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Spanish broom is 1 of 4 nonnative invasive broom species that occur in
North America. All are perennial, leguminous shrubs.
DiTomaso [16] provides a table of characteristics to distinguish
among broom species and common gorse. Spanish broom, French broom, Scotch broom and Portuguese broom
have some similar morphological characteristics, while common gorse
is morphologically distinct from the brooms.
Spanish broom is not as widely distributed nor
as common as Scotch and French brooms
(see Distribution and Occurrence),
and less is known about its biology and ecology. According to DiTomaso [16] Spanish broom may have
ecological characteristics similar to Scotch broom.
The following description of Spanish broom provides a
summary of the range of characteristics described in reviews [16,38] and florae [15,27]. It provides
characteristics that may be relevant to fire ecology, and is not meant for
identification. A key for identification is available in Hickman [27].
Spanish broom is a tall shrub to small tree, up to 10 to 15 feet (3-5 m)
tall. Its long, slender stems are erect with few branches. Stems are
cylindrical, rush-like, and green when young, maturing into woody branches with bark.
Mature plants have 1 to several trunks. Spanish broom leaves are
small, 0.5 to 1 inch (2-2.5 cm) long, oval, and smooth-margined. Leaves are ephemeral,
remaining on the plant for 4 months or less. The inflorescence is an open
terminal raceme with several flowers located on current-year shoots. Flowers are
large, pea-like, up to 1 inch long, and grow on short stalks on both sides of
the main stem. Fruit is a linear, dehiscent legume, 2 to 4 inches (5-10 cm) long
and 5 mm wide, with 10 to 15 seeds.
At the time of this writing (2005), no descriptions of Spanish broom root
structure or morphology are available for plants growing in North America.
Chiatante and others [9] describe root morphology of Spanish broom
growing in 3 different rooting environments in Italy: terrace, plane, and 40°
slope. The authors observed that the overall architecture of the root
system was modified on a slope by an increase in the length and number of root
apices of 1st-, 2nd-, and 3rd-order lateral roots. This suggests that Spanish broom reinforces its anchorage
strain by changing the organization of its root system, particularly in the up-slope
direction [9].
Although the leaves of both Spanish broom [36] and Scotch broom [5,36] are ephemeral, their canopies
have a constant positive carbon balance due to stem photosynthesis. Both species have
positive stem assimilation resulting in approximately 200 mmol per m²
per day carbon dioxide assimilation on study sites in California. Although these species grow in different
habitats with different vapor pressure and temperature, assimilation response to
vapor pressure is similar between species. Water-use efficiency is higher and
intercellular carbon dioxide is lower for Spanish broom compared to Scotch
broom. The constant carbon gain throughout the year, from stem assimilation, may enhance the growth
capacity of both species in disturbed habitats [36].
Botanical traits of Spanish broom vary somewhat between cloned individuals
and those grown from seed. In a greenhouse study, several mean growth traits were significantly
(P<0.05) different between ramet and genet populations, and the variance in these traits
tended to be higher in genet populations. Seedlings had consistently greater
whole plant dry mass per shoot length, a higher percentage of total biomass
in leaves, and more roots compared with cloned individuals. In contrast,
few mean physiological traits differed between ramet and genet populations, and
variance was similar between the 2 population types. Environmental variance
accounts for a large proportion of the variance in physiological traits, and
about 33% of the variance in growth traits [37].
Growth form and stand structure:
According to a review by DiTomaso [16], dense broom infestations produce substantial dry matter that can create a serious
fire hazard. While this is particularly true for gorse and French broom [16], Nilsen [38]
also suggests that mature Spanish broom stands should be considered a fire
hazard during the dry season, because patches can be dense and may contain a
large amount of dead wood.
Spanish broom is native to the southern Mediterranean region of Europe,
including Spain, Morocco, the Canary Islands, Madeira, and the Azores.
Spanish broom's North American distribution is from Washington to southern California
[53]. It has also established in Hawaii. Spanish broom occurs in other states as a cultivated ornamental
(e.g. Utah [57], the Intermountain west [2], Texas
[29]).
