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Securing the future of the Wollemi Pine -

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Robyn Williams: But here now with this week's PhD is an example of how you investigate a piece of ecology. Heidi Zimmer:

Heidi Zimmer: Once upon a time in the remote Blue Mountains, west of Sydney, an off-duty ranger was on a canyoning trip with friends. Walking along, he noticed something that looked a bit different, a tree he didn't recognise. He picked a small branch, put it in his pack and continued. Several days later he showed the specimen to someone, and they asked, 'Is this from a shrub or from a fern?', and the ranger, David Noble, answered, 'No, it's from a bloody big tree.' This tree would come to be known as the Wollemi pine, scientific name Wollemia nobilis. To discover a new species of tree within 200 km of one of Australia's most populous cities, was amazing. It was 1994 and the Wollemi pine was world news. It was also quickly listed as critically endangered. There are fewer than 100 mature Wollemi pines left in the wild.

The tree wasn't completely unknown, fossils very similar to the pine have been found across Australia, suggesting that it once had a much wider distribution, around the time of the dinosaurs. This is how the Wollemi pine got its reputation as being a dinosaur tree. It seems likely that the decline of the Wollemi pine was associated with increasing aridity and fire in Australia. The Wollemi pine is one of the few endangered species that is rare not because of humans, it has probably been rare for tens of thousands of years, hanging on in a few remote canyons of the Blue Mountains.

Since its discovery, the effort to conserve the Wollemi pine has been intense. The location of the wild population is top secret. An important strategy in the pine's conservation has been cultivation, making it available to buy in plant nurseries. Today, Wollemi pines are grown in gardens across the world. I reckon their distribution is likely larger than it has ever been.

With the immediate conservation concerns addressed, now comes my PhD. The focus of my work was to understand how is the wild Wollemi pine population going? My starting point was the observation that the wild population has a disjointed structure: there are large trees, to 40 metres tall, and seedlings, but only a couple of middle-sized trees. This is like arriving in a town, and finding toddlers and older people, but no teens. You begin to wonder, why aren't those toddlers growing up? We measured the seedlings, or toddlers, and found that they were only growing 1 centimetre in height each year.

Greenhouse experiments at the Australian Botanic Garden showed that Wollemi pine growth increased with light. Good. This is normal. When we measured the light beneath the mature Wollemi pines in the wild, in the understory, we found it was very dark, only 2% of sunlight was getting through. This suggested that the seedlings would need more light to grow up. This strategy is not uncommon in forest trees, that seedlings need a mature tree to fall over, to open a gap, before they can successfully grow. Perhaps we need to remember that the 20 years of Wollemi pine observations, while a long time for science, is not such a long time for a tree that can live to 500 years or more.

So the next question in my PhD was what are the biggest threats to the Wollemi pine in the wild? The pine is at particular risk from disturbance because of its very small distribution: one event could affect the whole population. For example, fire. Wollemi pine is a rainforest tree, and it's generally thought that rainforest and fire don't mix. But some trees in the wild have fire scars, and if a live tree has a fire scar then that suggests the tree has survived fire, right? So in the interest of science, I set fire to some Wollemi pines…no, no not wild specimens, these plants were provided by the Botanic Gardens. And excitingly, we found that all pines survived being burnt and re-sprouted. This was great news. I still would not promote burning the wild population, but this ability to re-sprout might explain why the Wollemi pines have been able to survive in Australia for so long.

In the last part of my PhD I put all this information together. To reduce the threat of Wollemi pine extinction in the wild we decided to make a new population. This provides insurance, it reduces the risk of losing all wild Wollemi pines in one go. Because we knew light is important to seedlings, we planted the new population across a range of light environments, from deep in the rainforest up to the rainforest-woodland interface, and so far we have found better survival where there is more light. Establishing new populations is a way to help species that are at risk of extinction because of their small numbers. As well, it might be a way to help species respond to climate change. We can use models that predict climate to choose planting sites that will provide appropriate habitat into the future.

I've been so lucky to work with the Wollemi pine. The tree is a great ambassador for threatened species, and it has a great story, of dinosaurs and discovery. And I'm hopeful, with careful management and a bit of luck, this threatened species will continue to survive long into the future.

Robyn Williams: Heidi Zimmer.