Exotic Grasses - Caesar Kleberg Wildlife Research Institute

Exotic
Grasses:
A Call to Restore Our Native Habitat
Dawn of a
Conservation
Crisis in
South Texas
article by Colleen Schreiber, reprinted in part and with permission from Livestock Weekly
I
t is known as the last great habitat,
that stretch of land running south
from Port O’Conner north to Victoria,
northwest to San Antonio and west to Del
Rio. It is the rich biodiversity of native
flora and fauna that makes it so. Some
fear, however, that this great biodiversity
is being changed forever by monoculture
stands of exotic grasses.
Dr. Tim Fulbright, research scientist
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| Texas Wildlife | February 2011
with the Caesar Kleberg Wildlife Research
Institute (CKWRI) calls it a conservation
crisis.
“We are losing hundreds of thousands
of acres of native habitat to urban sprawl
every year. Now, monoculture stands of
exotic grasses are further degrading the
habitat that remains,” Fulbright insists. “If
this continues, not only will there be fewer
places to hunt, but the places that remain
The
photos by Eric Grahmann, except where noted
will only be half as good.”
Exotic grasses like guineagrasses,
Lehmann’s lovegrass, bermudagrass,
buffelgrass and a whole host of Old World
bluestems, including Kleberg and King
Ranch bluestem, did not evolve in the
South Texas ecosystem. They were imported decades ago, many during the early
part of the 20th century, at a time when
cattle production was the primary income
Buffelgrass.
Floral monocultures
of exotic grasses
generally equate to
poor wildlife habitat.
for most ranchers.
In South Texas, buffelgrass was
considered a miracle grass, because it
kept many ranchers in the cattle business.
According to Eric Grahmann, a Ph.D. candidate at CKWRI, between 1949 and 1985
an estimated 10 million acres of South
Texas rangeland was converted to buffelgrass, and an additional 14.8 million acres
was planted in Mexico. In fact, one study
suggests that in a few years 12 percent of
Mexico will be covered in buffelgrass.
Probably that much or more acreage
has been overtaken by King Ranch (KR)
and Kleberg bluestems. At one time, KR
bluestem was one of Texas Department of
Transportation’s (TxDOT) most favored
restoration grasses, because it covered the
soil within the 60 days mandated by the
Environmental Protection Agency (EPA).
And, there wasn’t much native grass seed
available at the volume needed; supplies of
native grass seed are still lacking today.
The really troublesome part is that
KR and Kleberg bluestems are no longer
confined to highway-rights-of-ways and
seeded pastures. They’re now likely to be
found on most any farm or ranch in the
state. But the blame, if there should be
blame, can’t just be heaped upon TxDOT.
Throughout the 20th century, these grasses were staples of reseeding mixes recommended by the Soil Conservation Service
(now the NRCS), for erosion control,
pasture, and hay production and 13 Old
World bluestems remain in their recommendation list still today.
These grasses served a purpose
for that era, and they did so amazingly
well. However, for every action there are
intended and unintended consequences.
Times have definitely changed. No longer
are livestock king in South Texas. In fact,
there are thousands of acres that have been
totally devoid of livestock for a decade or
more. For the most part, these operations
are now primarily focused on wildlife. Consequently, these exotic invasive grasses are
in the spotlight like never before.
As noted by Fulbright, monoculture stands of exotics disrupt the entire
ecosystem by decreasing the biodiversity
of native flora and fauna. From a wildlife
perspective, a decline in forbs is particularly troublesome for quail as seeds from
these forbs are an important component of
A rank buffelgrass
monoculture burning
on the Hixon Ranch
(January 2008). Exotic
grasses pose a serious
threat by promoting
more frequent and
intense fires.
Texas Wildlife | February 2011 |
9
A monoculture of Kleberg Bluestem on the Hixon Ranch
(September 2009).
their diet. Likewise, in many parts of South
Texas, perennial forbs are the mainstay of
the diet of the white-tailed deer.
“When these exotics invade not only
do they reduce the abundance of forbs,
but they also reduce overall plant diversity,” Fulbright points out, “and the more
we understand the foraging ecology of
white-tailed deer, the more we realize that
a diversity of plants is really important.
The highest nutritional demand in the lifecycle of a doe is when she is lactating,” he
continues. “If she only has a solid stand of
exotic grasses to choose from and no forbs,
she will not likely meet her nutritional
demands.”
