Mighty Rainforest 'Oaks'

Skyrail Nature Diary: May 2009

The Wet Tropics World Heritage Rainforest is home to many mighty trees, including the Briar Silky Oak and Bull Oak, which can be seen flowering and fruiting on Skyrail Rainforest Cableway this month.

It should be noted that neither of these trees are true ‘oaks’, rather their common names refer to their lofty heights and mighty place amongst the rainforest canopy.

The Bull Oak, also known as the Northern Silky Oak, grows up to 40m tall and was once favoured by loggers for its strength, texture and oak grain appearance. In fact, during the first half of the 1900s, vast tracts of these trees were cleared and the timber was used extensively for interior work, including railway carriages, school desks, cladding, lining and flooring.

Fortunately, some mighty examples of the Bull Oak (Cardwellia sublimis) can still be found in the Barron Gorge National Park and seen on Skyrail Rainforest Cableway, particularly on the back-line as you approach Barron Falls Station from Red Peak.

Bull Oak’s are easy to identify this month: look for the large trees, emerging from the canopy and topped with large almond-shaped woody pods. These pods are filled with papery seeds, which are dispersed by the wind when ripe.

Bull Oak seeds are also very popular with Sulphur-crested cockatoos, which will break the pods open to access the seed cache before they blow away.

Bull Oak trunks are normally straight, although there are some buttressed examples, with a slightly flaky bark. Its heartwood timber is pale pink to brown in colour, while sapwood is almost white. The flowers of this magnificent rainforest tree are typical of silky oak flowers, creamy white to brown in colour and densely arranged on the crown of the tree during summer on large spikes.

The other ‘oak’ in review this month is the Briar Silky Oak (Musgravea heterophylla), which grows along the entire Skyrail Rainforest Cableway transect.

This mighty tree grows to 30m in height and also has white to brown flowers, which appear across its crown on long spikes. The Briar Silky Oaks are flowering extensively this month and can be seen throughout the canopy on Skyrail.

A striking feature of the Briar Silky Oak is its juvenile leaves, which are strongly lobed with distinctive jagged edges, usually tipped brown or pink. The undersides of these leaves are coated in glossy brown hairs, creating a felt-like texture.

Briar Silky Oaks were also favoured by timber-cutters and large specimens are now rare.

These are just two examples of the mighty rainforest trees which emerge from the canopy; others include the Kauri Pine and Red Pendas, which can also be seen on Skyrail. Whilst these trees were all popular with timber-cutters last century, they are now protected in the World Heritage listed Wet Tropics Rainforests of Queensland, in the Barron Gorge National Park.