Herds numbering in the tens of thousands make their way across the grassland, upturning the rich Earth with their feet and grazing as they go. Underfoot and in these herds’ wake, birds and rodents comb the freshly upturned dirt or gorge themselves on the new growth of grasses in this massive prairie.
Predators await nearby, sustained by these herds; at the right moment, they’ll spring into action to hunt down a weak or injured animal and make a meal for themselves. At times, the grassland is quiet except for a scavenging bird or canid. Other times, it’s an eruption of color and buzzing and humming as wildflowers feed millions. What’s clear is that this is one of the most diverse places on Earth.
This is not the African savanna. This is not Yellowstone. This is not the Great Plains. This is California – 15,000 years ago.
Across prehistoric California, grasslands were abundant: the massive expanse of the greater valley plains, the steppes of coastal prairies seemingly rising out of the ocean, and the extremes of desert grasslands and alpine meadows. And what exactly would become the charismatic megafauna of these prehistoric grasslands? Grazers are creatures who feed on growing grasses and herbaceous vegetation, clipping the vegetation at or near ground level.
In California during the Pleistocene epoch, ranging from 2.58 million to 11,700 years ago, grasslands supported a diversity of grazers that seem difficult to imagine today. Chief among them were mammalian “megafauna” (impressively large animals) who have existed throughout North America. Some of these megafaunas include the following: Ancient bison (Bison antiquus), Long-horned bison (Bison latifrons), the modern American bison (Bison bison), a couple species of Camelops (an extinct genus of camels), Western horses (Equus occidentalis), and of course the largest grazers on the plains—Columbian mammoths (Mammuthus columbi).
Alongside these long-lost grazers were the predecessors of large mammalian grazers still seen today: elk, pronghorn, and deer (although deer are technically more often considered “browsers,” but that’s a topic for another day!).
What changed? Why has the diversity of grazers declined so dramatically from then up to now?
Primarily, we observe adjustments in both the climate and human interactions. The Ice Age that defined the Pleistocene epoch ebbed, leading to warmer global conditions and driving ecosystem changes. This new interglacial period has been easier for plants to grow in, partially because more water is available, leading to more precipitation and a trend towards fewer grasslands and more forests. These changing climates, combined with more interactions with humans, led to the extinction of most of these grazing megafaunas. Yet the grasslands and remaining grazers persisted. Elk and pronghorn spanned most of what we know of as modern-day California, with estimated populations of up to 500,000 tule elk and more than 500,000 pronghorns found throughout the state.
Over time, as humans expanded into new areas, then came more exotic grazers: cattle, horses, and sheep. Some animals escaped over time, and feral herds roamed the Central Valley. Ranching as a proper industry began with the Gold Rush. The human population boomed, and the demand for meat, hides, and tallow rocketed. California grasslands became overgrazed as they supported (at least for a time) up to 3 million cattle and 6 million sheep. The composition of the grasslands themselves changed, too. Accidentally and intentionally, non-native grassland plant species accompanied livestock and quickly overtook native grassland plants.
Today, the most common grazers to dot our grasslands are cows. A UC Cooperative Extension study found about 1.8 million beef cattle grazed California’s rangelands in 2017. While a complex topic, the cattle’s presence in the landscape can still provide similar ecological benefits to the grassland that historic native grazers provided. Cattle reduce thatch, the buildup of old growth from year to year that, if lit, can lead to wildfires. Cattle eat the new growth while trampling old growth into the ground for decomposition.
Timely grazing by cattle can benefit many native grasses and wildflowers, who get a leg up in competing against aggressive non-native annual grasses and herbs that might otherwise shade them or crowd them out. Cattle grazing also keeps grasslands from progressing in ecological succession into woods and forests. While not a perfect stand-in for the native grazers of California, cattle–if managed correctly and in conjunction with other techniques, such as reseeding, restoration, herbicide, mowing, and burning–can help keep our remaining grasslands healthy.
And California grasslands do need that help. Scientists estimate that we have lost about 99% of our native grasslands due to agriculture, development, and invasion by non-native species. It is nearly impossible to return our grasslands to their former state. The ecological complexities, the introduction and domination by non-native species, and the extinction or local extirpation of native grassland flora and fauna all make it an arguably insurmountable task. However, doing nothing will assuredly lead to the loss of our remaining grasslands. It is only with action, intervention, and proper management that we can sustain and recover California grasslands and the wildlife that rely on them.