Plant and Animal Adaptations to Dune and Slack Environments and Human

Impacts on Dunes and Slacks

“The beach environment is hostile to plant life”.

Karl E. Graetz, Seacoast Plants of the Carolinas, 1973.

“The environment is an aggregate of extremes and only plants which have a particular constellation of adaptations can survive”.

Paul E. Hosier, Environmental Inventory of Kiawah Island, 1975.

Dune and Slack Environmental Factors• wind

• salt spray

• unstable substrates

• soil salinity

• soil nutrients

• soil and air temperatures

• soil water content

• saturated and waterlogged soils

• water table fluctuation

Dune and Slack Environment

• factors vary considerably across a dune

• highly dynamic

• location effects species composition

Life-cycle Patterns

Germination Requirements

• scarification trailing wildbean

• stratification sea elder

• both beach hogwart

• neither sea oats (enhanced by stratification)

Sea Elder, Iva imbricata

Life-cycle Patterns

• Plants are highly vulnerable during germination and seedling stages

• germination/seedling survival may be determined by its location on the dune (front, top, back)

• soil moisture

• soil and air temperatures

• sand movement

• salt spray

Life-cycle Patterns

Annuals & biennials

• germinate in spring or fall

• spring - trailing wildbean

• fall - cudweed

• poor competitors in the dunes

• maintain high rates of growth for short periods

• produce many seeds

Life-cycle Patterns

Perennials

• sea oats, American beachgrass, sea elder, seaside

goldenrod, pennywort

• reproduce vegetatively and from seeds

• dominant dune species tend to reproduce vegetatively from rhizomes

• large lateral spread and/or extensive roots

Pennywort, Hydrocotyle bonariensis

Unstable Substrates

• sand movement is a distinctive factor in dune environments

• accumulation or erosion

• moved by wind or water

• sand deposition may be rapid

Foredune on Assateague Island, Virginia

Burial....overwash

Burial

• the most distinguishing ecological characteristic of dune plants is their ability to survive burial

• sea oat and American beachgrass growth is stimulated by accumulating sand

• establishment of many plants on the ocean side of

foredunes is prevented by sand accumulation - examples are cudweed, Canada horseweed, and trailing wildbean

• production of adventitious roots allow plants to adapt to this environmental factor

• seed buried to deeply may not survive

Salt Spray

• impacts distribution of plant species in dune systems

• eliminates salt intolerant species

• many species that can tolerate high levels of salt aerosols are not found on the foredunes, and some species with a low tolerance are found in areas of considerable salt spray

• short life cycle, low profile, low light/ under canopy protection, leaf hairs, thick cuticles

Salt spray impact on arborescent plant

Soil Water Content

• low water content in dune soils

• may determine germination and seedling survival of some dune plants

• dune annuals are highly dependent upon rapid uptake of rainfall for survival

• root systems of most dune plants are between 3 and 15 inches deep - often shallow but wide spreading

• some perennials may have roots systems over 24 inches deep - sea elder, seaside goldenrod

Soil Salinity

• sea oats and American beachgrass do not germinate if soil salinity is greater than about 1.0 percent NaCl

• germinate on the dunes, not in low areas occasionally flooded by salt water

• saltmeadow cordgrass is very tolerant of high soil salinity

Soil Nutrients

• dune sand lacking in plant nutrients

• low organic matter and clay content

• basic pH values

• dune plants with extensive rhizome systems can best exploit available nutrients

Class holding 20-foot rhizome of Phragmites australis

Water Conservation

• many dune plants have xeromorphic features

• succulent leaves and stems - prickly pear cactus, sea elder

• thick cuticles and epidermal layers - pennywort, seaside goldenrod

• dense hairs or depressed stomata on leaf surface -

evening primrose, croton

• leaf inrolling reduces evapotranspiration - sea oats, American beachgrass

• C4 pathway for photosynthesis - enhances water conservation - sea oats, bitter panicum

Solar Radiation

• intense solar radiation occurs in dune systems

• limits distribution of plants

• plants respond to sunlight by:

• avoiding radiation - vertical leaf orientation

• solar tracking - shaded pennywort

• increasing surface area - leaf hairs

Saturated & Waterlogged Soils

• characteristic of mesic slacks

• affects plant development - in half- waterlogged soils roots may be confined to the drier soil

• physiological and morphological changes occur in some plants in waterlogged soils - Orchardgrass exhibits increased transpiration rates, bulrushes are shorter

