The Invasive Grass Phenomenon


The Invasive Grass Phenomenon
The Invasive Grass Phenomenon
Forrest S. Smith
Project Coordinator
South Texas Natives
Invasive Grasses
• How did they get here?
– Incidental introductions
(Natal grass, silky
bluestem, tanglehead)
– Intentional (buffelgrass, old
world bluestems)
– Change in native ecology
– Invasive grasses have
been present in south
Texas for decades
– Planted extensively in
south Texas from 1900today
Why are some grasses invasive?
• Introduced species lack
ecological constraints
• Evolutionary history of
native habitat is different
• Degradation of native
ecosystem in south
• Climatic fluctuations
• Plant “improvement”
through agronomy
• Exotic ecotypes of native
• Early successional plants
Invasive Grasses in South Texas
• South Texas has an assemblage of invasive
grasses (13 species in one study site in Lower
Rio Grande Valley, commonly 5-10 species)
• Competitive hierarchies exist between native
species & invasive grasses, & between invasive
• Recent observations & concerns suggest that
invasive grasses are increasing in abundance in
South Texas
• Land use changes (grazing) and disturbances
(energy development, highway expansion)
Old world bluestems
Old World Bluestems
• Kleberg bluestem (Pretoria 90,Kleberg, T587),
southeastern Asia & Africa, present by 1938
• Angleton bluestem (Gordo, Medio, Angleton, T587),
southern Asia, introduced by 1915, released 1924
• Australian bluestem (WW B Dahl), Africa & Asia
• Silky bluestem (Queensland Bluegrass), Australia,
present by 1930’s in LRGV, brought in with Rhodes
grass seed from Australia
• Yellow bluestem (WW Spar, King Ranch, Plains, WW
Ironmaster, Ganada, El Kan), Europe, Asia, and
• Hybrids, occurrence of other species possible
Old world bluestem distribution
Kleberg bluestem
1938 found in Rhodesgrass
pasture on King Ranch with
Yellow bluestem
1940 increased at Experiment
Station in Kleberg County,
compared to South Africa &
China collections
1944 Released by SCS
1945 “uncommon” weed in
Cameron County
1949 roadside weed in Kleberg
1950’s abundant in many
Today throughout south Texas
Australian, Angleton, Silky,
Yellow bluestems
Australian-appears to be well
adapted to the south Texas
sand sheet, established in
isolated locations, highly
problematic in coastal clay
soils in the eastern portion of
south Texas, T587 Cultivar-80
collections from “the near East”
Silky-sporadic, responsive to
rainfall, but not as invasive as
others, present since 1930’s
Yellow-more problematic in
northern portions of south
Texas, but common along
“the grass that saved south
T-4664 Common, 99% of
population approximately 2
million acres
Pecos, 150 miles N of S Tex.,
blight tolerant, Laredo, blight
tolerant, improved forage
Nueces, Frio, Llano-not readily
Extremely invasive in some
habitats, does not spread in
Native to Africa, India,
Indonesia, & Pakistan
1939 Bexar County, SCS
1953 Brooks County,
1953 Kleberg County, Ethiopia
& Kenya origin
1954 Kleberg County-roadside
1954 Dimmit County-roadside
1960 Widespread
1965 Common
Today, more seed sold, &
acres planted than any other
grass in S. Texas
Guinea grass
Introduced intentionally,
Escaped from unauthorized
trials in the LRGV (Richard
Hoverson, pers. Com.)
1931 Kleberg County, Riviera
1954 Kleberg County, nursery
1960’s-1980’s occasional in
LRGV (hard freezes ’62, ’83,
Late ’90s -widespread,
common, abundant
2004 Goliad County
2009 Texas Hill Country
Guinea grass distribution
“an interesting collection
made in 1960, along
a railroad right of way
in Corpus Christi”.
Native, introduced, changed?
Worldwide distribution
(Australia, Africa, India,,
Popular forage species in
these areas
Grass seed introductions of
from other regions?
Recent behavior is extremely
Exotic ecotypes may have
been brought to south
Tanglehead distribution
Lehman lovegrassproblematic on sandy loam
soils; introduced by SCS and
present in south Texas
rangelands by 1949. Native to
southern Africa
Natal grass-sand and sandy
loam soils, present by 1938 in
LRGV, predominantly along
HWYs and RR ROWs.
Common in LRGV by 1945,
present in rangelands in
Wilacy Co. by 1954, and
elsewhere by 1950s. Native to
Africa and southern Asia
And more…
Bermudagrass-problematic in
high rainfall areas (present
since late 1800’s)
without soil disturbance
Kleingrass-usually noninvasive in s. Tex. (1941)
Rhodesgrass-generally not
problematic, exported to south
Texas using Australian
produced seed in early 1900’s.
“Tens of thousands of acres” in
1930’s were wiped out by
rhodesgrass scale, eventually
controlled biologically. Other
exotic species may have been
brought in as weed seed in
Rhodesgrass seed.
Wilman lovegrass-not
invasive, recent introduction
1958 SCS
And more….
Swollen windmillgrassproblematic LRGV and Coastal
Bend, other exotic windmillgrasses are locally invasive
and may spread (Kleberg Co.
railroad ROW & US HWY 77).
From Nigeria, grass nursery
Carrizo Cane-herbicide
control shelved, intense
biological control program has
been initiated by ARS
Blue panicum-nutrient
requirements lacking in south
Texas, problem in riparian
Annual and weedy grassesSabi grass, liverseed grass,
Why are invasive grasses
Lower quail-ity habitat for some wildlife
Loss of biodiversity
Modification of natural ecosystem processes
Socioeconomic (fire intensity, highway mowing cost,
lease value for wildlife recreation, aesthetic value)
• Increases in disturbance and fragmentation of the south
Texas landscape may to lead to greater abundance of
exotic grasses. These disturbances provide pathways for
invasion, spread, and without management, perhapsdominance of the habitat…

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