Furthermore, such invasions have a
cascading effect impacting not only game
species but grassland birds as well as the
arthropod community. CKWRI research
has shown that bobwhite densities are 50
percent less and arthropod abundance is
60 percent less on non-native sites versus
native sites. Integrally intertwined, grassland birds and arthropods are indicator
species as to the health of the native habitat. Also scientists have found that while
bobwhites will nest in buffelgrass clumps,
they avoid foraging on sites where buffelgrass canopy cover exceeds 30 percent.
Additionally, exotics like guineagrass
and buffelgrass produce far more biomass
than native grasses. And, given that livestock grazing has been removed from so
many South Texas ranches, productivity
is even more pronounced. Consequently,
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| Texas Wildlife | February 2011
A patch-burn (Hixon Ranch, April 2010). Forbs have responded well in
several burns; however their response was better in sandy or rocky versus
loamy soils. Quail tend to use patch-burns, but only where native forbs or
woody plants provide adequate cover
prolific stands of exotic grasses can and
are altering the fire regime causing more
intense and more frequent fires. That’s not
always good for wildlife. Intense wildfires
tend to severely reduce woody vegetation
which can be particularly detrimental to
whitetails in that it reduces cover needed
during the summer for thermal regulation. Also, on the Faith and Comanche
Ranches, CKWRI has documented the
importance of mast in deer diets. A catastrophic fire which top kills these woody
plants reduces mast availability. Additionally, such fires potentially reduce mottes
of woody plants that are important escape
and loafing cover for quail.
Cullen Looney, owner of Anacahuita
Ranch in northwestern Hidalgo County,
has his own plant challenge. His beef is
not with an introduced grass but rather
with the native tanglehead. Looney first
noticed the plant on his neighbor’s ranch
in 2006. He didn’t think much about it
until it moved onto his property. His wife
informed him that she didn’t like it. His
cattle didn’t seem to be too crazy about
it either, but the defining moment came
when neither his bird dogs nor his hunters
could find any quail in the tangleheadinfested areas on his ranch.
“When your wife is against you, cattle
don’t like it, and quail don’t like it, you
better do something about it,” remarked
Looney.
In recent years, the rate of spread of
many of these non-natives and tanglehead,
particularly in the sand sheet in South Texas, has been unprecedented. CKWRI scientists have been closely following the expansion of these invaders across landscape for
some years. They have identified several
factors likely facilitating their spread. The
first, which is self explanatory really, is
the intentional planting of the species for
forage, erosion control, and pipeline and
rights-of-ways revegetation work.
“The seeds are inexpensive and they
establish readily,” Fulbright notes. “The
problem is again that they expand out
from the areas where they’ve been planted
and take over native plant communities.
There is also a lot of unintentional planting as these seeds are easily transported by
vehicles.”
Other likely contributors of the spread
of these exotics is a decline in livestock
grazing and changing weather patterns, i.e.
fewer extended freezes and a recent trend
toward greater summer rainfall as well as
natural disturbances such as hurricanes
and periodic drought and fire. Scientists
believe warmer temperatures, in particularly, have perpetuated the spread of
guineagrass to the north.
Perhaps, the one factor that has had
the greatest impact on the proliferation of
these exotics, and also the one that is most
troubling, is soil disturbance. It’s troubling
because there is so much of it going on
throughout the state, be it energy production, land fragmentation, highway infrastructure or urbanization in general.
A bobwhite hen near native
plant restoration plots.
Bobwhites and other wildlife
species have begun using
areas where exotic grasses
such as buffelgrass and Kleberg
bluestem have been replaced
with native plants (Hixon Ranch,
June 2010).
Photo by Eric Grahmann
To understand the real reason why disturbance is so troubling, one must dig into
the basic biology of these exotic grasses.
First and foremost, they are prolific seed
producers. They are also drought tolerant.
Unlike natives, which use dormancy during drought as their defense mechanism,
exotics thrive during drought. Their very
nature makes them more competitive; they
are the aggressor. This is why on disturbed
sites it is the exotics that typically move in
first. They get established before the native
species even have a chance.
In terms of disturbance, the Eagle
Ford Shale play is a huge concern for
wildlife enthusiasts concerned about the
spread of exotic grasses. The entire play
encompasses an estimated 6.5 million acres
of prime South Texas wildlife habitat.
Already there are approximately 105 active
rigs and greater than 300 producing wells
in place and another 350 wells are expected
to be drilled over the next year. In fact,
one engineering firm predicts as many as
90,000 wells could be drilled over the next
30-plus years. Additionally, over 1000 miles
of pipelines are anticipated over the next
three years.
