If there was one branch on the tree of life that could flourish in a hotter world, you might have expected it to be eucalypts. Yet an enormous study of 657 species of the eucalyptus genus and its closest relatives has found that 91 percent are likely to suffer from global warming, with 16 species expected to disappear entirely outside of botanical gardens and seed banks.
This hyper-diverse clade has dominated a continent to a remarkable degree, and some of its members have become invasive species elsewhere. Moreover, the iconic eucalyptus species that play such a huge role in images of Australia are adapted to hot and dry climates.
Such trees may be common, and the most economically important, but they are a small proportion of the biodiversity in the Eucalyptus, Corymbia, and Angophora genera, which together represent most of Australia's trees.
The study also helps to identify regions across Australia that will be evolutionarily important for the preservation of rare, ancient eucalypts.
Dr Bernd Gruber of the University of Canberra told IFLScience: “Eucalypts occupy most niches in Australia, and the most diversity is in cooler areas such as southwest Western Australia, Tasmania and along the Great Dividing Range. These areas will shrink and for many species, there is nowhere to go.” On average these species will lose more than half their range over the next 70 years if climate change continues unabated. For the animals, and smaller plants, that have evolved to live in the shade of the mighty gum trees, the consequences are similarly disastrous.
The study, published in Nature Climate Change, sets a new standard for predicting the way related species will respond to increasing heat. Gruber and his co-authors looked at locations that are dominated by very old lineages of eucalypts, along with others where young species dominate, which he described to IFLScience as “museums and nurseries”. Nurseries are often dominated by a few species, but museums can contain extraordinary diversity, which for all its longevity could be threatened in this century.
Despite all the pessimism, 9 percent of eucalypt species should find their natural territory growing as the world heats up, and some of these may come to the aid of their distressed relatives. One of the authors, Dr Carsten Kulheim, also of the ANU, published another study this week in Trends in Biotechnology showing that several eucalypt species are particularly well suited to producing fuels that can power airplanes.
"Renewable ethanol and biodiesel might be okay for the family SUV, but they just don't have a high enough energy density to be used in the aviation industry," Kulheim said in a statement. "Eucalyptus oils contains compounds called monoterpenes that can be converted into a very high energy fuel, and this high energy fuel can actually fly jets and even tactical missiles."
Finding carbon neutral ways to power long distance travel remains one of the trickiest technical problems in the fight against global warming. Kulheim hopes that selective breeding could produce varieties of eucalypts productive enough to make them a viable source of greenhouse-friendly jet fuel. Unfortunately, some of the genes that could bring this to fruition might lie in the diverse but threatened areas Gruber identified.