Document: DES-3-99-132

Factors influencing invasion of southern Californian grasslands by the herbaceous perennial mediterranean climate exotic, Cynara cardunculus.

DESIMONE, S.A.*

National Audubon Society's Starr Ranch Sanctuary, Trabuco Canyon, CA 92679 USA ¹

Abstract:
In southern California, the herbaceous perennial, Cynara cardunculus, invades grasslands, but mechanisms are unknown. Here I report on studies of weed traits and grassland invasibility factors. I measured seed production, dispersal, and storage as well as seedling numbers, microsite, growth, and flowering for three years in three invaded grassland sites. Traits of C. cardunculus only partially matched those as reported for weedy species in the scientific literature and included: Recruitment over a range of site conditions, annual seed crop production associated with rainfall, limited long distance dispersal, limited presence in grassland seed banks, seedling recruitment both under vegetation and in gaps, rapid seedling growth, low seedling herbivory, low numbers flowering at the end of the second growing season, and relatively low nitrogen requirements. In a preliminary analysis of factors associated with weed invasion, steep slopes, clay soils, and high density and cover of pocket gopher mounds were positively associated with C. cardunculus cover and density. Native perennial bunchgrass cover and density were negatively associated with weed cover and density. I used a factorial experiment to test hypotheses about biotic and abiotic predictors of grassland invasibility. I found that some biotic disturbances (pocket gophers) were important for weed establishment, while mammalian herbivory, especially granivory, was not influential. An abiotic factor (added moisture) interacted significantly with the simulated pocket gopher mound treatment to positively affect weed seedling establishment in the grassland.

Keywords: weed traits,grassland

This abstract is being presented at: 8:00 AM in session:
Oral Session #19: Grassland Restoration.