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 niño

• 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