they remove from the air. Louisville’s air quality problems have persisted for quite some time, but it’s likely worse than we originally thought.
Recent data from Resources for the Future revealed that 54 counties across the country have been wrongly classified as complying with fine particulate matter (PM2.5) standards set under the Clean Air Act. Jefferson County is listed among them. Considering that an estimated 46 Louisvillians die each year due to air pollution, it’s safe to say that a strong tree canopy is more than worth the effort.
Despite their numerous benefits, Louisville’s tree coverage has seen a significant decline between 2004 and 2012, particularly in certain “hot spots” where impervious surfaces have increased by at least 15 percent.
The study revealed these hotspots are more common in neighborhoods dominated by rental properties and low-income housing. Conversely, trees and parks appear more frequently in affluent neighborhoods populated by homeowners.
Not only does this data suggest an inverse relationship between tree density and economic status, but it also demonstrates how the UHI effect hurts poorer areas the most, where inexpensive rentals come in the form of townhomes and apartments that offer little to no yard space. These communities also have higher concentrations of older residents and others with cardiovascular or respiratory illnesses — groups that are especially vulnerable to urban heat.
Unequal distribution of green spaces also carries a racial bias. According to a 2013 study published by the University of California Berkeley, African-Americans are 52 percent more likely to live in such tree-deprived areas when compared with whites, while Latin Americans were 21 percent more likely.
In downtown Louisville, tree cover currently hovers at around 10 percent. Visit a city like Atlanta and that number jumps to about 45 percent. A big reason for this comes from the fact that Atlanta has a “no net loss” policy built into its tree ordinance, meaning the total amount of trees in the city should never decrease, but only increase or remain constant.
The Davey Institute made this very same recommendation for Louisville to ensure a “no net loss” result for the city and it seems Metro Council took the advice seriously. Last December, the council voted to update the existing tree canopy ordinance to include a stipulation for the maintenance of trees on public rights of way (the space between streets and sidewalks) which ensures a 1-to-1 replanting ratio for each tree lost.
Costs associated with replacing damaged and destroyed trees will fall on the adjoining property owner, but the ordinance does establish a special fund to help low-income residents. Violations for not maintaining public trees range from $50 to $10,000 — a price tag that District 18 Councilwoman Marilyn Parker said was “pretty punitive.”
When discussing the tree canopy, it would be remiss to not mention the invasive Emerald Ash Borer (EAB) and the multitude of problems it presents. According to the Davey Institute, ash trees make up 10 percent to 17 percent of the canopy in Jefferson County and are expected to disappear completely before 2025. Though the ordinance doesn’t directly confront the EAB threat, it does guarantee that all currently endangered ash trees would have a replacement no matter where they fall.
“The permitting processes will help staff members of the Division, who are trained in arboriculture, manage infestations and disease issues as they arise,” said Erin Thompson, an urban forester with the Louisville Division of Community Forestry.
For all of its positive aspects, the tree ordinance still falls short because it doesn’t address the fact that there are entire blocks that have sparse tree coverage because of existing utility poles. In many instances, trees have been rendered disposable because utility easements occupy parcels that could have belonged to a tree and are legally protected in ways that trees are not.
Section 10.4.4 of Louisville’s Land Development Code outlines the rules for planting new trees, including distance limits between utility poles, buildings, and other existing trees. Regulations require new trees to be planted five feet away from any utility structure, and that no tree over 25 feet be placed underneath power lines.
However, a stroll down any Louisville sidewalk will reveal just how many trees have overgrown their sidewalk tract and have begun strangling the utility wires overhead. Utility companies are then required to prune these “problem trees” which creates awkward “V” and “L” shaped branches around the power lines. This type of trimming often leads to weak limb structure that might end up killing the tree entirely.
The fault doesn’t fall entirely on utilities. Developers often disregard the seemingly small details that contribute to a community’s sense of place. Like how when a bank purchased the site of the old St. Matthews hardware store, then subsequently cut down a nearly century-old oak tree that stood as a natural asset connected to the neighborhood streetscape. It’s important to note this was done because the bank “needed” to make space for a car-oriented infrastructure like a parking lot and drive-through tellers.
Trees, parks, and other green spaces should be viewed through the same utilitarian lens used when designing schools, roads, and hospitals: requisites for a safe and habitable city. Perhaps our heat island problem is our coal mine canary — a warning that merits a re-examination of policies that dictate the ways in which we raise the built environment.
The new tree ordinance may not be perfect, but it’s an important part of a larger strategy to offset the UHI effect and make Louisville livable (and breathable) again. In the next installment, we will take a closer look at the problems presented by power lines as well as possible ways we can help our tree canopy to flourish.