Volume 6, Spring 2008 - Saddleback College

Fall 2007 Biology 3A Abstracts
Discussion
Plant invasion in California chaparral habitat
by plants such as Black Mustard (Brassica nigra) and
Artichoke Thistle (Cynara cardunculus) are often the
result of nature disturbances such as wildfires or
human disturbances (Le Houerou 1991). After the fire
on May 13, 2002 it has been demonstrated that the
Artichoke Thistle species was able to grow in an equal
ratio to Black Mustard (Figure 2). In the burned
chaparral habitat the plant count indicated that there are
more Black Mustard plants (174) than Artichoke
Thistle (58). When the density and coverage of the
Artichoke Thistle is taken in to consideration in the
importance values, a nearly one-to-one ratio can be
seen; 1.3484 Black Mustard and 1.3416 Artichoke
Thistle. Since Black Mustard is a tall plant (~2 meters)
but with a narrow diameter (< 1 meter) many
individuals could grow in a single area forming a dense
net of the species. Artichoke Thistle instead has a large
diameter (> 1 meter) that prevents and other individual
plant species to grow near it. One other species of
plant was found in the burned 100 m² section but was
not included in the chi square analysis because of the
statistically low prevalence of the species.
In unburned chaparral habitat the species
count indicated that Black Mustard (533) is more
prevalent than Artichoke Thistle (3). The importance
values confirmed that Black Mustard (2.8092) is more
prevalent than Artichoke Thistle (0.1908) with the 100
m² section containing only 6.79% Artichoke Thistle
(Figure 1). The absence of fire in the last fifteen years
in this area maintained a dense coverage of plant
species that Black Mustard with its narrow diameter
could infiltrate but was more difficult for the large
diameter Artichoke Thistle. No other species occurred
in the 100 m² section. Pasture grassland areas,
commonly found in Southern California, often show
pure strands of this (Brassica nigra) species (Bell and
Muller 1973). Non-native plant species invade the
California grasslands and become significantly more
prevalent after wildfires.
Literature Cited
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The Effect of Mycorrhizae on the Growth and Development of Bush Beans
69
Saddleback Journal of Biology
Spring 2008