The fall and winter rains have come, and Contra Costa's hills are turning green again. While we may enjoy California’s famous “golden rolling hills”, most of us are happy to see the green return. But did you know this cycle represents a relatively new landscape? Prior to European settlement, most grassland areas in California were made up of perennial bunch grasses such as purple needle grass. The almost-complete conversion of our hills to annual grasses represents one of the massive, unintended ecological consequences of European settlement.

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From the 1500s on, seeds of non-native annual grasses traveled to the New World accidentally in ship ballast, and intentionally as food, medicine, and ornamentation. The most common seeds were wild oats, filaree, and ripgut brome, which are now, along with the other common golden grasses, known as “California annual type.” These are the plants of Spanish barnyards, and they came to cover the ground of the Golden State.

Before this invasion, the Bay Area’s native grasslands were shaped by the grazing of vast herds of tule elk, while pronghorn antelope browsed the drier inland grasslands. Fresh, abundant forage was often heavily grazed by elk, but the elk would keep moving, always wary of the hungry predators. It is likely the grazed bunch grasses and herbaceous flowering perennials had plenty of time, perhaps a whole growing season, to regain their vigor before the elk returned. But the native bunch grasses could not tolerate the heavy grazing of fenced-in cattle and sheep introduced by Spanish and Mexican immigrants.

The Mediterranean annual grasses also grow faster and bigger than the native bunch grasses. Established annual grass stands can produce ten times the amount of seed as do native grass stands of equal area, and most important, their seeds are five to ten times larger, giving them a big jump on establishment and fast growth. Another advantage they have is their shallow, weblike root system, which quickly exploits the moisture near the surface of the soil, rendering tiny, slow-growing native perennial seedlings helpless. The competitiveness of the annual grasses has also curtailed the spectacular wildflower shows of times past.

But the proliferation of seeds and heavy grazing wasn’t enough to cause the takeover of the annual grasses. Ecologist Mark Stromberg discovered that plowing is what spelled the demise of the native grasses. Plowing cut off the growth of the perennials, allowing non-native species to thrive, eventually disrupting the biome.

Study of the California mission system gives ecologists insight into the spread of the annual-type grasses. Junípero Serra founded the first mission in San Diego in 1769. The mission buildings were built with bricks made from mud and local soil. At San Diego de Alcalá, the bricks show a small quantity of non-native seeds. As the missions were slowly built up the coast to Sonoma, each a day’s ride from the last, the bricks had an ever-increasing number of non-native seeds in them, illustrating the growing prevalence of the seeds as more and more Europeans came to the west coast.

But the Mediterranean annual grasses are a permanent part of the Californian ecology, and they are now as much a part of California’s grasslands as the native perennial grasses once were. We can understand their story, but there's no shame in appreciating the beautiful green hills!

Sources: 

Amme, David. "Grassland Heritage". Bay Nature. April-June 2004

Szalay, Jessie. "California's Lying Fields of Gold". Asparagus Magazine. March 22, 2018

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