Background
Ecological Monitoring After Bushfires, 2002 - 2007
After fires in January 2003 in the Australian Capital Territory (ACT)
See www.environment.act.gov.au/__data/assets/pdf_file/13702/wildfiresintheact.pdf
The catchment area burnt in ACT was largely in steep granitic hilly country, altitudes 450-1900 m asl, with dry sclerophyll forest or woodland.
Sampling was done from early February to late May 2003, in river, reservoir, sphagnum bog and other wetlands, as well as terrestrial areas. The area was in drought at the time of the fires.
All riparian canopy cover was lost or about to be lost in the sections burnt at high or very high severity (definitions of severity: very high - no canopy leaves remaining; high - canopy leaves scorched but still attached; moderate - canopy partially scorched or unburnt, but understorey burnt; unburnt - no damage in canopy or understorey).
Many riparian eucalypts, such as Snow Gum (Eucalyptus pauciflora) and Black Sallee (Eucalyptus stellulata), were regrowing strongly from epicormic shoots, or lignotubers by autumn, about 3 months later. Other species were also recovering: wattles, bottlebrushes, tea trees, snow grass, baeckia, lomatia, blechnum and hakeas. Full assessment of riparian recovery would require monitoring over months and years.
The sampling program found markedly reduced numbers of fish, at both burnt and unburnt sites in the area, soon after the fires.
Wetland damage from the fires was initially assessed visually, on-ground. Ground-area and shrub cover burnt, and depth of peat destroyed, were estimated. The loss of cover was thought responsible for the death of many Burrowing Spiny Crayfish, via foxes.
There were very few calling male Corroboree Frogs and nests, both before (from drought) and 2-3 weeks after the fires, but later surveys found individuals had been able to move to new pools.
Wetland vegetation such as Carex gaudichaudiana began regrowing within weeks of the fire, but sphagnum moss (already stressed by drought) was killed and will take years to recover. Some shrubs had begun to regrow from rootstocks but regeneration from seed, in competition with weeds and feral pigs, had not yet begun.
In Victoria, after fires in January 2003
See www.epa.vic.gov.au/water/rivers/bushfires.asp
Monitoring after the early-mid January fires ran from 2003 to 2005. The studies have found that river ecological condition was only really affected where rivers had lost riparian vegetation/cover or had suffered an influx of sediment after heavy rain in the area.
Terrestrial and aquatic ecology monitoring near Sydney, New South Wales, after fires in January 2002
On 25 December 2001 a series of lightning strikes initiated several wildfires in Sydney's drinking water supply catchments managed by the Sydney Catchment Authority (SCA). A combination of drought, high vegetative fuel load, strong north-westerly winds, low humidity and remote location of those ignitions resulted in a rapid expansion of several wildfires, eventually burning over 225,000 hectares of forested catchment.
The extent and severity of the vegetation destruction resulted in the SCA commencing a comprehensive scientific investigation into the impacts of wildfire on vegetation management, catchment health, erosion and water quality. A summary is given below. For the full paper see Key reference Chafer 2007.
- Fire severity can be quantified using pre and post fire satellite image interpretation. This can be used to infer impact on vegetation communities and soils and identify potential areas of increased erosion / sedimentation.
- Post-fire recovery of vegetation can be quantified using satellite image interpretation. This could be useful for post-fire monitoring of vegetation health and a proxy for reducing erosion risk.
- Recovery of vegetation in areas impacted by low to moderate fire severity can recover to pre-fire condition within 3-4 years. In areas impacted by high to extreme fire severity, vegetation recovery may take 5-10 years.
- Widespread severe wildfires have a long-term negative impact on fauna populations.
- It is unambiguously clear that the most important areas of concern after wildfire are those affected by a fire severity greater than high. In these areas, surface-soil temperatures reach or exceed 350°C, destroying surface-soil water-repellency, changing soil chemistry and creating a wettable layer that can absorb "normal" rainfall events but which becomes mobilised when rainfall exceeds 40-60 mm/day. Thus erosion potential is increased and post-fire redistribution of sediments can be locally extensive in rainfall events >60mm/day.
- As most large (severe) wildfires appear to occur during El Nino periods (below average rainfall), the occurrence of extreme post-fire rainfall events is reduced. Nevertheless, localised thunderstorms can initiate short-term high intensity rainstorms that do initiate erosion events. During such events large post-fire deposits of ash, debris and burnt soil can be mobilised. It may take several high rainfall events over several years to push ash/sediment plumes from their source to a stream's entrance to a given water storage reservoir.
- During high rain events post-fire, downslope erosion is increased, but riparian vegetation, litter dams and animal activity within the surface-soil can significantly reduce sediment/nutrient delivery to the drainage network channels.
- There is some evidence that post-fire water yield is initially increased in the years immediately post-wildfire, then becomes depressed for a couple of years before returning to prefire yields. This result is similar to the results of water supply catchments in the ACT following the 2003 wildfire in that territory, but significantly different from Victorian research. Further research is required to assess this preliminary finding.
