Environment & Science

Scientists document vanishing trees, greenery from LA area

Green cover for single-family homes fell in the LA area, thanks to add-on construction or mansionization.
Green cover for single-family homes fell in the LA area, thanks to add-on construction or mansionization.

A new study from the University of Southern California shows that trees and other greenery in the single-family neighborhoods of the Los Angeles area declined significantly in the busy construction years leading up to the housing bust. 

The researchers, who recently published their findings in the journal Urban Forestry and Urban Greening, said they observed the link between larger building footprints and decreasing green cover across 20 communities of varying socioeconomic levels throughout Los Angeles County. 

The amount of trees and greenery fell between 14 and 55 percent in the period 2000 to 2009 and some of the construction was not permitted, the study found.

Travis Longcore, assistant professor of architecture, spatial sciences, and biological sciences, said in some cases trees were disappearing because of mansionization, the building trend where smaller homes are replaced with structures disproportionately large to the size of the lot and neighboring properties.

Moreover, "there are a lot of situations where you’re seeing an additional bathroom put on the back or a second dwelling unit that may or may not be permitted," Longcore said.

The researchers shied away from making policy recommendations, or commenting on how to balance green cover with much-needed housing production in the county. But Longcore differentiated between the types of construction that was removing greenery.

"You know, someone living in a a garage out of financial necessity, and adding a room on the side is a different thing from tearing down a whole property and building lot line to lot line," Longcore said. 

Los Angeles, Arcadia and other communities have tried to address mansionization by passing stricter regulations. Some have also embarked on tree-planting programs. In Los Angeles, for example, more than 18,000 trees were planted last year, according to Mayor Eric Garcetti's office.

The USC team studied the neighborhoods with the help of aerial imagery. Longcore said the study was prompted by concern about disappearing green cover, which scientists say is critical to maintaining the environmental health of a neighborhood. Trees, for instance, shade houses and keep air-conditioning costs down. Their root systems control storm runoff.

Researchers could tell a lot of the new construction was unpermitted by comparing what they saw in aerial shots with property records on file with the Los Angeles County assessor’s office, Longcore said.

"There’s a bunch of uncollected property taxes for properties that were not reassessed for being larger," Longcore said.

Asked about the unpermitted construction, a spokesman for the L.A. Department of Building and Safety said he could not provide a comment immediately.