An interdisciplinary team of public health and environmental science researchers from across the University of California have found that despite efforts by the state and local school districts, many public schools fall short of providing sufficient shade, much less natural playing surfaces, for the 5.8 million children they serve – especially in an era of extreme temperatures.
“It’s hot, and it’s getting hotter, and trees are a good tool to cool down, for both kids and communities,” said Dr. Kirsten Schwarz, associate professor in the UCLA Fielding School’s Department of Environmental Health Sciences and a leader of the California School Tree Study, which is surveying public schools across the state. “Trees – and natural ground surfaces, as opposed to blacktop – are important in terms of the health impacts to children, and to mitigating the extreme heat they are experiencing in a place where they spend a lot of time.”
Approximately half of all students in California’s K-12 public schools attend a school where there is virtually no tree cover on their school campuses. Of 10,000 schools across the state, the typical tree cover, or canopy, is roughly 6.4%, according to project partner, Green Schoolyards America.
“It’s just not suitable for kids,” said Dr. Alessandro Ossola, a UC Davis scientist whose role on the project team includes measuring the amount of heat the blacktop playgrounds reflect back on the children using them, as well as how shade trees can reduce those temperatures. “Many kids might not have access to a backyard, they might not have access to nature, they might not have access to a safe space, a green space, where they can go and play with their families and friends, so the schools themselves are an opportunity to provide those sorts of benefits, as well.”
The study is a collaboration between researchers at the United States Department of Agriculture (USDA) Forest Service, Pacific Southwest Research Station (PSW), the University of California, the California Department of Forestry and Fire Protection (CALFIRE), and the non-profit Green Schoolyards America.
“We’ve been neglecting what our children need to be happy and healthy and learn,” said Dr. Julia Gowin, CALFIRE’s urban forestry supervisor for northern California. “This is a very comprehensive approach, not only to increase tree canopy cover for communities, but also to give those kids an environment where they can learn and thrive and develop.”
Forestry officials said the University of California’s unique expertise at researching a problem and providing potential policy solutions is why they brought the scholars into the project.
“The U.S. Forest Service shopped around for institutions that were the best equipped to analyze the problem and to come up with viable solutions for addressing that, and UCLA rose to the top of the list,” said Walter Passmore, California’s state urban forester and a veteran of both the federal and multiple state forestry services. “These are the organizations that are the best equipped, skilled, and have the experience to do this type of research work and come up with solutions.”
The study project began in 2024 and has completed its first phase, an analysis of land cover patterns in some 475 elementary schools in greater Los Angeles, the San Francisco Bay area, and the Central Valley. Findings showed extensive blacktop and other impervious surfaces, and state and local policies that created these school landscapes with few trees. This summer, the team has been collecting field data, including tree measurements, heat measurements, and interviews with district and school staff, including facilities, about how they manage trees, especially issues around maintenance to sustain existing and planned improvements.
“We’re wrapping up the field work, and our next step is going statewide, with workshops to connect with those who design, plant, and maintain trees on schoolyards,” said Schwarz, herself a parent of two children in public schools.
As an example, during the first phase, researchers found that in the schools surveyed, the amount of blacktop per school ranged from roughly 40% to almost 60% of the school sites, while the amount of natural space – landscaped with grass, trees, and shrubs – ranged from about 20% to 54%, with the remainder of the sites being structures, both classrooms and administrative buildings.
The best numbers were found in the Central Valley schools, where more than 53% of a typical campus is landscaped, although 40% remains covered by asphalt and similar surfaces; in the Bay Area schools, the percentages are about 27% landscaped and about 54% blacktop, while the numbers were the worst, relatively, in the southern California schools: roughly 20% landscaped and 59% blacktop. Some numbers were even higher – meaning worse – at specific schools, which given the temperate climate of the region, is questionable policy, researchers said.
“In Los Angeles, provided we have enough water, we can grow anything – it’s like an open-air plant conservatory, if you want it to be,” Ossola said. “In urban forestry, traditional canopy target goals, we have this goal of 30% tree cover, which is a lot for a built environment … but 15% would be nice.”
Funding
This project has been made possible with support from the USDA Forest Service, the California Department of Forestry and Fire Protection (CAL FIRE), the UCLA Fielding School of Public Health, the UCLA Luskin School of Public Affairs, the UC Davis College of Agricultural and Environmental Sciences, and the University of California, Berkeley’s (UCB) Rausser College of Natural Resources and the UCB College of Environmental Design, and is affiliated with the Los Angeles Center for Urban Natural Resources Sustainability.
