We are having incredibly intense and widespread bushfires in Australia. Figures suggest that the fires have been much bigger than those in the Amazon, earlier in the year. Some sources say the area of land burnt is equal to 10.7 million hectares which is 26 million acres, 107,000 square km, or 41,000 square miles. I’ve seen maps comparing the size of the areas burnt to Ireland or Belgium. The fires are still burning and not yet over. [Figures a few weeks later suggest burning of over 17 million hectares, when we include the Northern Territory. Over a billion animals may have died. More than 700 species may now be extinct.]
Everyone knows that bushfires are part of the natural cycle in Australia. Some plants need the fires to re-germinate and so on.
My question, because I don’t know the answer, is a simple one. Is it possible to have a fire so intense and widespread that it destroys this capacity for regeneration and new plant growth?
It seems reasonable to assume that if the temperature is too great for too long, seed pods and buried seeds could be killed, or just burnt up. Trees whose canopies might be normally expected to survive the fires, are burnt and their seeds along with them.
Ash can also seem to harden into a solid which covers the soil, and may protect it from blown in seeds, and remove the circulation of molecules between air and soil. I’ve seen this form of ash in fire zones before.
Birds spread seeds through their excreta. If most of the birds die in the fire (and I think they may have, because normally in bush fires the city is colonised by bush birds and I have not seen this happen this year), then this cannot happen.
Animals also spread seeds, and disturb the earth and the ash cover. They eat excess seeds thinning the forest and clear the leaf litter and lower the fuel load, by burrying it in the soil. Normally the soil in Australian forests is turned over, made soft, permeated by water (when available) and made full of nutrients by the activities of small mammals.
these mammals punch above their weight. A digging mammal can shift around 1.8-3.6 tonnes of soil per kilogram of body mass in a year. A woylie – a bettong from Western Australia – creates between 20 and 100 diggings per night while foraging, while a southern brown bandicoot can excavate over 3.9 tonnes of soil per year.
Fleming 2013
The loss of these mammals to intense fire, or to an influx of feral predators (before or after the fires), is likely to slow, or event prevent forest regeneration. Certainly these animals will take a long time to breed to normal levels in a hostile low nutrition environment.
Insects, native bees and so on, which can normally keep out of the fires, may not have been able to. In which case pollination is not going to happen, and any surviving plants will not reproduce. Certainly they will not reproduce rapidly. Termites, ants and so on which are vital to the ecology, as they decompose fallen timber, may also not survive, and take a long time to recolonise the burnt areas. It is possible for termite mounds to bake solid.
Fertile soil is composed of dead things, plus micro-organisms (plus rock dust etc). It is the micro-organisms that generally make it ‘work’, without those micro-organisms it is just dirt and dead things. The system of micro-organisms is generally quite complex. If they die in the heat, then the soil can be less fertile, more like a desert. I’ve no idea what it takes for bush soil to support larger forms of life, but it could be affected by severe enough fire.
Ecologies are systems, and all the parts of the ecology have a part to play in maintaining (and sometimes disrupting) that ecology. If a whole section of the ecology is dead, then regeneration may be far more difficult, as the system is no longer working in the same way.
This level of disruption of the bush breeding cycle, or resilience cycle, may mean that invasive species, at the margins of the bush, may get a massive hold on bush fire zones, before anything else can grow back, and Australia’s ecology could change for ever.
Changes in climate, if they continue (and there is no reason to assume they will not), will alter the potential and dynamics of ecologies. We may not be able to replace what we have lost. Other arrangements of flora and fauna could be encouraged by the new weather patterns and, if so, then everything will be different.
If any of this is so, then I suspect it may be dangerous to just leave the areas to regenerate by themselves. As a friend of mine said we might have to aim “at creating pockets of sustainability for the bush and wildlife,” so life forms can spread out from these pockets to produce the bush we used to know.
Hazzard reduction burning, even traditional burning, by itself, without a working ecology of other creatures will likely disrupt the process of regeneration, and may even produce greater hazards.
I don’t know.
Tags: climate change, disorder
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