INVASIVE SPECIES

Introduction to Watershed ScienceIntroduction to Watershed Science

Merritt CollegeMerritt College

Marc Epstein, InstructorMarc Epstein, Instructor

WHAT ARE INVASIVES

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

A species whose presence in the environment causes economic or environmental harm or harm to human health. Native species or non-native species may show invasive traits, although this is rare for native species and relatively common for non-native species.

TRAITS OF INVASIVE SPECIES 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

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)

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)

This aggressive grower has This aggressive grower has trailing stems that root trailing stems that root wherever they touch the wherever they touch the soil. This ability to re-soil. This ability to re-sprout from stem fragments sprout from stem fragments enables periwinkle to enables periwinkle to spread rapidly in shady spread rapidly in shady creeks and drainages, creeks and drainages, smothering the native plant smothering the native plant community. community.

ENGLISH & ALGERIAN IVY(HEDERA HILIX & CANERIENISIS)

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)

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)

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)

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)

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)

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) 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)

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)

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) 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 REEDBAMBOO – GIANT REED(ARUNDO DONAX)(ARUNDO DONAX)

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)

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)

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.

MEDUSAHEADMEDUSAHEAD(TAENIATHERUM CAPUT-MEDUSAE(TAENIATHERUM CAPUT-MEDUSAE))

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)

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)

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

Removing of invasive plants is labor intensive Removing of invasive plants is labor intensive and time consumingand time consuming