With all the sunshine, warm weather and winter’s atmospheric rivers soaking the West Coast, you’d think that California would be the home of a strong, ecologically complex native flora supporting an equally strong, complex fauna.
So I thought before moving in 1985 from my USDA Zone 6 homeland on the East Coast to Sonoma County’s Zone 9 Mediterranean climate, just north of San Francisco. Over the past 40 years, I have come to 2 broad conclusions about this fabled region.
Conclusions about Ecoregion 11
The first conclusion is to agree with Luther Burbank—a local guy from Santa Rosa and a horticultural genius who introduced over 800 new or improved plants into commerce from 1870 until his death in 1926—when he said, “I firmly believe, from what I have seen, that Sonoma County is the chosen spot of all this earth, as far as nature is concerned.”
The second conclusion is that this chosen spot has a delicate and easily damaged native ecosystem. It’s true that you can grow just about anything here. Danny O’Keefe wrote a song about it: “In Northern California (Where the Palm Tree Meets the Pine).” But that’s a problem as well as a blessing. Most of the flora that you find here has been imported from elsewhere and cultivated by human beings.
Related Article: Keystone Plants for Ecoregion 5
Climate diversity in Ecoregion 11
The native vegetation features tall trees along the coast and park-like associations of oak trees and madrone (Arbutus menziesii) interspersed with areas of grasses and shrubs in inland areas. Once you’re over the coastal mountains into California’s flat Central Valley, the climate is no longer Mediterranean; it becomes a hot semi-desert that takes its water from rivers flowing from the north or meltwater from the snowpack on the Sierra mountains that rises to the east. The Central Valley is America’s vegetable garden because of its mild winters and water resources.
To the west in the Mediterranean climate of the coast, those hundreds of thousands of acres of wine grapes you see covering the hills and valleys are Vitis vinifera from various parts of Eurasia. The towering eucalyptus trees along the roadsides? Originally from Australia. The gorgeous flowering trees, shrubs and escaped volunteer forbs? Many arrived as seeds in the ballast of sailing ships.
Find your ecoregion at: epa.gov/eco-research/ecoregions-north-america
Pressure on the local ecosystem from non-natives
A plantsman I met soon after arriving here gave me this insight: “The native grasses will all turn brown by June. Any grass that’s still green during the summer is an import from somewhere else.”
All these visitors tend to muscle out the natives. (People stuck in traffic on Highway 101 will know that’s true not only for plants.) Pressure against native species means pressure on the delicate ecosystem. And that’s an argument for gardeners and landscapers to include native plants in their designs as much as possible in order to strengthen the ecosystem’s fauna.
If you live here, you get used to the Mediterranean climate, in which the rain usually stops in May and doesn’t start again until October. That means green winters and golden-brown summers—just the opposite of the continent east of the Rockies. Scarce water during this 300-day growing season means a lot—really a lot—of precise irrigation.
Ecoregion 11 keystone plants
Trees, shrubs and herbaceous plants that are listed as Keystone Natives by the National Wildlife Federation are those that host caterpillar-producing Lepidoptera in Mediterranean California (which the NWF lists as Ecoregion 11).
Keystone species have co-evolved with the insects they support. Those insects’ caterpillars have therefore co-evolved with the native fauna. So, a keystone native black oak (Quercus kelloggii), valley oak (Q. lobata) or coast live oak (Q. agrifolia), each of which can host 275 species of butterflies and moths, are literally feeding troughs for birds and other animals that raise young and grow fat on the nutrition-packed caterpillars. Non-native eucalyptus, on the other hand, supports only two species.
Just as oaks are keystone trees for lepidoptera in Ecoregion 11, so too are native Prunus (Oregon cherry and chokecherries), Betula (yellow, paper and water birches), Pinus (gray pine and ponderosa pine), Alnus (white and red alders), Acer (bigleaf maple and box elders) and Abies (white fir).
Related Article: Celebrate Trees at The Morton Arboretum
Native shrubs and perennials help support wildlife
Among shrubs, the coyote willow (Salix exigua) and shining willow (S. lasiandra) are champs at supporting lepidoptera, even more so than the oaks. Lovers of our native ceanothus, whose abundant spring flowers range from light blue to dark midnight blue and look as ornamental as any shrubby-come-lately, should plant them for their strengthening effect on the ecosystem as well as their undeniable beauty.
Native forbs like sunflowers (Helianthus), Phacelia, goldenrod (Solidago) and fleabane (Erigeron) not only support lepidoptera but also produce pollen that dozens of specialist bees rely on. These are bees that have evolved to gather pollen exclusively or nearly exclusively from these herbaceous plants, guaranteeing their pollination and subsequent seeds to continue their contribution to the caterpillar populations so crucial for the health of the local ecosystem.
Related article: Native Plants, Reimagined | The Rise of Nativars
A word on redwoods
Mediterranean California extends from the southern edge of Humboldt County in the north down through Mendocino, Sonoma and Marin counties to the San Francisco Bay Area. It continues south along the coast through central California’s Big Sur to Cambria and down into Southern California’s Santa Barbara region and the Los Angeles basin. From there it stretches to San Diego and then crosses into Mexico at Baja California.
“All that the sun shines on is beautiful, so long as it is wild.”— John Muir
This region was once the province of the world’s tallest trees—redwoods (Sequoia) that grew 40 stories tall. To stand by an old-growth redwood with a trunk 30 feet in diameter whose top is lost in the fog is an otherworldly experience, and one you’ll never forget. Other than a few stands of old-growth trees, however, almost all of the original redwoods were cut down for lumber in the 19th and early 20th centuries. That doesn’t mean the species is extinct, for second-growth trees have sprouted from their roots and stumps throughout their range, which is defined by the fog belt. But it will take 500 years for these to grow to the size of the climax trees.
How fog plays a roll
The Pacific Ocean waters of California descend from Alaska and are so cold they’re not pleasant to swim in down to about Santa Barbara in the south, where the beach culture truly begins. (Surfing starts farther north around Santa Cruz, where surfers wear wet suits.) The air from the cold ocean is pulled inland by the sun-warmed land. Cold, wet air and hot, dry land produce frequent and prodigious fogs that have given San Francisco its nickname of Fog City.
Along with producing spectacularly beautiful effects, such as white fog glowing in moonlight and pouring like mounds of whipped cream over the coastal hills at night, the wet fog allows redwoods to comb its clouds with scads of their needles, dropping the collected water to the tree roots far below. The exaggerated height of the trees is due to the interaction of height with moisture. The taller the trees, the more needles aloft that can gather more moisture for the roots below during the five months of drought that characterize this climate. Over the millennia, the thirsty trees have grown enormous.
It remains to be seen whether climate change will alter the Alaskan currents that bring cold water down along the western coast and create the fog that slakes the redwoods’ thirst. I for one hope not. In the meantime, the Mediterranean climate means mild winters and warm summers—just the conditions needed for coddling plants (and making movies).
Jeff Cox is a longtime Horticulture contributor who gardens in Northern California.
