Severe fires: How the Australian forest rises from its ashes

Recent years have been characterized by multiple droughts and increases in temperature worldwide. Under these conditions, massive wildfires broke out in 2019 and early 2020, particularly in southeastern Australia where temperate forests contain very high biomass. At that time, 4 million hectares were burned, which is 20% of Australia’s forests.

During these fires, the forest burned from the ground up. Satellite images captured by the SMOS satellite, which allow before-and-after biomass estimation, show a rapid recovery of vegetation. As of the end of 2020, less than a year after the fires had passed, weeds, shrubs, and burnt eucalyptus were already starting to grow there. Under these conditions, how can the losses and gains of carbon stocks be estimated?

To answer this question, the INRAE ​​and Associate scholars evaluated two parameters for the first time:

  • loss of vegetation cover and biomass in forested areas of Australia (due to the simultaneous effects of drought, high temperatures and fires in 2019);
  • The ability of vegetation to recover after one year of this damage, thanks to relatively humid climatic conditions in 2020 (particularly in forested areas of southeastern Australia).

In addition to satellite images, the researchers used a whole arsenal of analytical techniques and predictive models for carbon stocks. They were thus able to assess changes in vegetation structure and function using specific parameters such as leaf surface or aerobic biomass.

The collected images show significant biomass losses in 2019, under the influence of fires, drought and high temperatures. The forest area has lost the equivalent of 200 million tons of carbon, or 15% of atmospheric biomass. Of the 200 million tons of carbon lost, 90 million are attributable to fires, and 110 million to the cumulative effects of drought and temperature extremes.

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2020 saw twice as much precipitation as in 2019. The result: significant gains in biomass in the same forest areas, which account for a total of more than 260 million tons of carbon stored in 2020. Of those 260 million, come 220 million from burned area, 40 million from unburned area.

Many eucalyptus species known for their ability to regenerate after fire and adapt to drought dominate the Australian forests. Above-average rainfall in 2020 may have encouraged the strong and rapid growth of forests and other vegetation components (grass and shrubs) in March, April, August and December 2020, and thus lead to a full recovery of the lost carbon stocks by early 2021.

reference

Yuanwei Chen, Xiangming Xiao, Jean-Pierre Wenneron, Philip Ciese, Josep G Canadell, Martin Brandt, Xiaojun Li, Li Fan, Xiaokui Wu, Hao Tang, Ralph Dubayah, Russell Dottie, Sean Crowell, Bo Cheng, Beren Moore, Significant loss and rapid recovery of aboveground vegetation and biomass over forest areas in Australia during 2019-2020Remote Environmental Sensing, Volume 278, 2022, 113087, ISSN 0034-4257, https://doi.org/10.1016/j.rse.2022.113087.

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