French Broom

More info for the terms: density, seed

The effects of fire on broom seed in the soil seed bank depends on temperature
maxima and duration of heating that occurs during fire and the depth of seed
burial, as well as seed bank density. Seed bank densities seem to increase with
soil depth with the age of the broom stand [49].

More info for the terms: cover, fire frequency, fire intensity, forbs, frequency, fuel, high-severity fire, seed, severity

Response of French broom plants and seeds to fire depends on fire frequency and severity, as
well as the age of the broom stand. It is unclear how French broom may respond
fire in different seasons, as this topic is not covered in the currently
available literature.

Frequency:
Substantially lower germination rates in the 2nd and 3rd postfire
growing seasons compared to those of the 1st postfire growing season
suggest that most French broom seed in the soil seed bank is depleted after one
fire [49]. Similarly, postfire germination response of
French broom decreases after sequential burning [3]. Alexander and D'Antonio [3]
examined the effects of fire on the seed bank under French broom stands of
varying ages, comparing broom (mostly French broom, with small amounts of Scotch
broom), native perennial grasses, native forbs, nonnative annual grasses,
nonnative perennial grasses, and nonnative forbs. They used 2 different
approaches. First they surveyed the soil seed bank across stands that had either
never been burned or had burned from 1 to 4 times. Next they sampled the seed
bank in 2 sites immediately before and after prescribed burning to look at
direct effects of fire on the number of viable seeds in the soil. They found a
large decrease in the number of broom seeds between the never burned and the
burned sites, though there was no statistical difference between sites burned
once versus sites burned more than once. The French broom seed bank did not
change with repeated burning, although the seeds of other species appear to have
been affected. The size of the nonnative seed bank (other than brooms) in twice-burned plots was
equal to or greater than the seed bank of the never-burned stand. However, a 3rd
burn decreased nonnative perennial grasses and nonnative annual grasses while
increasing native forbs. The results of comparisons of pre- and postburn samples
show similar trends; however, because of the low replication of direct burning
treatments, it is not clear whether these patterns are due to repeated burning
or to the nature of the individual fires [3].

Severity:
Control efforts and observations by Boyd [12,13]
indicate that when broom is hand-cut and left on site to cure, subsequent
prescribed burning is severe enough that postfire sprouting is prevented. The
timing of burns in Marin County is dependent on the occurrence of climatic
conditions that provide lower risk of an escaped fire (cooler, wetter, low-wind
days). Though fuel loads are increased by cutting and drying broom biomass
before burning, fire intensity and severity are rarely high (personal observation, cited by [3]).

Odion and Haubensak [49] studied
seed bank depletion and site alteration in French broom stands in relation to burning.
Pre- and postburn sampling was conducted in relatively young and old stands of broom
in which fuel was added, removed, or left undisturbed. Comparisons were made
with an adjacent unburned control stand. Addition of fuel in old stands did not
improve seed bank depletion and it resulted in much lower native species
cover compared to leaving broom slash where it fell. In contrast, if
stands are burned at a young enough age, with supplemental fuel, the seed bank
can be more rapidly exhausted [49]. Additional information
is available on the response of Scotch broom
plants and seed to varying heat treatments and varying fire severities.

Even with high seed mortality following high-severity fire, some French broom
seeds will probably remain in the soil. Often enough broom seeds remain to
replace a French broom [3] or Scotch broom
[24,62]
stand.

French broom

French broom is classified as a noxious weed in California, Hawaii, and Oregon [78]. See the Invaders
database for more information.

More info for the terms: association, fruit, shrub, shrubs

French broom is 1 of 4 nonnative invasive broom species that occur in
North America. All are perennial, leguminous shrubs. DiTomaso [22] provides a table of characteristics to distinguish
among French broom, Scotch broom, Portuguese broom, Spanish broom, and common gorse,
another leguminous shrub that occurs in similar habitats. All broom species have some similar morphological
characteristics, while common gorse is morphologically distinct from the brooms.
French broom is the most widespread of the brooms in California, but less is
known about its biology and ecology than Scotch broom.

The following description of French broom provides a summary of the range of
characteristics described in reviews [11,22,54] and florae [35]. It provides
characteristics that may be relevant to fire ecology, and is not meant for
identification. Hickman [35] provides a key for identification of French broom.

French broom is an upright, evergreen shrub, commonly less than 10 feet (3 m)
tall, occasionally to 16 feet (5 m) tall. Stems are
erect, dense, and green and densely covered with silky, silvery hairs. French
broom is typically leafy (as compared with Scotch broom, which has few
leaves), with compound, deciduous leaves with leaflets
0.4 to 0.8 inch (10-20 mm) long and petioles 5 mm long. French broom inflorescences are dense clusters
occurring in racemes on axillary short-shoots. They are composed of 4 to
10 pea-like flowers, 0.2 to 0.3 inch (5-7 mm) long on axillary pedicels 1 to 3 mm
long. The fruit is a legume, 0.5 to 1
inch (15-25 mm) long and 5 mm wide with 3 to 8 seeds per pod. French broom seeds
are round tooval and have elaiosomes.

Little mention of French broom root systems appears in the literature, although
Pitcairn [57] notes that plants have a deep, branching taproot. As a legume,
French broom forms a symbiotic association with nitrogen-fixing bacteria
located in nodules on its roots. Seedlings of French broom have well developed
root nodules, even at the 1st leaf stage [1].

Research on stem photosynthesis has been conducted and results reported on
Spanish broom and Scotch broom [7,48]. Spanish and Scotch broom rely heavily on
stem photosynthesis during the hot summer months, and are well adapted to open,
high sunlight environments. However, drought stress severely inhibits
photosynthesis of brooms [48]. Nilsen and others [48] also studied stem
photosynthesis in French broom and, while they did not provide data for this
species, they  stated that it has minimal stem photosynthetic capacity but
does well in similar environments (see Site Characteristics).

Growth form and stand structure:
Dense broom infestations produce large amounts of dry matter, which can create a serious
fire hazard. This is particularly true for gorse and French broom ([22],
and references therein).

