Native Willamette Valley Oak Habitat

And

Prairie Restoration

Site-Preparation And Seeding Information Sheet

 

Prepared by Lynda Boyer

Restoration Biologist and Native Seed Manager

Heritage Seedlings Inc.

www.heritageseedlings.com

September 29, 2004 (updated August 26, 2005)

 

Note: These are techniques that I, personally, have tried. For a full list of a variety of site prep and seedling techniques, please see the first reference at the end under “Additional Resources” in Appendix A.

 

Grassland Site-Preparation:  Define Your Starting Conditions

1) Remnant prairie with a good native component

2) Meadow with a good native component

3) Meadow with only a few natives

4) Uncultivated old fields and pasture with no natives

5) Cultivated agricultural field

6) Highly disturbed (excavation, logging etc)

7) Steep areas where erosion is a concern

 

(1 or 2)You need to tiptoe around the natives and only use herbicide in weedy areas with few or no natives. These areas can be planted with plugs of native plants in the fall, or seeded if the area is free of major weeds. In the native rich areas, you can spot-spray weeds or use mechanical control methods such as weed-eaters, pruners or hand-pulling.

(3) You must decide if it's OK to lose the few native species you have and then try to reestablish them from seed. For example, many of our old fields have yarrow and buttercup but little else; since these species are commercially available, you can focus your efforts on preparing a site substantially reduced of weeds, and re-seed them.

(4 and 5) Use herbicide (glyphosate) for AT LEAST two seasons to kill existing vegetation. This should be applied as soon as you can get into the site. Suggested rate is 1 – 1.5% glyphosate and 0.25-0.5% surfactant. Herbicide should be applied fall, early spring, summer, and fall at a MINIMUM. Please, no tilling!  Many grasses will be killed in one season; however, many of our deep-rooted or rhizomatous forbs such as Queen Anne’s lace, perennial vetch, St. John’s-wort, and clover take more than one season to control.  In addition, hard-seeded species and annuals such as crane’s bill, mustard, and speedwell will take advantage of the newly opened space and become flush the second season.  Timing of the herbicide application is crucial.  It is desirable to eliminate each suite of weeds prior to flowering.

Note: Cultivation is not necessary in the age of no-till drills. Tilling only brings weed seed continually to the surface and you will NEVER, EVER, EVER, exhaust the weed seed that has built up in the soil for generations. 

A recent Restoration site-preparation forum hosted by the Lane Council of Governments and attended by restorationists, researchers, water and soil scientists, and farmers concluded that the best way to prepare a pasture or agricultural field for native prairie seed reintroduction is herbicide application for at least two years without cultivation. Or, if you must till, do it ONLY ONCE and start the herbicide regime. If baresoil is a concern, plant a cereal cover crop such as wheat, oats, or barley in September to control erosion and suppress weeds.  According to The Oregon State Extension Service (see Appendix A Below) cover crops “protect the soil surface, smother weeds, ….and scavenge nitrogen from the soil before it is leached below the root zone by winter rains”. 

It is important to look at each site realistically and realize the weed seed bank is bigger than you are and that it will never be exhausted.  The seed drill will invariably dredge up weed seed no matter how “clean” it may seem post-herbicide application.  In uncultivated old fields and pasture, aggressive, non-native grasses such as bentgrass, tall oatgrass, and velvetgrass can be the long-term competitive issue for successful native plant reestablishment.  In cultivated fields, the long-term issue is often broadleaf weeds.  (See Seeding Options below for herbicide strategies depending on existing vegetation).

Many native species (both grasses and forbs) are very slow to establish. They need a site free of other vegetation in order to germinate unimpeded and to mature. Most bunchgrasses and perennial forbs grow slowly and don't set seed until their second season (some forbs not until the third.) They are also poor competitors. Once the prairie is established, it is critically important to burn the site every 3 – 5 years. If you can't burn, mow. Burning, however, is the most effective tool to maintain native prairie. Willamette Valley Prairie species evolved with fire. Fire reduces the competition from thatch and woody species and stimulates the root crowns of the native grasses and forbs. Burning may also discourage the non-native grasses and forbs that did not evolve with fire.  Burning every year is not recommended because it increases the abundance of weedy annual species and noxious thistles. It may also be necessary to continually augment the area with new native seed and/or plants after burning or mowing to try and tip the balance to a sustainable native stand.

