Scientists analyse the ashes of Australia's wildfires
14 April 2009
British researchers are studying the aftermath of the ferocious wildfires that swept across parts of southern Australia in February, killing people and animals and devastating the landscape.
Drs Stefan Doerr and Rick Shakesby from Swansea University are currently in the Marysville region, just outside Melbourne, where they are collecting soil samples and ash from the burnt forests. They must work quickly, before heavy rain washes away vital evidence that will help them determine the extent of environmental damage caused by the fires.
Analysis of the soils will show the severity of the burning and how much of the seed bank has survived. It will also shed light on the risk of accelerated erosion of the hill-slopes as winter approaches. 'All the ground vegetation gets stripped away by fire and in many areas the dry soil is water-repellent. This allows rainwater to run easily over the surface, moving debris down the hillside and sometimes causing landslides', explains Doerr. 'Australia has been suffering droughts for almost a decade and the weather has been erratic, but there have been a couple of heavy rainfalls since we arrived and we've seen soil and ash being transported by the water,' he adds.
He says his initial impression is that the environmental damage on the ground is less than he would have expected, perhaps because of the fast-moving fire front. 'The fires were racing through so fast it's possible that their residence time on any given point on the ground was comparatively short. We need to analyse our samples to see how much of the seed bank has survived as this will determine the nature and speed of plant recovery,' he explains.
Dr Rick Shakesby checks the moisture level of soil.
'Although the fires were very severe we were still surprised by how thick the ash layers are,' adds Doerr. 'Tests on the ash will tell us how much of the organic carbon originally stored in the vegetation is now on the ground. Some of the burnt material has turned to charcoal, which is extremely resilient to degradation and serves as a long-term store of carbon in the environment.'
The ash can, however, also cause problems, particularly if it is washed into the water supply. Melbourne Water keeps a close eye on water quality, helped by scientists at the University of Melbourne who have installed instruments to monitor the water catchments.
If ash gets into the water it is likely to encourage algal blooms to form, some of which may become toxic. The Melbourne scientists will be concentrating on water sampling as winter sets in and more rain falls. Melbourne Water did, however, have the foresight to pump water away from high risk areas affected by the fires to other areas which were not affected, so the potential impact on the highly populated greater Melbourne region may not be as catastrophic as it might otherwise have been.
Epicormic growth on a burnt tree trunk.
Although the fires occurred less than two months ago, new growth has already started around Marysville. Deep-rooted bracken is beginning to shoot through the earth and much of the oil-rich eucalypt forest is already starting to show 'epicormic' growth. This is new growth that usually appears on the main trunk, where dormant buds are activated after the trees have been scorched or burnt by wildfires. In parts of the region, temperate rainforests with majestic trees and extremely green biomass still stand alongside the charred remains of others.
'It is very sad that the combination of unprecedented high temperatures and strong winds that varied in direction, and which appears to have been a major factor in limiting the environmental damage on the ground, had such a devastating impact on human lives. Everyone has been shocked by the severity of the fires and the high death toll, and none more so than the wildfire science community,' says Doerr. 'We're used to seeing burnt areas but this region has been very hard hit in so many ways.' But the people are also very resilient and are rebuilding their lives and their homes. Much like the forests, the town of Marysville is starting to rise from the ashes.
The two scientists and their colleagues, Drs Patrick Lane and Gary Sheridan at the University of Melbourne, will continue to collect samples for analysis and will finish their fieldwork by the end of April. Their work will provide valuable data that will help scientists to predict more accurately the impact of wildfires on vegetation recovery, soil erosion, water resource management and carbon emissions. They expect to present their findings in July 2009, during the World Geomorphology Congress in Melbourne.
The research is funded by the Natural Environment Research Council.
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