The December edition of Australasian Science, now on the shelves, contains what may be the most important article I have written (subscriber only alas). I’m very keen to bring it some attention.
Professor David Lindenmayer (ANU) is already recognised as Australia’s leading expert on temperate forests. The paper he authored in the Proceedings of the National Academy of Sciences may well take that status global. Exciting, yes, but unfortunately his conclusions are, in his own words, “Very, very sad.”
Temperate forests can be divided into two sorts, there are those that are fire tolerant, and those that are not. Fire tolerant ecosystems contain many plants that thrive on fire – indeed many depend on it to regenerate. Although big fires will kill individual plants, the species are well adapted to bounce back, and many have seeds that only germinate after fire. (There’s some interesting work in WA on the mechanism for this, which is quite complex, using a combination of chemicals in smoke and increased light penetration into soil as the trigger.)
Since fire tolerant species benefit from fires it is not surprising that they tend to burn easily. On the other hand those species that are not well adapted to fire tend to resist it, forming natural fire breaks.
Given the horrors of the 2009 bushfires, and the forthcoming increase in temperatures, it is very important for Victoria to promote the survival of fire resistant ecosystems. Unfortunately, that is not what we are doing.
It has been known for a long time that modern logging techniques, in which the waste left after the big trees have been removed is firebombed to get a regeneration burn, promotes the colonization of the logged area with fire tolerant species, rather than fire resistant ones. In fact this is part of the reason the techniques are used – the tolerant species include those with more valuable wood. This makes the logged area more vulnerable to future bushfires.
Despite this, the myth persists that environmentalists are responsible for big fires, in part from the perception that if we remove lots of flammable material in a logging operation less will be left to burn thereafter. This may be true in the short term but, unless you want to concrete over the land on which the logging took place, within a few years something will have grown back, and that something is likely to burn more easily than what was there before.
This is not new, but what was not known was the overall impact of logging operations. Did a patchwork of recently logged areas, mixed with older pockets enhance or reduce fires? After being challenged by a logger who claimed the Black Saturday fires were a result of too little logging Lindenmayer set out to investigate.
In collaboration with leading forest ecologists around the world he discovered that Victoria’s mountain ash forests are now in a “landscape trap”. So many former coupes have become highly fireprone, that when a fire gets into the forests it becomes very hot as it burns through these parcels, gaining enough energy to destroy even untouched pockets within the forests. Even large, hard to burn trees succumb. These are replaced by more fire-tolerant species, and within a few years the area burns again, offering no chance for fire-resistance to reestablish itself.
The combination of logging and recent fires has created a tipping point where, Lindenmayer says, “The whole landscape is at risk of being consumed by mega fires.”
Lindenmayer explains “The core process underlying the landscape trap is a positive feedback loop between fire frequency and severity and a reduction in forest age at the stand and landscape levels caused by logging.”
The same process has been confirmed in tropical forests, and amounts to one of the main reasons for the decline of the Amazon Rainforest. However, it was only when Lindenmayer teamed up with international colleagues that it was revealed that many temperate forests worldwide are either in the same situation, or at risk of becoming so.
Just 1.2% of pre-European settlement mountain ash survives. Unless we get a dramatic reduction in both logging and fire, it will soon all be gone. What is more, if areas that have already been damaged experience fire too soon afterwards they can lose the forest species entirely, becoming dominated by wattle scrub. Highly flammable wattle scrub.
Ecologically the disaster here is obvious, but there are further problems. Lindenmayer has previously shown that Victoria’s intact forests are the densest carbon stores on Earth. The replacements store very little carbon indeed. Moreover, the tall forests are part of a feedback system with clouds as they pass over the ranges, increasing rainfall that provides Melbourne’s water supply. Where the forests are lost we also lose runoff. Finally, for those with homes in the area, the choice is between bushfires that slow as they encounter huge, hard to burn trees, and those that race through damaged ecosystems at astonishing speed, gaining energy as they go.
Over the last few decades ecologists have come up with the concept of Resilience, which has proven to have considerable significance for other complex systems, such as the Internet. A system with great resilience can survive even enormous shocks, such as those produced by tropical cyclones. However, when the resilience is reduced, through repeated minor damage, exposure to such a blow can flip it into another state, from which it cannot recover without the input of significant energy.
The lasting legacy of Victoria’s mountain ash forests may be to become the text-book example of destroyed resilience, just as the importation of the rabbit into Australia has become the exemplar of the damage that can be done by an introduced species lacking natural controls.
A remarkable feature of this research has been the mass media response. Being a monthly, we almost always get to stories after other media outlets have picked over them. Some catch on like wildfire in a logged forest, while others have not been covered at all prior to my article. This one is different. The Canberra Times wrote two huge articles on it – one full page, and the ABC has also given it quite a bit of attention. Other outlets ignored the story entirely. This is particularly depressing because the work is of such public significance that Lindenmayer paid, out of his own pocket, for it to be made public access, despite publication in a journal that normally requires subscription. (The media coverage has however, been enough that Lindenmayer has received hate mail for his research).
Credit for both photos to David Blair.