Doctor Greg Moore was Principal of Burnley from 1988 to 2007. He is chairman of the National Trust of Victoria’s Register of Significant Trees and has been on the board of Sustainable Gardening Australia since 2002. He supervises post-graduate students and is involved in research about trees in the urban environment. He spoke at a meeting of SGA Green Gardening Professionals in Fairfield in July on the topic “Evolution of Plants”.
Megan Hallowes reports.
The Carboniferous Period (300-360 million years ago) is an era in Earth’s history very relevant today.
It was during this ancient time, says Doctor of Botany Greg Moore, that plants “went absolutely gangbusters”.
“They photosynthesised so much that they changed the nature of the planet,” he said.
They sucked out carbon dioxide and released oxygen and changed the atmosphere. Fossils developed at an unprecedented rate.
Dr Moore said: “A lot of our fossil fuels come from the Carboniferous. It is relevant to the most pressing biological and ecological issue of the day – climate change. Because, in a way, by releasing fossil fuels and the CO2 and methane associated with it, we are pushing the atmosphere back to something like the Carboniferous,” he said.
“When you go to the service station or turn on a gas heater, you should think of the Carboniferous,” he said.
The extra CO2 in the atmosphere today means more photosynthesis, but the problem these days is that the world is warming. The Carboniferous wasn’t hot. When temperatures get above 40 degrees, the enzymes that enable photosynthesis stop working. But respiration (the plant expending energy) keeps going. This means plants can be in trouble.
Dr Moore said there would be interesting winners and losers in climate change and that, botanists are looking at strategies, for example, for managing urban forests as the climate changes.
Scientists studying climate change are also looking at the Carboniferous.
He said there was a Melbourne link to the topic. Melbourne botanist Isabel Cookson (1893-1973) was famous for her work on plant fossils – the fossils she was interested in were indicative of fossil fuel deposits, so her work was of great interest to the oil and gas exploration industry. The first land plant, Cooksonia, is named after her.
Since the evolution of that plant, 440 million years ago, much has changed. Dr Moore explained to the audience how 200 million years ago, the enormous land mass called Pangaea split into two supercontinents – Laurasia in the north and Gondwana (meaning southern land).
“Gondwana was a magnificent supercontinent with South America, Africa, India, Australia and Antarctica,” said Dr Moore.
Plants that evolved on Gondwana continued evolving after the continents separated. This explains why plants from the same family are found in different parts of the world. Australia and South Africa have the Proteaceae family in common, for example.
Dr Moore said many people assumed that flora in New Zealand and Australia would be similar, however, this is not the case. “They split apart 80 million years ago,” he said.
He said flowering plants (Angiosperms) evolved in Gondwana 65-100 million years ago.
“Angiosperms came along and were new, improved versions of plants – much more efficient at doing a whole range of things than Gymnosperms (non-flowering plants),” he said.
Angiosperms were better at regulating water, transporting water, using energy and reproducing. They took over in the South, almost completely.
“There are very few old-style Gymnosperms or Conifers in Australia, virtually none in Africa and not many in South America,” he said. In the North, Angiosperms “knocked off” Gymnosperms in Southern Europe, but further north, conifers still reign supreme.
Dr Moore said Australia’s oldest Angiosperm fossil is pollen from the Ilex. Most of what we know about the evolution of Angiosperms comes from the fossils of pollen.
More recent evolution, influenced by floods and ice ages, has left Australia with very diverse and unique flora. The Kallista forest in the Dandenong Ranges outside Melbourne, for example, has more plant diversity than the whole of the United Kingdom. Wilson’s Promontory is also a plant diversity “hot spot”.
Dr Moore said at times the ice in the north was up to 3km thick which “cleared the slate”. “Anything that wanted to survive that Ice Age was pushed south. The evolutionary pressures were enormous from the Ice Ages in the north and species of plant disappeared in large numbers.
In the South, in places like Australia, it got cold, but the ice never spread across the whole continent. Our floral diversity was maintained.
It was the ice ages that sorted that out. The ice comes in, things move south. The ice retreats, things move north and so on. And there are a whole lot of issues that are going to be revealed by climate change in terms of that movement over the next 20 to 40 years.”
