Terrestrial Invasive Plant Species
Habitat Workshop 2010
Carleton College
An introduction to the issues and a few answers (it’s a big topic)
Nancy BrakerArboretum Director – Carleton College
Definition"Invasive species" by MN law, means a non-
native species that can naturalize and:
1) causes or may cause economic or environmental harm or harm to human health; or
2) threatens or may threaten natural resources or the use of natural resources in the state.
(M.S. 84D.01, Subd. 9a)
DefinitionSpecies that have been introduced, or moved, by human activities to a location where they do not naturally occur andcause ecological or economic problems
We live in a highly mobile world
DefinitionAggressive natives vs invasive species:• Native species can also invade a site• Ecological changes can cause native species to
dominate areas where historically they have not
Consequences of Invasive Species
Ecology
Recreation
Economics
Ecological Consequences
• Changes in natural community structure and composition
• Changes in nutrients or chemical composition of soils (allelopathic responses)
Ecological Consequences
• Changes in habitat for birds, amphibians, invertebrates, etc.
Ecological Consequences
• Changes in biodiversity
Ecological Consequences
Recreational Consequences
Scenic and aesthetic changes
Hiking and hunting
Recreational Consequences
Economic Consequences• Damage and control
costs are estimated at $138 billion each year (USDA, 2000)
• In FY09 MDNR Parks spent approximately $600,000 on 226 invasive species control projects
• Average cost per acre for invasive species control is between $250 and $1500 depending on percentslope and infestation
Lost Revenue– Increased management cost
• Herbicide treatments• Timber stand improvement cost
– Loss of timber production• Invasive species may compete with desired
natives– Loss of target species regeneration
• Need to plant and not rely on natural regeneration
Economic Consequences
Types of Pathways
• Human activity– Intentional (nursery stock)– Non-intentional (ballasts, soil)
• Animal activity– Feeding– Travel pathways (garlic mustard)
• Abiotic activity – Floods/Storms– Wind
PathwaysVehicles
Mud in truck tires
Seeds orvegetationin grill
Seeds or vegetation stuck in variousparts of vehicle
Pathways
Foot Traffic Material brought to site
PathwaysRecreation
Horses, bikes, pets, and you canmove species from one habitatto the next.
PathwaysWildlife movement
Ingesting seed or transporting plant materials in their furor on their feet
Planning Your Attack
Survey and Map - Understand the problem
• What invasive species do you have?• What is the scope of the problem?• Keep informed of and look for potential
new problem plants
Mapping
Simple to complex• Hand drawn map• Aerial photo with notes• GPS• Geographical Information
System (GIS)
Planning your Attack
Survey Example
Black Swallowwort
Planning your attack
Develop a plan• What are your control options?• Where do you start?
– Prioritize: small infestations may be more important then largest
• What will you plant instead?– How will you fill the space that you
just cleared out?
Planning your attack
Monitor• How will you keep track of your
progress?• Are you making progress?• Do you need to try some other tactic?
Identification
Herbaceous Plants• Garlic Mustard• Spotted Knapweed• Wild Parsnip• Reed Canary Grass• Thistles
A few of many!
Woody Plants• Buckthorn• Bush Honeysuckles• Japanese Barberry• Black Locust• Amur Maple• Siberian Elm
Identification Buckthorn• Native to Europe• Single- or multi-
stemmed up to 20 ft• Forms canopies in
forest understory • Impacts
– Shades native species– Changes soil chemistry– Reduces regeneration
of tree seedlings and herbaceous layer
Common buckthornRhamnus cathartica
Glossy buckthornFrangula alnus
IdentificationBuckthorn• Leaves sub-opposite• Twigs tipped with sharp
thorn • Buds pressed to stem• Leaves with curved
parallel veins• Berries black with
several seeds
Can be confused with:• Wild Cherry• Wild Plum• American Plum• Grey Dogwood• Red twigged dogwood
Buckthorn
Cherry
IdentificationGlossy Buckthorn• prefers a wetter
environment than Common Buckthorn
• Bogs, fens, sedge wetlands, and disturbed areas
Common Buckthorn • prefers dry soils • open woods, savannas,
clearings, roadsides, and disturbed areas, also invades prairies
IdentificationBush Honeysuckles
(Lonicera spp.)
