Giant Eucalyptus Displays a Unique Dependency on Fire For Regeneration

One of the frequently occurring climatic disasters during the summers in Australia are the 'wildfires' or 'bushfires' that ravage massive chunks of land every year. But what is surprising is that certain native plants display a unique dependency on such wildfires for regeneration.

One such plant is the Eucalyptus, Australia's giant tree and the tallest flowering plant on earth. Eucalyptus's unique association with fire has surprised and puzzled several ecologists.

Professor David Bowman from the University of Tasmania's School of Plant Science attempts to explain the unique relationship of eucalyptus trees with fires and how it relates to their gigantism in an arid area like Australia.  The researcher hopes that this debate may determine their classification and help in conservation.

"The conifers of North America are often thought of as the largest trees on earth, yet the flowering eucalyptus trees of Australia reach comparable heights," Professor Bowman, said. "This is surprising as Australia is the world's driest inhabited continent. Yet, this apparent paradox may explain the evolutionary advantage of gigantism in trees,"he added.

Wildfires that are known for destroying trees do not really harm the seeds. The seeds are protected in aerial capsules which are later released on to the arid earth.

The fire basically clears away the potential seed predators and the forest covering that blocks sunlight. It releases certain nutrients in the blocked soil which helps in seed growth.

"This unique relationship with fire helps us understand how these giants evolved," said Bowman. "Our research suggests gigantism in eucalypts evolved opportunistically within the last 20 million when the ideal environmental conditions for rapid tree growth were combined with the presence of wildfire."

The study reveals that this fire dependence now threatens the tree's future as much as it had helped them to grow in the past. Hence, the foresters classify the tree as a unique type of Australian vegetation, rather than a rainforest tree.

"This classification has serious scientific and conservation implications for the remaining forests of mature (old growth) giant eucalypts," said Bowman. "Giant trees have huge value for the timber industry, yet there are strong environmental reasons for their protection. Classification as rainforest trees would support arguments in favour of conservation."

Through the study they explain that the species has evolutionary advantages which allow it to outcompete other species, they coexist on the margins of rainforests and should be considered part of that ecosystem.

The team went about presenting a comparative analysis that clarifies the relationship between the giant eucalypts and other rain forest species. 

"Our work seeks to resolve a century old dispute about rain forest classification," concluded Professor Bowman. "Rather than seeing them in isolation we place these giants into their global context by recognizing them as species of rainforest tree, albeit trees with a unique dependence on fire."

The first global assessment of these giants is published in New Phytologist.