Extreme droughts could lead to widespread death of eucalypts from embolisms, researchers say.
The trees cannot quickly adjust the size of their water transport vessels to cope with variability in water supply.
Dr Pfautsch and colleagues studied more than 24,000 vessels in 28 species of eucalypt in Australia and found, as expected, that species adapted to drier parts of the country had narrower water transport vessels than those adapted to wetter conditions.
The researchers also measured vessels in a subset of species, which grew across a range of areas with different annual rainfall.
This analysis showed no difference in the width of vessels of any of these species, regardless of how much rainfall it was exposed to.
This told the researchers that the width of the water vessels in eucalypts had a largely genetic basis.
Dr Pfautsch said eucalypts die once approximately 90 per cent of their vessels contain embolisms, and if they cannot adapt their vessels in response to drought, they will be in trouble.
He said the current worst-case scenario is for temperature rises of 4 to 6 degrees Celsius by the end of the century.
“That is something that, in itself, will create a very different climate very rapidly and we would probably see that lots of trees would die.”
Australia’s trees are a ‘living laboratory’
Professor Stefan Arndt from the University of Melbourne, who was not involved in the study, said scientists saw the Australian eucalypts as a “living laboratory” for studying how trees adapt to climate.
This is because they are a group of trees that are closely related and yet are adapted to very different environmental conditions.
He said Dr Pfautsch and colleagues were able to take advantage of this unique group of trees to show, for the first time, the influence of genetics on vessel width.
“This paper showed that … this is a very strong evolutionarily-determined signal that is based on the climate,” Professor Arndt said.
He said although mass tree death did not occur in Victoria’s drought between 1998 and 2010, there were already examples of mass death in Queensland and Western Australia.
After 20 years of drought in Western Australia, jarrah woodlands south of Perth endured mass forest collapse after the heatwaves that occurred during 2010 and 2011.
Professor Arndt said although scientists were still studying why these trees died, he said it was most likely partly related to embolism because those trees often grew in rocky outcrops with shallow soil and low levels of water.
Combined with 20 years of drought, these conditions proved to be too harsh for the trees, he said.