Volume 6, Spring 2008 - Saddleback College

Fall 2007 Biology 3A Abstracts
THE EFFECTS OF FIRE ON SOUTHERN CALIFORNIA PLANT SUCCESSION AND
THE PREVALENCE OF ARTICHOKE THISTLE, CYNARA CARDUNCULUS.
Lauren Ferris
Department of Biological Science
Saddleback College
Mission Viejo, CA 92692
Southern California chaparral habitat is fire dependent for seed propagation and
plant health. Artichoke Thistle, Cynara cardunculus, and Black Mustard, Brassica nigra,
have been observed to thrive and out compete California native species in fire burned
habitats. Plant plot sampling is used to determine the density, frequency, and coverage of
each species of plant in a 100 m² chaparral sample. The two locations were selected as one
burned in five to six years prior and the other as unburned in fifteen or more years. The
results indicated that Artichoke Thistle is statistically greater (p= 0.0001) in prevalence in a
chaparral habitat that has been burned than in unburned chaparral habitat; 58 Artichoke
Thistle compared to 3 Artichoke Thistle respectively. Black Mustard is statistically greater
in unburned chaparral habitat than in burned chaparral where competition against
Artichoke Thistle is greater; 533 Black Mustard compared to 174 Black Mustard
respectively. California wildfires are a significant factor in the increased prevalence of the
invasive Artichoke Thistle in chaparral habitat because the fires clear the habitat of any
plant species leaving the habitat open for recolonization by non-native species.
Introduction
Southern California wildfires are a common
occurrence. Underbrush and dead plant matter are
reclaimed quickly by fires and new plant succession
follows in the replenished soil. Frequent Southern
California fires have demonstrated a feedback response
in selecting for plants with physiological mechanisms
for fire tolerance (Naveh 1975). Post fire plant
communities will demonstrate different ratios of plant
species than areas that have not be recently burned,
approximately 20-30 years. Three to four years after a
fire in Southern California four categories of plant
species can be found in a community; generalized
herbaceous perennials, generalized annuals, specialized
“fire-annuals”, and specialized “fire perennials”
(Keeley et al. 1981). Locations sampled at different
periods post fire should be seen to represent different
ratios of plant species. As fire frequency increases,
non-native weeds increase dramatically (in prevalence)
(Haidinger and Keeley 1993). While Southern
California Chaparral depends of fires for seed
propagation and plant growth (Hanes 1971), the
wildfires are also propagating non-native species that
destroy the diversity of the habitat.
The wild artichoke came to the United States
in the mid – 1800s. Escape from cultivation and
subsequent propagation by seed resulted in a reversion
to of the aggressive and ‘wild’ characteristics (Kelly
and Pepper 1996). Artichoke Thistle (Cynara
cardunculus) is prevalent across much of Southern
California and the eradication of the species is difficult.
The seeds of Artichoke Thistle are wind-dispersed and
can disperse over 40 m in non-vegetated sites, such as
those opened by wildfires (Holt and Marushia 2006).
There has been little research on mechanical control of
C. cardunculus, although repeated cultivation has been
reported as an effective control method (DeSimone and
Ernie 2002).
Black Mustard (Brassica nigra) was
introduced into the United States with the cattle by the
Spaniards in the 1700s. Brassicas can produce up to
ten generations of seed per year (Williams and Hill
1986). Rapid seed production lends itself readily to
invasion of habitat that has been cleared by fire, either
wildfire or human initiated fire, or by cattle grazing.
Within California's inland grasslands,
nonnative annual vegetation has changed seasonal
patterns of resource availability (Dyer and Rice 1999).
These changes affect the native Bunchgrass species
such as Nassella pulchra. Chaparral native species
include Scrub Oak, Chamise, Laurel Sumac, Coyote
Brush, Yucca, and Bunchgrass. This natural diversity
67
Saddleback Journal of Biology
Spring 2008