1Fullerton College, Department of Environmental Science, 321 E. Chapman Avenue, Fullerton, CA, 92832, USA.
2Programme in Community and Agroecology, University of California, Santa Cruz, CA, 95064, USA.
Department of Environmental Studies, University of California, Santa Cruz, CA, 95064, USA.
*Correspondence author; E. Mail: wcolvin@fullcoll.edu
Allelopathy was proposed as one mechanism that allows introduced species to become invasive. With this examination being the first of a three-part series, we evaluated this concept for the invasive fennel plant (Foeniculum vulgare) whose allelopathic potential is recognized. Since the late 1980s, fennel has invaded grassland and soft chaparral vegetation communities on Santa Cruz Island in Channel Islands National Park. Using a rapid bioassay technique, we evaluated the germination response of forb and grass functional groups from different centres of origin. The response of 34 California native and introduced Mediterranean species to water soluble fennel leaf leachate was determined in the laboratory between April 2005 and August 2006. In general, germination of native species was significantly inhibited at fennel leachate concentrations above 2.0%. For introduced species, there was no significant effect on germination with most species able to germinate in leachate concentrations of 5.0%. Native species were negatively impacted at the most critical stage in their development, whereas introduced species were able to germinate even at the highest treatment concentration of fennel leachate used in bioassay.
Bioassay, fennel, Foeniculum vulgare, germination, interference, native, non-native invasive plant
