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Promoting health for people and communities

UC Master Gardeners take data on tree growth and health in partnership with Advisor Hartin on the 'Climate-ready Tree' study aimed at cooling urban he
UC Master Gardeners take data on tree growth and health in partnership with Advisor Hartin on the 'Climate-ready Tree' study aimed at cooling urban he

California is one of the most populated and urbanized states in the United States, with cities that span hundreds of miles and house millions of people. Urbanization has resulted in the formation of urban heat islands, where the temperature is significantly higher than in the surrounding rural areas. This is due to the large amount of concrete and asphalt in cities, which absorbs and reradiates heat. As cities grow, so does the number of heat-absorbing surfaces, leading to an increase in temperature.

The high temperature in urban heat islands can significantly affect the health, economy, and environment of California's cities. The increased heat can lead to higher air conditioning use, which can strain the energy grid and increase greenhouse gas emissions. High temperatures can also lead to increased health problems such as heat exhaustion and heat strokes, particularly among elderly and low-income populations. Increased heat can impact local ecosystems and wildlife, altering behavior and leading to a decline in biodiversity. By increasing the number of urban green spaces such as parks and gardens, the UC Master Gardener Program has started work to combat urban heat islands across California. Trees also play a crucial role in reducing urban heat islands by providing shade and transpiring water, which cools the air around the trees.

Research by Janet Hartin, a UC ANR Environmental Horticulture Advisor, found that shade produced by a single tree in inland California cities can reduce the surface temperature of black asphalt by over 70 degrees on a hot summer afternoon. In San Bernardino County, the UC Master Gardener Program partnered with the Inland Empire Resource Conservation District, the California Climate Action Conservation Corps, and nonprofit organizations to provide free drought-, heat-, and pest-resistant trees. UC Master Gardeners provide free help and resources to all recipients on proper planting and tree care to help ensure tree health. More than 700 trees have been given away to families residing in underserved neighborhoods since 2021.

“The education the Master Gardener volunteers provide on tree planting and care is critical to long-term tree survival,” says Hartin. “Since only about 40 percent of trees typically survive in urban settings for more than twenty years, this education helps ensure that maximum ecosystem and societal benefits are realized. It’s a legacy for our children’s children.”

In response to the local need for combating climate change, and drawing inspiration from projects like Trees for Tomorrow and UC's Climate Ready Trees, the UC Master Gardener Program of Sonoma County —with funding from the City of Santa Rosa—created a selection of tree species that are expected to flourish in the future even as temperatures increase. UC Master Gardener volunteers developed a recommended tree list using eight criteria, including drought and temperature tolerance. This comprehensive tree list has been incorporated into the City of Santa Rosa’s resources and recommendations to city residents for proper tree selection and planting.

“The City of Santa Rosa has been proud to partner with UC Master Gardeners on many water-saving initiatives over the years, including—most recently—the Climate Forward Trees project. This project will help Santa Rosa Water customers choose trees that will help our community adapt and thrive in the face of climate change.” - Claire Nordlie, Santa Rosa Water

To ensure the success of planted trees, ongoing support is available to all residents. UC Master Gardener volunteers are available free of charge to provide education outreach and guidance on proper planting, watering, and tree care throughout the lifetime of the tree. This support is critical to ensuring that trees are properly maintained and able to thrive for future generations.

Urban heat islands are a growing concern in California, and their impacts can be far-reaching and significant. By implementing measures today to reduce urban temperatures, such as increasing green spaces and promoting tree planting, the UC Master Gardener Program is making significant contributions toward creating a healthier and more sustainable environment for future generations.