Timothy E. Fulbright
Replace native plant
communities Semi-monocultures Persist indefinitely
>185 introduced African grasses
• Bermudagrass, buffelgrass, guineagrass,
Kleingrass, Lehmann lovegrass Old World Bluestems
• Angleton, Australian, Caucasian, Kleberg’s,
Yellow (King Ranch), others
Reasons for invasion
• Must understand before
we can manage • May be complex Ecosystem impacts Management
implications
Proximity to seed source Seed dissemination Soils Disturbance Climate change
Closer to source, more likely invasion
• Roadsides As surrounding area
with invasives increases, probability of invasion increases
Probability of invasion
• Planted pastures
Area planted (%)
Highways are point source TEXDOT replacing with natives
Seed dissemination along roads Animal vectors
• Lehmann lovegrass seeds in cattle rumens • Buffelgrass spikelets in fur • Guineagrass seeds in birds
Certain soils less prone to invasion
• Fine sands • Alkaline • Saline Combination of optimal soil, climate,
dissemination • Unlikely to prevent • Increase exponential
Fire Soil disturbance Energy development
Fire & buffelgrass Frequent, intense fires convert native to
buffelgrass CWMA – natives 30% greater with fire
Fire & guineagrass Considered fire resistant Can reduce guineagrass
• Hot fire reduced density 37% • Increased native richness 330%
Fire does not cause Lehmann to spread Grazing or drought - natives decline
• Lehmann then replaces natives • Factors allowing Lehmann to dominate >H2O use efficiency than natives >reproductive rate Fire can reduce Lehmann
• Reduction may result in increased natives Need better understanding of fire-
Lehmann relationships
Fire & Old World bluestems Conflicting information Kansas – fires exacerbates Caucasian
bluestem Texas • Fire reduced King Ranch bluestem • King ranch bluestem distribution unrelated to fire Variability
• Timing • Soils
Soil disturbance Buffelgrass and discing 50 Control
Disced in 1990
Canopy Cover (%)
40
30
20
10
0 1990
1991
1992
1993 Year
1994
1995
Energy development
Introduce exotics into new areas Petroleum and wind
• Roads & pipelines • Transmission lines • Seeds on Vehicles Mowers
Point sources of
spread
Climate change Buffelgrass
• Mean minimum temperature 5 C (41 F) • Seedlings tolerate – 6 C (21 F) Guineagrass
• Mean minimum temperature 12 C (54 F) • Killed at <-6 C (<22 F)
Yu et al. Mean of 21 stations
Yu et al. Mean of 21 stations
Yu et al. Mean of 21 stations
Mean rainfall (inches)
3.5 3 2.5 2 1.5 1 0.5 0 1904-1931
1932-1959
1960-1969
1970-1981
1983-2009
Tropical exotic grasses Favored by increasing
• Mean minimum temperatures • Mean temperatures • Summer rainfall Changes exacerbate invasion of native
prairie
Exotic grasses reduce abundance
and diversity • Native grasses • Forbs
Native
Buffelgrass
New Mexico:
breeding bird abundance and species richness > on native vs. Lehmann lovegrass Kansas: species richness 30% > on native vs. old world bluestems
Abundance reduced by half Avoid >25%
buffelgrass cover Buffelgrass reduces food • Seeds unimportant as food • Reduces forbs • Reduces arthropods
Greater arthropod
diversity in native versus nonnative
Invasive grasses alter
arthropod communities Review of 39 studies • Herbivorous insects lower
in 62% • Generalist species may increase or decrease
Kansas
• 4 times > biomass on native vs. old world
bluestem South Texas
• Arthropod abundance 60 times > on native vs.
Lehmann lovegrass/buffelgrass
Long. 2005. MS Thesis, Texas A&M-Kingsville.
Soil microbes and OWBs Kill native soil microorganisms
Inhibit germination of seeds of native plants
May not be detrimental to biodiversity in
soils where marginally adapted Thresholds in canopy cover of exotics below which they have little effect
Generalizations difficult
• Spatial variation • Rainfall – timing, amount
Restoration
• Diversity is key Functional groups Successional groups • Soil microbial communities Scaling effects
• Restoration at larger scales • Small tracts – more difficult to prevent reinvasion
when surrounded by exotics
Climate change and Clement’s ghost
• Lack of hard freezes • Precipitation cycles Restoring “original” impossible
• Climate, landscape function different • Focus on functional Wildlife habitat Biodiversity • Use locally adapted seeds
Tim Hixon and Hixon Ranch Jack and Loris Welhausen Experimental
Station South Texas Natives Department of Defense Houston Livestock Show and Rodeo Houston Safari Club South Texas Quail Coalition