L.

gorse, common gorse

Ulex europaeus

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CalEPPC List A-1,CDFA B

Marc C. Hoshovsky

Common gorse (Ulex europaea) is a
prickly evergreen shrub less than ten feet tall, with a profusion of yellow
pea-like flowers from March to May. By May plants are covered with half-inch- to
one-inch-long brown pods. The short, stout branches are densely packed and may
appear leafless. Spines, approximately half an inch long, are located at base of
leaves. The somewhat similar species, Scotch broom (Cytisus scoparius),
is not prickly.

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Fabaceae. Woody leguminous shrub, heavily armed but not gland-dotted. Stems: to

-flowered. Flowers: pea-like, calyx 2-lipped, membranous, yellow, persistent, 6 in (15 mm); petals +/- equal, yellow, persistent, less than 20 mm. Fruit:

In California gorse can be found in all
coastal counties and in the northern Sierra Nevada foothills. It invades
infertile or disturbed sites, sand dunes, gravel bars, fence rows, overgrazed
pastures, logged areas, and burned-over areas. It will grow on most soil types,
from good silt to plain boulders. It has been recorded as growing on serpentine
soils and, rarely, on highly calcareous soils.

Gorse is more tolerant of soil acidity than most legumes, and it
readily invades soils of poor fertility. The only restrictions to soil quality
seem to be adequate nutrition and availability of trace elements. It grows best
in moist soils and on shaded slopes. Gorse can thrive in well drained soils and
in areas with a high water table. It is intolerant of heavy shade, where it
produces coarse foliage and few flowers.

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Gorse is native to central and western Europe, where it has long
been cultivated as hedgerows. It has naturalized in Australia and New Zealand,
where considerable research has been done to control its spread. It has
established along the Atlantic coast of North America, from Virginia to
Massachusetts.

Gorse was introduced to the West Coast before 1894, and has been
established in Mendocino County for 100 years. By the 1950s gorse had spread
throughout western Washington and Oregon and northern California. It has been
reported in every coastal county in California from Santa Cruz to Del Norte, and
sparingly in southern California (Pryor and Dana 1952).

Gorse seeds are too heavy to be dispersed by wind, and usually
fall within six feet of the parent plant. Seeds may be spread by ants, quail,
water, and human activity.

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Gorse may be slow in spreading and becoming
established, but where it gains a hold, there are few other plants that will so
completely dominate an area. Besides becoming a significant fire hazard, it can
successfully outcompete native plants in part because of its association with
nitrogen-fixing bacteria, which facilitate its colonization of nitrogen-poor
soils. Gorse leaf litter acidifies and lowers the cation exchange capacity of
moderately fertile soils by immobilizing the bases, making it more difficult for
native species to establish. On San Bruno Mountain, San Mateo County, gorse is
considered the most difficult exotic species to control, and it has caused
considerable loss of valuable grassland habitat (Reid 1985).

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(click on photos to view
larger image)

Gorse reproduces by resprouting from stumps and by seed. Seed reproduction is far more troublesome to control. Seeds are very small, averaging 60,000 seeds per pound. Seed counts in the upper inch of soil may be up to 2,000 per square foot (Zabkiewicz and Gaskin 1978a).

Seeds are impermeable to water, preventing
immediate germination. They may remain dormant yet viable in the soil up to
thirty years, with reports of up to seventy years (Zabkiewicz 1976). Seed
germination may occur under suitable conditions at any time of year. Light is
not essential, but few seeds germinate in the shade of established gorse. When
dense gorse cover is removed, there is a flush of germination, because of either
increased light or increased temperature. Heat stimulates germination,
particularly at temperatures reached just below the soil surface during
fire.

Gorse plants grow quickly, producing considerable dry matter.
Year-old stands may contain 1,100 lbs/acre, with older stands producing 3,300
lbs/acre per year. Nitrogen in soils occupied by gorse can accumulate at an
annual rate of 20-30 lbs/acre, surpassing the production of some well managed,
fertilized pastures (Egunjobi 1971). Much of this production, with its high
nitrogen content, ends up as litter, accumulating faster than any other
temperate plant species.

Plants grow outward, forming a central area of dry, dead
vegetation. A single plant can be up to thirty feet in diameter. Plants are
typically medium-sized shrubs, but when exposed to constant wind they may be
mat-like or cushion-like.