Such development is particularly con-
cerning to restoration ecologists like Paula
Maywald. She points out that unless land
and mineral owners have a strong surface
use agreement that specifically requires
planting wildlife friendly natives, oil and
gas companies will continue to reseed pipeline easements and restore pad sites with
exotic grasses. Thus, the spread will not
only continue but worsen.
TWA Member Tim Hixon is one of
Maywald’s clients. He has a strong surface use agreement. His real challenge is
that much of his ranch, located in LaSalle
County, is already covered with thick
stands of buffelgrass and Kleberg bluestem.
Hixon is no different than his contemporaries. When he bought his first
ranch in the 1960s, his focus was largely on
cattle and again the SCS recommendation
back then was rootplow and reseed with
buffelgrass.
“I didn’t realize at the time the effect it
would have on wildlife,” remarked Hixon.
“We’ve tried really stuffing cattle in on top
of this stuff, and it opens it up some. Cattle
will eat the buffelgrass, but they have to be
plenty desperate to eat the KR bluestem.”
In fact, from a habitat perspective,
ranch manager Mike Hehman says it is the
Heavily utilized native forbs planted to replace exotic grasses on
the Hixon Ranch. Deer avoid buffelgrass and Kleberg bluestem
monocultures and prefer feeding on native forbs. (February 2010).
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| Texas Wildlife | February 2011
Kleberg that scares him most. Kleberg acts
like a turfgrass forming an impenetrable
mat across the surface. Not only is it a
prolific seed producer, but it also produces
runners making it much more aggressive
than even buffelgrass. If the two species are
mixed together on the same site, Kleberg
will eventually take over pushing even the
buffel out.
“We’ve learned to manage buffelgrass,
but we haven’t yet found a way to stop
Kleberg bluestem from spreading,” remarks Hehman.
That’s not to say, though, they’re not
all trying to find a solution. Hixon Ranch
and several other ranches are working
hand in hand with CKWRI researchers to
find answers. Scientists have determined
that the very popular management tool of
disking to promote the growth of forbs may
not be the best idea on sites where these
exotics are already established. Strips can
be disked in exotic grass monocultures to
increase bare ground and promote some
native forbs and grasses. However, disking
and other major soil disturbances should
be avoided in plant communities that are
predominantly native. Soil disturbance,
such as disking, has been shown to increase
Photo of a diverse native seed mix from South Texas
Natives used for restoration plots on the Hixon Ranch.
Texas-Wildlife.org
(In top & bottom photos)
Strips can be disked in exotic grass monocultures to increase bare ground and promote some native forbs and grasses (Hixon Ranch, September 2009).
Both are important components of bobwhite habitat. However, disking and other major soil disturbances should be avoided in plant communities
that are predominantly native. Soil disturbance, such as disking, has been shown to increase exotic grass cover and abundance on some soil types in
southern Texas.
Texas-Wildlife.org
Texas Wildlife | February 2011 |
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A research plot previously dominated by buffelgrass replaced by native
forbs from the soil seed bank after repeat Glyphosate spraying (Hixon
Ranch, May 2010).
An area previously dominated by buffelgrass restored to a diverse
native plant community after repeated plowing and disking. All
plants present were established from the soil seed bank (Hixon
Ranch, June 2010).
An area previously dominated by buffelgrass restored to a diverse native plant
community. The South Texas Natives program has been instrumental in selecting and
releasing adapted (ecotypic) natives for rangeland restoration in southern Texas (Hixon
Ranch, June 2010).
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| Texas Wildlife | February 2011
Texas-Wildlife.org
Grazing contrast between a patch-burn (left side of road) and an area not burned (right side). You can see that the cattle focused on
the burn even when immediately next to areas that were not burned. From a grassland heterogeneity stand point, patch-burning and
grazing appears to be a viable management option for managing exotic grass structure in terms of biomass.
exotic grass cover and abundance on some
soil types in southern Texas. Also, more
research shows that repeated burning
exacerbates the increase of buffelgrass and
tanglehead.
“That’s really troublesome, because
prescribed burning is probably one of the
most effective management tools available,” comments Fulbright. “I’m certainly
a little more thoughtful about recommending that practice now because of the presence of these exotic grasses and the impact
that fire has on their spread.”
CKWRI researchers are studying the
use of patch burning and grazing as a management tool to perhaps slow the spread of
exotics. Preliminary results for guineagrass
control are promising. They’re also investigating the use of patch burning and grazing to increase open space for bobwhites on
buffelgrass dominated sites, but the jury is
still out on its effectiveness.
