How changing L.A.’s tree rules could cool more neighborhoods

Expansive tree canopies are crucial for healthy ecosystems and livable cities. Yet, Los Angeles’ strict tree planting rules, originally meant to protect infrastructure and public safety, are now widening shade disparities, particularly in lower-income neighborhoods. A new study published in Landscape and Urban Planning, led by the Spatial Sciences Institute and Public Exchange, both based at the USC Dornsife College of Letters, Arts and Sciences, suggests that easing these decades-old restrictions could significantly grow the city’s urban tree canopy — without compromising safety.

This research builds on an earlier USC study comparing L.A.’s municipal codes, engineering standards and urban forestry guidelines to those of 25 other cities — 17 outside California and eight within the state. That study found L.A.’s tree placement rules are among the nation’s strictest, often limiting new planting. The team concluded that substantial changes could be made to existing tree-spacing guidelines without re-writing laws, but better coordination between city departments is essential.

“Fixing L.A.’s rules is a step toward addressing inequities and bringing the health and ecological benefits of green infrastructure to underserved communities,” said Laura Messier, PhD candidate in the population, health and place program at the Spatial Sciences Institute.

Testing looser tree spacing rules

To test how relaxing planting guidelines might increase tree coverage, Messier and her team compared two L.A. neighborhoods: Boyle Heights, a historically lower-income area east of downtown; and Studio City, a wealthier community in the San Fernando Valley. Both areas studied were similar in size, topography and parcel layout. But Studio City had about 3,020 trees per square mile, compared to 2,183 in Boyle Heights — a gap researchers linked to the neighborhood’s denser street grid, higher concentration of multi-family housing and smaller parcels, all of which limit where trees can be planted.

Using mapping software, the team identified obstacles like utility poles, gas lines and bus stops, then modeled potential new planting sites. They compared L.A.’s current planting restrictions with more flexible guidelines in other California cities — including San Francisco, Fremont, Oakland and Anaheim — and identified infrastructure changes that could further expand tree coverage.

The results were striking. Under L.A.’s current rules, Studio City could support up to 140 trees per square mile, while Boyle Heights maxed out at 121. But with looser guidelines, the gap nearly vanished — Studio City’s capacity rose to 158, while Boyle Heights jumped to 153, a 26% increase in the historically Latino neighborhood.

Still, Boyle Heights faces challenges beyond planting guidelines. Narrow sidewalks limit the ability to plant large shade trees. Even with the same number of trees, only 34.5% in Boyle Heights could be large-canopy species, compared to 61% in Studio City.

Small tweaks to tree spacing make big impact

Even modest policy changes could open up more space for tree planting in crowded areas.

The study found that easing restrictions near intersections could increase the number of trees in Boyle Heights by 7.6%, while relaxing rules around utility poles could add another 5.5%. Adjusting guidelines for gas lines (2.6%), streetlights (2.2%), driveways (1.4%) and other infrastructure could push the total canopy gain to 26%, helping expand shade in other dense, lower-income neighborhoods.

While planting trees at bus stops would add less than 1% to overall canopy coverage, it could make a big difference for transit riders exposed to extreme summer heat.

A major obstacle to planting more trees is L.A.’s 45-foot visibility rule at intersections, last updated in 1988. Studies show high-canopy trees don’t block drivers’ views, making this restriction ripe for revision.

Easier to change tree spacing rules than laws

Many of the restrictions are internal guidelines rather than laws, meaning changes could be implemented more easily. The city’s Urban Forestry Division would need to update its Tree Spacing Guidelines memo, but getting agreement from other departments — such as transportation and street lighting — could still be a challenge, Messier explained.

Ironically, the study found that half the street trees in Boyle Heights and nearly 40% in Studio City don’t comply with city guidelines. Yet, there’s little evidence that these violations create safety or liability issues.

Messier suggests that updating the guidelines is more practical than enforcing rules that are often ignored and seem to have little impact on safety.

While modernizing L.A.’s rules is an important step, closing the shade gap will require broader infrastructure changes. Messier and her team point to strategies like reducing street widths — known as “road diets” — to create more space for trees.

“To truly close the shade gap and ensure more equitable access to cooling and green spaces, the city must invest in infrastructure that makes room for more trees in underserved areas,” Messier said.