– Native to Japan– Multi-stemmed, deciduous
shrub– Up to 15 ft tall– Flowers in May or June– Cause declines in native
plant species of woodland and forest communities
Morrow’s
Bells
Tatarian
Bell’s
Identification
Bush Honeysuckles• Open woodlands,
abandoned fields, other disturbed areas; also invades forests, savannas and prairies
• Prefers moister soils, but can be found in drier environments
Morrow’s
Tatarian
IdentificationJapanese Barberry
(Berberis thunbergii)– Native to Japan– Small deciduous shrub 3-5 ft tall
– Slightly curving branches with thin, straight spines. Bright yellow inner bark
– Very small (0.5-1.5 in) green, blue-green, or reddish-purple leaves
– Flowers in early May; bright red berries
– Forms dense stands that displace natives
IdentificationJapanese Barberry
• Prefers well-drained soils
• Oak savanna and oak forest, but grows and bears fruit in full sun to full shade; wetlands -upland forests
IdentificationBlack Locust
(Robinia pseudoacacia)– Native to U.S. (Appalachian)– Deciduous tree up to 75 feet tall
– Seed pods are 2-4 in long; flowers are fragrant and grow in elongated clusters
– Flowers in May and June
– Was commonly planted for erosion control
– Alters nitrogen cycling and competes with native plants
IdentificationBlack Locust Invades woodlands,
savannas, prairies, edge habitats, abandoned fields, and disturbed areas
IdentificationAmur Maple (Acer ginnala)
– Native to Asia– Small deciduous tree to 20 feet
– Twigs are smooth and light
– Turns bright red in fall
– Fragrant flower clusters in May and June produce many seeds
– Forms dense stands that displace native plants
– Planted as an ornamental
IdentificationAmur Maple
• Grows best in moist, well-drained soils with full sun, but tolerates a wide variety of pH, soil, and shade conditions
• Especially successful in open woods and savannas
IdentificationSiberian Elm (Ulmus pumila)
– Deciduous tree to 70 feet– Silver-gray twigs have a zig-zag
shape with leaf bud at each turn – Leaves base only slightly
uneven (compared to American elm with asymmetrical base)
– Invades pastures, roadsides, and prairies
IdentificationGarlic Mustard (Alliaria petiolata)
– Native to Europe
– First recorded in 1933 (UM herbarium records)
– Biennial, herbaceous plant
– Flowers May-June (white)
– Causes declines in native plant species of the forest understory and bottom lands
IdentificationGarlic mustard life stages
Rosettes
Flowering Plants Seed pods
Infestation
IdentificationGarlic mustard
• Prefers disturbed areas; wet, shaded, deciduous woods, floodplain forests
• Also spreads to upland forests and other habitats
IdentificationSpotted knapweed (Centaurea maculosa)
– Native to Europe and Asia– Biennial or short-lived perennial– 3-4 feet tall– Small pale leaves– Single thistle-like pinkish-purple
flower– Tap root– Inhabits dry to wet sandy soils
IdentificationWild Parsnip (Pastinaca sativa)
– Monocarpic perennial– Rosette 6-12”, flowering
stage 4’ tall– Alternate leaves with 5-15
leaflets on both sides of common stalk
– Yellow flat-topped flower (parsley-like)
– Flowers in June thru late summer
IdentificationWild Parsnip
– Spreading widely in MN – mowing roadsides distributes seeds
– May produce severe rash
– Toxic response depends on prior damage to plant
IdentificationReed canary grass (Phalaris arundinacea)
– Planted for forage, silage, and fodder– Invades wetland and floodplain communities, also
found in crop field waterways – Perennial grass– Reproduces from rhizomes
and seed– 2 – 6 feet high– Forms dense monocultures
Identification• Thistles
– Musk thistle• Biennial, 2-6’ tall• Multi-branched stem with
nodding flowers– Canada thistle
• Perennial, 2-4’ tall• Stems branch at top only• Fibrous taproot with
spreading horizontal roots– Bull thistle
• Biennial, 3-6’ tall• Alternate, coarsely lobed
leaves with spines at each tip
Mechanical Control• Pulling• Cutting• Mowing• Grazing• Fire
Pulling• Most species can be pulled
(works better for some)• Soil disturbance may harm
native species or createseed bed for invasives
• Take enough root with the pull (usually root crown)
