Concrete Jungle: Navigating LA's Tree Coverage

Digital Humanities 131, UCLA

ROGER WILSON

October 30, 2023

On August 14, 2020, NASA's ECOSTRESS satellite, orbiting hundreds of miles above the earth, captured land surface temperature readings of Los Angeles County to gauge the intensity of an ongoing heatwave. In affluent areas like Westwood and Beverly Hills, land surface temperatures hovered around 100°F, while central Los Angeles neighborhoods, including Vernon and East Hollywood, experienced scorching land surface temperatures exceeding 112°F, which only intensified the overall air temperature of these neighborhoods. Despite the reported overall temperature of 90 degrees Fahrenheit in Los Angeles that day, the disparity in the mean land surface temperature points to a large issue – the disproportionate burden of heatwaves on poorer neighborhoods in LA.

Many neighborhoods in central LA are considered urban heat islands, or urban areas with significantly higher mean temperatures compared to their surrounding area. They are characterized by a dense population, heat-absorptive surfaces such as asphalt, and heat-generating industries, such as warehouses. They stay hot at night, too, because the concrete roads and parking lots hold on to heat from the day. These effects are only exacerbated by heat waves: everyday routines such as waiting for the bus, working outside, and even sleeping at night - often in homes without air conditioning - are unbearable.

As LA grapples with these alarming temperature differences, recent efforts have been made to combat the urban heat island effects prevalent in lower-income areas. Last year, LA unveiled La Sombrita, a prototype bus shade structure (with a $10,000 price tag). The county also hosts cooling centers, or free air-conditioned buildings operational during heatwaves. However, the urgency of the situation becomes apparent when considering the increasing frequency of heatwaves. LA County is currently facing seven days per year with temperatures exceeding 94°F, and projections indicate that this number could triple by 2053 (First Street). While the county has taken strides with remedies, a true indication of a cooler city is the presence of tree shade.

Trees block overhead sunlight, which directly reduces the radiation reflected from concrete surfaces. Research from UCLA reveals that a 10% increase in tree cover can reduce mean land surface temperature by 1.98°F. In other words, if a neighborhood has 40% tree canopy cover, temperatures are 8 degrees cooler than they would be without any tree cover (Chunyu Dong et. al. 2023). Trees also cool air temperature: according to the EPA, trees can reduce an area’s air temperatures by more than 20 degrees through water evaporation and transpiration, or evapotranspiration).

infrared (FLIR) image of a street in New Mexico

The ramifications of inadequate tree coverage are also evident in health statistics, because urban heat islands are linked with higher rates of year-related illness and other health difficulties. “People end up going to the hospital because heat affects their health, makes their asthma worse or something worse,” says David Eisenman, a professor of medicine and public health at UCLA. “But it’s not technically coded as that in the records. It’s coded as ‘worsening asthma.’ So we really undercount the number of cases where heat is a factor.” (High Country News). Even though it can be difficult to diagnose heat factors, heatwaves hospitalize over 1,500 residents in LA county per heatwave day. And, there is a very evident relationship between a neighborhood’s average canopy coverage and its average rate of daily excess ER visits related to heat complications by zip code (UCLA CPHD). There are of course other factors at play, such as access to air conditioning and housing conditions, but tree shade still has a great impact on an area’s environment.

A Vernon neighborhood, 1.49% average tree coverage (left) vs. a Pacific Palisades neighborhood, 55.09% average tree coverage (right)

The lack of crucial tree shade in urban neighborhoods can as always be traced back to historical redlining and disinvestment. As wealthier, predominantly white households migrated to the hilly suburbs of Los Angeles, where there are matured trees, inner-city neighborhoods became predominantly inhabited by low-income communities of color. This shift left these urban areas with minimal tree coverage, causing a cycle of environmental injustice.

Redlining is a discriminatory practice that originated from 1930s New Deal-era government homeownership programs, which tried to remedy home foreclosures during the Great Depression. However the HOLC neighborhoods ratings systematically denied financial services to neighborhoods based on racial and ethnic composition, labeling Black, Asian and Latino neighborhoods as unfit for house lending programs. These discriminatory practices relegated minority communities to less desirable areas with fewer resources, contributing to the absence of green spaces and tree-lined streets. Consequently, affluent areas like Beverly Hills and Silver Lake enjoy approximately 45% tree coverage, while certain central LA neighborhoods, such as Vernon, languish with a mere 2% tree coverage.

In the case of central LA, redlining not only determined the economic disparities but also dictated the distribution of environmental resources. Historical environmental racism has targeted these urban neighborhoods for freeways and industries instead of green spaces and parks. They are close to industrial areas, including factories, warehouses, and oil refineries, further worsening environmental imbalances, leaving them more susceptible to the effects of extreme heat (Shonkoff et al., 2011).

Highlighting environmental justice, the graph on the right reveals a clear link between a zip code's median household income and the rate of heat related hospitalizations. Again, lower-income households also have the lowest percentiles of tree coverage. Yet, this issue isn't straightforward – lower-income households also grapple with limited access to air conditioning, parks, and homes designed to cope with heat efficiently.

County and private neighborhood boundaries

In the face of these overarching issues, residents in tree-deficient neighborhoods face obstacles when raising saplings. The graphic above shows two types of trees on a homeowners' property: parkway trees, which usually have regulations from the county, and private trees. Unfortunately, LA county does not water or maintain any of these. It takes around five years of consistent watering from the homeowner for a tree to mature, and more years of maintenance after that. This process takes time and money, and a burden that may discourage residents in tree-deficient neighborhoods.