Spanish broom was introduced into the California ornamental trade in 1848 in
San Francisco. Beginning in the late 1930s, it was planted along mountain
highways in southern California. By 1949, Spanish broom had escaped cultivation
and established populations in Marin County ([38], and references therein). It
now occurs in the north coast counties of California, the San
Francisco Bay region, the Sacramento Valley, through the south coast counties
into northern Baja California [27,37], in the western Transverse Ranges, and the Channel Islands [38].
It also occurs on dry slopes in the eastern half of the Santa Monica
Mountains [15]. Of the invasive
brooms in California, Spanish broom is less widespread and is considered less of a problem
than Scotch broom (Cytisus scoparius) and French broom (Genista
monspessulana) [28]. There is no information in the literature on distribution of
Spanish broom in Oregon, Washington, or Hawaii. Plants database
provides a state distribution map of Spanish broom.
Spanish broom is 1 of 4 nonnative invasive broom species that occur in North America. Spanish broom, Scotch broom, Portuguese broom (C. striatus), and French broom occur in similar habitats. Common gorse (Ulex europaeus)
is another leguminous shrub that occurs in similar habitats.
The following lists include vegetation types in which Spanish broom is known to
be or thought to be potentially invasive, based on reported occurrence and
biological tolerances to site conditions from studies of Spanish broom in
California. There is no information about Spanish broom
distribution or site tolerances outside California; therefore, these lists are somewhat
speculative and may be imprecise.
Postfire colonization potential:
According to Nilsen [38], Spanish broom is especially invasive in southern California chaparral after
fire. No other information on postfire colonization potential of Spanish broom
is available.
Preventing postfire establishment and spread:
The USDA Forest Service's "Guide to Noxious Weed Prevention
Practices" [52] provides several fire management considerations for weed
prevention in general that may apply to Spanish broom.
Preventing invasive plants from establishing in weed-free burned areas is the
most effective and least costly control method. This can be accomplished through
careful monitoring, early detection and eradication, and limiting invasive plant
seed dispersal into burned areas by [23,52]:
re-establishing vegetation on bare ground as soon after fire as possible
using only certified weed-free seed mixes when revegetation is necessary
cleaning equipment and vehicles prior to entering burned areas
regulating or preventing human and livestock entry into burned areas until
desirable site vegetation has recovered sufficiently to resist invasion by
undesirable vegetation
detecting weeds early and eradicating before vegetative spread and/or seed
dispersal
eradicating small patches and containing or controlling large infestations
within or adjacent to the burned area
In general, early detection is critical for preventing establishment of large
populations of invasive plants. Monitoring in spring, summer, and fall is
imperative. Managers should eradicate established Spanish broom plants and small
patches adjacent to burned areas to prevent or limit postfire dispersal and/or
spread onto the site [23,52].
The need for revegetation after fire can be based on the degree of desirable
vegetation displaced by invasive plants prior to burning, and on postfire
survival of desirable vegetation. Revegetation necessity can also be related to
invasive plant survival as viable seeds or root crowns [23].
Managers can enhance the success of revegetation (natural or artificial) by
excluding livestock until vegetation is well established (at least 2 growing
seasons) [23]. See Integrated Noxious Weed Management after Wildfires
for more information.
When planning a prescribed burn, managers should preinventory the project
area and evaluate cover and phenology of any Spanish broom and other invasive
plants present on or adjacent to the site, and avoid ignition and burning in
areas at high risk for Spanish broom establishment or spread due to fire
effects. Managers should also avoid creating soil conditions that promote weed
germination and establishment. Weed status and risks must be discussed in burn
rehabilitation plans. Also, wildfire managers might consider including weed
prevention education and providing weed identification aids during fire
training; avoiding known weed infestations when locating fire lines; monitoring
camps, staging areas, helibases, etc., to be sure they are kept weed free;
taking care that equipment is weed free; incorporating weed prevention into fire
rehabilitation plans; and acquiring restoration funding. Additional guidelines
and specific recommendations and requirements are available [52].
