The final stronghold of Australia’s last remaining Wollemi pines continues to be threatened with extinction, but critical work of a handful of researchers may help turn the situation around.
Described as a living fossil, the Wollemi pine was discovered by David Noble in 1994, and thereafter granted the specific name Wollemia nobilis. Since then, the tiny population of conifers has been fiercely protected by researchers and park rangers in a bid to reduce human interference.
Unfortunately, these efforts haven’t managed to prevent one of the four wild subpopulations becoming infected with Phytophthora cinnamomi – a water-borne mould that could threaten the last remaining wild Wollemi pines if it were to spread further.
Dr Heidi Zimmer, a research biologist who has been working alongside the Wollemi Pine Recovery Team to learn more about the species, said that the discovery of phytophthora was a huge blow for the conservation research community involved with the species.
“Phytophthora was first detected in 2005 and the Recovery Team immediately halted all research and worked to minimise having people in the area as much as they could,” Zimmer said.
“The fact is, no one really knew what would happen. Previous research had shown that Wollemi pine seedlings were particularly susceptible to the fungus, but thankfully it seems there has been no widespread, rapid decline in the health of the existing population.”
By the time Zimmer came to propose her PhD project on the pines, the Recovery Team were able to approve access (albeit tightly controlled access) to the site.
Ecology of a Living Fossil
The Wollemia genus had been identified in the fossil record before the living species was discovered, yet despite being able to recognise the Wollemi pine as a plant that had persisted over the past 90 million years, precious little was known about its ecology, what conditions it is capable of tolerating and so on.
With fewer than 90 mature specimens in the wild, Zimmer needed to create a new population that could be subjected to more rigorous experimentation. Of course, the creation of such a population itself was something of an experiment.
“The contract to produce Wollemi pine seedlings on a commercial scale changed hands several times since its release around the turn of the millennium,” she recounted. “At one point I remember you could buy them from Bunnings very affordably. Yet by the time I chose to create my test population, they had become incredibly difficult to source.”
Zimmer ended up locating 191 seedlings from two different sources: the Royal Botanic Garden and a private interest. As a result, the quality of the seedlings varied, so Zimmer had additional work to do in accounting for the variety in her experiments.
“The plants sources from commercial suppliers were more hardened and looked a little more yellow, but they’ve proven to be hardier than the other group. They’ve had a higher rate of survival, but at the same time have hardly grown after four years in the ground. By contrast, those sourced from the Botanic Gardens have grown quickly, but have also suffered a higher rate of attrition through planting shock and infection from a naturally occurring fungus called botryosphaeria,” Zimmer explained.
Overall, Zimmer found that 80 percent of the new population has survived through four years in natural conditions, giving hope for the species’ ability to be reestablished elsewhere as a safeguard against extinction.
Yet Zimmer’s work over the past five or more years has answered many more specific questions, such as what light conditions individuals favour, how they react to fire and drought, and what annual variation in cone production exists.
“I was particularly interested in observing how different seedlings reacted to varying light levels, and we planted them in a range of light conditions caused by the thickness of overhead canopy,” Zimmer said. “We found that they tended to do better the more light they had access to, which may explain why some seedlings aren’t doing so well in the wild population.
“Like other forest trees, it may be that the seedlings grow very slowly in the understory until a larger tree falls over, allowing the light through and causing the seedling to shoot up.”
Although her results show the plants respond well to lots of light, this isn’t true of long exposure to dry, hot weather. On the contrary, Zimmer’s tests of the plant’s response to drought conditions was particularly negative.
“We found the Wollemi pine would continue to try to suck up water no matter how long they were exposed to drought conditions, therefore increasing their internal pressure to damaging levels,” she said.
In plants transpiration is most similar to the process of breathing in animals. As photosynthesis occurs, water is sucked up by roots, air is sucked in by leaves, while water and oxygen molecules are expelled as waste products, and then ‘transpired’ from the plants leaves into the surrounding atmosphere. In many drought-resistant species, this process is halted or modified in a bid to retain water.
“At first we thought their ability to continue increasing their internal pressure was amazing, because it looked like they could continue to function for longer in drought than the other trees. But after a short time the impacts of dehydration became evident.”
While drought tolerance is not the Wollemi pine’s forte, Zimmer found that Wollemi pines do recover surprisingly well from fire.
“Wollemi pines were thought to be highly sensitive to fire, because they are a rainforest species and live in a fire refuge, but an ex situ burning experiment revealed that they had the capacity to resprout strongly after being burnt by fires up to 600 degrees Celsius hot.”
Back from the Brink
Zimmer’s work is being hailed in the press as a success for the embattled Wollemi pine. Certainly, any additional knowledge that may help the Recovery Team to establish healthy wild-type populations of the plant elsewhere will not only ensure the future of the species, but also provides a positive exemplar for the conservation of other species, while giving other researchers more samples on which to conduct their work.
Also studying the translocation of the Wollemi pine, Jessica Rigg is a PhD candidate at Western Sydney University who has taken a specific interest in the soil and root microbial communities associated with the species, working alongside Zimmer to develop her own research.
With the establishment of the translocated population, Rigg was able to examine what soil conditions (properties such as pH, carbon and nitrogen levels) might impact on the growth of individual plants, as well as delving into how the assemblage of other microbial species present impacted the translocated Wollemi pine.
“We found that the growth and condition of individual Wollemi pines in the first 12 months was linked to soil properties,” Rigg said. “In the long term, the plants that truly flourished had gathered a unique microbial community that was different than that found in the surrounding soil or roots of other plants nearby. Those that weren’t successful over the first three years since planting didn’t exhibit this unique microbial community.”
The addition of Rigg’s research on the Wollemi pine shows that it may have evolved specific, mutually-beneficial relationships with a variety of microbes – information that may prove critical to the conservation of the species in time.
“Most translocation projects are conducted with seedlings growing in sterile potting mix that are planted into the wild,” Rigg said. “My research may ask them to consider the microbial element of the given plant’s ecology instead.”
Unlike in the case of many other species, the very discovery of the last remaining Wollemi pines can be seen as a significant turnaround in the species’ fortunes, as its subsequent cultivation led to horticulturalists and hobby gardeners from around the world to acquire and grow the plant.
“The global distribution of the Wollemi pine is now many times larger than it has been for centuries perhaps, indeed it may be larger than it’s ever been.
“The Wollemi pine is a great ambassador for conservation. It has a great story: its accidental discovery and the all-hands-on-deck response to protect it. My research is the next step in this process: finding out what is stopping Wollemi pines from further expanding their wild population. With increased understanding of the conditions they prefer, we can better care for the existing wild Wollemi pine population. As well, we can help give the Wollemi pine a jump start by planting new wild populations.” concluded Zimmer.
Zimmer et al, Recruitment bottlenecks in the rare Australian conifer Wollemia nobilis. Biodiversity and Conservation 2014
Offord et al, Growing up or growing out? How soil pH and light affect seedling growth of a relictual rainforest tree. AOB Plants 2014
Zimmer et al, Fuel flammability and fire responses of juvenile canopy species in a temperate rainforest ecosystem. International Journal of Wildland Fire 2015
Zimmer et al, Cone production in Wollemia nobilis (Wollemi Pine). Cunninghamia 2015
Zimmer et al, Drought avoidance and vulnerability in the Australian Araucariaceae. Tree Physiology 2015
Rigg et al, Conservation by translocation: establishment of Wollemi pine and associated microbial communities in novel environments. Plant and Soil 2016.