Group identifies benefits of grazing for grasslands

Ungrazed areas lose species diversity, research finds

Elizabeth Larson, Capital Press 1/19/07

SACRAMENTO -Farmers and ranchers have known for generations the positive impact that managed grazing can have on the land, but that knowledge hasn't been quantified scientifically.

Now, however, thanks to a group of researchers who set out to identify grazing's specific benefits, there is a clearer understanding of how cattle can interact positively with grassland habitat.

The research was presented Jan. 9 at the second annual California Rangeland Conservation Coalition summit.

The coalition, formed in August 2005, includes cattlemen's organizations and environmental groups, who have come together and agreed that 28 million acres of rangeland through California should be conserved as working ranches and open space.

A primary concern for many of the coalition's environmental members are vernal pools, commonly found on grasslands, a fact stated in the group's rangeland resolution.

Dr. Jaymee Marty, a project ecologist with The Nature Conservancy, said she wanted to understand grazing's effects on vernal pools.

She explained that vernal pools are surface water ponds in grasslands habitat, with a hardpan, clay or volcanic surface at the bottom, which causes them to hold water. Most of California's vernal pools are located within the Central Valley, an area the coalition identified as a particular concern. Less than 20 percent of that habitat remains, she said.

The pools are home to rare native plant species as well as native vertebrates and invertebrates.

"We're still finding new species in this habitat, which is remarkable," Marty said.

Some of the endangered animals found in vernal pools include the California tiger salamander and fairy shrimp.

More than 90 percent of the Central Valley's grasslands and vernal pools are grazed, Marty said.

When Marty joined The Nature Conservancy six-and-a-half years ago, she said the organization had just purchased a large ranch that had been grazed for about 150 years, and suggestions were made about changing the grazing patterns on the land.

There was no actual science behind those suggestions to remove grazing, Marty said, with no formal scientific studies conducted at the time on the subject.

That led her to ask the question: Is grazing compatible?

Particularly, she wanted to see how disturbances such as grazing and fire effect vernal pools, which she said are "islands of native plant diversity" which non-native species can't dominate very easily.

Her study, which took place on the 5,000-acre ranch in eastern Sacramento County, included grazed and ungrazed pools and experimented with removing grazing from certain pools for part of a season.

Marty said she found that over time continuously grazed pools showed an overall increase in native plant and animal species, while ungrazed areas actually lost species diversity.

Pools that were continuously grazed also held water longer, she said. She noted that, on average, removing grazing caused some pools to go from holding water for 150 days down to 65.

"This is statistically and biologically significant," Marty said.

That's because of the needs of the species that call the pools home. The tiger salamander, she said, needs 90 days for larvae to mature.

Cows help the pools retain water, she said, by removing vegetation around the pools that can remove the pools' moisture and compacting the soil in the pools.

If it's grazed and it has high diversity - and high diversity is what you're interested in - leave it grazed, Marty concluded, and closely monitor management changes.

Joe DiDonato of the East Bay Regional Park District and Barbara Allen-Diaz of the University of California-Berkeley, presented research that similarly illustrated grazing's benefits.

DiDonato looked specifically at grazing's impacts on amphibians and raptors.

Grazing, he said, helps with fire and weed management. The California ground squirrel thrives in grazed grasslands, he said, and is the No. 1 prey animal for raptors such as golden eagles. In addition, the squirrels' burrows provide homes for many other wildlife species, he said.

"It's a real simple equation," DiDonato said. "Grazing offers benefits for many species and encourages diversity.

"As grasslands become unmanaged and monotypic you start losing your grassland species," he said.

Allen-Diaz reported on her long-term studies to measure the effects of grazing on spring-fed wetlands.

For more than 15 years she looked at species composition, water quality, channel morphology, nutrient cycling and insects in 16 springs at a field research station in Southern California. Some of the springs were ungrazed, while others had been grazed a long time, said Allen-Diaz, as long as 150 years in some cases.

Removing grazing increases the amount of nitrates that flow into downstream waters, Allen-Diaz said. Reductions in grazing also account for a decrease in methane production, she said, which is tied to temperature and water conditions.

Allen-Diaz said the study concluded this past summer and all of the streams are now being grazed once more.