Impacts of Invasions

• Measuring impact is complex– What should be measured and how?

−For individual plant, individual species, or multiple species?

− Over what time frame?

− Lack of comprehensive data

Impacts of Invasions

• Ecology– Species replacement – Ecosystem functions – Threatened & endangered species

• Economic– Total environmental damage estimates

• Social – Water quantity and quality – Human health

Conceptual model: Walker & Smith in Lukens & Thieret (1997)• Invasive species affect different community &

ecosystem processes

Ecological Impacts

Ecological Impacts

• Types of impacts (Parker et al. 1999)– Impacts on ecosystem properties– Impacts on community structure– Impacts on individual species

Ecological Impacts• Impacts on ecosystem properties

1. Disturbance regimes

D’Antonio in Mooney & Hobbs (2002)

Ecological Impacts• Impacts on ecosystem properties

2. Resource dynamics

Ehrenfeld (2003) Ecosystems 6: 503-523

Question: How is N cycling affected by exotic grass invasion?

Method: Examined rates of N mineralization & nitrification, and characterized soil microbial communities

Ecological Impacts: Nitrogen

Hawkes et al. (2005) Ecology Letters 8:976-985

Hawkes et al. (2005) Ecology Letters 8:976-985

Ehrenfeld (2003) Ecosystems 6: 503-523

Ecological Impacts: Carbon

Woody plant invasion into grasslands is thought to increase amount of C stored

Question: Does woody plant invasion increase C sequestration?

Method: Examined 6 sites along precipitation gradient

Ecological Impacts: Carbon

Jackson et al. (2002) Nature 418:623-626

Jackson et al. (2002) Nature 418:623-626

Jackson et al. (2002) Nature 418:623-626

Ehrenfeld (2003) Ecosystems 6: 503-523

Ladenburger et al. (2005) J. of Arid Env 65: 111-128.

Tamarix ramosissima

Kulmatiski et al. (2006) Plant & Soil 288: 271-284

Question: Does plant invasion shift timing of water use?

Method: Used stable isotope ratios in soil and plant tissue

Ecological Impacts: Water

Ecological ImpactsEcosystem engineers: species able to physically alter habitats (Crooks 2002)

•Alter ecosystem physical processes (sedimentation, water availability, N cycling)

•Change habitat structure (more or less complexity)

•Effects cascade through community

Crooks (2002) OIKOS 97: 153-166

Ecosystem Impacts: Transformers

• Question: What is the long-term impact of C. pubescence invasion on Galapagos vegetation?

• Methods: Monitoring permanent plots over 7 years

Jager et al (2009) J of Ecology 97:1252-1263

Jager et al (2009) J of Ecology 97:1252-1263

Jager et al (2009) J of Ecology 97:1252-1263