Forests are a vital carbon sink and understanding how they recover after fire is crucial. A recent study examined how both fire severity and post-fire drought affect forest recovery. The researchers found that when fires are more severe, forests take longer to return to their pre-fire levels of ‘live tree carbon’ — the amount of carbon that trees absorb through photosynthesis and stores in its trunk, branches, roots, leaves, and other tissues throughout its lifetime.
Between 2017 and 2019, much of south-eastern Australia experienced severe drought, this weakened ecosystems and contributed to the conditions that led to the worst fire season in recent history. The Black Summer wildfires of 2019/20 burnt approximately 7 million hectares of mainly temperate Eucalyptus forests. This single fire season released roughly the same amount of carbon dioxide as Australia’s total annual net greenhouse gas emissions. Greenhouse gases, including carbon dioxide absorb and trap the suns radiation in the Earth’s atmosphere, increased quantities of these gases are increasing the overall temperature on Earth.
The study focused on Silvertop ash (Eucalyptus sieberi), a species that dominated forests three years after the fires. It compared two scenarios: high- and moderate-severity wildfire sites from 2019/20 versus low- to moderate-severity prescribed burn sites, burnt during the drought in 2018 that then did not burn in 2019/2020.
Findings
The results showed that at sites affected by the wildfire, 30% of small E. sieberi trees (10–20 cm diameter) continued to die three years after the event, regardless of fire severity. Three years after burning, forests exposed to low-to-moderate severity fire had recovered to 92% of their pre-fire live tree carbon, irrespective of the burn being a wildfire or a prescribed burn. In contrast, forests that experienced high-severity wildfire recovered only to 76% of their previous carbon levels. Notably however, prescribed burn sites continued to show increasing tree mortality for another two years. New eucalypt seedlings were found only at wildfire sites, not in areas treated with prescribed burns, where the latter was dominated more by Acacia seedlings. The authors suggests that this difference may be affected by the variation in post-fire rainfall rather than fire severity itself, with drier post-fire conditions witnessed between 2017-2019 potentially suppressing recruitment in the prescribed-burn areas.
Other sources of stored carbon, such as surface litter and coarse woody debris, returned to pre-fire levels within six months. In fact, in areas affected by low- to moderate-severity burns, surface fuel loads in some cases had doubled compared to pre-fire levels by three years after the event.
Conclusion
In summary, the study indicated that both fire severity and post-fire weather, influence how quickly forests can recover their carbon stores. As fire severity increases, so does the time needed for forests to rebuild their carbon pools. Even if a low-intensity fire is prescribed, the interaction between post-fire drought and fire history may lead to increased tree mortality, further delaying the rate of carbon recovery. Therefore, the impacts of climate change, increasingly driving more frequent and more severe fire events as well as more variable or drought-intensified post-fire rainfall, may inhibit the carbon recovery of these highly productive forests over time.
The original paper was authored by Volkova et al 2025 and the project was funded by the Australian Government Department of Climate Change, Energy, the Environment and Water (DCCEEW).
Image by Jack Bass, sourced from Unsplash
This article was written by Campbell Goff, Healthy Ecosystems Project Officer with the Nature Conservation Council of NSW
