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INVASIVE SPECIES
Introduction to Watershed Science
Merritt College
Marc Epstein, Instructor
WHAT ARE INVASIVES
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Non–indigenous (non-native) species: with
respect to a particular ecosystem, any species
that is not found in that ecosystem. Species
introduced or spread from one region of North
America to another outside their normal range
are non-indigenous, as are species from other
continents.
IMPACTS OF INVASIVE SPECIES
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A species whose presence in the environment
causes economic or environmental harm or
harm to human health. Native species or nonnative species may show invasive traits,
although this is rare for native species and
relatively common for non-native species.
TRAITS OF INVASIVE SPECIES
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Capable of doing significant harm to ecosystems, economy, or
human health
Capable of spreading without apparent natural controls (natural
predators, disease)
Population levels are unchecked
Causing major change faster than native ecosystem can
accommodate
Changing major ecological processes (nutrient cycling,
hydrology, fire regime, energy)
Destabilizing environmental (physical or community) structure
Forming undesirable monotypic stands of vegetation that replace
diverse communities
Reducing biodiversity/integrity, causing extirpations and
extinctions
Reducing or eliminating a natural product, ecological service or
other valued attribute
ARRIVAL OF INVASIVES
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Natural – Unusual wind patterns (lost birds)
Human importation
Decorative
Erosion control
Agricultural production including timber and
floral
EXAMPLES OF INVASIVES
ICEPLANT OR HOTTENTOT FIG
(CARPOBROTUS EDULIS)
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Small mammal can carry
seeds from iceplant form
landscape settings to nearby
coastal dunes. The vigorous
groundcover forms
impenetrable mats that
compete directly with native
vegetation, including several
rare and threatened plants
along the coast.
PERIWINKLE
(VINCA MAJOR)
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This aggressive grower has
trailing stems that root
wherever they touch the
soil. This ability to resprout from stem fragments
enables periwinkle to
spread rapidly in shady
creeks and drainages,
smothering the native plant
community.
ENGLISH & ALGERIAN IVY
(HEDERA HILIX & CANERIENISIS)
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When birds carry seeds of
these popular plants into
wildlands ivy’s can
smother forest trees and
understory plants by
completely shading them,
which also prevents
regeneration of new tree
and shrub seedlings. Ivy
also harbors pests, such at
rats and snails.
LICORICE PLANT
(HELICHRYSUM PETIOLARE)
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Seeds are wind
dispersed, and
spreading branches will
root at any point of
contact with the
ground. Licorice plant
has been found
displacing native plants
in sensitive coastal
areas.
SCARLET WISTERIA
(SESBANIA PUNICEA)
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Birds spread the fruits
of this small tree or
shrub away from
urban plantings. It
has formed dense
thickets along creeks
and streams.
BROOM – SCOTCH, FRENCH, SPANISH,
PORTUGUSE (CYRUS SCOPARIUS, GENISTA
MONSPESSULANA, SPARTIUM JUNCCUM,
CYTISUS STRIATUS)
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These four brooms have invaded
over one million acres in
California. The showy flowers
produce thousands of seeds that
build up in the soil over time,
creating dense thickets that
obliterate entire plant and animal
communities. Brooms also create
a serious fire hazard.
PAMPASGRASS
(CORTADERIA SELLOANA)
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Wind can carry the tiny
seeds up to 20 miles. The
massive size of each
pampasgrass plant with its
accumulated litter reduces
wildlife habitat, limits
recreational opportunities
in conservation areas, and
creates a serious fire
hazard.
COTONEASTER
(COTONEASTER LACTEUS)
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Birds have spread
the berries and
seeds of these
specimen shrubs to
many different
habitat types. With
their rapid growth
and competitive
roots, cotoneasters
displace native
plants and animals.
STARTHISTLE – YELLOW & PURPLE
(CENTAUREA - SOLSTITIALIS &
CALCITRAPA)
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This is a widespread
invasive found in cultivated
land as well as roadsides,
wastelands, and rangeland.
The leaves and stems have
sharp spines. These weeds
not only discourage feeding
they also can cause disease
to animals that do eat them.
SALT CEDAR
(TAMARISK RAMOSISSIMA)
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Also known as tamaris, this plant is
shrub like and grows to 12 – 15 feet
in height and forms dense thickets.
The slender branches have leaves that
are scale like and overlap each other
along the stem. The plant is very
disruptive to native plant
communities.
RUSH SKELETONWEED
(CHONDRILLA JUNCEA)
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Belongs to the chicory tribe of
the sunflower family. A
distinguishing characteristic of
rush skeleltonweed is the
presence coarse, downward
pointing broken hairs near the
base of the stem. The broken
leaves and stems produce an
milky white sap. This weed
likes disturbed soils of
roadsides, grain fields, pastures,
and rangelands.
WHITE HORSENETTLE –
SILVERLEAF NIGHTSHADE
(SOLANUM ELAEAGNIFOLIUM)
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All the leaves and the
stems have a dense, hairy
covering giving it a
silvery appearance. The
stems are sparsely covered
with short yellow thorns.
The berries and to a lesser
degree the foliage, are
poisonous to livestock.
BAMBOO – GIANT REED
(ARUNDO DONAX)
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A perennial grass that can grow to
over 20 feet in height. Its fleshy,
creeping rootstocks form compact
masses from which tough fibrous
roots emerge. The plants choke
riversides and stream channels,
crowd out native plants, interfere
with flood control, increase fire
potential, and reduces wildlife
habitat. Root and stem fragments
can float downstream and initiate
new infestations quickly.
BARB GOATGRASS
(AEGILOPS TRIUNCIALIS)
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A winter annual closely
related to and
resembling winter
wheat, it is primarily a
rangeland weed. It
prefers dry, disturbed
sites and will also
invade grasslands.
Mechanical injury to
livestock can occur
form the barbed awns
on the seeds.
PERENNIAL PEPPERWEED
(LEPIDIUM LATIFOLIUM)
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Dense colonies of this
weed can grow to over 6
feet tall and have a
spreading underground
root system. Flowing
from May to July, the
small white flowers are
produced on the ends of
stems. It is an
aggressive invader of
wetlands in California
and also found in native
hay meadows and
cultivated fields.
MEDUSAHEAD
(TAENIATHERUM CAPUT-MEDUSAE)
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Dense stands of this grass
can develop in rangeland
communities. Desirable
vegetation, along with the
ability to graze livestock, in
greatly reduced. It contains
much silica, which makes it
unpalatable to livestock and
native wildlife. The sharp
awns can injure eyes and
mouth of livestock.
KLAMATH WEED
(HYPERICUM PERFORATUM)
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This erect perennial
which grows to 3 ½ feet
tall, has showy, bright
flowers. The foliage
contains a pigment that
is toxic to light colored
livestock when
consumed in quantity.
The animals can loose
weight and develop a
skin irrigation when
exposed to sunlight.
HOARY CRESS
(CARDARIA DRABA)
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Also known as
whitetop, it is a noxious
weed, which grows to 2
feet tall. It has creeping
horizontal roots that
vigorously produce new
plants. It can establish
itself in many soil types
and it highly
competitive with other
plants.
REMOVING INVASIVES
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Removing of invasive plants is labor intensive
and time consuming