California trees are not just helpful in increasing property value, but also help to clear the air of carbon dioxide and other pollutants. The ecosystem services provided by California’s 173.2 million city trees are valued at $8.3 billion per year. Despite all of these benefits, a new study reveals that California has the lowest canopy cover per capita in the country.
The researchers found that California has 109 square yards of city tree canopy per person, which falls way behind the states with the best numbers such as New Hampshire with 1,514 square yards of tree canopy per person or Alabama with 1,182 square yards of tree cover per person.
Greg McPherson is a research forester with the U.S. Forest Service’s Pacific Southwest Research Station and the lead author of the study.
“There’s no question that Californians are deriving significant benefits from their urban forests,” said McPherson. “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 urban forests.”
Thousands of trees have been killed in southern California by the invasive shot hole borer. This beetle invades while carrying fungal spores that infect and kill trees, and poses a threat to 33 percent of the urban tree population in the region. Over 50 tree species in southern California are reproductive hosts for the insect, making them vulnerable to its lethal fungus.
Study co-author Natalie van Doorn, a research urban ecologist with the Pacific Southwest Research Station, explained that the state’s population and summer climate are also likely contributors to California’s tree canopy ranking.
“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 trees,” said van Doorn. “California’s arid summer climate also can suppress tree establishment and growth, which also could be a contributing factor for the results we observed.”
Van Doorn pointed out that there are about 236 million vacant tree sites within these California cities, and so there is abundance of space for new trees to be planted.
“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.
The study, which is entitled “The structure, function and value of urban forests in California communities,” is published online in Urban Forestry and Urban Greening.
Image Credit: US Forest Service