Invasive Species

Invasive Plants and Their Ecological Consequences Timothy E. Fulbright

What does invasive mean?  Replace

native plant communities  Semi-monocultures  Persist indefinitely

Exotic grasses  >185

introduced  African grasses • Bermudagrass, buffelgrass, guineagrass,

Kleingrass, Lehmann lovegrass

 Old World

Bluestems

• Angleton, Australian, Caucasian, Kleberg’s, Yellow

(King Ranch), others

Outline  Reasons

for invasion

• Must understand before

we can manage • May be complex

 Ecosystem

impacts  Management implications

Reasons for invasion  Proximity

to seed source  Seed dissemination  Soils  Disturbance  Climate change

Reasons for invasion: Proximity to source, more likely invasion

• Planted pastures • Roadsides

 As

surrounding area with invasives increases, probability of invasion increases

Probability of invasion

 Closer

Area planted (%)

Reasons for invasion: Proximity  Highways

are point source  TEXDOT replacing with natives

Reasons for invasion: Seed dissemination  Seed

dissemination along roads  Animal vectors • Lehmann lovegrass seeds in cattle rumens • Buffelgrass spikelets in fur • Guineagrass seeds in birds

Reasons for invasion: Soils  Certain

soils less prone to invasion

• Fine sands • Alkaline • Saline

 Combination

of optimal soil, climate, dissemination • Unlikely to prevent • Increase exponential

Reasons for invasion:  Fire  Soil

disturbance  Energy development

Reasons for invasion:  Fire

& buffelgrass  Frequent, intense fires convert native to buffelgrass  CWMA – natives 30% greater with fire

Reasons for invasion:  Fire

& guineagrass  Considered fire resistant  Can reduce guineagrass • Hot fire reduced density 37% • Increased native richness 330%

Reasons for invasion:  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 fireLehmann relationships

Reasons for invasion: Disturbance  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

Reasons for invasion:  Soil

disturbance  Buffelgrass and discing Control

50

Disced in 1990

Canopy Cover (%)

38

25

13

0

1990

1991

1992

1993 Year

1994

1995

Reasons for invasion:  Energy development  Introduce exotics into  Petroleum and wind

• Roads & pipelines • Transmission lines • Seeds on  Vehicles  Mowers

 Point

sources of spread

new areas

Reasons for invasion:  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)

Mean minimum temperatures

Yu et al. Mean of 21 stations

Mean minimum temperatures

Yu et al. Mean of 21 stations

Mean maximum temperatures

Yu et al. Mean of 21 stations

July precipitation 4.00

3.00

2.00

1.00

0

1904-1931

1932-1959

1960-1969

1970-1981

1983-2009

Reasons for invasion:  

Tropical exotic grasses Favored by increasing • Mean minimum temperatures • Mean temperatures • Summer rainfall

 Changes

prairie

exacerbate invasion of native

Ecological consequences:  Exotic

grasses reduce abundance and diversity • Native grasses • Forbs

Native

Buffelgrass

Ecological consequences: ď&#x201A;&#x17E; New

Mexico: breeding bird abundance and species richness > on native vs.

Lehmann lovegrass ď&#x201A;&#x17E; Kansas: species richness 30% > on native vs. old world bluestems

Ecological consequences:  Abundance

reduced by half  Avoid >25% buffelgrass cover  Buffelgrass reduces food • Seeds unimportant as food • Reduces forbs • Reduces arthropods

Ecological consequences: ď&#x201A;&#x17E; Greater

arthropod diversity in native versus nonnative

Ecological consequences:  Invasive

grasses alter arthropod communities  Review of 39 studies • Herbivorous insects lower in

62% • Generalist species may increase or decrease

Ecological consequences:  Kansas

• 4 times > biomass on native vs. old world

bluestem

 South

Texas

• Arthropod abundance 60 times > on native vs.

Lehmann lovegrass/buffelgrass

Ecological consequences: Rodents

Long. 2005. MS Thesis, Texas A&M-Kingsville.

Ecological consequences: Soils  Soil  

microbes and OWBs

Kill native soil microorganisms Inhibit germination of seeds of native plants

Ecological consequences ď&#x201A;&#x17E; May

not be detrimental to biodiversity in soils where marginally adapted ď&#x201A;&#x17E; Thresholds in canopy cover of exotics below which they have little effect

Management Implications  Generalizations

difficult

• Spatial variation • Rainfall – timing, amount

Management Implications  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

Management Implications  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

Acknowledgements  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