Fire as a control agent:
While prescribed fire is sometimes used in management of French broom and Scotch broom,
no information is available on using fire to control Spanish broom.
Spanish broom occurs along the west coast of North America, in scattered
populations in upland areas on interior sites of the coastal mountains and in
the foothills of the Sierra Nevada [18,36]. It rarely grows in coastal sites in
California [36]. Spanish broom invades disturbed riparian sites in the Sierra
Nevada [18]. No information is available on Spanish broom site characteristics
outside California, other than that it occurs on unstable
river islands in coastal Oregon [37].
Spanish broom was planted along roadsides [10,26] and seeded in
chaparral sites for revegetation after fires in California in the early 1900s [3].
Populations of Spanish broom have persisted and spread along roads [8,15,35]
and in other disturbed areas such as eroding slopes, riverbanks, and abandoned or disturbed lands [27,35,38].
Earlier accounts indicate that Spanish broom is not invasive in native habitats
[26], (McClintock 1985, as cited by [47]). It escaped cultivation and invaded chaparral in southern
California, particularly after fire [10,38].
According to Conrad [10], Spanish broom was planted along roadsides
below 6,900 feet (2,100 m), while Hickman [27] states that it occurs
below 2,000 feet (600 m). Spanish broom commonly occurs on steep slopes [38].
The invasive brooms are successful in high irradiance, disturbed habitats,
most likely due to their photosynthetic stems, rapid growth, and ability to fix nitrogen.
Drought stress severely inhibits photosynthesis of brooms. Photosynthetic stems allow them to
utilize a deciduous leaf phenology (to avoid water stress) and still maintain a large
photosynthetic surface area in summer and fall after leaves have abscised.
On interior mountain sites where Spanish broom occurs, there is a large
difference between summer and winter climate compared with coastal sites [36].
Although the leaves have twice the photosynthetic rate of stems [36], photosynthesis in
stems provides most to the whole plant carbon gain because of their longer life
span and larger surface area (Nilsen and Bao 1990, cited in [38]).
As of this writing (2005) no information is available on the immediate effects
of fire on Spanish broom plants or seeds. Based on information from fire effects
on Scotch and French broom, and reproductive characteristics described by Nilsen
[38], it is likely that Spanish broom is top-killed by fire, and that perennating
tissues below ground survive and sprout after fire.
Spanish broom seed in the soil seed bank is probably not damaged by fire, and
may be stimulated to germinate. High-severity fire may kill
Spanish broom plants and seeds. Research is needed on the effects of fire on
Spanish broom to support or refute these conjectures.
See FEIS reviews on
French broom and
Scotch broom
for more information on fire effects on these species.
Impacts:
Spanish broom rapidly colonizes disturbed habitats and develops thick shrub communities that
prevent colonization by native chaparral species. It may be a fire hazard during
the dry season [38]. However, it is listed by the California Invasive Plant Council
as a "wildland pest plant of lesser invasiveness" [8].
As a nitrogen-fixing plant, Spanish broom may enrich soil nitrogen levels in
invaded communities. Although nitrogen fixation has not
been studied in Spanish broom, Scotch broom is capable of fixing nitrogen
throughout the year in regions with mild winters [58]. The ability of the brooms to fix nitrogen increases the total
amount of nitrogen and the way in which nitrogen cycles in invaded communities [25].
Nitrogen enrichment is unlikely to benefit native plants and may reduce species
diversity [14], except in ecosystems dominated by nitrogen-fixers. This may have implications for restoration and
rehabilitation efforts [25].
Control:
There is little information on controlling Spanish broom.
Nilsen [38] presents a summary of possible control approaches based on the biology of
the plant, rather than on information derived from controlled experiments [38]. See FEIS reviews on Scotch broom and French broom
for information on controlling these similar species.
It is likely that the success of any control method will vary with site
characteristics (topography, soils, climate), age and density of plants in the stand, and the
availability of human and technical resources. Since a large and persistent seed
bank is predicted for this species, it is likely that seedlings will establish
rapidly following fire or mechanical removal of aboveground biomass [38].
