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
Ecological Impacts
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: 503-523
Ecological Impacts: Nitrogen
Question: How is N cycling affected by exotic grass
invasion?
Method: Examined rates of N mineralization & nitrification,
and characterized soil microbial communities
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
Ecological Impacts: Carbon
Question: Does woody plant invasion increase C
sequestration?
Method: Examined 6 sites along precipitation gradient
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
Tamarix ramosissima
Ladenburger et al. (2005) J. of Arid Env 65: 111-128.
Ecological Impacts: Water
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
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: 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