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Sand dunes
The information presented here has been written by Ted Brambleby, Adventure Education,
Marine Environments Field Study and Resource Centre, Hastings Point Beach, NSW

Humble beginnings - The infant dune and its journey

Whether they be of the stable uniform stretch of low dune characteristics of our northern NSW coastline or the gargantuan sand cliffs of Cooloola and the huge packed parabolic dunes of Stradbroke, Moreton and Fraser Island's transgressing inland as wind blown deltas of fine white sand called blowouts they all started in the same humble way. A stray piece of flotsam blown high above the tide line onto a berm or sand ridge by a winter storm, a straggle of seaweed or parts of a mangrove plant, small potential nuclei for the seeding of a dune. Trapped by drying sand around them they in turn become catchments for further wind blown sand that eventually creates a tiny hillock around it: a mini dune.


Spinifex on Primary Dune

The sea weed brings with it passengers that feed on the tiny diatoms attached to it's surface. Sea birds aggregate on bare areas like beaches on which they find refuge from the ravages of the oceans changing moods. These are spots, especially if there are raised areas where they can detect predators easily. They also like to eat amphipods (small crustaceans).

The little Hillock now receives bird droppings rich in nitrates and phosphates, good plant food. Inevitably some of these beach "pimples" will stop the wind blown march of a strange spider like tumble weed, the seed capsule of that hardiest of all grasses called spinifex. Soon after, it germinates to establish a root hold and spreads web like rhizomes (creeping stems) to capture the hillock and other rolling tumble weeds in it's first act of sand stabilisation and dune formation. These are the pioneer colonisers of sand dunes.

Consolidation of adjacent mini dunes by the hopping action of wind blown beach sand (called saltation) Birds, flotsam and those amazing sand holding perennial grasses called Spinifex improves local conditions for other binders such as pig face and the goastfoot vine to join the battle for stabilisation. Together with time, isolation and minimal interference they help create the first thin skin of coastal protection called a primary dune.

   


Morning glory, another
dune colonising plant


Coastal Wattle


Heathland plants

Over further time and the prevailing south easterly wind the build up of original berm and the merging of mini dunes a green fuzzy ridge of Spinifex and sand, forms a low natural wall of defence against intense invasion from the sea. Behind this wall a snug valley called a swale nurtures conditions for nutrients to accumulate and other specialised plants to further diversify. The salt and wind loving pioneers of the fore dune that helped establish this swale now gives way to new varieties of plants. Low sand holding shrubs like coastal wattle (acacias), banksias with their remarkable predilection for poor soils and accumulating phosphates and adaptations against salt wind and severe dehydration.

Mean while in front of the primary dune new mini dunes continue to form. Over time compounded by the dropping of sea levels they become new primary dunes relegating the original dune to a highly vegetated sand hill called a secondary dune. As sea levels continue to drop over the last glacial period, tertiary dunes form. The original dune has become a coastal forest heathland and it's extended swale a luxurious insect and bird rich heath land.

We must ask ourselves what would happen to the great spread of coastal urban development that have displaced so many sand dunes of their natural barrier systems if a reversal was to occur and sea levels started to rise? From the air a series of parallel beach ridges fringing the seaward edge of many coastal plains indicate a history of coastal advance and sea retreat. The highest sand hill in the world is Mt Tempest of Moreton Island it is 280 metres tall and is in fact a huge transgressive dune.

This whole evolutionary give and take process of dune formation and its protective establishment and sustenance of developing coastal forest is called succession, the journey of the dune. Like the adding and shedding of our skin over time the dunes and sea cliffs form a dynamic living security system that surround our continent. It nurtures the essential feedback processes of homeostasis that keeps coastal terrestrial eco systems in balance enabling them to operate autonomously with relative impunity. Our dune system also alike to the skin is a fragile sensitive organ that functions most effectively within the natural parameters set by it's own evolving tolerance to interference and change.

The coastal forests, heathlands, wetlands and mangroves, sea grasses and salt marshes that this dune succession spawns promotes outgoing sediments of sand and detritus (waste organic matter) which unless contaminated by alien infusions of questionable origin and intent feed the capillaries of it's creek and river systems to fuel the oceans and ultimately refurbish the very basis for it's own continuously recycled and sustained existence.

Next - Sand is made from 2 sources    

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Find out about:

The beauty of sand dunes, more than just skin deep, but that is where it all starts
Function of dunes
Humble beginnings - The infant dune and its journey
Sand is made from 2 sources
Key members of nature's green dune squad and their significance
Beach Life Zones
Food Webs on Coastal Beaches
Skin Care Stategies or Dune Management
 
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