More info for the term: shrub

French broom is native to the Azores and countries surrounding the Mediterranean
Sea. It has been introduced to other areas including Australia, New Zealand,
and North America [11]. In North America it occurs from southern British
Columbia south to southern California [40]. French broom is thought to have been
introduced to the San Francisco Bay Area in the mid-1800s as an ornamental [11]
and has since become invasive in California, southwestern Oregon, and Washington
[57]. It is currently the most widespread of the brooms in California. In
California, French broom is found in the North Coast Ranges, San Francisco Bay,
southern Coast Ranges, southern Channel Islands, Western Transverse, and
Peninsular Ranges [35]. Plants database provides a state
distribution map of French broom.

French broom is 1 of 4 nonnative invasive broom species that occur in North
America. Scotch broom (Cytisus scoparius), Portuguese broom (C.
striatus), and Spanish broom (Spartium junceum)
occur in similar habitats and have some similar morphological
and ecological
characteristics. Common gorse (Ulex europaeus) is another leguminous
shrub that occurs in similar habitats, but is morphologically distinct from the
brooms.

The following lists include vegetation types in which French broom is known or thought to
be potentially invasive, based on reported occurrence and biological tolerances
to site conditions. Precise distribution information is limited; therefore,
these lists may not be exhaustive.

More info for the terms: competition, fire exclusion, fire frequency, fire intensity, fire regime, forbs, forest, frequency, fuel, grassland, herbaceous, long-term effects, natural, nonnative species, prescribed fire, presence, root crown, seed, severity, shrub, shrubs, top-kill, tree

Fire adaptations:
French broom sprouts from the root crown and aboveground stem after top-kill from fire [12]
or cutting (Bossard, unpublished data in [11]). Its ability to sprout may vary with season and severity of damage
(see Fire Effects).

Several reports indicate a postfire flush of French broom germination from
the soil seed bank [12,13,20,49]. Several studies indicate increased germination
of French broom ([1,11,49] and references therein) and Scotch broom [8,60,67,74]
following heat treatment of seeds, indicating an
adaptation for postfire germination.

Fuels/flammability:
A review by Bossard [11] suggests that
French broom burns readily and carries fire to the tree canopy layer, increasing
both the frequency and intensity of fires in invaded areas. Similarly, Parsons and Cuthbertson [54] suggest that
French broom causes concern in forest areas in Australia because it forms a flammable understory at
the forest edge, where fires are most likely to start. Conversely, combustion of live,
standing broom is difficult under conditions in which prescribed burns are
typically conducted in California (cool, wet, low wind days that provide lower
risk of an escaped fire), unless fuel loads are artificially increased. Despite high temperatures and low humidities,
researchers in Marin County, California were unable to burn a mature,
uncut French broom stand, and a young uncut stand
had only spotty combustion [49].

FIRE REGIMES:
There is no information available on FIRE REGIMES in the native range in which French broom
evolved. However, Scotch broom and Genista florida, a close relative of
French broom, were early successional species following fire in their
native range in Spain [34].

It is unclear how the presence of French broom might affect FIRE REGIMES in invaded
communities. In general, in ecosystems where French broom replaces plants similar to
itself (in terms of fuel characteristics), French broom may alter fire intensity or
slightly modify an existing fire regime. However, if French broom invasion introduces
novel fuel properties to the invaded ecosystem, it has the potential to alter
fire behavior and potentially alter the fire regime (sensu [14,19]). No experimental
information is available regarding FIRE REGIMES changed by French broom.

French broom occurs in a variety of ecosystems in North America that
represent a range of historic FIRE REGIMES. In many areas where French broom
occurs, historic FIRE REGIMES have been dramatically altered due to fire
exclusion and due to massive disturbances associated with human settlement. The
historic FIRE REGIMES of native communities in which French broom occurs range
from high frequency fires in grasslands, to high frequency,
low-severity surface fires in open ponderosa pine forests; and moderate
frequency, high severity fires in California chaparral (see Fire Regime table,
below). French broom did not occur in these communities at a time when presettlement FIRE REGIMES
were functioning, but has established since fire exclusion and habitat alteration began. It is unclear how
presettlement FIRE REGIMES might affect French broom populations.

Herbaceous communities dominated by nonnative annual grasses and forbs
of Mediterranean origin occur throughout the Coast Ranges and foothills of the
Cascade Range and the Sierra Nevada. A review by Keeley [41] indicates that 
much of the nonnative annual grassland in the coastal ranges of central and
southern California derives from a fire-induced type conversion of shrublands.
The herbaceous communities that have long dominated these landscapes were largely created by anthropogenic burning
by Native Americans, and were further maintained by intensive land use with fire
and livestock grazing by European-Americans. In recent decades, however, grazing has been eliminated
in some areas and
anthropogenic fires reduced such that woody vegetation is reestablishing. Along with
native shrubs, nonnative shrubs such as French broom, Scotch broom, and gorse
colonize these sites. Nonnative shrub colonization of grasslands may decrease
fire frequency but increase fuel loads and alter fire behavior ([41] and references therein).

It is also unclear how the use of fire to control broom in invaded communities
might impact native species. Plants are adapted to particular FIRE REGIMES, or
combinations of fire frequency, intensity, extent, and season. The
frequency, intensity, and season of burning prescribed to control nonnative
species must be carefully chosen to avoid damaging native species. Prescribed
fire may have undesirable effects if introduced into an ecosystem that has
undergone shifts in species composition, structure, and fuel characteristics
outside a natural range of variability of these attributes [2]. When the natural fire regime is altered,
even highly fire-adapted plant communities may be vulnerable to competition from
nonnative species [41].

According to Swezy [73], fire is an effective management tool for
French broom, but is used primarily in mixed evergreen forest and grassland communities in
California, where repeated annual burning for broom control "appears to have no
unwanted side effects." Prescribed fire is used less frequently in chaparral
communities where frequent burning or burning outside the natural fire season
may have adverse effects on native communities. It has been suggested that
prescribed fire may have the added benefit of promoting
native species in California grasslands [49]; however, the
long-term effects of repeated burning on the grassland seed bank are not known [3].

