Throwing shade at L.A.: USC Dornsife researcher measures impact of trees, or the lack of them
John Wilson uses satellite imaging data and interdisciplinary research to better understand how different systems work together to make a city run. (Photo: Peter Zhaoyu Zhou.)

Throwing shade at L.A.: USC Dornsife researcher measures impact of trees, or the lack of them

USC spatial scientist John Wilson discusses the benefits of more trees in the urban core, the differences between Beverly Hills and Boyle Heights, and how trees will shape L.A.’s future.
ByPaul McQuiston

The sprawling hardscape of Los Angeles does not provide many opportunities to escape the ravages of climate change. However, not all Angelenos suffer equally. Some neighborhoods provide oases from adverse conditions, while others suffer disproportionately.

An expanded canopy could help with moderating temperatures and decreasing air pollution, says John Wilson, founding director of the Spatial Sciences Institute at the USC Dornsife College of Letters, Arts and Sciences and principal investigator of the Urban Trees Initiative, a project of USC Dornsife’s Public Exchange.

In his research, Wilson uses satellite imaging data paired with interdisciplinary research to better understand how different systems work together to make a city run. Wilson spoke about his work with the Urban Trees Initiative and how greening the city could fix some of its ills.

What inspired you to research the urban canopy?

The driver here in large measure is inequality. When you think of climate change and global warming, how much different parts of the landscape are going to warm up varies tremendously, particularly in Southern California. In the next 30 years, the everyday temperatures at the coast might not change much, but if we go to downtown and L.A.’s Eastside, the number of 90-degree days are likely to double or triple. What happens if we had 10 days in a row above 90 degrees — how would that impact people’s lives? In thinking about that, the most likely path to being able to address people’s exposure to excess heat would be to improve the urban canopy.

What role does the urban canopy play in worsening equity?

One of my PhD students conducted a painstaking study a number of years ago where he looked at changes in tree cover on single-family home lots from 2002–13. We looked at the 15 council districts in the city of L.A. and tree cover in the next 19 largest cities and, lo and behold, there were tremendous disparities in urban canopy. But when you looked at change, those places that had low canopy to start with had the fastest retreat in terms of percentage of tree cover. In places like Pasadena or Pacific Palisades, there was still a loss of tree cover, but it was slower.

The synopsis was already poor — at-need people and people of color had a lot less benefits from tree canopy than well-to-do people. But we found out the trends were heading in the wrong direction, as well.

What role does spatial science play?

Satellites have made an enormous difference to how we can understand and interpret the Earth. We also now have a lot of tools for calculating relationships — where things overlap and where they occur separately — and you can link the two.

Lately, I’ve compared … Beverly Hills and Boyle Heights. I have two graphs that show distribution of green cover versus hardscape [non-living elements]. On the side measuring hardscape, Boyle Heights and Beverly Hills look almost identical — lots of buildings, lots of streets. The difference comes when you look at the side of the graph where you would expect green infrastructure. … Beverly Hills has a huge spike because there are large properties with lots of green cover that isn’t even seasonal, it’s year-round. When you look at Boyle Heights, it just fades away to nothing.

How do you determine what areas would benefit the most from an expanded canopy?

What my group is developing is a three-dimensional shade model utilizing GIS [geographic information science] so that we could capture the likely benefits in terms of heat mitigation. We can run scenarios where we add 20% to the canopy and find what that would mean for people’s everyday lives in terms of cooling.

For instance, roughly 20% of households have no car, so they’re either walking or they’re on transit. … With so few trees and such poor transportation options, it’s really difficult to find some relief from the heat — which will have some negative impacts on their everyday health and well-being.

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