A comprehensive monitoring of control effectiveness is critical because there
is no scientifically based knowledge about control of Spanish broom. Experimental
manipulations should be monitored at least annually. Each monitoring visit
should determine the number of new plants and the size or age distribution of
the recovering populations. Attention should be placed on the
proportion of new individuals coming from the seed bank or sprouting from old
plants. Monitoring should continue for at least 5 years after control treatment
[38].
Prevention:
The most effective method for managing
invasive species is to prevent their establishment and spread. Some methods of
prevention include limiting seed dispersal, containing local infestations,
minimizing soil disturbances, detecting and eradicating weed introductions
early, and establishing and encouraging desirable competitive plants [44]. One way to help prevent continued
introductions of Spanish broom into wildlands is to prevent its sale as a horticultural
species.
Integrated management:
A particularly effective control combination for
Spanish broom may be saw cutting followed by application of herbicide to the cut
stem to kill adult plants. Spanish broom seedlings are likely to
establish from the soil seed bank so monitoring and follow-up treatments of new
seedlings is necessary for several years [38].
Physical/mechanical:
In general, physical and mechanical control methods are likely to be effective only when Spanish broom is
young [38]. The Nature Conservancy's Element Stewardship Abstract
on Spanish broom provides a general overview of physical and mechanical control methods that may be effective for
controlling infestations [28].
Pulling with weed wrenches is effective for small broom infestations or in
areas where an inexpensive, long-duration labor source is dedicated to broom
removal [51]. Hand-pulling Spanish broom plants may be most practical and
effective when the stand is 1 to 4 years old, and plants are small enough, as
long as roots are removed and follow-up treatment of seedlings is done. The
optimal season for pulling may be July to September when plants are experiencing
water stress [36]. When plants have matured to small tree size, they cannot easily be
removed with hand tools [38].
Nilsen [38] suggests that machines such as brush hogs are probably impractical
for Spanish broom removal, since it commonly occurs on steep slopes, and
because the trunks of Spanish broom grow rapidly to a size outside the range of
effectiveness for this technology. Saws can be used to cut plants with larger
stems; however, Spanish broom has a great facility for sprouting from a saw cut
even when the cut is close to the ground. When brush
hogs or saws are used to cut Spanish broom stems, sprouting should be expected.
Among all the mechanical methods, saw cutting is least likely to be effective in
preventing sprouting [38].
Fire: See the Fire Management Considerations section of this summary.
Biological:
Biological control of invasive species has a long history,
and there are many important considerations before the implementing a biological
control program. Tu and others [51] provide general information and considerations for biological
control of invasive species in their Weed control methods handbook. Additionally, Cornell University, Texas A & M University, and NAPIS websites offer
information on biological control.
As of this writing (2005) there are no USDA approved biological
control agents for Spanish broom. In greenhouse situations
plants are susceptible to mealy bugs and show evidence of viral
depression of growth [38]. An insect purposely introduced for control of Scotch broom,
the Scotch broom bruchid (Bruchidius villosus) [11], also attacks Portuguese broom,
Spanish broom, and French broom. See Coombs and others [12] for more information on this
insect, its distribution, and effects.
Domestic goats are said to be effective at controlling reestablishment of broom [28].
Chemical:
Herbicides are effective in gaining initial control of a new
invasion (of small size) or a severe infestation, but are rarely a complete or
long-term solution to invasive species management, as they do not change
conditions that allow infestations to occur [7]. Herbicides are more effective
on large infestations when incorporated into long-term management plans that
include replacement of weeds with desirable species, careful land use
management, and prevention of new infestations. See the Weed control methods handbook [51]
for considerations on the use of herbicides in
natural areas and detailed information on specific chemicals and adjuvants.
Spanish broom is sensitive to applied pesticides. In greenhouse
situations only mild pesticides can be used without detrimentally affecting the
plants. Therefore, it is highly likely that application of chemicals such as glyphosate or
triclopyr will drastically reduce population size. The ramifications of applying
herbicides to a plant community must be carefully considered, because effects on
nontarget species are likely, especially when foliage spray methods are used [38].
