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News Article

Recovery of mountain ash soils takes decades longer than previously thought

Impacts of bushfires and clear-cut logging detectable in soil decades after event

Soils are key in the functioning of any ecosystem; supporting both terrestrial and subterranean life and ensuring a continual cycling of nutrients within the environment. However, they are also highly sensitive to disturbance and finely balanced as a function of biotic and abiotic factors present in the ecosystem. Soil defining qualities such as nutrient content, texture and microbial community therefore form slowly over time, meaning the impact of any disturbances to the surrounding ecosystem may take years to reverse. A study at the Australian National University, published in Nature Geoscience, has recently revealed just how long this recovery can take. By studying areas of mountain ash in South Eastern Australia that have been impacted by clear felling or forest fires, the authors have revealed that the time needed for recovery can be up to eight times higher than previously thought.

Southern Australian mountain ash forests (Eucalyptus regnans) are some of the tallest and most-carbon dense forests worldwide, creating large carbon sinks and maintaining a diversity of soil nutrients. However, many of these forests are at risk of clearance or degradation from human activities; in the last 8 years alone nearly all of Victoria’s Mountain Ash forests have been lost.

To determine the long term consequences of this disturbance on measurable soil qualities, a multi-century chronosequence was used to assess a total of 729 soil cores, collected from 81 sites which had experienced 9 different disturbance histories. Results showed areas which had experienced multiple fires, clear-cut logging or post-fire salvage logging were characterised by lower available phosphorous and nitrate. Lower nutrient content was also observed in forests which had experienced burning. This loss of nutrients is perhaps unsurprising when it is reported that soils can be exposed to over 500 degrees Celsius during a fire. Summarised, this chronosequence showed that it can take up for 80 years for forest soils to recover from a bushfire and 30 years after logging. When burning and logging are combined the most severe effects are seen.

Though this research was only conducted in a single region, the findings are still applicable to the wider study of human and natural disturbances on long term recovery of forest soils. Forest soils harbour a diversity of insects, bacteria and fungi which are instrumental in maintaining the proper functioning of ecosystem cycles. Maintaining this biodiversity is just one of the ecosystem services provided by forests, along with carbon capture and in the case of the Victoria Mountain Ash forests, providing clean water for Melbourne. From a more direct economic standpoint, the forest is also used for timber, pulpwood and tourism by local industries. The findings presented here show how the impacts of fire and logging may have long-term and largely unseen impacts on forest recovery at the soil level. These results which should be considered in future forest management and conservation decisions and lengthen the span of thinking when considering forest recovery.

Read the full paper here: Bowd, E.J., Banks, S.C., Strong, C.L. and Lindenmayer, D.B., 2019. Long-term impacts of wildfire and logging on forest soils. Nature Geoscience, p.1.

To find over similar papers use the following search in the Forest Science Database: (“forest fire*” OR “burning” OR “clear felling”) AND (forest*) AND (soil*) AND (recovery)