During the first growing season, it may be necessary to spot treating noxious weeds with herbicide or hand-pulling.  It is more advantageous to target perennial broadleaf weeds such as St. John’s wort, tansy ragwort, clover, and perennial grasses.  Annual weeds will not persist in great numbers once the native perennials have established during the second and third growing season.

(6) If the site has been disturbed by earthmoving it is absolutely essential to not let it lay fallow during the winter. Both erosion concerns and the tendency of weeds to occupy bare soil emphasize the need to sow something on the site as soon as possible. If the desire is to re-vegetate the site with native plant species, try to allow any weed seeds that might be present to germinate and then spray them with glyphosate. Species to be sown should be fall and/or winter germinating grasses and forbs that compete well with non-native species. This ensures that they 1) establish prior to erosion problems; 2) they occupy the spot before fall and winter weeds establish; and 3) they can compete with any non-native species that may still be present on the site. For suggested species, see option 3 below. 

(7) Since native species are extremely small, even those that germinate in the fall or winter, it might be advantageous on erodable sites to first sow a nurse crop of a spring cereal grain.  Sow the spring grain early so it will winter kill, then oversow the area in October with the native seed crop.  The native grasses sown should only be low bunchgrasses that do not flower the first year (Roemer’s fescue, Koeleria macrantha, Poa secunda, Danthonia californica) so the barley can be mowed at a height of 6-8 inches.  The grain can be drilled at a moderate rate and, perhaps, on wider spacing than the native seed.  This should ensure little competition from the nurse crop.  Barley has been recommended due to its lack of regrowth if mowed.  This would be necessary if the barley does not winter kill.  Mowing when the barley is just starting to flower will also reduce the chance of regrowth.   

 

Native Seeding:  Options

  1. If the site is clean of weedy grasses but non-native forbs are still a problem (common in cultivated agricultural fields), seed grasses only the first year, then overseed with native forbs.  This will allow additional growing seasons where a broadleaf herbicide can be applied. Some herbicides, such as 2,4-D, are only completely effective on a relatively small group of weeds.   Thus, it is advisable to use a wider spectrum herbicide (see Appendix B for suggestions). 

If the site is clean of weedy forbs but non-native grasses are still a problem (common in old fields, meadows, and pasture), seed native forbs only the first year, then overseed with native grasses.  This will allow additional growing seasons where grass-specific herbicides such as Poast® or Envoy® can be applied.

After the first stand is established, burning or mowing the site prior to the second native seed application is a good method for opening up the site.  For drilled seed, the suggested sowing rate is 7 – 9 lbs/acre for grasses and 4-5 lbs/acre for forbs. For seed that is broadcasted or hydroseeded this rate should be doubled (this allows for seed predation, and loss due to erosion, desiccation, and poor soil contact). Seed size should be taken into consideration with higher rates used for large seeds and lower rates for small seeds. Seed mixes can be calculated to take into account the seeds/lb of species desired.  Drill seed to a maximum depth of ¼”. Mulching is not recommended for drilled seed due the necessity of light for most native prairie species to germinate. For broadcast seed, light mulch may be applied but it must be weed free! 

