Giant old trees are survivors. But their size and age do not protect them against everything. They face threats such as logging or intensifying drought and fire as the climate changes.
Tasmania has long been home to plants ancient and giant. One rare shrub, King’s lomatia (Lomatia tasmanica), has been cloning itself for at least 43,000 years.
But in recent years, even some giants have succumbed. The devastating 2019 fires in southern Tasmania killed at least 17 of the largest trees. That included the largest blue gum (Eucalyptus globulus) ever measured, the 82 metre high Strong Girl.
But giants still exist. In southern Tasmania’s Valley of the Giants (Styx Valley), there is a mountain ash (Eucalyptus regnans) named Centurion now over 100m tall. Centurion is a leading candidate for the tallest flowering plant on Earth and the tallest tree in the Southern Hemisphere. (California’s coastal redwood ‘Hyperion’ reaches 116 metres, but is a non-flowering tree).
For years, I have been drawn to Centurion as a botanical science landmark. I have climbed it, measured it, and observed it carefully. But after the 2019 fires, my colleagues and I realised the urgency of preserving physical genetic samples before the chance was lost forever. During the 2019 fires, Centurion itself narrowly escaped death. It was saved only by the efforts of firefighters.
Our recent research sequencing a high-resolution genome of Centurion turned up an intriguing finding – this giant shows greater genetic diversity than we had expected, which may boost the adaptability of the species. Finding and preserving samples of Australia’s other remaining giants will help scientists learn from these remarkable trees.
Where Centurion stands
Giant trees are found only in a few locations in Australia, such as Victoria’s Central Highlands (mountain ash) and Western Australia’s southwest forests (red tingle, Eucalyptus jacksonii). These regions tend to have higher rainfall and less frequent fires.
Centurion is named for its height, at more than 100 metres high. But it is also at least three centuries old.
It has been lucky to survive this far. Centurion stands in a small patch of uncut state forest in a heavily logged area. Logging in the region is continuing, though nearby areas of old growth forest were added to the World Heritage area in 2013.
It was found in 2008, when forestry workers analysing aerial laser scanning data identified the tree as a 99.76 m tall giant.
In 2018, I measured its height using laser ground measurement. The living top of the tree had grown to more than 100m in height.
When I climbed Centurion, I saw the uppermost branches had actually sprouted from the side of a snapped upper stem about 90m tall. This suggests the tree could have once been significantly taller.
Branches resprouting from the lower trunk suggest the tree is taking advantage of a change in light conditions after neighbouring trees died. The resprouting abilities of Eucalyptus species mean these trees can better recover after fire – and outcompete less resilient species such as rainforest plants.
When the fires came
In early 2019, I had planned to collect leaf samples from Centurion for deeper study, alongside geneticists from two universities. But then the fires came. Large tracts of southern Tasmania burned over that summer. Giants turned to charcoal. Centurion was left charred, but with a green, growing top.
After the fires burned out, we were able to collect samples from Centurion and began analysing its genetic code in the lab. My colleagues and I have now posted its genome to an open-access public server for wider use.
We used cutting-edge methods to create one of the best genetic fingerprints of a forest tree so far. It’s the first time we have documented an individual Eucalyptus including genetic contributions from both parent plants across the full length of the chromosomes. This totals nearly a billion DNA base pairs – individual “bits” of genetic information.
Centurion’s genome showed us the tree’s parents had each bequeathed it very different genetic sequences. This combination may have contributed to its extreme growth, though we don’t know for sure.
The genome reveals a surprising amount of genetic variation. In Centurion’s DNA lie new genetic sequences, deleted genes and duplicated genes. These variations suggest mountain ash trees have high adaptability. Not all trees are like this – some have very little genetic variation, or even rely on cloning. Trees bred for agriculture or forestry tend to have low genetic diversity.
Read more: Where the old things are: Australia's most ancient trees
Building an archive of giant eucalypts
After the 2019 fires turned some of Australia’s largest trees to ash, my colleagues and I realised the moment was urgent. If we didn’t preserve the genes of these trees, they could be lost forever.
The Tasmanian Herbarium now hosts our project to curate and store samples through the Giant Eucalyptus Specimen Archive project. We have sampled several of the largest remaining giants in the Styx Valley, lodging samples with the Herbarium and genomic researchers at the Australian National University.
Conservation – of specimens?
Mountain ash like cool, wet mountains. But as the world warms, drought and fire become more common. Recent Tasmanian bushfires have burned traditionally cooler, wetter parts of Tasmania, where rare species such as pencil pines and King Billy Pines grow.
Conserving old growth forests and their giants in national parks or World Heritage listing can only go so far in the face of these threats. This year, we have seen widespread browning and dying among eucalypts.
Preserving leaf and flower specimens costs a fraction of what it takes to keep living plants or store frozen seeds.
Future scientists may find these giant trees have some genetic talent for survival, as demonstrated by their longevity. Preserving their genes could help the species survive.
We may well need long-term preservation of specimens in Herbariums, which preserve plant material for decades or even centuries. Museums, botanical gardens, seedbanks and laboratories can also archive specimens from significant individual plants.
If the genetic stories of Earth’s ancient and giant trees are to be read in the future, we must take the time to record them and keep them safe.
Acknowledgements: Thank you to the Borevitz Lab (ANU), the Tasmanian Herbarium, and the Eucalypt Genetics Group (UTAS). This article is in memory of Tasmanian ecologist Dr Jamie Kirkpatrick (1946-2024)
The Giant Eucalyptus Specimen Archive was made possible in part by funding from the Jayne Wilson Bequest from the Tasmanian Museum and Art Gallery. Daniel Bar-Ness runs Giant Tree Expeditions, a forest tourism company.
This article was originally published on The Conversation. Read the original article.
