When we talk to people about plants, they often use “drought tolerant” and “native” interchangeably. (Sometimes we do it too) So why differentiate between them? Isn't drought tolerant enough? Everybody understands the “drought tolerant” part but what’s often overlooked is “native”. When we bust lawns or consult homeowners on which tree or shrub or grass to plant we often steer the conversation to native plants. At first glance this might appear to be some kind of strange, institution-wide, plant-focused xenophobia. It’s not. Really. We swear. One of the reasons we emphasize native plants is that they’re already adapted to California’s wonky weather patterns and soil. (Not every species can withstand years of flooding followed by years of drought). The other, more subtle benefit is that native plants help wildlife by creating habitat, something that has been lost in the face of human expansion.
Map of the eastern portion of the Santa Clara Valley as re-constructed by historical ecologists. We see the valley dominated by grassland and valley Oak savanna.
From: Grossinger RM, Striplen CJ, Askevold RA, Brewster E, Beller EE (2007) Historical landscape ecology of an urbanized California valley: wetlands and woodlands in the Santa Clara Valley. Landscape Ecol 22: 103–120
The south eastern portion of the Santa Clara Valley reconstructed by historical ecologists. The oak woodlands of Morgan Hill have been replaced with urban development; the southern alkali meadows no longer exist.
From: Whipple AA, Grossinger RM, Davis FW (2011) Shifting baselines in a California oak savanna: nineteenth century data to inform restoration scenarios. Restoration Ecol 19: 88–101
Prior to 1800, the Santa Clara Valley hosted more than five habitats. Majestic valley oaks (Quercus lobata) their trunks six or seven feet in diameter, draped their branches over a savannah of purple needlegrass, elderberry (Sambucus mexicana), honeysuckle (Lonicera interrupta) and white yarrow (Achillea millefolium californica). Willow groves hugged the braided floodplains of the Guadalupe River and Coyote Creek. Tule (Schoenoplectus acutus) marshes hosted red-legged frogs (Rana draytonii), fish and waterfowl. Milpitas was a meadow of salt-water grasses that in May would erupt with enormous, white yerba mansa flowers (Anemopsis californica). Morgan Hill was an oak forest flanked by swaying grasslands, fed by periodic floods from Coyote Creek. These habitats were home to numerous species from the now-endangered checkerspot butterfly (Euphydryas editha bayensis), tiger salamander (Ambystoma californiense) and burrowing owl (Athene cunicularia) to mountain lion (Felis concolor), elk (Cervus elaphus nannodes) and Chinook salmon (Oncorhynchus tshawytscha) in the streams.
From: phytoimages.siu.edu/ A Yerba Mansa flower in full bloom
After Spanish and American settlement Santa Clara Valley rapidly changed from a wild land to agricultural “Valley of Heart’s Delight” to our contemporary urban sprawl. Urbanization in the Santa Clara Valley has resulted in 87-99% habitat loss, depending on the habitat in question. We now depend on historical ecologists to uncover what the character of the land once was. This is troubling not only because habitat-loss is one of the primary drivers of extinction but also because this urbanization impedes valuable ecosystem services. Mediterranean biomes are especially vulnerable to the impacts of urbanization. We often talk about the benefits of trees in terms of clean air, groundwater and flood protection but these services are not limited to trees. Healthy rivers and wetlands act as sponges against flooding and recharge groundwater. Savannas and grasslands hold topsoil in place, preventing erosion and landslides. Tidal marshes are fish nurseries and buffer against storms. The infrastructure benefits of these activities can’t be overstated.
Our City Forest doesn’t only stock native plants. We also stock drought tolerant and urban-friendly trees, grasses and shrubs. The demands put on the urban forest by human activity and the potential safety and infrastructure hazards of large roots or certain pollen types make some natives less suitable for planting. We however, encourage native plants as a means of restoring ecosystem function within the urban environment. Properly selected, maintained and managed native plants can go a long way to restoring some of the ecosystem function to the Santa Clara Valley. Native plant-dominated green spaces can also serve as wildlife corridors, permitting animals to travel safely to suitable habitats and allowing pollinators access to urban plants. Urban environmental restoration projects have met with some success at preserving endangered and threatened species. The Albany Pine Bush Preserve, in Albany NY, is a fantastic example of urban wildlife range that maintains the world’s only surviving population of the Karner Blue Butterfly. Closer to home, LA is undergoing a massive river restoration project. While our focus isn’t on such large-scale restoration projects, Our City Forest acts as a plant provider for restoration projects such as the Ulistac Natural Area and Education Project, Santa Clara. We also encourage residents to plant native plants. We hope that by doing so we can contribute to ongoing greening and restoration efforts while improving the health, water use and character of Silicon Valley.
Thumbnail image comes from Clyde Frogg