Cutting Edge: David Cantrill

November 2, 2001

Growing up in the eastern suburbs of Melbourne, I often escaped to the bush to explore. The variety of unusual plants held a fascination that I suspect stemmed largely from my father's work as a horticulturist. It also meant that botany was an obvious choice at university, but what was not so obvious was to study geology.

My passion for both disciplines ultimately led to a career studying fossil plants. Botanical knowledge allows interpretation of fossil plants and gives insights into rock sequences that are not obvious to the geological specialist. The opposite is also true, as rocks yield information that tells us something of the past life that is contained in them.

Antarctica may seem a strange place to go to collect fossil plants, but it is not all glaciers and snowfields. Large mountain ranges preserve sedimentary rocks that contain a wealth of information about past life on the planet. For much of the past 100 million years, the continent was ice-free and covered in lush vegetation.

Camping in Antarctica is cold, and sitting on a windswept mountain collecting fossils from warmer times, such as delicate impressions of fern foliage, always brings home the message. The earth has experienced a huge range of environmental and climatic conditions. For more than 90 per cent of its his-tory, it was substantially warmer than today.

Antarctica occupied a central position within Gondwana, a supercontinent composed of what is now South America, Africa, India, Australia, New Zealand and Antarctica. About 180 million years ago, Gondwana began to break up. This had a profound influence on the patterns of diversity across the southern hemisphere. Many groups of plants and animals in southern South America have nearest living relatives in Australia, New Zealand and New Caledonia. Fundamental to the development of these patterns was the isolation of Antarctica into a polar position and the cooling of its climate. The history of the Antarctic vegetation is central to our understanding of how patterns of diversity arose in the southern hemisphere.

About ten years ago I started documenting the composition and ecology of the fossil communities. It was obvious that these were unusual. High-latitude floras differed wildly from those at mid-latitudes. Groups that occurred either in high diversities or in high abundance were absent or ecologically unimportant in lower-latitude vegetation. What was responsible for the unusual composition of these plant communities? The unique combination of warm polar conditions with high carbon-dioxide levels and three months of continuous summer light no doubt played a role.

To understand the ecology of these extinct biomes, a modern analogue is needed. The closest analogue to the vegetation that grew on Antarctica some 40 million to 80 million years ago is the low to mid-altitudinal cool temperate rainforests of Valdivia in southern Chile. The ecology of modern Valdivian rainforests is controlled by environmental disturbance brought about by volcanism, and palaeoecological studies of Antarctic floras indicate that environmental disturbance by volcanic activity may have played an equally important role.

We still have much to learn from the Valdivian forests. Unfortunately, clear felling of these forests may take with it our chance to further our understanding of their ecological diversity and dynamics, and an important legacy of a unique ecosystem that existed 40 million to 80 million years ago in the high latitudes of Gondwana will be lost for ever.

David Cantrill leads a small team of palaeobotanists at the British Antarctic Survey.

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