    1. Native bunchgrasses can be sown as a mix with the majority of the mix (85%) comprised of slower growing bunchgrasses: Festuca roemeri (Roemer’s fescue), Poa secunda/scabrella (pine bluegrass), and Koeleria macrantha (prairie junegrass); 10-15% of mix the quickly establishing species Elymus trachycaulus (slender wheatgrass) and Elymus glaucus (blue wildrye).  If the most aggressive native grass, Bromus carinatus (California brome) is used, it should be no more than 2-5% of a mix. 
    2. Danthonia californica (California oatgrass) should be planted in mono-culture plots. This grass does not germinate until early March and may not be able to germinate well if sown with the grasses listed in part “a” which germinate in fall. This also allows an additional application of glyphosate mid-winter. If erosion is a concern, it can be sown with a SMALL amount of Deschampsia elongata (slender hairgrass) which germinates in the fall but is not very aggressive. Suggested sowing rate for Danthonica californica is 5-7 lbs/acre.  It is important to note that California oatgrass is very small the first growing season (3-5 blades) so it leaves a lot of room for weedy species.  The tufts will get larger the following year - about 1 ft in diameter.
    3. Forb mixes (see Table 1) should have no more that 10 species, with annuals comprising 25% of the mix and perennials comprising 75%. This increases the chance of successful establishment of each species.  Establishing the perennial forb species while the soil is bare gives a greater chance of long-term persistence as the grass starts to dominate the site.  The annuals will drop out in significant numbers by the second year, but periodic disturbance by burning or mowing will re-open the site to the annuals.  A variety of mixes can be applied to a site by designating plots. This patchwork approach will give the site a more “natural” look over time.  In our current restoration project, the most successful forb species by the second season have been 4 species that spread via rootstock, Sidalcea sp (checkermallow), Prunella vulgaris var. lanceolata (self-heal), Achillea millefolium (yarrow) and Eriophyllum lanatum (Oregon sunshine).  Other perennials such as Lomatium dissectum (fern-leaved lomatium) and Lupinus albicaulus (sickle-keeled lupine) are still small the second season but it is expected they will be more robust by the third. 
    4. Many annual species are great nectar and seed sources for birds and butterflies.  Since they become reduced by perennial dominance by the second season, sowing a border area with a mix of annual forbs and no grass, will allow the populations of these species to be maintained on the site and add additional color and habitat value to the restoration area.
  1. If the site is very clean you can apply grasses and forbs at the same time (this only occurs when the top layer of weed seed has been exhausted – for example, by solarization).  If you have access to a seed drill, one option is to drill grasses in one direction and forbs perpendicular to the grasses. However, this disturbs the ground twice and may intensify the weed issue. Another option is to drill the grasses and broadcast the forbs using a hand-crank spreader, a large spinner-spreader pulled by an ATV or tractor, or by hand. This ensures the forbs (especially those that do not germinate until spring) do not compete with the grasses and that all the space between drill lines is occupied. If the latter option is chosen, the forbs must be sown at a much higher rate which could increase the cost of the project. If no drill is available, broadcast seeding everything together is still effective (see #1 for sowing rate suggestions.) For ease and uniformity of application, (both drill and broadcast), seed should be mixed with a cutting agent. Medium-grade vermiculite (available from nursery supply stores) or sifted, moist sawdust works well.  Rice hulls or crushed hazelnut shells have also been suggested.
  2. If the site is in poor condition or has been disturbed you can sow species that germinate quickly and are good competitors. Elymus glaucus, Elymus trachycaulus (90% of grass mix) and Bromus carinatus (10% of grass mix) germinate quickly and are robust the first year. The following forbs germinate in the fall and early winter: Perennials Achillea millefolium, Lomatium utriculatum, Lupinus albicaulus, Prunella vulgaris var. lanceolata and Rannunculus occidentalis (75% of forb mix) and annuals Clarkia amoena, Clarkia purpurea, Collomia grandiflora, Gilia capitata, Lotus unifoliolatus, Madia gracilis, and Sanguisorba occidentalis (25% of forb mix.)

