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Glimpses of Gondwana

Story and photos by Shaun Barnett - Parts of South America and Australia bear an uncanny resemblance to places in New Zealand, living proof our countries were once linked together in the ancient continent of Gondwana.

Moss enveloped the heavily buttressed trees of the beech forest and a small cascading creek gurgled under drooping ferns. The scene before me was so typical of New Zealand that I was more than a little surprised when a wallaby bounced into view.

Actually, I stood in Tasmania, but excepting wallabies, the similarity to a New Zealand silver beech forest proved so strong it was uncanny.

A year later, in the Patagonian reaches of Chile, I tramped amongst beech forests skirting the spectacular ice towers of the Grey Glacier, again bearing an astounding resemblance to scenes in the Southern Alps.

I knew not to be surprised; after all, I had the benefit of knowledge about Gondwana, the ancient continent which split to form these lands, and the original home of the southern beech forests we now share. Yet, actually being in the beech forests of these vastly separated lands consolidated my visions of Gondwana in a way not possible from merely reading about it.

The key to many of New Zealand's current conservation problems may lie with understanding how Gondwana split into the modern landmasses and their evolutionary history. In fact, it was the similarity of flora and fauna throughout parts of the Southern Hemisphere which helped form Charles Darwin's first ideas about evolution.

During his epic four-year journey on the Beagle in the 1830s, Darwin observed countless examples of closely-related but geographically widely separated species.

Darwin believed these species must have common ancestors which had somehow become isolated and slowly changed over long periods of time. A classic example was the strikingly similar Nothofagus species, the  southern beech trees of New Zealand, Australia (including Tasmania), and Patagonia.

The similarities didn't stop with trees. In Patagonia, Darwin collected samples of the beech strawberry - a golf-ball shaped fungus which parasitises beech forests. Fungus of the same Cyttaria genus also occur in the beech forests of both New Zealand and Tasmania. Aside from fungi, there are also similar species of beech associated mosses, lichens and even some flightless sap-sucking bugs.

In Darwin's day, however, there was no explanation for how terrestrial species like beech could have colonised lands separated by vast oceans. Because beech nuts are not eaten by birds, and their seeds don't survive in salt water, how could Nothofagus have spread? Not until over a century later did geologists come up with a plausible answer, when they proposed the lands of Australia, South America, Antarctica, New Zealand, New Guinea, India, and Africa were once united in a super-continent which they named Gondwana. Over millions of years Gondwana, by means of plate tectonics and continental drift, cleaved into the landmasses of today.

Gondwana is like a scattered jigsaw puzzle with the pieces now widely separated. While the pieces would still fit back together geographically, some of them (India and Africa) have changed, biologically, almost beyond recognition.  The pieces of Gondwana fit together, but the surface patterns no longer match. While the flora of pieces like Tasmania, Patagonia and New Zealand certainly seem closely related, why are there so few similarities between the animals? Australia has marsupials galore and a few more primitive monotremes. New Zealand had numerous strange flightless birds but only three bats. Patagonia has a few marsupials, but mostly placental mammals. Why so much difference?

The answer lies with the critical timing of Gondwana's break-up which began some 130 million years ago. Working out when the various pieces of the puzzle broke off provides some explanations, for the biological differences between them.

Before the split, three important evolutionary groups were just coming to prominence on Earth - flowering plants, birds and mammals. While the newly emerged flowering plants and birds had just begun to spread in Gondwana, the first primitive mammals had not yet arrived. Flowering plants rapidly became successful with their superior pollination, seed dispersal and other adaptations. They began to displace many of the earlier evolved, more primitive plants (ferns and conifers). Beech forests were amongst the first of these flowering plants.

Today the cold-adapted beech forests reach their greatest extent in New Zealand and Patagonian South America, with sizeable forests in Tasmania, and smaller ones in New Guinea, New Caledonia, and southeast Australia. At the time of Gondwana's break-up, however, the beech forests did not prevail over the conifer forests. The ancient forests were then dominated by podocarps, such as the ancestors of kahikatea, rimu and miro in New Zealand, along with ancestral kauri and araucaria, such as the monkey puzzle trees in Chile. The understoreys consisted of tall treeferns and luxuriant mosses.

Gradually, the beech forests expanded and began to take over some of the conifers' territory, while in other places mixed forests formed. As Gondwana fractured further, the beech forests became isolated - leading to the evolution of different species of Nothofagus on the different landmasses. Ice began to envelop Antarctica as it drifted south, and glaciers eventually overwhelmed the beech forests there until they were gone.

New Zealand split from Gondwana after the beech forests arrived but, crucially, before the first mammals. Once the Tasman sea formed, around 80 million years ago, the only mammals to reach New Zealand had to swim or fly - and consequently the only ones which made it were several marine mammals and three bats.

New Zealand retained its ancient Gondwana fauna, however, including the tuatara, giant weta, carnivorous land snails and primitive non-croaking frogs. Later, birds came to fill niches in New Zealand which are occupied elsewhere in the world mostly by the mammals.

Australia split off from Gondwana not long after the first marsupials appeared and soon became a land of weird and wonderful pouch-bearing mammals. Placental mammals evolved later in North America and spread into South America only after those two continents collided. South America retained some of its marsupials, but many were replaced by the placental mammals.

Some of the first Gondwana bird species were the ratites, a group of large, stout-legged birds which were probably already flightless at the time of the split. Modern descendants of the ratites include New Zealand's moa and kiwi, South America's rhea, South Africa's ostrich, and Australia's emu and cassowary.

Later bird arrivals came to New Zealand on the wing. Here, without any predatory land mammals, they set a strange evolutionary course, some becoming flightless. Many of the conservation problems we face in New Zealand are really born of our Gondwanan heritage. When humans first brought mammals and aggressive northern hemisphere plants to New Zealand, they were introducing modern elements into an ancient biota - invading something of an evolutionary time warp. It is hardly surprising the ancients have not fared well.

Rats and stoats quickly relegated many bird and reptiles (including the tuatara) to off-shore islands. New aggressive plants like willows invaded wetlands, and possums began to destroy forest canopies, while deer ate out the understorey. Current conservation efforts, ranging from possum and weed-control to rat eradication, are in a way attempts to preserve a precious slice of our Gondwanan heritage.

Shaun Barnett is a freelance writer and outdoors photographer based in Petone.