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Understanding the impacts of
invasive plants in natural areas
John M. Randall
The Nature Conservancy
Wildland Invasive Species Team
University of California, Davis
http://tncweeds.ucdavis.edu
May 2003
- v. 1.1 -
"On a global basis...the two great destroyers of
biodiversity are, first habitat destruction and,
second, invasion by exotic species”
- E.O. Wilson
1998-1999 Survey of The Nature
Conservancy field staff
• 110 TNC staff from 50 states responded
• 49% said INVASIVE PLANTS were among
the top 3 threats
• 84% said INVASIVE PLANTS were among
the top 10 threats
• Only 5% said INVASIVE PLANTS were not a
problem
• 271 INVASIVE PLANT taxa were reported
WEED
EXOTIC ~ ALIEN ~ NON-NATIVE ~ NON-INDIGENOUS
INVASIVE
NOXIOUS
Conservation Goals
Conservation Targets
(What are you managing for?)
• Ecosystem Level Impacts
- Disturbance regimes (i.e. fires)
- Hydrology
- Geomorphological processes (i.e. erosion, sedimentation)
- Soil chemistry (i.e. nutrients)
• Community and Population Level Impacts
- Vegetation structure
- Community composition
- Resource competition
- Negative impacts on native animals
- Promotion of non-native invasive animals
- Population reductions, eliminations
- Reduced recruitment of natives (succession)
- Hybridization with native species
• Positive Impacts
• Lack of Impacts
Ecosystem Level Impacts
• Disturbance regimes (i.e. fires)
• Hydrology
• Geomorphological processes
(i.e. erosion, sedimentation)
• Soil chemistry (i.e. nutrients)