However, there's hope for increasing tree coverage in Los Angeles. Utilizing remote sensing data from the Los Angeles Region Imagery Acquisition Consortium, the Center for Urban Resilience (CURes) at Loyola Marymount University was able to classify LA terrain by land cover to determine potential tree coverage by neighborhood. If we subtract the current tree coverage percentage from this metric, we have the following graph: which neighborhoods have the most potential for new trees. Understandably, neighborhoods north of the Angeles Forest are in a desert: they have no trees, and have the opportunity to plant more. Another notable region is that most of East and South LA have a tremendous opportunity to plant trees given their land type.

Fortunately, Los Angeles is actively addressing the challenge of limited tree coverage, with initiatives aimed at creating a greener and more resilient urban landscape. In 2019, Mayor Garcetti unveiled an ambitious initiative to plant 90,000 trees in Los Angeles by 2021, aligning with the city's broader environmental commitment known as pLAn : LA's Green New Deal. Despite encountering challenges, the city's planting plan has made progress, with 65,000 trees successfully planted as of 2022.

In partnership with the Los Angeles Urban Cooling Initiative (LAUCC), pLAn has developed a system called City Plants where Angelinos can request for yard (private) trees to be delivered or street (parkway) trees to be planted, all free of charge. In addition, LA Environment Sanitation will also provide free mulch at various LASAN locations throughout the city. TreePeople , a major inspiration for this project, has routine volunteer tree planting events at parks, campgrounds, and neighborhoods throughout LA. They are also at the forefront of nature-based policies and research.

With the work of these organizations, Los Angeles has the potential to foster a healthy urban forest. The structural value alone, considering the replacement cost of trees, is astounding. For instance, TreePeople has concluded that 40 years after planting 24,003 trees in L.A. Council District 8, the newly created forest holds a remarkable structural value of approximately $50.6 million, with annual functional values reaching $111,810 per year covering air pollution removal, energy savings, carbon sequestration and avoided runoff. And, an analysis of local life cycle costs in Los Angeles County and the City of Santa Monica by TreePeople has determined the annual cost for maintaining and watering a tree is only around $96, making trees one of the most cost-effective ways for LA to implement green architecture against heatwaves.

In addition, a UCLA study concluded that increasing tree canopy and green vegetation to median levels in each census tract (around 19%) could collectively add between 570,300 and 908,800 years to residents' life expectancy. Similarly, increasing LA's park acreage to median levels could contribute approximately 155,300 years in life expectancy across the county. Notably, this increase includes over 110,000 years in life expectancy for Black and Latino residents alone (UCLA Fielding School of Public Health).

And beyond their environmental and health benefits, trees are also simply beautiful. Parks, forests and street trees bring so much life to Los Angeles, enhancing the cityscape in ways that often go unnoticed. Stephanie Carrie on @treesofla highlights the various tree species speckled around downtown and LA neighborhoods and brings commenters together to enjoy them. In the fast-paced metropolis of LA, trees are a refreshing pause, encouraging residents to appreciate the nature of Southern California.

Los Angeles is at a crucial point in its climate crisis, experiencing more heatwaves that disproportionately burden marginalized communities in Central and East LA. Economic disparities often translate to a lack of tree shade.

While this report has explored ways trees mitigate heatwave effects, they are still often overlooked. Trees go beyond providing shade; they play a key role in shaping our urban environment, lining streets, and enlivening parks, and LA’s landscape would be incomplete without palm trees.

As LA grapples with excessive heat, it must prioritize residents, especially those in historically disenfranchised neighborhoods. By recognizing trees as a tangible solution to urban heat islands, Los Angeles can chart a course toward a more sustainable, inclusive, and resilient future. Progress involves more than just planting trees; it requires fostering collective awareness that values and protects these green guardians.

Community engagement, policy initiatives, and ongoing research are crucial for ensuring equitable distribution of tree benefits across Los Angeles' diverse landscape. Adopting a holistic approach that prioritizes trees in urban planning can position the city as a model for climate-conscious development that genuinely includes every community. May the concrete jungle of LA transform into an urban forest haven.

The table information summarizes all statistics used in this project, as well as park access: the percentage of residents that have access to parks, as determined by a USC Lusk study.

Data Source	Data Description	Uses
LMU CURes	"Using high-resolution remote sensing data (imagery and LiDAR) from the Los Angeles Region Imagery Acquisition Consortium (LARIAC) Program, we created fine scale 8-class land cover, and combined the resulting data with CalEnviroScreen, demographic, and urban heat data. This allowed us to assess existing conditions and identify potential priority areas where enhanced urban greening could contribute to climate resilience, environmental equity, and public health improvement."	Existing Tree Coverage (%): percent of LiDAR land cover occupied by trees. Possible Tree Coverage (%): total possible coverage (including existing). Park Access: "The percentage of residents that live within 1/2 mile of a public park that was considered to be in “good condition” by the 2022 LA County Parks Needs Assessment." Source: Los Angeles County Department of Parks and Recreation: 2022 Parks Needs Assessment Plus
LA Almanac	Median household income ($) by zipcode.	Used for visualizing income by heat hospitalizations.
UCLA Heat Maps	"The map shows the daily excess number of emergency room (ER) visits and rate of excess ER visits (number of visits per 10,000 persons per day) due to extreme heat across the state."	Urban heat island effects map.

A description of each dataset. Results were merged into one .csv file for the data table above.