A biogeographical journey of New Guinea forests

Once upon a geologic time, New Guinea and Australia were part of a ‘super-continent’ called Gondwanaland, formed about 200 million years ago.  When this ‘super-continent’ began splitting up, landmasses such as current day New Caledonia, South America, Africa and India formed and began drifting away from their former location.  The Australia-New Guinea tectonic plate chose a northward direction.

The island changes

During the course of its northern migration, the Australia-New Guinea plate was almost completely isolated. Because the overall climate was arid at that time, many species sought refuge in the relatively cool and well-watered Great Dividing Range along Australian’s eastern board.

Today, pockets of remnant vegetation from that period remain in New Guinea's cool uplands, with some species relatively unchanged from the Gondwanan forms of 60 or 90 million years ago.

Collision of continental proportions

Eventually, the Australia-New Guinea tectonic plate collided with the Eurasian plate to the north, about 25 million years ago. In an accordion-like effect, New Guinea was pushed out of the sea, while a downwards buckling trend took place in the Torres Straits, which now separate New Guinea and Australia.  

What New Guinea’s journey has meant for its wildlife

New Guinea’s trajectory, from its early days as part of Gondwanaland, to its solitary life in the Tropics, has pushed the island’s wildlife to adapt to changing environmental conditions.

The islands of Wallacea to the east, which were also pushed up by the collision of the tectonic plates, paved the way for plants from Southeast Asia's rainforests to colonize New Guinea, and some plants from Australia-New Guinea to move into Southeast Asia.

The gap between the islands were narrow enough to allow plant dispersal, but prevented the exchange of land mammals between Australia-New Guinea and Asia.¹

The result of New Guinea’s isolation

Because the island was isolated over extended periods, for a long time very few outside species were able to colonize it, and unique native forms developed unchallenged.

During the last Ice Age (1.6 million – 10,000 years ago), whereas much of the rest of the world was experiencing a significant cooling effect - and thus loss of species diversity - the Australia-New Guinea tectonic plate was moving north so that the overall global cooling effect was roughly equalled by the landmass movement toward the warmer Equator.

As a result, temperatures in Australia-New Guinea remained more or less constant, allowing wildlife species to evolve to fit particular ecological niches.²

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¹ Wikipedia. Australia-New Guinea. Accessed 12/01/2006.
² Wikipedia. Australia-New Guinea. Accessed 12/01/2006.