South Texas Natives (STN) is also integrally involved in finding solutions to these
challenges. STN’s mission is to develop and
promote native plants for restoration and
reclamation of native habitats on public
and private lands of South Texas.
Texas-Wildlife.org
A decade in the making, working
with USDA-NRCS Plant Materials Center
in Kingsville, STN has released 14 seed
sources of native plants adapted specifically
to South Texas. They have also done extensive research work on restoration methods.
A product of that is the Restoration Manual
for Native Habitats of South Texas, published
by CKWRI. It is an incredibly wonderful,
easy to use guide that should be in every
land manager’s ranch truck right along
with a plant identification book.
Steps for successful revegetation with
native plants are as follows:
³reduce non-native grasses, prepare a
firm seedbed, plant when the weather
dictates -- not by the calendar;
³plant native cultivars, plant a mixture
of several species -- annuals forbs, i.e.
tallow weeds, clammyweed and competitive perennial grasses like hooded
windmillgrass, Arizona cottontop,
multilflowered rhodegrass, pink
paappusgrass, plains bristlegrass and
sideoats grama;
³50 percent of the mix should be fastestablishing plants;
³use all available tools to manage
Texas Wildlife | February 2011 |
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This restoration plot, previously 100 percent buffelgrass canopy cover, was converted to a
diverse mixture of native forbs. Exotic grasses return but are kept in check by a grass specific
herbicide and competition from native plants. Treatment longevity has yet to be determined.
the site, i.e. cow, plow, axe and fire,
and finally,
³be patient.
STN and CKWRI’s Eric Grahmann
are working with the Hixon Ranch to reestablish patches of native plants on sites
that are interspersed with buffelgrass and
Kleberg bluestem. They’re trying a combination of shredding, mowboard plowing
and deep disking. Patch burning and
grazing is another treatment method.
Hehman says it’s been incredibly rewarding to see the wildlife, particularly
the avian population, respond so positively to these newly established native
plant sites. The downside is that these
treatment methods are not only time
consuming to employ, they’re also costly, and maintaining the rich diversity of
native plants on these newly reseeded
areas remains a constant struggle with
buffel and Kleberg lurking on the edges.
One other potential concern is the
availability of native seed. In fact, STN
says the biggest challenge they are fac-
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| Texas Wildlife | February 2011
ing is that commercial seed producers
have yet to be convinced that there is
widespread demand for such natives. It’s
a touchy subject for STN Director Forrest Smith. He insists that the revegetation work on the new pipelines from the
Eagle Ford play on the Hixon Ranch
alone will use up the entire supply of
commercial STN native plant seeds currently available. Plus TxDOT is, in fact,
required to use native plants in rightsof-way revegetation projects.
Several commercial seed companies
are working hand in hand with STN, as
is TxDot, but because TxDOT still has
to meet EPA requirements, they are not
willing to specify the use of these seeds
until adequate commercial quantities
are available. Seed dealers are reportedly ramping up production.
In the meantime, Maywald notes
that annual cover crops are a good alternative for restoration and revegetation
projects until natives can be established.
In the fall cereal grains like triticale,
oats, Austrian winterpea work well.
Spring alternatives are millets, haygrazer and cowpeas.
For the spread of exotics to finally
slow, the bottom line, Hehman says, is
landowners need to stop buying exotic
seed. Smith agrees.
“Exotic grasses are literally choking the lifeblood out of the South Texas
landscape,” he insists. “Birds, plants,
insects, water, income generators like
nature tourism and hunting operations
even the more traditional ranching
enterprises are all impacted by exotics.
The whole system is changed when exotic grasses are allowed to dominate.”
No question about it, exotic grasses
are here to stay. Learning to successfully
manage them is paramount if the last
great habitat is to be saved. Scientists
are hopeful that in time, research will
provide some tangible answers. In the
meantime, educating the public about
the threats of exotic grasses to the native
habitat is the next best solution.
Texas-Wildlife.org
Identifying the Invaders
Buffelgrass
Kleberg Bluestem
Photo by Timothy Fulbright
Photo by Timothy Fulbright
Guineagrass
King Ranch Bluestem
Photo by Timothy Fulbright
Photo by Forrest Smith
Bermudagrass
Tanglehead
Photo by Forrest Smith
Photo by Timothy Fulbright
Texas-Wildlife.org
Texas Wildlife | February 2011 |
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