Rusmore and Butler [42] compared the efficacy of basal
bark applications of varying rates of triclopyr on different size Spanish broom shrubs, at 3
phenological stages, under different moisture and shade conditions on a
California riparian site. Small differences were observed among treatments,
although results were not statistically significant. The kill rate averaged over
90% across all treatments [42].
See The Nature Conservancy's Element Stewardship Abstract
on Spanish broom for a more detailed review of chemical control [28].
Spanish broom provides poor forage for native wildlife [38], and
presumably poor forage for livestock as well. Domestic goats may eat young Spanish broom
plants [28].
Palatability/nutritional value:
No information is available on this topic.
Cover value:
No information is available on this topic.
The following description of habitat types and plant communities in which
Spanish broom occurs
is taken from the few examples found in the literature on Spanish broom
occurrence in California. Spanish broom is probably not restricted to these types
within these areas. There is very little information in the
literature on vegetation types in which Spanish broom occurs.
Spanish broom seems to be most
common in disturbed areas, especially along roadsides [15,35,38], where it was seeded in the early 1900s [38]. In
1958, Hellmers and Ashby [26] stated that Spanish broom has been planted along roads for 20 years, where
it survives and grows well, but has not been able to invade the adjoining stands
of chaparral. It has since become invasive in chaparral in southern California [10], where it was
seeded for revegetation after fires in the early 1900s [3].
According to the California Invasive Plant Council [8], Spanish
broom occurs in coastal scrub, grassland, wetlands, and
oak (Quercus spp.) woodland throughout
California, and forests in the northwestern part of the state.
Spanish broom is associated with coyote bush (Baccharis pilularis) in the interior Santa Cruz Mountains,
with a large monospecific stand of French broom located downslope [36].
Spanish broom also occurs in redwood (Sequoia sempervirens) forests [8,43].
Most of the information on regeneration in Spanish broom comes from a review by
Nilsen [38], and no indication of the source of the information is
given in the review.
Spanish broom spreads by producing abundant seeds. No research has been conducted on
Spanish broom seed banks, germination, or seedling recruitment [38].
Breeding system:
Spanish broom plants are monoecious and outcrossed [37].
Pollination:
Spanish broom flowers are pollinated by bees [38].
Seed production:
Seed production begins when Spanish broom plants are 2 to 3 years old. Each inflorescence
produces 10 to 15 pods containing approximately 15 seeds each. One plant can
produce 7,000 to 10,000 seeds in one season [38].
Seed dispersal:
Spanish broom seeds fall near the parent plant and are subsequently moved by erosion, rain
wash, and possibly ants [38].
Seed banking:
According to Nilsen [38], Spanish broom seeds remain viable for at least 5 years,
suggesting that a large seed bank may be present in Spanish broom stands. The source
of this information is not given, nor is there any additional information in the
literature about seed banking in Spanish broom. More research is needed in this area.
Germination:
Spanish broom seeds, collected in the Santa Cruz Mountains of California and germinated in the
greenhouse, had 100% germination rates [37]. Similarly,
Spanish broom seeds from Israel that were used in an experiment in California "germinated readily
with no pretreatment" [26]. However, scarification is
said to result in "greater" germination rates (Cabral 1954, as cited by [28]). More
research is needed on germination and seed bed requirements of Spanish broom.
Seedling establishment/growth:
Results from an experiment in California indicate that ambient temperature affected
Spanish broom growth form. Spanish broom plants grown for 24 weeks at day/night temperatures of
73/79 °F
(23/26 °C),
86/39 °F (30/4 °C), and
86/63 °F (30/17 °C) were weak
and did not stand erect; whereas Spanish broom plants grown at cooler temperatures
(63/39 °F (17/4 °C),
63/63 °F
(17/17 °C), and 73/39 °F
(23/4 °C)) had shorter
and thicker stems that were able to support their own weight. Leaves were
retained on Spanish broom plants grown at cooler temperatures.
