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In heat wave conditions, Tasmania’s tall eucalyptus forests no longer absorb carbon

Female mate stringybark (Eucalyptus obliqua) in southern Tasmania. Credits: Shutterstock

The tall eucalyptus forests of southern Tasmania are excellent at extracting carbon dioxide from the atmosphere and converting it into wood.


For many years, it was believed that these forests had a reasonable buffer of safety from climate change due to the cool and moist environment.

Unfortunately, Research published today Shows that these forests are closer to the edge than we expected. During the heat wave, I discovered that these forests were switching from carbon uptake to pumping out.

That’s not good news, given that heat waves are expected to increase as the world heats up. While working to reduce emissions, we need to find ways to make these important forests more resilient.

From carbon dioxide inflow to emission

It has been established from Forest sampling A moist, cool environment, such as southern Tasmania, provides ideal growth conditions for tall eucalyptus forests.

We have these types of forests There is a buffer Against the worst impact of Climate change Come and probably benefit from even limited warming.

But this is no longer the case.

I watched what happened to my female mate stringybark (Tasmanian oak) Forest during the three-week heat wave in November 2017. Under these conditions, forests became a net source of carbon dioxide, releasing nearly 10 tonnes of greenhouse gases per hectare during that period.

Under normal conditions a year ago, forests were the net sink of carbon dioxide, absorbing about 3.5 tonnes per hectare.

How can I find out about this? The forests I surveyed are located at the Wara Supersite, upstream of the Huon Valley, one of Australia’s 16 intensive ecosystem monitoring field stations. Land Ecosystem Research Network..

Instruments mounted on the 80-meter-high tower of straw give us great insight into how the forest behaves. You can measure how fast carbon dioxide, water, and energy move between forests and the atmosphere.

So what actually happened in the forest during the hot spell? Two important things.

The first is that forests emit more carbon dioxide. This is what was expected. This is because the living cells of all air-breathing organisms (yes, this includes trees) breathe more as the temperature rises.

But the second was very unexpected. Due to the reduced photosynthetic capacity of forests, less solar energy is converted to sugar. This happened while the trees were rapidly transpiring (releasing water vapor).

In heat wave conditions, Tasmania's tall eucalyptus forests no longer absorb carbon

For now, the straw forest remains intact.Credit: Provided by the author

So far, we have seen a decrease in photosynthetic output with heat waves as trees try to limit water loss. They can do this by closing the pores of the leaves (stomata).When the tree closes the pores, it becomes more difficult carbon dioxide It enters the leaves in the air and fuels the photosynthetic process.

In contrast, this heat wave saw the tree release water and at the same time produce less food.

What’s wrong? In short, the temperature was simply too hot for the forests of southern Tasmania. All forests have ideal temperatures for best results from photosynthesis.This temperature in Australia Linked to the historic climate Of the local area.

This means that straw trees require lower temperatures for optimal feeding compared to most other Australian forests.

During the 2017 heat wave, temperatures soared outside the comfort zone of the forest. During the hottest months of the day, the forest could no longer produce enough food to feed itself.

Outside the comfort zone of the forest

So far, the straw forest is still intact. After the heat wave, the female mate’s filamentous bark forest quickly regained its ability to feed itself, carbon It sinks again.

But as the world warms, these forests will increasingly be pushed out of comfort zones. They can only withstand a great many of these types of heat waves. If they keep coming Turning point Beyond that, the forest will be irreparable.

So what do you do?If you look at the ocean of Tasmania, you can see a disturbing glance. heat wave Hotspot. Completely 95% of Tasmanian giants Kelp forest It’s gone now, killed By a temperature that exceeds its capacity to withstand.

It is no exaggeration to say that the sharp rise in temperature is the most serious threat to the health of tall eucalyptus forests that we have encountered while studying forest health and threats in Tasmania for 40 years.

Unlike the kelp forest, our tall eucalyptus forest has not yet reached a turning point. There is still time to mitigate the risks posed by global heating.

Work is already underway to test promising new ways to help future forests cope well with the new climate in which they are located.

These technologies include: Climate-adjusted proofwhere Woods Managers sow local seeds collected from the hottest areas of the range.Another attempted for giant kelp Find individual plants Better heat resistance and breed them.

Our eucalyptus forest is increasingly in need of our help. By providing more proactive information about the risks to forests that we have long considered to be resilient, we are more likely to protect them.

One way to do this is to publish monitoring data in real time. This will give you an idea of ​​the tensions that forests face as the world warms.


Decreased rainforest productivity may accelerate future climate change


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In heat wave conditions, Tasmania’s tall eucalyptus forests no longer absorb carbon

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