• Put plant in plastic bag or burn on site (when seed can germinate)
Grazing• Can either promote or
reduce weed abundance• Will not completely
eradicate invasive plants• When combined with
biological control or herbicides it may eliminate the species
Fire• Will sometimes promote
invasive vegetation• Timing and intensity are
important• Most effective before
flowering or seed set• Often used to reduce
litter so herbicide will be more effective
Mowing
• Can be somewhat effective (most usefulwith species that spreadthrough seed and notvegetatively)
• Timing is important—before seed set is most effective
• Like fire, may stimulate invasive species growth
Chemical control• Type of chemical depends on the target species• Always follow directions & wear safety equipment• Broadcast, cut stump, or
basal bark treatments• Research and
know which is most effective, how it works, and how to use it
Biological Control• Available for some species;
research underway for others• Goes through extensive testing• Monitoring the target species
and the bio-control agent is important
• Host specificity testing– Taxonomically associated plants– Plant species growing in the same
habitat as target weed– Important agricultural plant species
(Smith and van den Bosch, 1967; Pearson and Callaway, 2003)
Purple Loosestrife Biological Control
• Releases (1992-2005)• 1735 releases
– 800 sites– 80 million beetles
• Evaluation (2005)– 320 sites visited– 31% significant
defoliation
Purple Loosestrife Biological Control
Buckthorn Biological Control
• Research began in 2001• Potential agents identified
– 5-10 species of interest• Host specificity testing 2003 -
present • 4-6 years of testing remaining
(Gassman et al. 2002)
Garlic MustardBiological Control
• Research began in 1998• Potential agents
– 4 weevil species • Host specificity testing near
completion• First release in 2007 or 2008• Implementation
– Establishing field sites– Developing rearing methods– Releases – Evaluation C. scrobicollis
Tree/Shrub ControlBuckthorn-Honeysuckle-Barberry-Amur Maple-Elm
Control measures include:– Pulling: be careful about soil
disturbance– Chemical
• Treat cut stump with:– Triclopyr—Garlon– Glyphosate—Roundup
• Basal bark spray with:– Triclopyr—Garlon 4
– Burning: long-term management tool to reduce reinvasion
Tree/Shrub ControlBlack Locust-Siberian Elm
Control measures include:– Chemical
• Treat cut stump with:– Triclopyr—Garlon– Glyphosate—Roundup
• Basal bark spray with:– Triclopyr—Garlon 4
– Manual• Elm: girdle large trees, dig seedlings• Locust: mostly ineffective• Burning may reduce re-invasion (seek
out and remove seed trees)
Biennial/Short Lived Perennial Garlic Mustard-Parsnip-Spotted Knapweed
Control measures include:– Pull plant or cut tap root (collect
seed heads)– Cut/Mow before seed production
(not effective with Knapweed)– Summer burn – Chemical: Treat areas of dense
cover with broadleaf herbicide (non-target impacts a problem)
– Burning: long-term management tool to increase native plant cover
Biennial/Short Lived Perennial Garlic Mustard-Parsnip-Spotted Knapweed
Develop a plan that integrates plant biology into the land management tools you use
Seed reduction or elimination is key! Seed may be viable for many years.
Fall: plant dies
1st Summer:develops rosette and large root
2nd Summer: Plant flowers and sets seed
Spring:seeds germinate
Winter: Plant dormant
Mow/Cut/dig
Dig
Herbicide
Growing season burn
Perennial Reed Canary Grass/Thistles
Control measures include:– Dig if very small patch– Chemical treatment of small patches (non-target
impacts a problem)– Cover with shade cloth– Cut/Mow before seed production– Mow multiple times/year– Mow followed by herbicide – Burn prior to herbicide
These are difficult to control, and willtake many years of treatment!
Monitoring
• Can be as simple as photo plots • Can be as complex as experimental designs
testing different management techniques• Monitoring is key to
understanding if we are accomplishing ourmanagement goals
Before
After
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