The following list provides fire return intervals for plant communities and
ecosystems where French broom is or may be important. It may not be inclusive. Find further fire regime information for the plant communities in which this
species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
California chaparral Adenostoma and/or Arctostaphylos spp. < 35 to < 100
California montane chaparral Ceanothus and/or Arctostaphylos spp. 50-100
California steppe Festuca-Danthonia spp. <35 [70]
western juniper Juniperus occidentalis 20-70
Rocky Mountain juniper Juniperus scopulorum 56]
Jeffrey pine Pinus jeffreyi 5-30
Pacific ponderosa pine* Pinus ponderosa var. ponderosa 1-47 [5]
quaking aspen (west of the Great Plains) Populus tremuloides 7-120 [5,32,44]
coastal Douglas-fir* Pseudotsuga menziesii var. menziesii 40-240 [5,46,61]
California mixed evergreen Pseudotsuga menziesii var. menziesii-Lithocarpus densiflorus-Arbutus
menziesii < 35
California oakwoods Quercus spp. 5]
coast live oak Quercus agrifolia 2-75 [31]
canyon live oak Quercus chrysolepis <35 to 200
blue oak-foothills pine Quercus douglasii-P. sabiniana <35
Oregon white oak Quercus garryana 5]
California black oak Quercus kelloggii 5-30 [56]
redwood Sequoia sempervirens 5-200 [5,27,71]
western redcedar-western hemlock Thuja plicata-Tsuga heterophylla > 200 [5]

*fire return interval varies widely; trends in variation are noted in the species review

More info for the terms: cover, density, fire management, forbs, fuel, grassland, prescribed fire, restoration, seed, shrubland, shrubs

Postfire colonization potential:
Based on observations and experiments by
several authors, a high potential for postfire colonization of French broom
exists wherever there are existing stands or viable seeds in the soil seed bank
(see Plant Response to Fire).

Fire as a control agent:
Unlike mowing or slashing, fire may remove
most of the aboveground vegetation and leave the soil bare, thereby providing a
large number of open sites for the establishment of species, such as French
broom, from the seed bank [3]. In many places in California, prescribed fire is used to control French
broom by consuming aboveground vegetation (which is typically cut and left on
site to cure before burning) and stimulating germination from the seed bank [3,12,13,49,73]. The dry fuel helps carry the
fire, but fires often do not burn evenly and are affected by weather and microtopographic
conditions [3]. Follow-up treatments (burning, pulling, herbicides) are then
used to kill seedlings. After the 2nd treatment, seedling emergence is
usually reduced to low levels; however, follow-up monitoring and treatment are
required indefinitely [3,12,13,49,73]. Swezy and Odion [73]
provide fire management principles and guidelines to consider for
managing French broom in wildlands.

Control of French broom with repeated prescribed burning, preceded by cutting adult
broom (both French and Scotch broom) plants, was first reported from Mt. Tamalpais State Park by Boyd [12].
Continued efforts to remove broom from the Park allow some conclusions to be drawn
regarding the effectiveness of this method there [13]. When the control
project began, French broom occurred on about 70 acres (28 ha) of the 91-acre
(37-ha) project area. One
stand was almost continuous French broom, while others formed a mosaic with surrounding
grassland and native shrubland. Large stands of Scotch broom were also present in some
areas. All areas were grassland sites before the establishment and spread of
broom. Adult broom was cut to within 3 to 24 inches (8-60 cm) of the ground
using chainsaws. Cut stems were left in place, providing a 2 to 3-foot- (0.6-0.9 m) deep
fuel bed. Because of the long-term viability and
abundance of the broom seed bank, reestablishment of broom stands must be prevented
by killing postfire germinants before they produce seed. At Mt. Tamalpais, this is accomplished by
establishing a cover of annual grasses (agricultural barley (Hordeum vulgare)
and a 'Blando' brome (Bromus hordeacus)-'Zorro' rattail sixweeks grass (Vulpia myuros) mix)
to provide fuel for subsequent prescribed burns to
kill broom seedlings. Treatments on 3 sites were as follows [13]:

Site Date cut Date burned Date seeded Grass burned
Panoramic
(27 acres) April 1994 May 1994 Oct.-Dec. 1994 July 1995, July 1996
Upper Muir Woods (12 acres)  Dec. 1994-March 1995 June 1995 Nov.-Dec. 1995 Oct. 1996, Sept. 1997
Lower Muir Woods (20 acres)  Nov.1995 April 1996 Dec. 1996 Sept.1997

All burns resulted in complete mortality of mature broom, broom seedling
establishment, and vigorous coyote bush sprouting. Some differences in fire
behavior and response of broom to timing of cutting and burning were observed.
None of the cut broom stems cut in April 1994 sprouted before burning in May
1994. Broom burned in May was very dry
and extremely flammable; the weather was moderate (73 °F (40 °C), 52% relative humidity), but very
intense upslope headfires were possible. Rainfall occurred soon after burning,
and numerous broom seedlings established and survived the summer.
Due to the abnormally wet winter, the site cut in December 1994
could not be burned until June 1995. Substantial stem sprouting had occurred by
that time. The fires were less intense, but still consumed all of the cut
material. The April 1996 burn was conducted during relatively cool conditions
due to rainfall, but again resulted in complete
consumption [13].

The results of seeding grass for fuel were not uniform. Agricultural barley did not provide an adequate fuel bed,
while the 'Blando' brome-'Zorro' rattail sixweeks grass mix did. Both of these species, while
nonnative, are already present in the larger area. After the planted annual grasses had cured, there were patches
of broom seedlings that would clearly survive the fire in areas where
grass fuels appeared inadequate to produce mortality. These patches were cut with
weed-eaters before burning. The fires that burned the
grass fuel killed almost all of the broom seedlings, even though many stems were
not consumed. Seedling size seems to influence vulnerability to fire with
minimum heat needed to kill small plants. Limited basal sprouting of larger
seedlings after burning was observed in some cases, but the sprouts were very
small compared to native coyote brush and nonnative sweet fennel (Foeniculum vulgare)
sprouts. The number of broom seedlings that established after the 2nd burns were
far fewer than after the 1st, suggesting a reduction in seed bank abundance. If seedlings are too
large to be vulnerable to burning, an herbicide spot treatment may be necessary [12,13].

