Plant and Animal Adaptations to Dune and Slack Environments and Human Impacts on Dunes and Slacks

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Plant and Animal Adaptations to Dune and Slack
Environments and Human Impacts on Dunes and Slacks
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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.
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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

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Dune and Slack Environment

• factors vary considerably across a dune
• highly dynamic
• location effects species composition

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Life-cycle Patterns Germination Requirements

• scarification trailing wildbean
• stratification sea elder
• both beach hogwart
• neither sea oats (enhanced by
  stratification)

Sea Elder, Iva imbricata
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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

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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

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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
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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
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Burial....overwash

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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

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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
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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

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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

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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
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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

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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

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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
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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

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Plant Adaptations Waxy, Leathery or Fleshy Leaves

• resist salt damage
• retain moisture
• sea elder
• sea rocket
• yaupon holly
• live oak

Yaupon, Ilex vomitoria
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Plant Adaptations Hairs on Leaves

• trap and retain moisture
• resist salt spray
• camphor weed
• croton
• Gaillardia

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Plant Adaptations Inrolled leaves

• minimize dehydration by reducing surface area
  and preventing water loss from surface pores
• sea oats
• bitter panicum
• saltmeadow cordgrass

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Plant Adaptations Vertically Oriented Leaves

• decrease the exposed leaf surface to the sun
• pennywort

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Plant Adaptations Leaves flattened against the
sand

• withstand high winds
• less salt accumulation
• trap sand
• sea purslane
• seabeach amaranth
• euphorbia

Seabeach Amaranth, Amaranthus pumilus
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Plant Adaptations Flexible stems and leaf blades

• withstand high winds without breaking
• sea oats
• American beachgrass
• bitter panicum

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Plant Adaptations Succulent Leaves and Stems

• store water to tolerate xeric conditions
• prickly pear cactus
• sea elder
• sea rocket
• Russian thistle

Prickly pear cactus, Opuntia humifusa
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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.
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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

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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
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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

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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

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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
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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

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Succession in Dune Slack Environments
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References
Amos, 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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