Forest scientist Tim Wardlaw from the University of Tasmania warns that hotter temperatures in Tasmania could detrimentally impact eucalyptus trees to the point they would no longer absorb carbon.
Wardlaw observed a messmate stringybark (Eucalyptus obliqua) forest during a three-week heatwave in November 2017. Under these conditions, the forest became a net source of carbon dioxide, with each hectare releasing close to 10 tonnes of greenhouse gas during that period.
Not only did the forest emit carbon dioxide, its ability to photosynthesise also diminished during the heatwave. This means the eucalyptus trees were simultaneously losing water and not able to make enough food for themselves.
While we have seen trees stop photosynthesising in heatwaves before, this is usually an effort to conserve water. The fact the forest was emitting carbon dioxide and losing water suggests that in this instance the temperatures were too hot for the trees to handle.
Southern Tasmania’s tall eucalyptus forests are generally very good at absorbing carbon dioxide and thrive in moist, cool conditions. It was believed these forests would still be able to absorb carbon and thrive even in warmer conditions. These recent findings challenge that assumption.
There is hope, however, thanks to research underway to build our forests’ climate resilience.
One method is climate adjusted provenancing, where forest managers sow seeds taken from plants in the hotter end of their range. Another ongoing test for giant kelp that could be applied to eucalyptus trees is to breed plants to have better heat tolerance.
In the meantime, Wardlaw suggests that making forest monitoring data publicly available and staying engaged around potential risks will aid the forests’ long-term survival.
