Recent years have been marked by multiple droughts and temperature increases across the globe. Under such conditions, massive forest fires occurred in 2019 and early 2020, particularly in southeastern Australia where temperate forests have very high biomasses. In that time, 4 million ha have burned, representing 20% of Australia’s forest.
During these fires, the forest burned from the ground up. Satellite images captured by the SMOS satellite, allowing the biomass to be estimated before and after, show a rapid recovery of vegetation. From the end of 2020, less than a year after the passage of the fires, grasses, shrubs and burnt eucalyptus are already growing back there. Under these conditions, how can the losses and gains of carbon stocks be estimated?
To answer this question, INRAE scientists and their partners assessed two parameters for the first time:
- loss of vegetation cover and biomass in forest areas in Australia (due to the simultaneous effects of drought, high temperatures and fires in 2019);
- the ability of vegetation to recover one year after this damage, thanks to relatively wet climatic conditions in 2020 (especially in the forest regions of south-eastern Australia).
In addition to satellite images, the researchers used a full arsenal of analytical techniques and predictive models of carbon stocks. They were thus able to assess changes in the structure and function of the vegetation using specific parameters such as the surface of the leaves or its aerial biomass.
The images collected show significant biomass losses in 2019, under the effect of fires, drought and high heat. The forest zone has lost the equivalent of 200 million tonnes of carbon, or 15% of the aerial biomass. Of these 200 million tons of carbon lost, 90 million are attributable to fires, and 110 million to the cumulative effects of drought and extreme temperatures.
The year 2020 saw a level of precipitation twice as high as in 2019. Result: significant biomass gains in these same forest areas, representing a total of more than 260 million tonnes of carbon stored in 2020. Of these 260 million, 220 million come from the burned area, and 40 million from the unburned area.
Several species of eucalypts known for their ability to regenerate post-fire and their adaptation to drought dominate in Australian forests. The above-average rainfall in 2020 may have encouraged strong and rapid growth of forest and other understory vegetation components (grass and shrubs) in March-April and August-December 2020, and thus lead to full recovery of lost carbon stocks by early 2021.
Reference
Yuanwei Qin, Xiangming Xiao, Jean-Pierre Wigneron, Philippe Ciais, Josep G. Canadell, Martin Brandt, Xiaojun Li, Lei Fan, Xiaocui Wu, Hao Tang, Ralph Dubayah, Russell Doughty, Sean Crowell, Bo Zheng, Berrien Moore, Large loss and rapid recovery of vegetation cover and aboveground biomass over forest areas in Australia during 2019–2020Remote Sensing of Environment, Volume 278, 2022, 113087, ISSN 0034-4257, https://doi.org/10.1016/j.rse.2022.113087.