Landscape & Geology

 

Hinchinbrook Island is dominated by a mountainous backbone featuring peaks such as Mount Bowen (1142 m), Mount Diamantina (955 m), Mount Straloch (922 m), Mount Pitt (722 m), Mount Burnett (655 m) and Mount Barra Castle (579 m).

 

These mountains comprise two distinct rock types. The main mass centred on Mount Bowen consists of granite, while the mass projecting north-west and including Mount Pitt and Mount Burnett consists of silicic volcanics. The granite of the main mountain mass has weathered to spectacular, often jagged peaks.

 

The island is separated from the mainland by the narrow Hinchinbrook Channel, which represents the flooded valley of the Herbert River.

 

Vegetation Communities

 

Hinchinbrook Island lies in the wet tropical rainforests biogeographic region. It is subject to hot and humid conditions and high rainfall, with occasional short spells of cooler, dry weather in winter. These factors, along with generally poor, shallow soils, determine vegetation patterns. To date, about 30 plant communities have been identified, with around 700 species recorded.

 

While areas of rainforest occur at low and high altitudes, most of the mountainous part of the island is covered with open forests and low heaths on shallow soil. The mangroves which line Missionary Bay and Hinchinbrook Channel form one of the largest mangrove areas on the Australian continent and include 31 species of mangrove. Some small but significant areas of broad-leaved tea tree Melaleuca viridiflora woodland occur on the north coast.

 

Vegetation types such as this have assumed conservation importance as similar types on the mainland face increased rates of clearing. This is true of most of Hinchinbrook Island's plant communities, particularly lowland types, which may well be restricted to Hinchinbrook Island in years to come. A survey of all the tropical lowlands from Ingham to Cooktown indicated that Hinchinbrook Island National Park and Hinchinbrook Channel are of outstanding importance because of the diversity of rare communities.

 

About 14 species of rare and threatened plants have been recorded on the island, although it is highly likely that others exist awaiting discovery. One species of the shrub Comesperma—Comesperma praecelsum—is known only from Hinchinbrook Island. Other species such as the blue banksia Banksia plagiocarpa and sundew Drosera adelae (photo) are restricted to the island and adjacent mainland.