1. 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

2. Impacts of Invasions Ecology –Species replacement –Ecosystem functions –Threatened & endangered species Economic –Total environmental damage estimates Social –Water quantity and quality –Human health

3. Conceptual model: Walker & Smith in Lukens & Thieret (1997) Invasive species affect different community & ecosystem processes Ecological Impacts

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

5. Ecological Impacts Impacts on ecosystem properties 1. Disturbance regimes

6. D’Antonio in Mooney & Hobbs (2002)

7. Ecological Impacts Impacts on ecosystem properties 2. Resource dynamics

8. Ehrenfeld (2003) Ecosystems 6: 503-523

10. 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

13. Ehrenfeld (2003) Ecosystems 6: 503-523

15. Ecological Impacts: Carbon Woody plant invasion into grasslands is thought to increase amount of C stored

16. 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

19. Ehrenfeld (2003) Ecosystems 6: 503-523

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

21. 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

23. Ecological Impacts Ecosystem 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

24. Crooks (2002) OIKOS 97: 153-166

25. 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