A review by Bossard [11] indicates that using fire to remove uncut
French broom in late spring or early summer has
also had some success at Mt. Tamalpais State Park. Repeated burning is necessary 2 and 4 years after the initial
burn to kill broom sprouts and
seedlings. Follow-up burning is most successful if there are either naturally occurring or seeded grasses to carry
the fire [11].

The effectiveness of fire as a control agent for French broom depends on a number of
factors, including stand age, seed bank density, and vertical distribution of
seeds in the soil profile [49,73]. It is
important to identify what stage an infestation is in and the density and depth of the soil
seed bank before initiating control treatments.

Odion and Haubensak [49] found French broom stands about 10 years old or
younger have a small, relatively shallow persistent seed bank and can be treated
with cutting and repeat prescribed burning. Addition of fuel before burning
helps deplete the soil seed bank in young French broom stands, but not in older
stands. French broom seed accumulation at soil
depths from which seedlings do not emerge (>3 inches (8cm))
requires regular monitoring and treatment to eliminate emerging plants [49].
Some researchers in Australia suggest that older broom stands should be
left intact (not burned) unless follow-up treatment is assured [23,55]. Results
in California presented by Alexander and D'Antonio [3] indicate that older broom stands pose similar challenges to
control as stands of younger ages (similar broom seed bank size); however, lower
densities of native species in the soil seed bank under older stands increase concern that restoration will
become increasingly difficult as stands age.

In some ecosystems, prescribed fire may have the added benefit of promoting native species
(see Fire Ecology).
However it is not clear that repeated burns
are the most effective means of both reducing the broom seed bank and also
promoting native species. Burning generally encourages native forbs in
California grasslands, but the fire frequencies required for broom control may
have negative effects on native species overall, and alternative follow-up
treatments (e.g. spot-burning, cutting, or herbicides) might be considered [3].

Ken Moore (personal communication, cited in [11]) reports that California State Parks has been very
successful (100% mortality) using a propane torch to remove French broom seedlings, up to
8 inches (20 cm) tall, that emerge from the seed bank after removal of adult
brooms. This is done at the end of the rainy season when
seedlings have emerged and fire danger is low. The
torch is set so it is hot, but not flaming, and it is passed over the French
broom seedlings. The heat does not burn the seedlings, but within a day the
seedlings are wilted and dead. Flame throwers have also been used to
spot-treat roadsides or small areas of seedlings emerged from the seed bank
after removal of adult brooms in Redwood National Park and in New Zealand ([11]
and references therein).

Another approach for using fire to control broom, which was the most effective removal treatment tested
by the CalEPPC broom committee, involves integrating prescribed fire and
herbicides. Mature shrubs in a dense infestation were killed in early July with a basal bark
application of triclopyr herbicide. After 4 weeks, all the shrubs were dead and
were cut down, left on site, and burned. A flush of French broom seedlings followed the
next rain. For the next 2 years seedlings were either killed with glyphosate or
cut with a brush cutter. Mean percent cover of French broom was reduced from 87%
to less than 0.2% in plots treated with basal bark triclopyr, cut, burned, and
seedlings treated with glyphosate. French broom seed banks in burned plots were
reduced to less than 5% of their original size 3 years after prescribed burns.
Seed banks of unburned plots otherwise treated the same were reduced to 15.5% of
their original size, and control plots exhibited no substantial decrease in seed
bank size (Bossard and others 1995 as cited by [11]).

More info on this topic.

More info for the term: phanerophyte

RAUNKIAER [59] LIFE FORM:



Phanerophyte

More info for the terms: forest, grassland

The native range of French broom includes humid and subhumid areas of the
Mediterranean region. In Australia French broom is invasive in forest margins, "neglected"
areas, roadsides, and watercourses, and it occasionally encroaches
in pastures receiving more than 20 inches (500 mm) annual rainfall [54].
In California, French broom is common on coastal plains and mountain slopes,
colonizing grassland and open-canopy forest. Differences in growth habit have been
observed at different sites. For example, French broom retains much of its foliage in coastal areas, and is more
deciduous in inland areas [11].

French broom is common in disturbed
places such as riverbanks, road cuts, logged or burned areas, pastures, and
road and utility rights-of-way [11,35]. It often occurs on steep and exposed
slopes [53].

In California, French broom occurs on sites with varied soil moisture conditions, but
seems to prefer siliceous soils. Unlike other broom species in California, it
grows reasonably well on alkaline soils with pH 8. Its ability to fix nitrogen
allows growth in low-fertility soils [11].

French broom seedlings are less tolerant of frost
than Scotch broom seedlings, and consequently are less often found at high elevations
[11]. Hickman [35] reports that French broom occurs to 1,600 feet (500
m), and Bossard [11] reports that it occurs to 2,600 feet (800 m) in California. In the Santa
Lucia Ranges, southern Los Padres region, and San Diego region, French broom is
reported below 1,700 feet (520 m) [68].

More info on this topic.

This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

More info for the term: cover

SAF COVER TYPES [26]:





217 Aspen

221 Red alder

222 Black cottonwood-willow

229 Pacific Douglas-fir

230 Douglas-fir-western hemlock

232 Redwood

233 Oregon white oak

234 Douglas-fir-tanoak-Pacific madrone

243 Sierra Nevada mixed conifer

244 Pacific ponderosa pine-Douglas-fir

245 Pacific ponderosa pine

246 California black oak

247 Jeffrey pine

248 Knobcone pine

249 Canyon live oak

250 Blue oak-foothills pine

255 California coast live oak

More info on this topic.

This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

More info for the term: shrub

ECOSYSTEMS [30]:



FRES20 Douglas-fir

FRES21 Ponderosa pine

FRES27 Redwood

FRES28 Western hardwoods

FRES34 Chaparral-mountain shrub

FRES37 Mountain meadows

FRES41 Wet grasslands

FRES42 Annual grasslands

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This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

More info for the terms: forest, shrub

KUCHLER [42] PLANT ASSOCIATIONS:





K002 Cedar-hemlock-Douglas-fir forest

K005 Mixed conifer forest

K006 Redwood forest

K009 Pine-cypress forest

K010 Ponderosa shrub forest

K025 Alder-ash forest

K026 Oregon oakwoods

K028 Mosaic of K002 and K026

K029 California mixed evergreen forest

K030 California oakwoods

K033 Chaparral

K034 Montane chaparral

K035 Coastal sagebrush

K036 Mosaic of K030 and K035

K048 California steppe

More info on this topic.