Wet slack environment, Assateague Island, Virginia

Water Table Fluctuations

• fluctuating water tables are common in slacks

• 0.3 - 0.6 meter fluctuations can cause major disturbances in wetland ecosystems

• plants are killed and species change

• dry periods allow for decomposition of organic matter

Plant Adaptations

Waxy, Leathery or Fleshy Leaves

• resist salt damage

• retain moisture

• sea elder

• sea rocket

• yaupon holly

• live oak Yaupon, Ilex vomitoria

Plant Adaptations

Hairs on Leaves

• trap and retain moisture

• resist salt spray

• camphor weed

• croton

• Gaillardia

Plant Adaptations

Inrolled leaves

• minimize dehydration by reducing surface area and preventing water loss from surface pores

• sea oats

• bitter panicum

• saltmeadow cordgrass

Plant Adaptations

Vertically Oriented Leaves

• decrease the exposed leaf surface to the sun

• pennywort

Plant Adaptations

Leaves flattened against the sand

• withstand high winds

• less salt accumulation

• trap sand

• sea purslane

• seabeach amaranth

• euphorbiaSeabeach Amaranth, Amaranthus pumilus

Plant Adaptations

Flexible stems and leaf blades

• withstand high winds without breaking

• sea oats

• American beachgrass

• bitter panicum

Plant Adaptations

Succulent Leaves and Stems

• store water to tolerate xeric conditions

• prickly pear cactus

• sea elder

• sea rocket

• Russian thistlePrickly pear cactus, Opuntia humifusa

Plant Adaptations

Climbing or Vine Growth Habits

• enables plants to hug dune or other plants for support against strong winds

• compete for sunlight

• morning glory

• beach pea

• catbrier

• grape

Fox grape, Vitis sp.

Plant Adaptations

Extensive Root and Rhizome Systems

• anchor the plant against wind and wave action

• compete for water and nutrients

• continued growth when buried or exposed to the air

• broken rhizomes move with wind or water and establish in another location

• American beachgrass

• sea oats

• bitter panicum

Plant Adaptations

Seed Dispersal

• forcibly ejected trailing wildbean

• wind-dispersed Canada horseweed, cudweed

• water-dispersed sea rocket, sea elder

• animal sandspur, prickly pear cactus

Sandspur, Cenchrus tribuloides

Plant Adaptations

Reproductive Strategies

• seed dormancy

• after-ripening - a period of dormancy after dispersal during which seed undergo physiological changes - ex: camphorweed

• high seed production levels

• vegetative - rhizome fragments of American beachgrass root easily

• seeds and/or rhizomes depending on conditions

Plant Adaptations

Symbiotic Relationships

• rhizosphere bacteria and mycorrhizal fungi have been shown to increase the growth and nutrient uptake of dune grasses

• nitrogen-fixing bacteria

• ability to solubilize phosphorous

Plant Adaptations

Facilitative Effects

• Northern Bayberry, a woody nitrogen-fixing shrub,

has been shown to have a positive growth effect on American beachgrass and seaside goldenrod growing beneath its canopy

• more shaded

• lower soil temperatures

• higher soil nitrogen levels Bayberry, Myrica pensylvanica

Plant Adaptations

Salt Spray• killing of terminal leaves and buds results in lateral branching causing a dense canopy to develop and branching away from the salt source

Succession in Dune & Slack Environments

ReferencesAmos, W. H. and S. H. Amos. 1985. National Audobon Society Nature Guides:

Atlantic and Gulf coasts. Random House: New York, NY: 670p.

Graetz, K. E., 1973. Seacoast Plants of the Carolinas. U. S. Department of Agriculture Soil Conservation Service, Raleigh, North Carolina, 206

pp.

Environmental Inventory of Kiawah Island, 1975. Environmental Research Center, Inc., Columbia, South Carolina.

Kraus, E. Jean Wilson, 1988. A Guide to Ocean Dune Plants Common to North Carolina. The University of North Carolina Press, Chapel Hill,

North Carolina, 72 pp.

Packham, J. R., and A.J. Willis. 1997. Ecology of dunes, saltmarsh and shingle. Chapman and Hall: Cambridge: 335pp.

Shumway, Scott W., 2000. Facilitative effects of a sand dune shrub on species growing beneath the shrub canopy. Oecologia (2000) 124:

138-148.

Will, M. E., D. M. Sylvia, 1990. Interaction of Rhizosphere Bacteria, Fertilizer, and Vesicular-Arbuscular Mycorrhizal Fungi with Sea Oats. Appl. Environ. Microbiol., July 1990, p. 2073-2079.

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