Revegetation of Weed-Infested Plant Communities

Jane MangoldExtension Invasive Plant Specialist

Begin with the end in mind. . .

• Kill the weed—Yes, but not the whole story

• Healthy plant community that meets management objectives

Vicious (and Frustrating) Cycle

Treat weed

Open spaces (niches)

Weed reestablishes from seed bankTreat weed

Open spaces (niches)

Weed reestablishes from seed bank

Traditional Weed Management

WEED

Biocontrol

Revegetation

Tilling/diskingMowing

Herbicides

Grazing

Fire

Hand-pulling

Fertilization

Prevention

Irrigation

Future Management

Life cycle of weed

Biocontrol

Revegetation

Tilling/disking

Mowing

Herbicides

Grazing

Fire

Hand-pulling

FertilizationPrevention

Irrigation

Plant Community

Desired Vegetation

What caused this?

What can we do to cause this?

Plant Community Undesired State

Plant Community Desired state

Necessary Components for Plant Community Change

Site Availability

Species Performance

Species Availability

Managing Plant Communities

Step 2Determine Necessity of

RevegetationIf unsure, contact local

Extension, weed coordinator, NRCS, or Conservation District office and schedule a site visit.

Is revegetation necessary?

Step 1Make a Goal Statement

Describe desired condition.

Step 3Assess Soil and Site Properties

Are they acceptable?

Can soil be amended or are species

available that are adapted to the soil?

Step 4Site Preparation Consider seedbed

preparation and/or soil amendments.

Are invasive weeds a

problem at the site?

StopRevegetation is

not recommended.

StopAllow natural recovery.

Monitor frequently to identify and rectify problems.

Step 6Design Seed Mix

Create seed mix based on goals and site characteristics.

Is the site a natural area?

Step 7Determine Seeding or

Planting Method Is site accessible to

equipment?

Step 8Calculate Seeding

RateRates vary depending

on many factors.

Always use native species when their abilities meet your

needs. Non-natives are sometimes the only choice when needs are based on considerations like forage

production and competitiveness with

invasive weeds.

Use native species to provide ecological

stability and maintain plant community

integrity.

•Hydroseed sloped sites

•Roughen soil surface before and after broadcast seeding and apply hydromulch

•Hay mulch seed

•Plant rhizome sprigs in high-salinity sites.

•Broadcast seed a non-prepared seedbed at double to triple seeding rate

•Hand-plug wetland/riparian plants.

Step 9Determine Best Time

to Seed Indicated by selected species, method of

planting, and soil texture.

Step 10Assist Establishment May include actions that precede or immediately follow seeding/planting.

Step 11Monitor

Monitor establishment to identify and rectify

problems in time to allow successful revegetation.

Step 12Long-Term

ManagementCarefully manage to

favor seeded species.

Step 5Reduce Weed Interference

Methods vary depending on many factors.

yes

no

yes

no

no

yes

yes

no

no yesyes

no

Step 1—Make a goal statement

• Revegetation – Returning vegetation to a site; little emphasis on

amending ecological function• Rehabilitation

– Returning a site to a functioning state, but not necessarily its original state

– Native species not required• Restoration

– Returning a site to its original, functional state– Native species are required

difficult

very difficult

“Assisted Succession” Restoration of weed-infested rangeland may

require multiple steps

Cheatgrass/ annual forbs

Introduced, competitive grass

Native vegetation

Example Goal Statements• Short-term goals

– At the end of YR1, reduce weed cover by 25% and increase desirable grass and forb cover by 25%.

• Mid-term goals– At the end of YR5, reduce weed cover to <20% and

increase desirable grass and forb cover to >50%. Hand-pulling and or spot treatment is used to control weeds.

• Long-term goals– At the end of YR10, weeds occur only infrequently

(controlled by hand-pulling) and site is dominated by desirable grasses and forbs.

Step 2—Determine if revegetation is necessary

• Sites with >20-30% canopy cover of desired vegetation can usually recover naturally if performance of weeds is hindered

Canopy cover = area of ground covered by plant foliage

Step 3—Assess soil and site properties

• Assess soil properties to determine if they are acceptable or can be feasibly amended

Soil PropertiesSoil

parameterIdeal

conditionAcceptable

rangeMy soil

Acceptable? Yes or No

Bulk density (gm cm-3)

1.4 1.2-1.6

Soil texture (%sand, silt, clay)

Loam Clay loam to sandy loam

Salinity—EC (mm/hos/cm soluble salts)

0-2 <8

Organic matter (%)

>3 >2

pH 6.5-7.5 5.5-8.5

SAR(Na:Ca+Mg)

<6 <12

Site Properties

• Precipitation• Temperature• Elevation• Aspect• Soil moisture

– sub-irrigated– dry, upland

Step 4—Prepare site• Seedbed

– Firm enough to allow good seed-soil contact

– Loose enough to allow seed to sprout and penetrate soil

• Preparation depends on seeding method– Usually not necessary for drill

seeding– Highly recommended for

broadcast seeding

It’s all about balance!

Site Preparation

• Compacted soil (high bulk density)– Limits air exchange, water infiltration, and

number of safe sites– Scarify, till, disk, or plow

Site Preparation

• Chiseling or harrowing• Plowing• Disking• Dragging small chains• Limit the amount and intensity of

disturbance!– Weed like disturbance!

