Despite city tree benefits, California urban canopy cover per capita lowest in US

December 4, 2017, USDA Forest Service
Despite the benefits of city trees, California has the lowest urban canopy cover per capita in the United States, with room to accommodate an estimated 236 million more plantings. Credit: US Forest Service

Trees in California communities are working overtime. From removing carbon dioxide and pollutants from the air, intercepting rainfall and increasing property values, California's 173.2 million city trees provide ecosystem services valued at $8.3 billion a year. However, according to a recent study, more benefits could be realized if the Golden State's urban forests didn't have the lowest canopy cover per capita in the nation.

"The structure, function and value of urban forests in California communities," recently published online in Urban Forestry and Urban Greening, reports that California's 109 square yards of tree canopy per person lags behind other urban canopy-poor states, such as Nevada (110), Wyoming (146) and Montana (148). And there's no comparison with well-treed , such as New Hampshire (1,514), Connecticut (1,214) or Alabama (1,182).

"There's no question that Californians are deriving significant benefits from their urban forests," said Greg McPherson, lead author of the study and a research forester with the U.S. Forest Service's Pacific Southwest Research Station. "However, the fact remains that more can be done and will need to be done in light of the recent tree mortality epidemics plaguing some of our ."

In southern California, for example, the invasive shot hole borer has killed thousands of city trees and poses a threat to 33 percent of the urban tree population in the region. More than 50 tree species there are reproductive hosts for the insect, making them vulnerable to the lethal fungus it transmits.

Percent tree canopy cover within California urban areas. Credit: University of California, Davis

City tree population and species composition figures were generated through an analysis of 1,385 study plots located across the state. Costs and benefits of were derived through numerical models that factored in the tree's species, size and location across six climate zones within the state. Canopy cover estimates and state comparisons were calculated by analyzing aerial imagery from the 2012 National Agricultural Imagery Program.

"One of the factors driving the low per capita rating for California city trees could be the fact that 20 of the nation's 100 most densely populated cities are in California, meaning there's a higher volume of people in a confined space for ," said Natalie van Doorn, study co-author and research urban ecologist with the Pacific Southwest Research Station. "California's arid summer climate also can suppress tree establishment and growth, which also could be a contributing factor for the results we observed."

Still, with about 236 million vacant tree sites within cities, van Doorn noted that Californians have ample room for new tree plantings.

"In fact, our study results are already being used by municipal and state agencies to identify priority areas for planting and tree conservation, as well as examining potential disparities in disadvantaged communities," she said.

Explore further: California 'street tree' benefits valued at $1 billion

More information: E. Gregory McPherson et al, The structure, function and value of urban forests in California communities, Urban Forestry & Urban Greening (2017). DOI: 10.1016/j.ufug.2017.09.013

Related Stories

California 'street tree' benefits valued at $1 billion

June 14, 2016

Streets lined with gold? Not exactly, but a new report from the U.S. Forest Service's Pacific Southwest Research Station estimates trees lining Californian streets and boulevards provide benefits to municipalities and residents ...

Millions of city trees at risk from rising temperatures

November 14, 2017

A new study has found that almost one quarter of trees in Australian cities are at risk from increasing temperatures in urban environments due to climate change and urban heat islands, posing a threat to some tree species ...

New Hampshire leads nation in percent tree cover

August 6, 2012

Tree cover in the nation's Lower 48 states covers 659 million acres, more than one-third of the nation, according to a U.S. Forest Service study of national tree cover and impervious surfaces. New Hampshire leads the nation ...

A win-win for spotted owls and forest management

October 4, 2017

Remote sensing technology has detected what could be a win for both spotted owls and forestry management, according to a study led by the University of California, Davis, the USDA Forest Service Pacific Southwest Research ...

Urban trees are growing faster worldwide

November 14, 2017

Trees in metropolitan areas have been growing faster than trees in rural areas worldwide since the 1960s. This has been confirmed for the first time by a study on the impact of the urban heat island effect on tree growth ...

Recommended for you

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.