14 January 2015
Eucalypt trees have been described as the ideal Australians - versatile, tough, sardonic and self-mocking. A new study has found that these distinctly Australian qualities are what gives the native trees the ability to thrive in the harsh local climates.
Hawkesbury Forest - Eucalyptus saligna
Published in leading environmental journal Ecology Letters (opens in new window), the study from Western Sydney University, CSIRO and the University of Sydney, has shown how toughness, contrariness and complexity help this remarkable tree genus cope with Australia's diverse environmental conditions.
The study of 28 species from across Australia, led by Dr Sebastian Pfautsch from the Hawkesbury Institute for the Environment, found the structure of water-conducting vessels in the trees (similar to the system of veins and arteries in people) were forced to evolve in vastly different ways in order
to adapt to local climates.
For the first time, we have pinpointed the evolutionary journeys of the vessel architecture in various species to provide new answers as to why they are so widespread in Australia....
"Eucalypts are known to the world for their 'toughness' in the face of drought, and generations of scientists have investigated how they came to thrive across the huge range of climates in which they grow," says Dr Pfautsch.
"What's particularly remarkable about eucalypts is how they maintain the delicate balance between need to transport water to their crowns, and eventually to the atmosphere, against the requirement to maintain hydraulically functional."
"For the first time, we have pinpointed the evolutionary journeys of the vessel architecture in various species to provide new answers as to why they are so widespread in Australia."
The study found that species adapted to the driest conditions (e.g. Mallee eucalypts) have vessel systems with very different physical properties to those adapted to cooler, wetter conditions (e.g. Alpine Ash). The differences among species serve to ensure that water transport remains continuous, and
doesn't break down under stress. One of the principal differences lies in the diameter of the vessels, with narrower vessels better for coping with arid conditions, and broader vessels suited to moving larger amounts of water.
"Surprisingly, we found that all species have a mixture of vessel sizes, which helps them cope with both drought and flooding rains," says Dr Pfautsch.
"When there is plenty of water available, the larger vessels work to ensure more water can be safely transported to the crowns."
The findings cast doubt on theories derived for a wide range of tree species around the world, which suggest tree height, and not climate, is a better predictor of vessel dimensions.
"Importantly, the features of vessels and wood structure in eucalypts appear to be dictated by genetically fixed information, and not just an adaptation within species – an 'arid' species growing in a wetter environment maintains the same 'arid' vessel structure," explains Dr Pfautsch.
"This means that different Eucalyptus species have adapted over long periods of time to best cope with the environmental conditions in which they grow."
"This difference makes the trees distinctly Australian, echoing Stephen J. Pyne's description of eucalypts as 'the ideal Australians - versatile, tough, sardonic, contrary, self-mocking, with a deceptive complexity amid the appearance of massive homogeneity.'"
With thanks to co-authors Dr Marco Harbusch (University of Sydney), Anita Wesolowski, Renee Smith, Dr Craig Macfarlane (CSIRO), Prof Mark G. Tjoelker, Prof Peter B. Reich, and Prof Mark A. Adams (University of Sydney)