Do so shallowly to avoid nitrogen release

disked strips—notice brown, cured cheatgrass

Site Preparation

• Herbicide application• Burning• Imprinter Create safe sites

Site Preparation -Soil Amendments

• Fertilizer is typically not necessary• Organic matter

– May also decrease nitrogen availability• Mycorrhizal innoculants

Step 5—Reduce Weed Interference

• Herbicides• Mowing• Grazing• Biocontrol• Cover crop• Late season herbicide application

combined with fall dormant seeding (single entry revegetation)

Do for a couple years prior to seeding to weaken weeds

Herbicide Selectivity

• Non-selective– Kills/stresses any plant – E.g. Roundup, Journey

• Selective– Affects some plants, but not all– Tolerance varies from species to species– E.g. 2,4-D, Tordon, Transline, Milestone, most

range and wild land herbicides

Herbicide Selectivity

• Roundup• Tordon• 2,4-D• Plateau• Transline• Milestone

> NONE> MODERATE> MODERATE> MODERATE to HIGH> HIGH> MODERATE

Single Entry Revegetation

Single Entry Revegetation

Control plot

• Tested on Russian knapweed in eastern OR

Single entry revegetation plot

Step 6—Design seed mix

• Avoid pre-made mixes from unknown or far away sources!

Step 6—Design seed mix

• Customize to meet goals– Forage production– Minimize erosion– Minimize weed invasion and re-establishment– Restore a healthy and diverse plant community

• Customize to site conditions– Soil properties (e.g. texture, salinity)– Precipitation, temperature, elevation, aspect, soil

moisture

Seed Mixes

• Functionally diverse– Grasses– Forbs– Shrubs

• Species-rich• Productive• Weed-free, quality seed

Increased resource capture and reduced risk of re-invasion

Step 7—Determine planting methods

• Drill– Most often preferred

• Broadcast– Steep, rocky, or remote sites

• Hydroseed– Slopes 3:1 or steeper

• Hay-mulch– Spread hay containing seeds over prepared

seedbed• “Island” seeding

Drill Seeding• Seed depth and rate are closely

controlled• Good seed-to-soil contact• Shortcomings

– Rows look unnatural– Long, narrow seeds may become

lodged in seeder– Species require placement at

different depths– Seeds of different sizes separate in

box—add carrier such as cracked corn or rice hulls

– Drill furrows can enhance erosion—seed along contour

Island Seeding

Distance to Recruit Patches

Species

Dis

tanc

e (m

)

0

20

40

60

80

20022003

Echinacea Sagebrush

NS: P = 0.44

P < 0.0001

Reever Morghan et al. 2005. Ecological Restoration 23(3):214-215

Step 8—Calculate seeding rate

• Typically 20-50 seeds/ft2

• Determine rate based on pure live seed (PLS)• Determine rate based on seeding method and

situation– Increase rate 2-3x for broadcast seeding– Increase 2-3x for weed-infested areas

• Adjust individual species rates according to its desirable proportion of the mix

Pure Live Seed (PLS)

• Measure used by seed industry to describe the percentage of a quantity of seed that will germinate

• PLS = %purity X %viability

• Standardizes quality so puchaser can compare quality and value of different seed lots

100

Read the label!

Do the math!

• Lower $/lb., but lower purity and viability = buying more seed to achieve target seeding rate

• Higher $/lb., but higher purity and viability = buying less seed to achieve target seeding rate

Step 9—Determine best time to seed

• Cool season species– Fall-dormant during late fall

• Riparian plugs– Warm temperatures, long days, adequate

water• Late summer planting only if supplemental

water is available

Step 10—Assist establishment

• Seedling establishment is most vulnerable stage of revegetation program

• Implement management to protect sensitive seedlings– Supplemental irrigation– Defer grazing– Mulch

Step 11—Monitor progress

• Identify and fix problems in time to allow for success

• Level of monitoring increases with severity of site conditions

Step 12—Long-Term Management

• Tailor management to maintain developed plant community

• May include– Multi-species grazing– Allowing low-intensity disturbance, e.g.

fire, proper grazing– Controlling re-establishing weeds

Plant Community Undesired State

Plant Community Desired state

Site Availability

Species Performance

Species Availability

Information adapted from:

Revegetation Guidelines for Western Montana: Considering Invasive Weeds

by K. Goodwin, R. Sheley, and J. Marks

Montana State University Extension Bulletin 170

http://msuextension.org/publications/AgandNaturalResources/EB0170.pdf

$3/copy from Extension Publications (994-3273)

Questions? Thank you!• For more information:

• EB0019 “Dryland Pastures in Montana and Wyoming” http://msuextension.org/publications/AgandNatural Resources/EB0019.pdf

• Jane Mangold, Extension Invasive Plant Specialist– 994-5513; jane.mangold@montana.edu

Plant Communities Always Change (“Succession”)

• Process whereby one plant community changes into another. It involves the immigration and extinction of species, coupled with changes in the relative abundance of different plants.-Plant Ecology by M.J. Crawley

Initial Plant Community

Site Availability

Species Performance

Species availability

Final Plant Community

Grazing

Fire

Revegetation

Biological control

Grazing

Biological control

Hand pulling

Repeated Spring Grazing

Fertilization

Mowing/cutting

Tilling

Hand pulling

Herbicide

Herbicide

Tilling improved establishment of seeded species in Russian knapweed infestation

Year 1 Year 2

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l den

sity

(ste

ms

and

tille

rs/m

2 )

0

5

10

15

20

Control Burn Till

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c

d

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a

Mangold et al. 2007

Sheley, R. 2007. Weed Science 55:365-370

Competitive Effects of Seeded GrassesSeeding

TreatmentPerennial GrassBiomass (kg/ha)

Cheatgrass Biomass (kg/ha)

% Reduction

Critana thickspikewheatgrass

792 913 32

Bozoisky Russian wildrye

900 737 45

Sodar streambankwheatgrass

1135 207 85

Luna pubescent wheatgrass

1714 0 100

Hycrest crested wheatgrass

1596 124 91

Unseeded control --- 1337

Whitson and Koch 1998