Roots tend to grow in the top few inches of soil, with only the
tap root extending to greater depths. Extensive lateral roots are supplemented
by a fine mat of adventitious roots that descend from the lower branches.

Gorse is a successful invasive plant because it grows on a
variety of soil types, fixes nitrogen, and may impoverish soil of phophorus. It
produces copious amounts of heat-tolerant seeds with long-term viability, and
regenerates rapidly from seeds and stumps after disturbances such as brush
clearing or fires.

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Because of the longevity of buried seeds,
gorse control efforts must be long-term to be successful.

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Manual/ mechanical methods: Gorse seedlings and young plants
less than five feet tall may be hand pulled, especially after rain has loosened
the soil. It is important to remove the root system, which may resprout if left
in the ground. Any piece of root left in the soil may produce a new plant.
Hoeing is effective when plants are small. This method either cuts off the tops
or exposes seedlings to the drying action of the sun. A claw-mattock is
effective in pulling out large plants and their root systems.

Cutting of above-ground plant parts is only marginally
effective, but it is a useful technique to prepare for other removal methods.
Repeated cuttings may help to exhaust the reserve food supply in roots. Cutting
is most effective when plants begin to flower. At this stage the reserve food
supply is nearly exhausted, and new seeds have not yet been produced. After
cutting or chopping, gorse will resprout in greater density if not treated with
herbicides.

In 1983 the San Mateo County Department of Parks and Recreation
manually removed dense gorse from San Bruno Mountain, a task requiring
approximately 350 person-hours per acre. Gorse also was removed by chaining by
bulldozers and with the use of a bulldozer-mounted rototiller. Herbicides were
used as a follow-up treatment (Reid 1985).

Prescribed burning: Fire has frequently been used to eliminate
gorse thickets, although burns may easily get out of control because of the high
flammability of the plants. Fire may stimulate germination of buried seeds, so
repeated burns may be necessary to exhaust the seedbank (Amme 1983).

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Insects and fungi: There are no USDA approved insects for
biocontrol of gorse. The gorse weevil (Apion ulicis) was accidentally
introduced into the United States in 1953 from France, and by 1982 it had become
established in California and Oregon. The weevil grub eats the seeds in the
unopened legume. When the pods open, adult weevils are released to feed on
spines and flowers, sometimes defoliating large plants. In California the weevil
has been only partially successful in controlling gorse (Amme 1983). Plants
often have enough food reserves to recover rapidly after serious injury.
Additionally, the climate on the northern California coast is cool, delaying
dehiscing of the pods and leaving the weevil larvae to die in the
pod.

Other potential insect enemies of gorse exist but have not been
tested for controlling gorse in the United States (Julien 1982).

Vegetative competition: Reseeding with native perennials after
initial burning or chemical treatment of stumps may be productive. Once
established, these species may displace gorse by competing for water or
nutrients or by shading out lower-growing gorse plants. Amme (1983) has
experimented with reseeding with native grasses in Jughandle State Reserve in
Mendocino County.

Grazing: Goat grazing is effective in controlling gorse (Hartley
et al. 1980, Hill 1955), as goats prefer woody vegetation to most grasses and
herbaceous plants. Goats are less costly to use than mechanical and chemical
methods. They are most cost-effective when used to clear or suppress young
regrowth rather than to do the initial clearing of mature stands. A period of at
least two years of goat grazing is required before there is any significant
reduction in gorse (Hill 1955).

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Chemical control of gorse has been well researched in New
Zealand. The most effective chemical treatment was a combination of picloram (as
Tordonå¨), which is not registered for use in California, and 2,4,5-Tå¨ which is
not legal anywhere in the U.S. (Ivens 1979). Good results were obtained with
picloram applied during summer months. Larger plants needed retreatment, and
burned stumps showed a high degree of recovery (Ivens 1979). Both chemicals have
distinct disadvantages, including persistence in soils, difficulty in being
leached out of organic and clay soils, and damage to other plant species. Check
with your county agricultural agent or a certified pesticide applicator to
determine which herbicides are currently registered for use on gorse in
California.

Gorse is difficult to eradicate with a single application of
herbicide (Balneaves 1980). Greater success is possible with a combination of
methods, including crushing, cutting, or burning.

Glyphosate (as Roundupå¨) is most effective with gorse seedlings
in early summer. Plants began to die the following fall and winter as herbicide
was carried to the roots.åÊ

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