From Ag Alert
Giving 1,200-pound cows access to one of California’s most fragile and biologically rich ecosystems seems a strange way to protect its threatened and endangered species.
But a published study suggests that reintroducing low to moderate levels of cattle grazing around vernal pools under certain conditions leads to a greater number and greater variety of native plants.
“We found that after 40 years of rest from grazing, reintroducing conservation grazing had, across the board, positive impacts on vernal pool plant diversity,” said Julia Michaels, a visiting professor at Reed College who led a three-year study in a Sacramento-area reserve during her time as a University of California, Davis, Ph.D. student.
Ecologists consider vernal pools—ephemeral ponds that form seasonally—”islands of native habitat” amid California’s grasslands that are dominated by exotic grasses. These biodiversity hotspots harbor about 200 native species of animals and plants, such as the coyote thistle, which germinates under water and forms a snorkel-like straw to deliver oxygen to its roots and then “fills in” its stem as the pool dries.
Specially adapted to survive in those stages of wet and dry, many of these species are found only in vernal pools scattered across California, making those pools a priority for conservationists.
During the 1970s and 1980s, vernal pools were fenced off in parts of the state in the hopes of protecting the flora and fauna from grazing cattle. In the early 2000s, however, UC Davis researcher Jaymee Marty found that grazing was actually crucial to vernal pool biodiversity: once livestock were removed from areas that had been grazed historically, the diversity of plants plummeted.
“Her research was critical to rethinking the best ways to protect the diversity in California’s vernal pool ecosystems,” said Valerie Eviner, a UC Davis plant sciences professor and UC Agriculture and Natural Resources affiliate.
Eviner is a co-author of the study, along with UC Davis colleague Kenneth Tate, a UC Cooperative Extension specialist.
The Michaels-led study, published in the Journal of Applied Biology, builds on Marty’s work by looking at scenarios where cattle had been blocked from vernal pools for decades, and then observes the rate at which biodiversity returns after reintroduction of the animals. Michaels said she wanted to provide answers to the practical questions that ranchers and land managers have about reintroducing cattle.
“A lot of them had these areas that had been fenced off from grazing for the last 20–30 years, and they were very concerned about what happens if we let cattle back onto these vernal pool grasslands: Are there going to be negative impacts because that land had been at rest for a few decades?” Michaels explained.
The researchers focused on transition zones, the “battlegrounds” between vernal pool native species and invasive grasses, where they are able to detect the effects of disturbances such as grazing.
They discovered that, after reintroducing cattle to areas that had been fenced off since the 1970s, there was a greater abundance of native flora—species like the vernal pool buttercup, bractless hedge-hyssop and bristled downingia—as well as increased diversity.
“Encouragingly, diversity is rapidly restored,” Eviner said, “providing conservationists with strong data to show that rapid action can enhance plant diversity.”
Meawhile, instead of cattle making a snack of vernal pool plants, Michaels and her colleagues say the cattle appear to be more interested in munching on grasses.
“Anecdotally, we saw very few signs of herbivory on the vernal pool species because the timing is such that [the plants] are underwater for a good part of the late winter and early spring, and then by the time they’re blooming, there’s plenty of good forage around for the cattle,” Michaels said.
In fact, the cattle seem to be performing a function filled for millennia by native grazers, namely, the once-abundant tule elk, helping to knock down vernal pool species’ chief competitor in those transition zones: the grasses. Although the researchers were concerned about a loss of biodiversity, excessive nutrients in the ponds due to defecation and harmful compaction of “fluffy” soil, none of their worries materialized on the test sites where grazing was reintroduced.
This article was originally published by University of California Agriculture and Natural Resources.
