The tree dilemma in Los Angeles

Los Angeles is known for its skyline that is lined with palm trees. However, these palm trees offer little to no benefits to human or environmental health. Heat is one of the leading weather-related causes of death in the U.S., and in such a hot and dry region, trees are crucial to ensure clean air, provide shade and negate the impacts of scorching temperatures.

Trees filter ozone and carbon from the air and replace them with oxygen. While palm trees are emblematic of LA, they remove few toxins, produce hardly any oxygen and provide little shade for humans and other plants to thrive in the high temperatures of Southern California.

“In planning for more climate resilience our choice of tree species has to consider quite a few factors that will affect the health of the trees, humans and other wildlife who may depend on them as habitat,” said Esther Margulies, associate professor at the University of Southern California School of Architecture. “We need to be planting trees that will be tolerant of hotter, drier conditions. Some of the species that you see frequently in the region now will not successfully adapt to these changes.”

Climate change is expected to increase the number of days in central LA with temperatures over 95°F by three times. Rainfall is expected to decrease, causing an increase in the severity of droughts.

As temperatures rise, increasing shaded areas and planting drought-tolerant trees will be a top concern. Margulies said that one way appropriate tree species can be found is by looking at plants that thrive in similar regions. LA’s environment has a Mediterranean climate similar to that of southern Europe and Australia.

In addition to their lack of ecological benefits, palm trees in the region are also being attacked by fungi and pests such as bark beetles. City officials put the number of palms in LA at 75,000 in 1990; the current count is unknown but is expected to plunge in coming years. Since 2010, an estimated 129 million trees in California have died due to issues such as droughts, pests and climate change.

Mayor Eric Garcetti adopted a Green New Deal in 2019 that outlines a plan to plant 90,000 new trees by the end of 2021 and to increase the forest canopy in low-income areas by 50% by the year 2028. Assuming these goals are accomplished, the choice of tree species will be crucial to the efficacy of the plan.

Margulies said that traditionally a single species would be planted throughout an area to create a uniform appearance, but this homogenous planting technique can increase the risk of pests and diseases. Having a variety of species reduces this risk.

“There is no magic formula but we need to be planting a diverse palette of species now that are ready for heat, drought and are disease and pollution resistant,” Margulies said.

Tree People, an LA-based non-profit, has worked for several decades to support the ecology of the area. Along with promoting environmental education, they host habitat restoration events and support local communities planting and caring for trees.

“[Palm trees] are just grass at the end of the day,” said Miguel Vargas, Southeast LA Community Organizer for Tree People. “The only reason why there [are] palm trees here ... is because people want it to assert, ‘There [are] palm trees here, therefore, it means money's here, like Hollywood, Beverly Hills,” he said. “Other than that, there's no reason why palm trees would be good here.”

Adding trees or other greenery to major cities reduces the effects of urban heat islands. Covering buildings and roads, surfaces that absorb and re-emit heat, with vegetation can drastically reduce temperatures. Areas that are shaded by greenery can be 20-45% cooler than surrounding areas that lack foliage covering their pavement. The benefits of greenery are greater with large plants that have bigger, thicker leaves and denser canopies.

“Even one tree can make a tremendous difference,” said Edith de Guzman, a researcher at the University of California, LA, Institute of Environment and Sustainability. “A properly planted tree will not only shade [a] home … [but also] less AC will be needed, and when the AC unit is in use it’ll work more efficiently.”

Native plant species aren’t necessarily the route to go. Vargas explained that the right tree needs to be planted in the right place because some can lift up sidewalks or crack pipes with their roots.

“There are not very many tree species native to Los Angeles,” Margulies said. “Our native landscapes are the coastal chaparral, dunes and grasslands.”

Unfortunately, some trees that are native to the region can be hosts or victims to pests. It can take a long time for a plant to adapt to a certain climate, meaning that the ideal trees to plant here are already acclimated to heat and don’t require tons of water to survive.

“The trees that we planted, they're not native to California,” Vargas said. “But … we plant them there because they're not [an] invasive species, they're not going to lift the sidewalk, they're not going to break the pipes.”

Tree People takes into account the surroundings of a neighborhood to determine where trees should be planted, then decides what type of tree would be best by looking at statistics such as how tall or wide it grows. Other factors include available planting space, water needs and how appropriate a species is to the climate.

Some of the species that Tree People plant include crape myrtles, gold medallions, pink and golden trumpets, water gums, chitalpa trees, New Zealand Christmas trees, palo verdes, Brisbane boxes and lemon bottle brushes. Vargas says his favorites are strawberry trees, for their tasty berries, and Hong Kong orchids, for their beautiful pinkish-purple leaves.

City Plants, a non-profit organization that partners with the city, estimates that a budget increase of $40-$50 million is needed to grow and sustain LA’s tree life. While this may seem like a high cost, the city’s annual per-tree budget is as much as 212% lower than that of similar cities.

Vargas believes that Tree People has greatly improved the neighborhoods of Huntington and Cudahy in southeast Los Angeles. “Every time we went out and did tree care [in those areas], we always had positive feedback from the community,” Vargas said. “You can see the birds coming back to these streets and all kinds of different animals in the area.” He hopes to expand the initiatives of Tree People to other southern LA neighborhoods, such as Long Beach, Compton, and South Central.

Palm trees provide few health benefits, and their thin structure does not considerably reduce the urban heat island effect. By adding to the diversity of LA's tree life, the severity and rate of asthma attacks and even heart conditions can be reduced because the air will be cleaner, and there will be more shaded areas available.