Subtropical Rainforest

Subtropical Rainforest

By Gary Opit

The surface of the lava that created the landscapes of Byron Bay and much of the rest of north-eastern New South Wales weathered over 20million years into the rich red basalt soils that now cover much of the scenery. These fertile, well-drained soils formed the perfect habitat for subtropical rainforest that once covered much of Australia. The continent’s climate changed from warm and wet to cool and dry. The rainforest was replaced by the eucalypt forest that was better adapted to drier soils and more frequent fires. Thunderstorms blowing against the volcanic slopes surrounding Byron Bay provided sufficient rain to ensure the survival of the ancient remnant rainforest. The largest area of subtropical rainforest to survive anywhere on Earth is now found in south-eastern Queensland and north-eastern New South Wales.


Subtropical rainforest requires about 1300 mm of rain every year to survive and warm temperatures. High soil phosphorus levels of about 1000 ppm are essential and is the reason that subtropical rainforest usually grows on soils from basalt and other basic igneous volcanic rock. A southern or eastern aspect provides protection from dry northern and western winds. Valleys provide particularly ideal conditions with the accumulation of soils, nutrients and water and protection from cyclonic winds. The dense rainforest canopy is essential in modifying the environment by reducing sunlight intensity, wind,and rain to produce a stable, cool, shady micro climate. All of these protect the rainforest from its greatest enemy, fire!


Our rainforests are classified as Complex Evergreen Vine Forest. With approximately 210 different tree species and another 40 different shrubs, 75 species of vine, 55 ferns, 26 orchids, 10 lilies and gingers, plus all of the herbs, mosses and fungi, these ancient forests arevery complex. Except for the red cedar and the deciduous Fig, which shed their leaves in the winter, the rainforest trees remain evergreen throughout the year.


Some of the plants in this rainforest have survived from the days of the dinosaur and are living examples of the kind of vegetation that dominated the world in the far past. The most ancient, large plants in this forest are four species of tree fern that formed some of the oldest forests on Earth. In the Mesozoic Era, vast areas of damp soil were covered by these tree ferns. It is believed that the longest dinosaurs, the Diplodocids that reached lengths of 30 m and the Titanosaurids that reached 21 m and lived in Australia had peg-like teeth and fed on these ferns.

Straw Tree Ferns (Cyathea cooperi). Photo by Wendy Bithell

The straw tree fern loves moist soils, grows naturally along waterways and is often grown in gardens. The rough tree fern, the bristly tree fern and the prickly tree fern prefer slightly drier soils in rainforest. The shining burrawang or zamia palm is a cycad that grows in drier, sunny situations, reaches 3 metres in height, has thick glossy leaflets, and grows a large pineapple-like cone on the top of the trunk, full of big red seeds.Cycads of many species covered all of the drier, less fertile open ground In the Mesozoic Era and were eaten by all of the medium-sized herbivorous dinosaurs.


In the age of the dinosaurs, most of the more fertile areas were covered by mighty forests of Hoop Pine, Bunya Pine, Kauri Pine, Brown Pine, Norfolk Island Pine, and the newly discovered Wollemi Pine. Hoop pine and Brown Pine still grow in the Byron rainforest. Bunya Pine and Kauri Pine still grow in south-eastern Queensland rainforests, though many individuals of these pines have been planted throughout north-eastern New South Wales. Norfolk Island Pines have been planted in Byron Bay and within other coastal towns where they grow very successfully in the sandy soils enjoying the salt-laden air.


All of these pine are in the ancient Gondwana family of Araucaria and grow to be our tallest trees. Except for the Brown Pine, which offers edible plum-like fruit to animals for the dispersal of their seeds, the other still keeps their spiky seed cones at the top of the tree out of reach of the tallest of all the long-necked sauropod dinosaurs, the Brachiosaurids, and the Titanosaurids that fed like gigantic giraffe. Today we can look at our magnificent native pines and imagine the dinosaurs that once fed upon them.

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