Control of Invasive Plant Species in Restoration Projects

 

EHUF 473 Lecture 3

 

I.  Site selection and assessment of invasive species problems

          A.  Some sites are too heavily invaded to restore economically

                   1.  Reed canarygrass can be intractable in much of northern U.S.

                             a. Seeds, rhizomes

                             b. Broad ecological amplitude

                             c. Fierce competitor

                             d. Whatever kills it kills everything else

                   2.  Purple loosestrife

                             a. Is beginning to be controlled by bioagents (Gallerucella beetles)

                             b. Still produces millions of tiny seeds.

                             c. Excludes other plants

                   3.  Brazilian pepper [Schinus terebinthifolius (S. molle)]

                             a. Currently mechanical removal by heavy equipment is used

                             b. Biocontrol agents are being evaluated

                   4. Water hyacinth (Eichhornia crassipes)

                   5. Spartina spp (S. alterniflora, S. townsendii)

                   6. Phragmites australis (P. communis)  Common reed

                   7. Solutions for heavily invaded sites

                             a. Lots of money (soil removal or site burial)

                             b. Shading for some species

                             c. Biocontrol

 

          B. Other bad things

                   1.  Star thistle, knapweeds (Centaurea spp.)

                   2.  Cheat grass (Bromus tectorum)

                   3.  English ivy (Hedera helix)

                   4.  Himalayan blackberry (Rubus discolor)

 

          C.  Are these bad things?

                   1.  Cattail (Typha latifolia)

                   2.  Red alder (Alnus rubra)

                             a. Nitrogen-fixing colonizer

                             b. Self-thinning rule

                   3. Willows (Salix spp.)

 

          D.  Assessment of site

                   1. Determine vegetation cover of natives

                   2.  Determine cover of invasives (extent, life form, vertical layer)

                             a. Determine extent of heavily infested areas

                             b. Inventory invasion pathways (roads, streams, clearings, old fields)

                             c. Determine which species occur in what area

 

         

          E.  Assess off-site sources

                   1.  Disturbances

                             a. Roads or trails

                             b. Construction

                   2.  Corridors

                             a. Roads, trails

                             b. Streams

                   3.  Seed production areas

                             a. Fallow fields

                             b. Un-maintained edge of agricultural fields

                             c. Road R.O.W.’s

                   4.  Transport mechanisms

                             a. Prevailing winds

                             b. Flowing water

                             c. Waterfowl, livestock

                             d. Gravity, slope

                             e. Traffic

 

II. Site treatment

 

          A. No-till

                   1. Dibble

                   2. Container plant

                   3.  Agricultural no-till (plant behind narrow tractor-mounted blade)

 

          B. In-planting

                   1. Requires existing overstory

                   2.  In Northwest, usually shade-tolerant conifers

 

          C. Phased planting

                   1.  Plant fast growing trees (alder, willow, poplar, ash)

                   2.  Follow with herbaceous or woody natives

                   3.  Shade suppresses weedy species

                   4.  Shade is preferred by some seedlings, understory spp.

 

          D. Selective clearing

                   1.  Sites may commonly have “good” areas and “bad” areas.

                   2.  A useful strategy is

                             a. Apply minimal effort in good areas

                             b. Attack invasives  in bad areas.

 

          E. Herbicides

                   1.  Pre-emergents suppress weed seed growth

                             a. Last for a season

                             b. Also suppress natives

                   2. Herbicides are now quite selective: grasses, broadleaf

                             a. Will attack grass only, broadleaf only

                             b. Some will kill grasses except for fine-leaved fescues (Idaho fescue)

                   3. Some cause concentration in food chain (2, 4- D), but are very effective

                   4.  Some have little residual effect

                             a. May require several applications

                             b. Glyphosates

 

          F. Fire

                   1.  Many ecosystems have evolved with fire

                   2.  Fire frequency has diminished because of suppression

                   3.  Invasive plants, especially woody ones, are controlled by regular fires

                   4. With moderate fuel load, native plants will survive

 

          G. Prescription grazing

                   1.  Most grasslands evolved with grazing pressure

                   2.  Natural grazing was intense, and of short-duration

                   3.  Modern livestock grazing is continuous and damaging (fenced pastures)

                   4.  Livestock may be used for controlled, intense grazing.

 

          H. Flooding and draining

                   1.  Some wetlands naturally dry out; when dry, different species appear.

                   2.  Controlling water level can be used to:

                             a. Encourage the growth of  some plants (draining, summer annuals),

                             b. discourage others (flooding to suppress weeds)

 

          I. Cover crops

                   1.  Annuals are commonly planted

                             a. To prevent erosion

                             b. To inhibit germination of weed seeds on cleared sites.

                   2.  Sterile wheat is used on logging road restoration.

                   3.  Winter rye, Japanese millet also used.

                   4.  Plants will not persist, theoretically

                             a.  Will not set seed

                             b.  Will be poor competitors in the restored environment.

