Range Reseeding Relies on Rodents
Kangaroo rats and their relatives are responsible for more than 90 percent of
the germination and establishment of Indian ricegrass seedlings.
A key to establishing rangeland plants may be the kangaroo rats and
chipmunks that eat the seeds.
Land managers often reseed areas disturbed by fire or mining to hold the
soil in place, provide food for livestock and wildlife, and ward off invasive
weeds. When possible, they try to use plants native to the area they are
planting. But their success can depend not only on soil type and precipitation,
but on the local animals as well.
"A revegetation plan is likely to fail if rodent populations aren't
considered," says Agricultural Research
Service animal ecologist William S. Longland.
That's because Longland and others have found that certain native plants
depend on rodents for germination in the wild. Longland works at the ARS
Ecology of Temperate Desert Rangelands Laboratory in Reno, Nevada. He's
studying local wildlife to develop the best strategies for establishing native
plants on the range.
Two of the most economically important plants in Nevada's Great Basin are
Indian ricegrass and the shrub called antelope bitterbrush. The basin extends
from the Sierra Nevada and Oregon-Idaho border east to the Wasatch Range in
Utah and south to the Mojave Desert.
"In the winter, many Western ranchers rely on rangeland grasses to feed
their cattle, and mule deer depend on shrubs like antelope bitterbrush,"
says ARS rangeland scientist James A. Young, who leads the Reno laboratory.
Frosty Tipton is one of those ranchers. He feeds about 1,100 cows on 250,000
acres of owned and leased land.
Animal ecologist William Longland inspects Indian ricegrass growing in Nevada's
Great Basin during the Hot Springs Mountain granivore study. The pen in the
background was designed to allow access to rodents but exclude other
"If we didn't have access to rangeland, we'd have to put up hay for the
winter," he says. "But we don't own enough land to produce up to 1
ton of hay needed for each cow per monthI don't know what our ranch would
do without the winter range," he says.
Planting's a Costly Affair
Replanting with native seeds can get expensive. Indian ricegrass seeds cost
between $5 and $30 per pound, depending on whether the variety is commercially
grown or locally harvested from the wild. Antelope bitterbrush seed costs up to
$18 per pound. For comparison, a non-native grass, crested wheatgrass, sells
for only $1.70 per pound.
That's where understanding the seed-eating granivores comes in.
Longland just finished a 4-year study of Great Basin granivores, including
birds, ants, and rodents. He found that birds have little influence, because
other granivores generally beat them to the seeds. Ants eat the seeds or take
them too far below ground to germinate. But the rodents can be essential.
Labor That's Wild and Free
In field experiments, Longland discovered that kangaroo rats and their
relatives were responsible for more than 90 percent of the germination and
establishment of Indian ricegrass seedlings.
"These rodents gather hundreds of seeds in their cheek pouches and then
bury them in shallow hiding places, or caches," Longland says.
"Later, they'll return and eat the seeds, but some get missed. The caches
put the seeds in an ideal location for germination and protect them from other
rodents and ants," he says. Scientists also believe that chemicals or
friendly microbes in the cheek pouches break the seeds' dormancy, another
needed step before seedlings can sprout.
Research technician Charlie Clements (left) and animal ecologist William
Longland inspect bitterbrush, which is a major source of browse for mule
Steven B. Vander Wall, an animal ecologist with the University of Nevada at
Reno, found that antelope bitterbrush has an ever greater association with
chipmunks and squirrels.
In contrast to these beneficial effects on natural seedlings, however,
rodents can hamper artificial revegetation efforts by eating the planted seeds.
"With some traditional reseeding operations, rodents will go up the
closely spaced rows of shallow-planted seeds just like they're in a buffet
line," Longland says.
A Battle of Wits
Young, Longland, and colleagues have come up with two strategies for
outwitting the crafty rodents.
The first is to plant fewer seedsbut at a greater depth and more
widely spaced than traditional seeding operations. "Normally, the
shallow-planted seeds would have a better chance to germinate," says
Young. "But planting deeper seems to deter the rodents, so a greater
percentage of the total planted stays in place long enough to sprout."
Another plus: An ultra-low seeding rate reduces the cost of native plant
restoration up to 25-fold.
Since this technique was developed in 1994, it has become the standard for
seeding Indian ricegrass in the Great Basin. The tricky part is getting the
seed drills to plant the seeds sparsely. Adding an inert material like
vermiculite or rice hulls in the drill box allows the equipment to work
normally but spreads out placement of the seeds.
The second approach takes advantage of the animals' natural tendency to
The long-tail pocket mouse, a close relative of kangaroo rats, exhibits cheek
pouches characteristic of this family of rodents. Seeds carried in the pouches
as the mouse forages are then buried in various locations, aiding the
distribution and establishment of new Indian ricegrass stands.
"Kangaroo rats and other caching rodents don't eat most of the seeds
they collect until later," Longland says. The new method, still under
development, would allow the rodents to cache the newly planted, desired seeds.
Then, land managers would provide a cheaper commercial seed that the rodents
prefer, such as millet. This cheaper seed would be a decoy, or
sacrificerecovered first from the cache, since the rodents like it
better, leaving more of the native seeds in the ground to germinate.
"Our tests to date indicate this could work," Longland says.
Rodents did like the millet better than the native plant, four-wing saltbush.
But so far, they haven't found anything the animals like better than Indian
The most immediate practical application for Longland's work may be as a
"If we know which rodents live in an area that has been disturbed, we
should be able to estimate how the area will recover without artificial
reseeding," he says.
For example, in 1985, a fire burned 6,800 acres near Flanigan, Nevada, by
the California border. Land managers planted seeds to stabilize the area. The
next year, lush growth of Indian ricegrass appearedbut it was not from
the seeds in the revegetation mixture.
"If we'd had a good understanding of the rodent-Indian ricegrass
ecology at that time, we might have been able to save the time and money that
went into the reseeding," Longland says. "In some cases, disturbed
areas will recover naturally."By Kathryn Barry Stelljes. To
reach the author, contact Marcia
Wood, Agricultural Research Service, Information Staff, 800 Buchanan St.,
Albany, CA 94710; phone (510) 559-6070.
William S. Longland is at the
USDA-ARS Ecology of Temperate
Desert Rangelands Laboratory, 920 Valley Rd., Reno, NV 89512; phone (702)
784-6057, fax (702) 784-1712.
"Range Reseeding Relies on Rodents" was published in the
January 1998 issue of Agricultural Research magazine. Click
here to see this issue's table of