Swamp she-oak

Swamp she-oak

What is the swamp she-oak?

The swamp she-oak is a tree endemic to the east coast of Australia.

The scientific name for the swamp she-oak is Casuarina glauca. The word Casuarina is derived from cassowary, referring to similarities between the drooping appearance of she-oak foliage and cassowary feathers. Glauca comes from the Greek word ‘glaukos’, describing the blue-green colour of the foliage.

Swamp she-oaks are found along the shorelines and banks of water environments.

Depending on specific environmental conditions, swamp she-oaks can grow as low-lying shrubs or trees up to 30 metres tall. They can live up to 200 years.

What do swamp she-oaks look like?

Swamp she-oaks have trunks with scaly greyish-brown bark and long, thin greyish-green branchlets that hang down. These branchlets, called cladodes, resemble pine needles and are divided into segments.

Even though they are green, the branchlets are not the leaves of the tree. The actual leaves of the swamp she-oak are tiny ‘scales’ that are difficult to see. These scale leaves are less than a centimetre long, tooth-like, and arranged in a ring around the joints of the branchlets.

Swamp she-oaks are dioecious, meaning there are separate male and female trees. They can be distinguished by the flowers and fruit produced. Male trees produce brown flowers that are arranged in long spikes about 1-3 centimetres long at the end of their branchlets, whilst female trees produce clusters of small red flowers. Female trees also produce spiny, woody cones (fruit), whilst male trees do not produce any fruit.

Where are swamp she-oaks found?

Swamp she-oaks can be found along the east coast of Australia, from central Queensland to southern New South Wales.

They grow in or near brackish water along the banks of rivers, estuaries and coastal areas. Brackish means slightly salty.

By stabilising the soil with their roots, swamp she-oaks play an important role in their ecosystem by reducing erosion and maintaining water quality.

What animals use swamp she-oaks?

Nodules on the roots of swamp she-oaks are dug up and eaten by small mammals such as long-nosed bandicoots. Bandicoot snout pokes can often be found around the base of these trees in the Field of Mars Reserve.

In autumn, the pollen from the she-oak branchlets attracts insects, which then provide food for insect-eating birds such as grey fantails. 

In winter, glossy black cockatoos, yellow-tailed black cockatoos and crimson rosellas can be found feeding on the seeds of swamp she-oaks. Cockatoos will snap the woody cones of the branches and extract the seeds inside while grasping the cones in their claws, whilst rosellas will feed directly from the cones. Red-browed finches will eat seeds on the ground which have fallen after been dispersed from the cones.

Birds such as willy wagtails, magpie larks and butcher birds make their nests in swamp she-oaks.

How are swamp she-oaks adapted to their environment?

Swamp she-oaks are allelopathic. Throughout their life cycle they drop large amounts of leaf litter. The fallen branchlets release chemicals into the soil as they decay. These chemicals prevent other plants from germinating, providing swamp she-oaks with a competitive advantage over other plant species.

Swamp she-oaks are well adapted to survive extreme environmental conditions. They have a particularly high salt tolerance, allowing them to grow in soils that are occasionally inundated by king tides.

Their shallow root system spreads wide and not deep, allowing them to easily absorb water and nutrients from the soil, especially in areas that might flood. In urban environments, these roots can even invade underground water and sewer pipes. 

The small, scale-like leaves help the tree tolerate drought by reducing the amount of water lost through transpiration and evaporation.

The woody fruit protects the seeds inside from being eaten by animals and harsh environmental conditions. 

Swamp she-oaks can sprout from existing root systems in a process called suckering. This allows swamp she-oaks to take over new areas or regrow quickly after disturbances such as fire.

How do swamp she-oaks reproduce?

Swamp she-oaks are dioecious, meaning there are separate male and female trees. Like all flowering plants, trees reproduce through pollination.

How are swamp she-oaks used by Aboriginal Peoples?

The wood of the swamp she-oak is dense, very hard and strong. Aboriginal Peoples along the east coast of Australia use wood from the branches as firewood and to make a variety of tools including land spears, digging sticks, shields, clubs and boomerangs.

To the Dharawal and Darug Peoples, swamp she-oaks are known as 'babysitter trees'. This is because they provide a safe place for mothers to leave their children while they work. The trees offer shade, the soft carpet of needles is comfortable to sit on and the children would be safe from snakes who do not like crossing over the bed of she-oak needles. The lack of undergrowth makes it easy for adults to see the children from a distance. When the breeze blows through the trees, it creates a soothing sound that helps lull young children to sleep.

Children were encouraged to use swamp she-oak seed pods as dreamcatchers before taking a nap or sleeping. They would roll the seed pods between their palms to transfer their worries into them. Then, they would place the seed pod nearby while they slept, allowing any bad dreams to be captured in the small openings. In the morning, the seed pod would be discarded.

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