                  

          J. Agricultural tillage

                   1.  Repeated tillage is a common method of depleting weed seeds in cultivated fields.

                   2.  Seeds are brought to the surface by cultivation.

                             a. They germinate,

                             b. Are killed by subsequent cultivation (a week or two later)

                   3.  This may be repeated many times.  It is weather dependent.

                   4.  May be done around restoration plants if  planted in rows

 

          K. A clean site is a good thing

                   1.  An agricultural field is usually a very “clean” site in terms of weeds.

                   2. An abandoned field or “old field” is usually quite badly infested

                   3.  Keeping a site clean before restoration is important.

 

III. Installation techniques

          A. Landscape fabric

                   1.  Water and gas permeable, weed resistant

                   2.  Reed canarygrass has a tendency to ignore it, or come through seams

                   3.  You can plant stakes or container plants through the fabric

                   4.  Weeds will come through the planting hole

 

          B. Mulch as top-dressing, not amendment

                   1.  Thick mulch (one foot) will suppress many weeds and grasses

                   2.  Blackberry will come through it. 

                   3.  Reed canarygrass will root in it.

 

          C. Other barriers (cardboard, rugs, plastic sheeting)

                   1.  Similar problems as landscape fabric.

                   2.  Plastics make an ugly mess after a few years

 

          D. Sandwiches, layered geo-fabrics

                   1.  Desperate measures for desperate times.

                   2.  You may layer mulch, landscape fabric, and mulch.

                   3.  Or landscape fabric, mulch, and landscape fabric.

 

          E. Islands

                   1.  A strategy used with English ivy

                             a. Pull it away from the base of a tree or planting site,

                             b. Start rolling it back and pulling up roots.

                   2.  This creates an ivy-free area that may be expanded

                             a. Ivy grows slowly

                             b. Subsequent work parties can expand clearing

 

IV. Successional strategies

          A. Planning for structural differentiation, shading, growth-form competition

                   1.  Trees outcompete shrubs, shrubs out-compete herbaceous species and grasses.

                   2.  “Going up one growth-form”

                             a. Will allow a planted species to outcompete an undesirable weed.

                             b. Will shade out weeds

                   3.  Weeds often require sun, water and nutrients

                   4.  Native sub-canopy species may have evolved with limited resources.

 

 

          B. Resource control

                   1. A poor soil is a fine thing

                             a. Weeds often require sun, water and nutrients

                             b. Many native species are at risk when stressed sites are disturbed

                            

                   2. Soil modification

                             a. Increase porosity to make a “quick” soil

                             b. Increase grain-size to decrease cation-exchange capacity

                             c. Nitrogen-uptake modification:

                                      -Add carbon source to increase loss of nitrogen

                                      -(wood chips, sugar)

                  

          C. Salinity control

                   1.  Coastal wetlands are partitioned according to salinity.

                   2.  Freshwater wetlands adjacent to brackish ones may be converted

                             a. Many are diked

                             b. Breaching allows saltwater to enter them.

                             c. This will eliminate freshwater weeds.

 

          D. Flooding

                   1.  Flooding will eliminate terrestrial weedy species

                   2.  Flooding in winter and dropping water level in summer

                             a. Will discourage aquatic weeds

                             b. Will encourage competition from terrestrial species

 

          E. Draining

                   1.  Aquatic weeds are killed by draining in summer and allowing them to desiccate.

                   2.  Aquatic weeds are killed by draining in the winter and allowing them to freeze.

 

IV. Monitoring and maintenance

          A. Presence required

                   1.  After a restoration is installed, inspect regularly.

                   2.  At the start of the growing season, inspect more frequently.

                   3.  Minor problems can become major problems quickly .

 

          B. Visual keys

                   1.  You must know what invasive species look like.

                   2.  You must know what the juvenile state of an invasive species looks like.

 

 

 

          C. Thresholds

                   1.  A few shoots, for a fast-growing species

                   2.  For a slow-growing species, you have more time.

                   3.  Response to the first removal of an invasive may be a good indicator .

                             a.  If regrowth is fast, mobilize.

                             b.  If you cannot keep up, consider herbicides. 

 

          D. Actions

                   1. Staff, volunteers: 

                             a.  Regular attention to a site

                             b.  Removal must be repeated

                             c.  Weather will dictate resources that are needed

                   2. Equipment:  a tractor is worth 40 or 50 people

                             a.  Site must be set up for equipment.

                             b.  Equipment increases the force you can apply

                             c.  And speed you can work

                   3. Herbicides

                             a. Type of herbicide

                             b. Mode of action

                             c. Method of application

                             d. Site of application

                             e. Applicators licenses

                             f. Aquatic rider to applicator’s license; approved aquatic formulations

                             g. ATV helpful for large acreages

 

                   4. Prescribed burns

                             a. Require permits

                             b. Prescriptions take into consideration

                                      -temperature, time of day, wind speed, relative humidity,

                                      -fuel load, fuel moisture content and fuel volatility

                             c. Require firebreaks (blacklines, mowed and wetted strips, roads)

                             d. Require equipment

         

          E. Tractor-accessible sites

                   1.  If a site is large (five acres or more), design for tractor access may be important.

                   2.  Slopes not too steep

                   3.  Access to edge of water features

                   4.  Planting in rows

                   5. Five meters between planting rows for access (for mowing, cultivating, spraying)

                   6. Turn-arounds available

 

          F. Herbicides: See the Iowa State website:

 

                             http://www.weeds.iastate.edu/reference/siteofaction.htm

 

          G. Phased planting:

                   1.  If site is designed as a phased planting, it must be monitored

                   2.  Invasive species must be kept down

                             a. They will seek sun and avoid shade

                             b. Some species must be removed from trees

                   3.  If ready for later phases, site will have to be prepared again:

                             a. Tillage, mulching, intallation or refurbishing of irrigation systems.

                             b. Care must be taken to not damage existing plants