At higher temperatures the leaves dropped soon after they were formed.
All Spanish broom plants had green stems, were branched, and had a very bushy appearance,
especially at temperatures higher than the 17/4 temperature condition. The
roots were nodulated and branched, and permeated the entire medium in a 1-gallon can
at the end of the growth period [26].
Asexual regeneration:
According to Nilsen [38] Spanish broom is "an effective stem sprouter," suggesting that
Spanish broom may sprout from stumps or root crowns following damage or
destruction of aboveground biomass.
Research by Williams [59] suggests that broom stands are early successional and
can be replaced by later seral vegetation if left undisturbed. No
other information is available on this topic. Research is needed to characterize
Spanish broom's invasiveness and impacts in native plant communities of various seral
stages.
Shade tolerance:
Seedlings of Spanish broom had greatest survival (~97%) in moderate
shade (30% full sunlight), ~70% survival in 100% full sunlight, and ~10%
survival in deep shade (3% full sunlight). Rates of net photosynthesis were
somewhat (although not significantly) higher in full sun versus
moderate shade, and dark respiration was significantly (P<0.005) higher in full sun than
in moderate shade. Spanish broom was tentatively classified by the authors as a shade
avoider, being neither highly tolerant nor intolerant of shade, although further
tests are needed for this to be definitive [55].
Spartium junceum, known as Spanish broom,[1] rush broom, or weaver's broom,[2] it is a species of flowering plant in the family Fabaceae and the sole species in the genus Spartium.[3][4][5] It is closely related to the other brooms (in the genera Cytisus and Genista).
Spartium junceum is a vigorous, deciduous shrub growing to 2–4 metres (7–13 feet) tall, rarely 5 m (16 ft), with main stems up to 5 centimetres (2 inches) thick, rarely 10 cm (4 in). It has thick, somewhat succulent grey-green rush-like shoots with very sparse small deciduous leaves 1 to 3 cm (1⁄2 to 1+1⁄4 in) long and up to 4 millimetres (1⁄8 in) broad. The leaves are of little importance to the plant, with much of the photosynthesis occurring in the green shoots (a water-conserving strategy in its dry climate). The leaves fall away early.[6] In late spring and summer shoots are covered in profuse fragrant yellow pea-like flowers 1 to 2 cm across. In late summer, the legumes (seed pods) mature black and reach 8–10 cm (3–4 in) long. They burst open, often with an audible crack, spreading seed from the parent plant.
The Greek name Spartium given to the genus denotes the use of the plant for 'cordage'.[7] The Latin specific epithet junceum means "rush-like", referring to the shoots, which show a passing resemblance to those of the rush genus Juncus.[8]
This species is native to the Mediterranean in southern Europe, southwest Asia and northwest Africa,[9] where it is found in sunny sites, usually on dry, sandy soils.
Spartium junceum has been widely introduced into other areas, and is regarded as a noxious invasive species in places with a Mediterranean climate such as California and Oregon, Hawaii, central Chile, southeastern Australia,[10] the Western Cape in South Africa and the Canary Islands and Azores.[9][11] It was first introduced to California as an ornamental plant.[11][12]
The plant is used as an ornamental plant in gardens and in landscape plantings. It has gained the Royal Horticultural Society's Award of Garden Merit.[2][13]
In Bolivia and Peru, the plant is known as retama,[9] (not to be confused with the genus Retama) and has become very well established in some areas. It is one of the most common ornamental plants, often seen growing along sidewalks in La Paz.
Retama has made its way into the ethnobotany of the indigenous Aymara and Quechua cultures.
The plant is also used as a flavoring, and for its essential oil, known as genet absolute.[9][14] Its fibers have been used for cloth and it produces a yellow dye.[14][15]
.jpg)
A stand of plants with many blooms, France
Flowers
Close-up of a flower
Mature fruit
Spartium junceum, known as Spanish broom, rush broom, or weaver's broom, it is a species of flowering plant in the family Fabaceae and the sole species in the genus Spartium. It is closely related to the other brooms (in the genera Cytisus and Genista).
