Tuesday, June 20, 2023

The Tragic History of the Golden Rolling Hills of California

Drone pic of golden rolling hills along Interstate 5 in California (2023). Note that the road in the photograph is NOT Interstate 5, but a side road from it.

Every time I travel to California, I always marvel at the wide open vistas of the state's iconic golden rolling hills. The trip I took last month to the Golden State was no different, and as I drove along Interstate 5 between Los Angeles and Sacramento, I could not help but compare the beautiful hilly terrain with the flat and somewhat monotonous landscapes of Florida, especially after flying my drone and gazing at the land from tens of meters up.

Ground level view of the hills from an older 2005 pic. Not the same location as drone pic above.

For many Californians, the golden hued hills are just as representative of their state as the Hollywood sign in the City of Angels, or the Golden Gate Bridge in San Francisco. But most of them probably do not know the tragic history of the creation of these scenic wonders. They do not realize that these hills were not always like that.

Instead, the hills before the arrival of Europeans in the 1700s were covered in a patchwork of perennial bunchgrasses and wildflowers. Native grasses like Elymus elymoidesNasella (Stipa) pulchraHordeum jubatum, and other bunchgrasses dominated the landscape. The hills were mostly green all the way until autumn due to the preponderance of perennial plants, a far cry from the golden hue suffusing them today.

Native bunchgrass species Elymus elymoides

These perennial grasses had deep roots that allowed them to withstand drought, and they formed the basis of an ecosystem that had a diverse set of forbs and other plants that provided homes and food for the native animals in the area. They were also long-lived, with some researchers saying that some specimens may have lived for hundreds of years (Marty et al, 2005).

It was into this milieu that the Europeans arrived in the late 1700s, and brought with them (whether accidentally or not) the seeds of what would initiate a major and very rapid ecological shift in the landscape. Seeds of Eurasian grass species were introduced to the continent, along with grazing animals such as sheep and cattle. 

Avena fatua along highway

Instead of being perennials, these exotic grasses were annuals, and when they senesced they turned a golden color. Within a short timespan, they had almost completely replaced the perennials. The latter were not driven to extinction,  but were instead bracketed into increasingly smaller spots by the invading species. They could not withstand the competitive abilities of the annuals, nor the new herbivores that came along with them.

One of the most notable exotics are some oat species, Avena barbata, and Avena fatua. These 2 species have beautifully drooping inflorescence, and are cosmopolitan in distribution. 

Avena fatua with empty and ripened spikelets

From a distance they are mostly a light golden color after senescenece, their bodies coating the hillsides in countless multitudes.   

Empty glumes of Avena fatua

Avena fatua

In addition to the wild oats, other species contribute to the golden hue of the hillsides. Bromus rubens is another exotic that has become a component of the hillsides.  

Bromus rubens

Another species from the genus is called Bromus diandrus, which has beautiful spikelets and is somewhat similar looking to the dreaded cheatgrass (Bromus tectorum). But in the case of this species, the spikelets are much larger and longer.

Bromus diandrus

All the above species, as well as various Hordeum spp, are now called "naturalized exotics" because over the past several hundred years they have become an integral part of the ecosystem of California. They have become so much a part of the state that most people nowadays think they are natives, and even those who find out that they were once invaders cannot repudiate and deny the nice memories they had of driving along the roads surrounded by golden hills. 

But there are newer and more damaging species that have entered into the picture just recently. 

Hordeum (?) sp

These winter annual invasive grasses are also part of the golden hillsides, and they are rapidly conquering ground against the older naturalized exotics. One of the more notorious among them is Taeniatherum caput-medusae (medusahead grass), whose silica-rich bodies allows it to smother the competition and slowly form vast monocultures.

Taeniatherum caput-medusae (medusahead grass)

Another is Aegylops triuncialis, a relative newcomer that is also becoming a big component of the golden hued hillsides.

Aegylops triuncialis

The interesting thing is that some studies have shown that the old native perennials actually can do better against these newer invasives, unlike the naturalized exotics. But unfortunately, the tragic loss of so much of the old natural grasslands has allowed medusahead grass and its ilk to spread almost unencumbered.

Drone pic of golden rolling hills along Interstate 5 (2023)

In the end, it's still ok to marvel and gawk at the beauty of California's rolling golden hills. Change is constant in biological systems, and an irrefutable part of life. Just remember that these are the products of an invasion that started hundreds of years ago, and is still going on today.

Literature Cited

Marty, J. T., S. K. Collinge, and K. J. Rice. 2005. Responses of a remnant California native bunchgrass population to grazing, burning and climatic variation. Plant Ecology 181:101112.

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