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
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
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
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
More than 90 percent of the Central Valley's
grasslands and vernal pools are grazed, Marty
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
That led her to ask the question: Is grazing
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
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
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
"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
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