As you hike across the hillsides of East LA, it’s hard to miss the Southern California Black Walnut, a native tree that dots the commonly dry hillsides with a wide green canopy. Reaching heights of 20–35 feet, the black walnut used to be so common in Southern California that the ecosystem was called the Southern California Walnut Woodlands. Unfortunately, due to urbanization and resulting habitat fragmentation, the black walnut has suffered extensive loss. Its numbers have dropped dramatically, and this protected species is now endangered in large portions of its natural range. The Southern California Black Walnut is a large deciduous tree that commonly grows with many trunks. Its wide canopies provide shelter and habitat for a variety of wildlife, including birds, mammals, and insects. Raptors, such as owls, use the upper reaches of the tree as roosts and nesting places, and ground squirrels dig burrows at the base. Its leaves are deep green, flowering in early spring, with small, round walnuts maturing by late fall. The nuts themselves are a valuable food source for numerous species, providing essential forage for many birds and native animals throughout the more difficult fall and winter.

The black walnut also holds a significant place in the region’s history, having been utilized by local indigenous tribes for centuries. For the Kizh, Gabrielino-Tongva and Chumash people, who once inhabited the Los Angeles area, the nuts were a nutritious food source, the shells used as dice, the hulls as a dye, and the wood for crafting tools, illustrating the tree's cultural and practical significance. And the black walnut continues to serve local communities, playing an important ecological role wherever it is found. Often growing on the edge of chaparral dry habitat, black walnuts stabilize stream banks, help water flow, and have been recorded acting as a fire break. On our hillsides more specifically, the black walnut mitigates the risk of landslides. With the increasing frequency of intense rain events in Los Angeles, preventing erosion has become ever more critical. Native trees reduce the risk of disastrous landslides in vulnerable areas, with their root networks acting as a natural anchor. The forest service has even planted the black walnut for the specific purpose of erosion control near roads in the Southern California mountains.

As climate change brings heavier rainfall and more extreme weather patterns, the preservation of our native vegetation becomes increasingly important. Yet hillside development continues, putting the remaining black walnut trees at risk. The removal of these trees weakens the resilience of our hillsides, potentially leading to increased soil erosion and heightened landslide susceptibility. Thankfully, the city of Los Angeles has implemented an ordinance prohibiting the removal of black walnut trees. The measure underscores the municipality’s commitment to preserving the vital functions provided by native flora, recognizing their ecological significance, and safeguarding the biodiversity and landscape stability black walnut trees provide.

As native species that have long contributed to the region's cultural heritage and ecological balance, upholding their protection not only honors their historical importance and supports biodiversity but also plays a crucial role in fortifying hillsides against the mounting challenges posed by climate change. By preserving these iconic trees, Los Angeles embraces a sustainable approach to environmental stewardship, ensuring the safety of our hillside communities and providing assurance that these natural assets remain intact for future generations.