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
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:
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:
Ehrenfeld (2003) Ecosystems 6:
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:
Ehrenfeld (2003) Ecosystems 6:
Ladenburger et al. (2005) J. of Arid Env 65: Tamarix ramosissima
Kulmatiski et al. (2006) Plant & Soil 288: Question: Does plant invasion shift timing of water use? Method: Used stable isotope ratios in soil and plant tissue Ecological Impacts: Water
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
Crooks (2002) OIKOS 97:
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: