Coastal Dune Systems

Western North America

Extensive sand dunes occur along the coast from Cape Mendocino north to Vancouver Island

–      Wind regime is predominantly onshore and continuous

–      Climate is mild.

–      Rain, cloudy skies and fog occur on more than half the days of the year.

Dune vegetation

–      Seral meadow, shrub and plant communities

–      Species composition determined by sand stability and moisture availability

–      Stable or climax communities not common

Environmental factors

–      Sand burial

–      Nutrient limitation

–      Salt spray

–      Lack of moisture

–      Seed predation

–      Mycorrhizae

–      Nematodes

Characteristics of dune vegetation

–      Large seeds, burial-enforced dormancy

–      Fast stem elongation

–      “Cheap” leaves, rapid N resorption

–      Burial stimulates stem growth (reactive growth)

–      Burial stimulates flowering

Dune plant categories (Purer 1936)

–      Water accumulators

–      Suffrutescents

–      Deep-rooted shrubs

There are recurring cycles of dune stabilization and rejuvenation.

–      Dune building may occur as a result of:

•       Sea level rise

•       Seismic uplift or subsidence

•       Tidal maxima cycles

•       El niρo

•       Clusters of activity 400, 1050, 1650, 2400 ybp

Ammophila arenaria (European beachgrass)

–      Introduced in 1868

–      Stabilizing large areas of dunes

–      Threatening native plant communities

 

Dune Vegetation Restoration

Wiedemann and Pickart, 1996.  The Ammophila problem

–      Introduced in 1868

–      Spread all along North American coast

–      Creates a high foredune

•       Blocks inland movement of sand

•       Eliminating habitat of native dune species

–      Manual removal has worked in Humboldt Bay

–      Ammophila is able to stabilize sand so effectively because of vertical rhizomes.

•       Sand burial stimulates the production of new shoots from vertical rhizomes.

•       Buds on the rhizome are localized near the parent ramet, and produce clusters of shoots.

•       Can tolerate a meter a year of sand burial.

The foredune is the ridge of sand along high tide line.

–      It is formed by accumulation of sand in vegetation that is tolerant of sand burial.

–      Native plants have historically formed a scattered, low and temporary foredune.

–      Ammophila forms a tall (up to 10 m) and persistent foredune.

Consequences of stabilized foredune

–      Active sand dunes, especially winter transverse dunes, are becoming starved.

•       Sand surface on lee of foredune is eroded to water table, forming a deflation plane, which becomes vegetated.

–      Native plant communities are being lost.

 

Bennett/Corps of Engineers 2005

–      Study of methods to establish Leymus mollis (American dunegrass) on dredge spoil

–      Carried out on South Jetty beach fill, Grays Harbor

•       Persistent erosion occurred at site

•       American dunegrass was proposed to slow erosion

–      Experimental approach

•       Plants on 15” centers

•       With N fertilizer and without N

•       Control

•       Three plants together, 15” centers, no N

•       Broadcast seeds

–      Results

•       N had no effect, 84% survival (1 y)

•       Three plants together had 99% survival (1 y)

•       Control increased from 0 to 2% cover (not dunegrass)

•       Broadcast treatment increased from 0 to 25% cover

•       In areas not planted, there was some volunteer colonization by  European beachgrass.

–      Recommendations

•       Plant live plants

•       Seed

–      The idea that American dunegrass seeds are sterile is not correct.

–      They do have a low germination percentage.

•       Continue to remove volunteer shoots of Ammophila

 

Pickart and Sawyer 1998. Ecology and restoration of Northern California coastal dunes. 

–      Two main elements in restoration:

•       Removal of invasive plants

•       Revegetation with native plants

–      Removal of invasive plants

–      European beachgrass

•       Manual removal

–      Plants dug out

–      Sand then sifted with rakes to remove rhizomes

–      Several times

•       Burning

–      Sometimes can replace first dig

–      Stimulates beachgrass shoot growth

•       Chemical control

–      Usually glyphosate (Rodeo or Roundup)

–      Moderately effective, but at higher concentrations (10%)

•       Saltwater control

–      Ammophila is sensitive to elevated salinity.

–      Application of seawater causes transient increase in salinity, but most plant parts are not killed.

•       Heavy equipment

–      Bulldozers with deep scarification attachments.

–      May facilitate subsequent hand removal

–      Other weeds

•       Yellow bush lupine (Lupinus arboreus)

•       Ice plant (Carpobrotus edulis)

–      Revegetation with native plants

–      Substrate

–      Genetics

–      Seeding

–      Transplanting

–      Substrate stabilization

–      Fertilization and mycorrhizae

–      Irrigation

–      Substrate

•       Dune revegetation usually occurs on two kinds of substrate.

–      Unvegetated because of blowout or moving dune or fill that is brought onto site.

»      Sterile

»      May use fertilizers, irrigation, artificial stabilizers

–      Substrate from which invasives have been removed.

»      Contains organic material, mycorrhizae, seeds

–      Genetics

•       Follow standard guidelines for seed collection

•       If you buy, use common sense

–      Ask about genetic diversity of seed batch

–      Do not use seeds from a different ecosystem

»      There are beaches on Lake Huron.  Do not use seeds from there.

–      Seeding

•       There are documented methods for seed collection

•       Seeds are usually broadcast manually or with a spreader, then raked into sand.

•       Can be mechanically sown, with proper equipment

•       Can be hydroseeded

•       Seed mixes are commonly used

•       Application rate varies from 200 to 1000 per m2

–      Larger seeds, plant less

–      Transplanting

•       Divisions and cuttings

•       Container plants

–      Planting

»      Harden off

»      Allow roots to fill containers

•       Plant in fall and winter

•       Plant on 24” centers

–      Substrate stabilization

•       Hydromulch

•       Nurse crop

•       Emulsions

•       Crimped straw

•       Erosion control netting

•       Sand fencing

–      Fertilization and Mycorrhizae

•       Fertilization is subject to fast leaching in sand

•       Favors weeds, suppresses germination of native seeds and inhibits mycorrhizae

•       If you fertilize, use slow release (Osmocote)

–      500 to 1000 kg/ha

•       AM (arbuscular mycorrhizae) inoculation may have positive benefit but may not be cost-effective.

–      Irrigation

•       Short term solution

•       May impair project if timing is imperfect

•       Encourages weeds

•       Most important at germination

•       Sprinkler irrigation most common