This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):

More info for the terms: cover, forb, grassland, shrub, shrubland, woodland

SRM (RANGELAND) COVER TYPES [66]:




109 Ponderosa pine shrubland

110 Ponderosa pine-grassland

201 Blue oak woodland

202 Coast live oak woodland

203 Riparian woodland

204 North coastal shrub

205 Coastal sage shrub

206 Chamise chaparral

207 Scrub oak mixed chaparral

208 Ceanothus mixed chaparral

209 Montane shrubland

214 Coastal prairie

215 Valley grassland

216 Montane meadows

217 Wetlands

409 Tall forb

411 Aspen woodland

More info for the terms: seed, top-kill

Fire is likely to top-kill French broom, although some reports (e.g. [49,50]) indicate that French broom is
difficult to burn in some situations. Conversely, high-severity fires or fires
in some seasons may kill the entire plant and prevent postfire sprouting [12,13].

Fire may kill some French broom seeds in the soil seed bank, although seed
bank densities are not substantially decreased immediately following fire [3,49].
Observed reductions in French broom seed banks following fire (see Plant Response to Fire)
are more likely due to subsequent germination rather than direct fire-induced seed mortality [3].

More info for the terms: cover, fire management, grassland, invasive species, natural, prescribed fire, restoration, seed, shrub, shrubs, tree

Impacts:
French broom is listed by the California Invasive Plant Council as one of the most widespread and invasive
wildland pest plants in California [16].

Several reviews suggest that French broom invades native vegetation, displaces native plant and forage species,
and dominates the invaded community, sometimes forming dense, monospecific,
almost impenetrable stands [11,43,57].
Experimental evidence indicates that French broom invasion
causes changes in plant community composition by displacing vegetation
and decreasing local native plant alpha diversity [49]. A comparison of 12 "old-growth"
French broom plots and 12 uninfested
California grassland plots indicates that the number of native species (11.7
species + 0.8 s x, versus
3.1 + 0.3) and cover (15.1 + 5.0% versus 5.1 +
1.7%) are higher in plots where broom is absent [49]. A
study of seed banks in California grassland indicates a decrease in seed banks
of native species in invaded stands, even in French broom stands as young as 5 years [3].

Some authors suggest that French broom invasion leads to changes in soil
properties that may have implications for restoration and rehabilitation
efforts. Invasions may change microclimate conditions on and in the soil [11].
French broom invasion is thought to be responsible for reducing arthropod populations
by 1/3 in Golden Gate National Recreation Area (Landforn and Nelson 1992,
ctied by [11]). As a nitrogen-fixing species, French broom may enrich
soil nitrogen levels and alter nitrogen dynamics in the invaded system [33].

French broom along roadsides obstructs views,
requiring expensive ongoing road maintenance. Since it grows more rapidly than
most trees used in forestry, it shades out tree seedlings in areas that are
revegetated after harvest and makes reforestation difficult [11].

While it has been suggested that French broom invasion increases fire hazard
(e.g. [11,54]), this relationship may be
site-specific, as others authors (e.g. [49]) indicate that
French broom is difficult to burn
(see Fire Ecology).

Control:
As with other broom species, the best method for removal of a French broom
infestation depends on climate, topography, age and size of the infestation, importance
of impact to nontarget species, and type, quantity, and duration of resources
available to remove and control broom at the site. All methods require
appropriate timing and follow-up monitoring. Because of the seed bank, monitoring
removal sites to locate and kill new seedlings is essential. Location and treatment
of sprouts is also necessary. Sites should be examined annually following broom seed germination
(usually late spring) for 5 to 10 years, and every 2 years thereafter [11].

Controlling the seed bank is an important obstacle for French broom control. To do this it
is necessary to determine the conditions for stimulating germination of the
greatest number of seeds to exhaust the seed bank. In the case of
French broom, a sizeable seed bank may remain dormant in the
soil indefinitely in the absence of fire or other treatments that break dormancy [49].

The following is a general review of control methods and includes information that may
be applicable for better understanding of French broom's fire
ecology. Given their similar biology and lack of information on all of the broom
species, much of this information comes from research on Scotch broom and is generalized to apply to all brooms. More
research is needed, however, to understand how this information applies to
French broom, Portuguese broom, and Spanish broom. The reader is referred to other reviews [4,10,37,38,58] and the Weed control methods handbook
for more details on control methods.

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 [64].

Invasive broom species (French, Scotch, Portuguese, and Spanish brooms)
should not be used for horticultural and landscape purposes. McClintock [43]
indicates that several ornamental brooms are not invasive. An effective
step in preventing further introduction and spread of the weedy brooms may be in
asking nurseries to carry only the nonweedy species of broom [43].

Integrated management:
Integrated management approaches for French broom involve combining
prescribed fire with other control methods. See the Fire Management Considerations
section of this summary for more information.

Physical/mechanical:
Manual methods of broom removal, such as hand-pulling and removal with hand tools, have the benefit of
being highly selective, thus allowing removal of weeds with minimal damage to
surrounding desirable vegetation. Hoshovsky [37] suggests
the Bradley method, as described by Fuller and Barbe [29], as
a sensible approach to manual control of brooms. He also suggests some logistics
for securing and managing volunteers for manual control programs. Manual removal
must be repeated regularly, since broom seedlings continue to establish from the
seed bank after removal of adult plants [37]. See the Nature Conservancy's Element Stewardship Abstract
on French and Scotch broom for more information on management of these species.

