Photo by Shira Bezalel

Before 1900, native oaks were abundant in many of California’s valleys. These trees thrived on hot open plains, enabling them to endure California’s long dry season and frequent drought. Oaks also played a foundational role for an exceptionally diverse array of native wildlife, reflecting a deep shared history of coexistence. By the early 1900s, agricultural conversion of many of California’s most fertile valleys had eliminated many oak woodlands. During the 20th century, urban expansion led a second transformation, replacing agriculture with cities as California’s economy boomed.

Today, the plants and animals that are distinctive of oak woodlands have vanished from our cities, replaced by vegetation from around the world and urban-adapted wildlife. These urban ecosystems do not provide the same support for wildlife, and they are not ideally suited to thrive through drought or hot summer temperatures. For example, trees from the eastern United States are adapted to frequent rainfall during the summer, and require irrigation to survive through California’s dry season.

“Re-Oaking” is an approach to reintegrating oaks and other native vegetation within the developed California landscape to restore this ecologically diverse and distinctive ecosystem to our cities. This idea could benefit people too - native oaks are drought- tolerant, provide heat-tempering shade in the summer, and sequester more carbon than many other common urban trees. Drawing on the beauty of California oak woodlands, Re-oaking could also help bring a unique sense of place back to our cities. As we design ecologically healthy and resilient cities of the future, Re-oaking could help integrate nature into our urban landscapes to benefit both ecosystems and people.

Re-Oaking Silicon Valley

In Silicon Valley, oak ecosystems were the defining feature of the landscape before large-scale transformation. Oak savannas and woodlands were so extensive that the valley was christened the Llano de los Robles, or Plain of the Oaks, by early explorers. In little more than a century, Silicon Valley’s oak woodlands were felled, replaced with orchards, and then replaced again with a patchwork of urban trees.

The rapid and continuing transformation of Silicon Valley creates an unusual opportunity to recover some of the region’s natural heritage by re-incorporating elements of oak woodland ecosystems. These changes could contribute to building landscape resilience in the region, increase biodiversity, and benefit people. Much of Silicon Valley's urban forest, planted 50-75 years ago, is nearing the end of its lifespan. Over the next few decades, local communities will create the next urban forest, shaping the sense of place, human health, and biodiversity of Silicon Valley for the rest of the 21st century. Given the challenges of drought and climate change, do Silicon Valley's native oaks – largely gone for a century – have a greater role to play in the coming century? This report begins to explore that question, focusing first on the benefits the re-oaking could have for local biodiversity and native wildlife.

Learn more about Re-Oaking Silicon Valley.

 

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Further Reading

The Napa Atlas (University of California Press, Spring 2012) explores the grand oak savannas of the 19th century, their sudden loss and surprising resilience, and the potential for re-oaking.

This publication by UC Agriculture and Natural Resources offers a comprehensive look at the management of oaks in urban areas, and includes a section by SFEI on "Oak Landscapes in the Recent Past."

Historical Reconstructions of Valley Oak Savanna

Programs and Focus Areas: 
Resilient Landscapes Program
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