Wildlife, Animals, and Plants
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BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Cirsium vulgare | Bull Thistle
GENERAL BOTANICAL CHARACTERISTICS :
Bull thistle is an introduced biennial herb which produces a first-year
rosette. Several primary roots develop from the root crown, and each
bear a number of smaller lateral roots. One becomes longer and thicker,
forming a short, fleshy taproot up to 27.5 inches (70 cm) long. The
(usually) second-year flowering stem is 1.6 to 6.6 feet (0.5-2.0 m)
tall, with many spreading branches. Flower heads are 1 to 2 inches
(2.5-5.0 cm) in diameter, few or solitary on naked peduncles up to 6
inches (15 cm) long. All flowers are hermaphroditic. Achenes are about
0.1 inch (2.5 mm) long [3,12,15,18].
RAUNKIAER LIFE FORM :
Hemicryptophyte
Geophyte
REGENERATION PROCESSES :
Bull thistle is a monocarpic herb which must regenerate from seed.
Seeds have little dormancy, and germinate rapidly whenever conditions
are favorable [13,18].
In the Netherlands, seed germination varied between 60 percent and 90
percent, and was highest in the temperature range 50 to 86 degrees
Fahrenheit (10-30 deg C). Seeds stored for more than 3 years at room
temperature did not germinate [18].
In west-central Idaho, bull thistle seeds were found in the seedbank of
three forest habitat types, although bull thistle plants were rare or
absent. Eighty-seven percent of bull thistle seeds were found in the
upper 2 inches (5 cm) of soil, and 13 percent at 2 to 4 inches (5-10 cm)
[19].
In Yosemite National Park, California, clipping in plots where bull
thistle was previously absent promoted bull thistle seedling
establishment, and digging further promoted it. Establishment was
greatest in areas of intermediate soil moisture, and least in very wet
and very dry areas [23].
SITE CHARACTERISTICS :
Bull thistle grows in dry to moist habitats [5] in fields, pastures,
grasslands, first-year meadows, road verges, fertile spoil heaps,
coastal dunes, and wastelands. It also occurs in woodland clearings,
rock outcrops, on the banks of rivers and streams, and in hedgerows. It
is an agressive weed, but it will not survive where cultivation has cut
back its stem and destroyed its root system [18,28].
Bull thistle occurs from cool-temperate zones to warm-temperate
subtropical zones [18].
Bull thistle makes good growth on gentle slopes, fair growth on moderate
slopes, and poor growth on steep slopes [5]. It occurs on soils with a
wide range of pH values, having a peak on almost neutral soils, and
being very rare on soils of pH less than 4.8 to 5. It thrives on
nitrogen-rich soils [18], and it grows on gravelly- to clayey-textured
soils.
Bull thistle has been reported at the following elevations in several
western states [5,23]:
Elevation (feet) Elevation (m)
CA 0-9,000 0-2,750
CO 5,000-10,800 1,525-3,290
MT 3,600-4,600 1,100-1,400
UT 5,500-7,700 1,675-2,345
WY 4,400-6,800 1,340-2,070
SUCCESSIONAL STATUS :
Facultative Seral Species
Bull thistle was present in New Jersey fields that had been abandoned 2,
5, 10, and 40 years [2]. In northwestern Montana, it was present in all
7- to 16-year-old clearcuts studied, though it always provided less than
1 percent coverage. It was not present in uncut stands [1].
Bull thistle cannot withstand deep shade, and is nearly absent if light
is reduced to less than 40 percent of full sunlight [18].
SEASONAL DEVELOPMENT :
Bull thistle seeds generally germinate in the spring and fall. The
rosette grows until winter, partly dies back, and begins to grow again
in early spring. Age at bolting is controlled by plant size. Bull
thistle is usually a biennial, but can be a winter annual. Under
low-fertility conditions, bolting may be delayed several years. Almost
all plants require vernalization to bolt. After flowering and seed
production the plant dies [12,13,18].
Bull thistle flowering times have been reported for some states and
areas [3,5,12,23]:
Begin Peak End
Flowering Flowering Flowering
CA June October
CO July August September
KS June October
MT July July July
ND July August September
UT June August October
WY August August September
Great Plains June October
Related categories for Species: Cirsium vulgare | Bull Thistle
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