Pulling with weed wrenches is effective for small infestations or in areas
where an inexpensive, long-duration labor source is dedicated to broom removal [76].
Weed wrenches remove the entire mature shrub, eliminating sprouting. Wrench
removal allows targeting broom plants and minimizing impact on neighboring
species and can be done on slopes. However, soil disturbance caused by weed wrenches
tends to bury broom seeds and create microsites that favor broom seed
germination. Sites must be monitored annually and seedlings removed before
reaching maturity (2-3 years) until the broom seed bank is depleted [11].

The following procedures are recommended for control of brooms by cutting:
Cut broom shrubs with a saw or brush cutter, at or below ground level,
after broom has gone to seed and soil moisture is at a seasonal low. Remove or burn cut plants the following spring.
The following summer, after grasses are dry and have dispersed their seed, mow
French broom seedlings as close to the ground as possible with a heavy-duty brush cutter.
Repeat for 5 or 6 seasons, until the seed bank is exhausted.
Timing and height of cutting is critical in this technique to minimize sprouting. Cutting
French broom in June in Mendocino County at 2 to 3 inches (5-8 cm) above the soil surface resulted in
extensive sprouting. Brush hogs twist off aboveground plant
material and are more destructive to perennating tissues than is
cutting; however, sprouting still occurs [11].

Mulching with 3 to 4 inches (8-10 cm) of straw (certified weed-free) during winter or spring
(before seedlings are over an inch tall) may prevent broom seedling emergence.
A controlled study by the Habitat Restoration Team
in California demonstrated that mulching with rice straw was 99% effective in preventing
French broom seedlings from emerging through straw throughout the germination period from
December to April. Mulching also increased the mortality of brush-cut French
broom in the same study when applied during winter (Alvarez unpublished data,
cited by [4]).

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 [76] 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.

Foreign exploration for biological control agents for French broom began in
2000, and several promising agents have been found. As of 2003, at least one
insect was undergoing host specificity testing. An insect purposely introduced for control of
Scotch broom, the Scotch broom bruchid (Bruchidius villosus) [17], also attacks
French broom. See Coombs and others [18] for more information on this
insect, its distribution, and effects.

The native moth Uresiphita reversalis, which is known as "the genista
caterpillar," has built up high numbers on local French broom populations in central California. Large genista
caterpillar populations can be very damaging to local French broom populations;
however, most populations of the moth are transitory and thus
do not provide long-term control [57].

Heavy grazing by domestic goats for 4 or 5 years during the growing season is
reported to effectively control broom in New Zealand [39], and has been tried at
a few sites in Marin County (Archblad, personal communication cited by [11]). Rice [64] reports that
goats were "very effective at reducing heavy brush, including that of...French
broom" in the Hill Area watershed of San Francisco Bay." The disadvantage is that goats are
not selective, and native species may also be eaten [11].

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 because they do not change
conditions that allow infestations to occur [15]. 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 [76]
for considerations on the use of herbicides in natural areas and detailed
information on specific chemicals and adjuvants. Also see the broom Element Stewardship Abstract [37]
and other reviews [11] for more detailed information on chemical control.

Glyphosate is effective in some situations, but is likely to impact nontarget
species, and broom sprouting occurs. Triclopyr ester is effective in killing French
broom with a low-volume, basal bark application to the main stem. This
application does not impact nontarget species but is time consuming. Used alone
and in combination with other herbicides, 2,4-D has been used to control French broom ([11]
and references therein).

Cultural:
No information is available on this topic.

More info for the term: cover

As of this writing (2005) no information is available on the use of French broom by livestock
or wildlife. However, it is probably eaten by domestic goats, and goat grazing is used
to control broom species in New Zealand [39] and California [64]
(see Biological Control). Cattle do not eat broom [39].

Palatability/nutritional value:
According to Hickman [35], French broom flowers, and perhaps all parts, are
toxic. French broom foliage and seeds contain a variety of quinolizidine
alkaloids, especially in young leaves. In some livestock, ingestion of plant
parts can cause staggering followed by paralysis. French broom foliage can cause digestive
disorders in horses ([11], and references therein).

Cover value: No information is available on this topic.

More info for the terms: cover, forbs, grassland, shrubs

The following description of habitat types and plant communities in which French
broom occurs
is taken from examples found in the literature. The objective is to provide
examples of vegetation types in which these species occur, and is not meant to
imply that they are restricted to these types within these areas. There is very little information in the
literature on vegetation types in which French broom occurs.

In California,
French broom
occurs in annual grasslands, oak woodlands, coastal scrub, chaparral, conifer, and
relatively open mixed evergreen forests [11,68,73]. At sites in California where nonnative annual grasses typically codominate with
native perennial grasses and forbs, there has been substantial French broom invasion into the
otherwise intact open grassland. At more than half of these sites, Scotch broom
is also invading [33]. On the edge of Mt. Tamalpais State Park, French broom occurs on an
exposed, west-facing slope dominated by nonnative grasses with patches of
coyote bush (Baccharis pilularis)
and several nonnative forbs and shrubs including bigleaf periwinkle (Vinca major), silverleaf
cotoneaster (Cotoneaster pannosus), narrowleaf plantain (Plantago lanceolata),
evergreen blackberry (Rubus laciniatus), and poison hemlock (Conium maculatum).
Here French broom and Scotch broom grow interleaved, with Scotch broom
individuals somewhat more sparse (about 15% cover) and spread out than French
broom (about 30% cover). At China Camp State Park, French broom and Scotch broom
grow in patches and
as scattered individuals, with a total cover of about 35% and 15%, respectively.
Other common species included coyote bush, toyon (Heteromeles arbutifolia), poison-oak (Toxicodendron
diversilobum), nonnative musk thistle (Carduus nutans),
Uruguayan pampas grass (Cortaderia selloana), and other nonnative grasses
[53]. On a coastal grassland site in Marin County, dense cover of French broom occurs in a
matrix currently dominated by
nonnative annual grasses including oats (Avena spp.), sixweeks grasses
(Vulpia spp.), and bromes (Bromus spp.), and thought to have formerly been
composed of purple needlegrass (Nasella pulchra), California oatgrass (Danthonia
californica), red fescue (Festuca rubra), and blue wildrye (Elymus glaucus).
Scotch broom was also present in small numbers (<5% of aboveground plants) in
some areas [3].

