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Eucalypt forests have a reputation for bounce back from fire. The green shoots that emerge as they start to recover from fire are some of the most iconic images in the Australian bush.
Resprouting allows trees to survive and quickly start photosynthesising again, which keeps carbon “alive” and stored in the tree. However, if a tree is killed and begins to rot, it can be revived. the carbon stored in the tree is released into the atmosphereAs a source of greenhouse gases emissions.
But our new research finds more frequent, severe bushfires and a hotter, drier climate may limit eucalypt forests’ ability to resprout and reliably lock up carbon. This could severely undermine our efforts to reduce climate change.
Our findings provide yet another reason to reduce global emissions and are a warning tale about a less-known problem posed by climate change.
T Fairman
For climate change to be stopped, forests are essential
More than 100 countries pledged to end deforestation at the international climate summit held in Glasgow last month. This put a much-needed spotlight on the importance of the world’s forests in storing carbon to mitigate climate change.
Victoria’s national parks alone store almost 1 billion tonnesequivalent to carbon dioxide For perspective, that’s roughly a decade’s worth of Victoria’s net CO₂ emissions in 2019 (91.3 million tonnes).
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Climate change is testing the resilience of native plants to fire, from ash forests to gymea lilies
Australia’s forests have forged a tight relationship with bushfire. But climate change is already changing – and will continue to change – the size, severity and frequency of bushfires. For example, Victoria over 250,000 hectares have been burnedWithin 20 years, at most two major fires.
This unprecendented frequency led to the declineThis is fire sensitive forests, such the alpine ash.
Geary et al, 2021
Reprouting eucalypts may be possible resilient to periodic fires, we know surprisingly little about how they’ll respond toFires that are severe and destructive are becoming more common, especially when they’re accompanied by factors like drought.
Early evidence supports this conclusion resprouting can fail when fire is too frequentAs seen in snow gum forestsIn the Victorian alps.
Understanding why is essential area of active research, but reasons could include damaged resprouting buds (as their protective bark is thinned by successive fires), or the depletion of the trees’ energy reserves.
T Fairman
Forests that have been burned by two fires store half of the carbon.
What might this mean to carbon stocks in widespread fire-tolerant eucalypt forest forests?
In our new paper, we tackled this question by measuring carbon stored in Victoria’s dry eucalypt forests. We chose areas that had been burned at least once by severe bushfires in the past six years. These areas are often the sites of severe bushfires that occur decades apart.
We found that climate change impacts are rerouting forests on two fronts.
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These forests will store less carbon as the climate gets warmer and dryer.
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As more severe fires are common, forests will store less carbon and more trees will die, resulting in more dead wood.
T Fairman
First, carbon stores were lower at the hotter and dryer parts of the landscape than in the cooler and wetter areas. This makes sense – as any gardener knows, plants grow much better where water is plentiful and it’s not too hot.
Forest carbon storage decreased even more when frequent fire was added. A forest that has been burned by two severe fires per day is half the carbon of one forest burned by only one fire. This is true even in warmer areas.
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More trees were killed with more frequent fire, which means what was once “living carbon” becomes “dead carbon” – which will rot and be a source of emissions. After two fires, less that half of the forest carbon was found in living trees.
Carbon stored in large living trees is an important resource and is often considered stable. given larger trees are generally more resilient to disturbance. We also found that their carbon stocks declined significantly with more frequent fire.
T Fairman
What can we do?
Given the extent of this forest type in southern Australia, it is important to better understand how it responds and how to set off frequent fires. This will allow us to accurately account changes in their carbon stock.
We also need to explore new ways of managing our forests. Reinstating Indigenous fire managementIncluding traditional burning practices active forest management may mitigate some of the impacts we’ve detected.
We could also learn from others and adapt. management approaches in the dry forests of North America, where the new concept of “pyro-silviculture” is being explored.
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Australia, you have unfinished business. It’s time to let our ‘fire people’ care for this land
Pyro-silviculture may include targeted thinningIt is used to reduce the forest’s density, which can decrease their vulnerability to drought and encourage large tree growth. You can also do controlled burns to reduce future fires.
With the next, inevitable fire season on Australia’s horizon, such approaches are essential tools in our management kit, ensuring we can build better resilience in forest ecosystems and stabilise these crucial stocks of carbon.
