Widespread salvage logging for 30 years after the 1939 fires had huge ecological impacts. It favoured cutting fire damaged (but living) larger diameter trees. After a fire, generally there will be a return of a healthy multi-staged forest required to provide maximum habitat. Bushfires usually leave a high level of this structural complexity in the forest. Wildfires typically consume less than 10% of the wood. However, salvage logging (clearfelling) will convert the forest to an even aged, plantation-like structure.
If we value high species diversity, we need to maintain multi-aged forests. What helps provide this diversity is the cavities and hollows in older trees. The arboreal marsupial population increases by 50% with each additional age class. This is especially the case where wattles have regenerated without the widespread destruction of the Ash overstorey and its nesting sites.
Even if the fire kills trees, they can be biologically valuable. Dead trees still occur in post ’39 regeneration, providing critical habitat for arboreal marsupials, bats and birds. Trees that fall are habitat for ground dwellers and aid germination of rainforest plants.
After a disturbance like wildfire, the biomass needs to be left undisturbed to recover fully. Two mass disturbances on top of each other can tip the scales and destroy the natural forest systems, especially the lower order components like fungi and invertebrates.
The theory that fire destroys Mountain Ash is not true. The majority of Eucalyptus Regnans survived in about 70% of their range which was burnt in the ’83 Ash Wednesday fires. Ash trees don’t tolerate fire well, but they can survive if their upper crown is not scorched. The other species can recover from shoots.
Other problems from salvage logging are erosion from machinery after ground cover hasn’t stabilised the soil. This is when the soils are at their most fragile. Logging and roading would increase the impact of sedimentation in streams.
For regeneration it is crucial that surviving living stands remain and there is no disturbance. Natural regeneration will be severely impacted on by bulldozing the soil and roots, and compacting the fragile soils.
Remaining live trees are more valuable compared with before the fire, mostly in terms of regeneration and habitat value. What fauna survives a fire is much more dependent on the remaining live trees. These trees are able to provide food and shelter much more quickly than seedling trees. If forests areas are fragmented and small, it would be difficult or impossible for some animals and plants to return. It could take between 10 – 30 years.
Forests are made up of thousands of plants and animals all interacting with each other to keep that ecosystem functioning. Fire removes nutrients, the fallen leaves, branches and whole trees, that are broken down by a community of insects, worms, bacteria and fungi living in the top few centimetres of soil. These invertebrates mostly die and fire sterilizes the living soil damaging this process greatly. This lower level of the ecosystem is what afar managers call hazardous fuel. Whole communities feed on these: invertebrates, lizards, frogs, mammals and birds. These animals rely on the litter, trees, shrubs, logs and branches for shelter. Recovery from here is a long and delicate process, not aided by heavy bulldozers and chainsaws.
Claims that trees need to be used soon after a fire is untrue. There were dead ash trees being cut years after the ’39 fires which were sound and useable.
Sources – Lindenmeyer (1997 and 2002), Mackie (pers comm), McCarthy (1997, 2002), Horton (2003).
Late news: Minister Thwaites has allowed 300 ha of fire damaged ash forests to be logged between now and June. These forests were planned for clearfelling over the next three years. We are asking they be logged using special prescriptions so the fragility of the soils are considered.
All up 400,000 ha of forest was burnt. Of this 70,000 is loggable and 23,000 is ash. The mixed forest will be allowed to recover and the ash will be checked in Spring to determine if trees are dead or will regrow. We hope this job is given to independent scientists and not Department foresters.