French broom also occurs in the understory of bristlecone fir (Abies
bracteata) forests [68]. Scotch broom and French broom are
also persistent problems along roadsides in redwood (Sequoia sempervirens)
ecosystems of California,
and occur in redwood forests after clear-cutting, persisting until the canopy closes [63].

French broom
invades disturbed areas in maritime chaparral stands around Monterey Bay,
where several native species of concern occur. These include Hooker's manzanita
(Arctostaphylos hookeri ssp. hookeri), Pajaro manzanita (A. pajaroensis),
Monterey ceanothus (Ceanothus cuneatus var. rigidus),
Monterey spineflower (Chorizanthe pungens var. pungens),
Eastwood's goldenbush (Ericameria fasciculata), and Yadon's piperia (Piperia yadonii)
[79].

There was no information in the literature on plant
communities in which French broom occurs in either Oregon or Washington.

More info for the term: shrub

Shrub

More info on this topic.

More info for the terms: seed, shrub

Germination of broom species in California occurs from December through July [3,10,11]. The period of most rapid
growth is April to July [11].

French broom flowers from March to May in southern California [47] and on
inland sites, and from March to July on the northern coast. Flowers appear just prior to
emergence of new leaves. Seeds mature in June and July. French broom seed pods
burst in the heat of spring and summer, dispersing seed. Sometimes a 2nd
flowering occurs towards the end of summer [54].

As in other brooms, most photosynthate is moving up in the shrub toward branch tips during
flowering, bud break, and seed set. Photosynthate starts moving down toward
roots of French broom after seeds are well grown but before seed release (Bossard
and others 1995, cited in [11]).

French broom produces new growth each winter and spring [54].

More info for the terms: grassland, seed

Germination of French broom from the soil seed bank appears to be induced by
fire, as high seedling densities occur after a single fire [1,12,13,20,49].
Laboratory tests support the notion that heat from fire scarifies French broom
seed and stimulates germination ([1,11,49] and references therein) (see Germination).

D'Antonio and Haubensak [20] found that more French broom seeds germinated in
burned than in unburned grassland habitat in Marin County, and that growth and
survival of seedlings were enhanced in burned areas. Data from various studies
on French broom and Scotch broom indicate a reduction in broom seed bank
densities of 43% to 97% after one fire [9,11,24]. Similarly, a small roadside
population of French broom in Australia was burned, and seedling emergence
following burning was 174 seedlings/m². French
broom seed continued to germinate without further
disturbance for up to 3 years after the fire. Some postfire sprouting was also
observed [1].

More info for the terms: adventitious, ground residual colonizer, shrub

POSTFIRE REGENERATION STRATEGY [69]:




Small shrub, adventitious bud/root crown

Ground residual colonizer (on-site, initial community)

More info for the terms: density, forbs, fresh, grassland, litter, monoecious, root crown, scarification, seed, shrub, top-kill

French broom spreads by prodigious seed production. French broom may also
sprout from the root crown [11] or upper stem [12] when
aboveground parts are removed by cutting, freezing, or fire.

Breeding system:
French broom is monoecious
and does not show appreciable levels of selfing [53].

Pollination:
Both native and nonnative insects pollinate French broom. Parker and others [51,53]
demonstrated pollinator limitation in French broom, underscoring the potential
importance of pollinators to its fecundity and spread. Patterns of fecundity
were not, however, strongly predicted by differences in pollen limitation
between species (French and Scotch broom) or between sites [53]. Because nonnative honeybees are
often themost common pollinators of brooms [52,72], potential negative
impacts of beekeeping on broom management have been suggested [52].

Seed production:
French broom becomes reproductive at 2 to 3 years of age, or on reaching a height of about 1.5 to 2 feet (45-60 cm)
[1,11]. A medium-sized shrub can produce over 8,000 seeds a year (Bossard, unpublished
data, cited by [11]). Adams and Simmons [1] found an average of 7,400
pods per bush, with an average of 4.8 seeds per pod, and 5% of the pods damaged
by insects in a dense infestation of French broom in dry sclerophyll vegetation in
Victoria, Australia.

Seed dispersal:
French broom pods burst open explosively, ejecting seeds up to 13 feet (4 m). Seeds are further
dispersed by ants, birds, and other animals and in river water, rain wash, and mud,
and by vehicles and machinery [1,11].

Seed banking:
Dormancy of French broom seed is enforced by a hard coat that prevents imbibition. A large
proportion (60%-82%) of French broom seed is dormant upon dispersal ([1,49], and
references therein). The high rate of seed production
coupled with high rates of seed dormancy result in a rapid build-up of
persistent, soil-stored seed [1]. French broom seeds are known to
survive at least 5 years in soil (Bossard, unpublished data cited in [11]).
A large number of dormant French broom seeds in the soil seed bank can lead
to high germination rates following soil and vegetation disturbance such as that
caused by fire [1]. Even though seed densities tend to decrease with distance
away from broom stands, there
may be sufficient numbers to support a population expansion after fire ([49] and
references therein). 

A review by Bossard [11] reports French broom seed bank densities range
from 465 to 6,733 seeds/m². An average of
10,000 dormant broom seeds/m² occurred in the litter and soil under mature
French broom stands in Marin County (Parker and Kersnar 1989, cited by [49]). Average French
broom seed bank densities of 3,774 seeds/m²
and 2,563 seeds/m² were recorded at 2 sites
in Australia [1]. Seed bank densities seem to increase with soil depth with the
age of the broom stand [49].