 

TABLE 1 – Willamette Valley Native Wetland and Upland Prairie Species

wp = wet prairie; up = upland prairie; w = woodland

Species

Annual or

Perennial

Common Name

Grasses, Sedges, Rushes

Carex tumulicola (up)

P

Foothill sedge

Danthonia californica (up, wp)

P

California oatgrass

Deschampsia cespitosa (wp)

P

Tufted hairgrass

Elymus glaucus (up, wp)

P

Blue wildrye

Elymus trachycaulus (Agropyron caninum) (up)

P

Slender wheatgrass

Festuca californica (w, up)

P

California fescue

Festuca roemeri (up)

P

Roemer’s fescue

Juncus tenuis (wp)

P

Slender rush

Koeleria macrantha (up)

P

Srairie junegrass

Luzula comosa (L. campestris) (up)

P

Woodrush

Poa secunda (P. scabrella) (up, wp)

P

Pine bluegrass

Forbs

Achillea millefolium (up, wp)

P

Yarrow

Agoseris grandiflora (up)

P

Large-flowered agoseris

Allium amplectens (wp)

P

Slim-leaf onion

Allium accuminatum

P

Taper-tip onion

Aquilegia formosa (up)

P

Columbine

Asclepia speciosus (up, wp)

P

Showy milkweed

Aster hallii (up, wp)

P

Hall's aster

Aster subspicatus (w)

P

Douglas' aster

Balsamorhiza deltoidea

P

Balsamroot

Brodieae coronaria (up, wp)

P

Harvest brodieae

Calochortus tolmiei

P

Cat’s ears

Camassia leichtlinii (up, wp)

P

Leichtlin's camas

Cammasia quamash (wp)

P

Common cammas

Castilleja tenuis (Orthocarpus hispidis) (wp)

A

Hairy Owl clover

Clarkia amoena (up, wp)

A

Farewell to spring

Clarkia purpurea ssp purpurea (up)

A

Purple godetia

Clarkia rhomboidea (up)

A

Rhombic-petaled clarkia

Collinsia grandiflora (up, wp)

A

Large-flowered blue-eyed mary

Collomia grandiflora (up)

A

Large-flowered collomia

Delphinium menziesii (up)

P

Menzie’s larkspur

Delphinium oreganum (up)

P

Willamette Valley larkspur

Dichelostemma congestum

(Brodieae congesta) (up)

P

Ookow

Dodecatheon hendersonii (up, w)

P

Broad-leaved shooting star

Dodecatheon pulchellum (wp)

P

Few-flowered shooting star

Eriophyllum lanatum (up, wp)

P

Oregon sunshine

Erythronium oregonum (up)

P

Fawn lily

Geranium oreganum (up)

P

Oregon geranium

Gilia capitata (up)

A

Blue field gilia

Iris tenax (up)

P

Oregon iris

Ligusticum apiifolium (up)

P

Licorice root

Lomatium dissectum (up)

P

Fern-leaved lomatium/biscuit root

Lomatium nudicale (up)

P

Bare stem lomatium/biscuit root

Lomatium utriculatum (up)

P

Spring gold

Lotus micranthus (up)

A

Small-flowered deervetch

Lotus unifoliolatus

(L. purshianus) (up, wp)

A

Spanish clover

Lupinus albicaulis (up)

P

Sickle-keeled lupine

Lupinus bicolor (up)

A

Small-flowered lupine

Lupinus polyphyllus (wp)

P

Large-leaf lupine

Madia elegans (up)

A

Showy tarweed

Madia gracilis (up)

A

Common / grassy tarweed

Perideridia oregana

or P. gairdneri (up, wp)

P

Yampah

Potentilla glandulosa (up)

P

Slicky cinqufoil

Potentilla gracilis (up, wp)

P

                    

Prunella vulgaris var. lanceolata (up, wp)

P

Self-heal

Psoralea physodes (up)

P

Scurf pea

Ranunculus occidentalis (up)

P

Western buttercup

Sanguisorba occidentalis (up, wp)

A

Western burnet

Sanicula bipinnatifida (up)

P

Purple sancicle

Sidalcea campestris (up)

P

Meadow checker mallow

Sidalcea malviflora ssp. virgata (up)

P

Rose checker mallow

Silene hookerii (up)

P

Hooker’s silene