French broom seed bank densities may be related to stand age, although no
clear relationship was found in French broom
stands of varying ages on a coastal grassland site in Marin County, California
[3]. Seed density of French and Scotch broom, native perennial
grasses, native forbs, nonnative annual grasses, nonnative perennial grasses,
and nonnative forbs were compared in areas where the grassland matrix under the broom stands
was dominated by nonnative annual grasses. Scotch
broom was present only in small numbers (<5% of total aboveground plants),
and no distinction was made between seeds of the 2 broom species. Broom stands
ranged from 5 to 15 years old, and broom seed bank density ranged between 900
and 10,582 seeds/m².
Younger and older stands tended to have fewer seeds than stands in the middle
age range, with a general trend of increasing seed numbers as stands age, a
stabilization of numbers in middle-aged stands, and a decrease in seed density
among the oldest stands [3]. A similar trend was observed in a 4-year study of
Scotch broom in Australia [65]. However, variation in seed bank
density among sites was large, and there was no clear relationship between stand
age and seed bank density. Density of all nonbroom seeds as a group decreased
with stand age, although seed densities of individual species were not
different between sites of different ages. There were no significant
relationships (p=0.734) between stand age and the number of dormant or dead broom seeds in
the seed bank. However, there was a trend toward an increasing percentage of deeply
dormant seeds with increasing stand age. The large variation in broom seed
numbers among sites may be due to differences in productivity and fecundity
brought about by differences in availability of soil resources and/or
pollinators; or by differences in seed dispersal or predation by granivorous
insects among sites [3].

Germination:
French broom is polymorphic in its germination behavior, with about 18%
[1] to 40% (Parker and Kersnar 1989, cited in [49]) of fresh seed germinating immediately on exposure to suitable conditions,
and the remainder dormant. Scotch broom seed buried below about 3 inches (8 cm) does not
germinate [8], and very few
broom seeds occur below 4 inches (10 cm) (Parker and Kersnar 1989, cited in [49]), [3,24].
French broom seed may be stimulated to germinate by rain, scarification during soil disturbance, or fire.

In field studies in Australia, Adams and Simmons [1] observed
a flush of French broom seedlings after autumn rains in April 1988. Average seedling counts
were 790 seedlings/m² under dense mature stands without disturbance.

Several researchers have observed a flush of French broom seedlings following
fire [12,13,20,49], and laboratory studies indicate that heat scarification
stimulates germination of French broom ([1,11,49] and references therein) and Scotch broom [8,60,67,74] seeds. Heat of
122 to 212 °F (50-100 °C) doubled French broom germination rates, and seed mortality ensued at about
257 °F (125 °C) (Parker and Kersnar 1989, cited in [49]). Cheng (in press)
reports that heat treating seeds with temperatures of 149 °F (65 °C) improved germination
of seed in some populations but not in others [11]. Seeds that
were heat treated with boiling water "to simulate the cracking of the
testa by fire" germinated rapidly in light at 68 °F (20 °C), with over 50% of viable seeds
germinating within 12 days, and 90% within 14 days [1].

Hand scarification also stimulates germination of French broom seed [49].

Seedling establishment/growth:
Very little information is available on French broom seedling establishment and
growth. There is a high potential for seedling recruitment following fire [1,12,13,20,49] (see Plant Response to Fire).

Regular recruitment can lead to rapid French broom population expansion.
At a site in Australia the invasion front moved over 10 feet (3 m) in 12 months [1].

Asexual regeneration:
French broom can sprout from the root crown after cutting. Once seedlings are taller than
approximately 8 inches (20 cm), their rate of sprouting after cutting can be
over 90%, particularly if cut in the rainy season (Bossard, unpublished data in
[11]). Boyd  [12] also reports sprouting from the stem
following top-kill by fire.

More info on this topic.

This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

BLM PHYSIOGRAPHIC REGIONS [6]:





1 Northern Pacific Border

2 Cascade Mountains

3 Southern Pacific Border

4 Sierra Mountains

5 Columbia Plateau

6 Upper Basin and Range

7 Lower Basin and Range

(key to state/province abbreviations)


UNITED STATES

CA OR WA



CANADA
BC

More info on this topic.

French broom seedlings can tolerate up to 80% shade (Bossard, unpublished data
in [11]). French broom's life span is typically 10 to 15 years (Waloff, personal communication in [11]),
(Alvarez, personal communication in [3]).

Cytisus monspessulanus L. [21,36]

Teline monspessulana (L.) K.Koch [75]

The currently accepted name for French broom is Genista monspessulana (L.)
L. Johnson (Fabaceae) [35,40].

No naturally occurring hybrids are reported in the literature. There may be
a number of ornamental hybrids, as Hickman [35]
indicates that most plants reported as French broom
may be hybrids.

Perennial, Shrubs, Woody throughout, Taproot present, Nodules present, Stems erect or ascending, Stems less than 1 m tall, Stems 1-2 m tall, Stems greater than 2 m tall, Stems solid, Stems or young twigs sparsely to densely hairy, Stems silvery, canescent, tomentose, cobwebby, or wooly, Leaves alternate, Leaves petiolate, Stipules conspicuous, Stipules green, triangulate to lanceolate or foliaceous, Stipules deciduous, Stipules adnate to petiole, Leaves compound, Leaves palmately 2-3 foliate, Leaf or leaflet margins entire, Leaflets 3, Leaves glabrous or nearly so, Inflorescences racemes, Inflorescences globose heads, capitate or subcapitate, Inflorescence axillary, Bracts conspicuously pres ent, Flowers zygomorphic, Calyx 2-lipped or 2-lobed, Calyx hairy, Petals separate, Corolla papilionaceous, Petals clawed, Petals orange or yellow, Banner petal ovoid or obovate, Wing petals narrow, oblanceolate to oblong, Wing tips obtuse or rounded, Stamens 9-10, Stamens or anthers dimorphic, alternating large and small, Stamens monadelphous, united below, Filaments glabrous, Anthers versatile, Style terete, Style sharply bent, Fruit a legume, Fruit unilocular, Fruit freely dehiscent, Fruit elongate, straight, Fruit oblong or ellipsoidal, Fruit exserted from calyx, Fruit glabrous or glabrate, Fruit 3-10 seeded, Seeds ovoid to rounded in outline, Seed surface smooth, Seeds olive, brown, or black, Seeds with appendage - aril, caruncle, funiculus, or strophiole.

Genista monspessulana, commonly known as French broom, Montpellier broom, or Cape broom (Australia), is a woody leguminous perennial shrub. The yellow-flowering bush is native to the Mediterranean region, and while it may still be commonly sold in some garden stores, it is considered an invasive plant in most places where it has been introduced. It is a noxious weed on the western coast of the US and in parts of Australia.