Australasian Science Magazine

Foreground and mid-ground: young mountain ash regeneration unburnt after 7 February wildfire. Background: burnt 1939 ash regrowth, same wildfire. (Photo: A. Leong, courtesy Victorian Association of Forest Industries)

By Ian Ferguson and Phil Cheney

An alternative view to a report published in Australasian Science last month.

We take issue with several aspects of the Lindenmayer interview reported in the December issue of Australasian Science (http://www.australasianscience.com.au/article/issue-december-2011/exclus...) and the parent paper (Proc Natl Acad Sci USA 108:15887-15891) on which it was based. A detailed response to the parent paper has been published (Aust For 74(4): 362-365).

Our concerns about the Australasian Science interview include the omission of interventions to avert the landscape trap, and misconceptions about fire behavior and the effectiveness of logging and associated roading and skilled workforce in aiding wildfire suppression.

In the interview, Lindenmayer describes the formation of landscape traps. Mountain ash or alpine ash regeneration resulting from an initial wildfire converts to wattle or other species following a second wildfire, if not carrying sufficient seed to regenerate prolifically, as it would otherwise do at older ages. Substantial occurrences (e.g. Toorongo Plateau, Black Spur and large areas of alpine ash regeneration from the 2003 wildfire, burnt again in the 2006 Great Divide wildfires) are well known to foresters and forest scientists. In State forests, these do not become permanent landscape traps because they are regenerated using the same techniques of aerial seeding or planting used after logging. Appropriate seed collection and storage measures have recently been examined using stochastic modeling that included recognition of seeding cycles, climate change and the contagion element inherent in wildfire (Aust For 72: 195-205; Aust For 74: 97-107).

Lindenmayer fails to acknowledge that the combination of drought, extreme weather and the very high fuel loads that generally characterise these forest types create conditions under which wildfires, once ignited and significant in perimeter, are virtually impossible to suppress until those weather conditions ease. With the exception of very young regeneration (under 4 years), virtually all mountain ash and alpine ash forest – regardless of its history or age - will carry wildfire of varied but high intensity, with widespread consequent mortality on a landscape scale under such conditions. Past wildfires in 2003, 2006-07 and 2009 have therefore put large areas of the landscape at risk of change of species in the mountain ash and alpine ash forests from a subsequent wildfire for the next 20 years, irrespective of prior disturbance.

Regrettably, much of the area burnt in 2009 included old growth forest in national parks that were also closed water catchments so that "just 1.25% of old growth mountain ash forests existing prior to European settlement survives". That may dismay but should not surprise us. A much-respected forest ecologist, David Ashton, who studied these very forests intensively over a long period, sadly but accurately concluded the abstract of his seminal paper saying: "Whether the Big Ash will be spared from fire in future centuries is very doubtful" (Aust J Bot, 2000, 48, 1–26).

Lindenmayer claims that "a core process underlying this landscape trap … is the reduction in forest age at the stand and landscape level caused by logging". The statistics on areas of mountain and alpine ash burnt and killed do not support this claim (see Aust For 74: 97-107). Furthermore, State forest sites are regenerated by aerial seeding or planting after logging and, if necessary, after wildfire. Parks Victoria acknowledges that artificial regeneration may be needed in national parks and reserves if another wildfire kills regenerating areas in the next 20 years. While the prospect of a large wildfire in that time cannot be discounted, artificial regeneration measures are available to avoid Lindenmayer’s so-called 'tipping point' in terms of changes in dominant species.

Contrary to Lindenmayer’s assertions, the logging workforce and machines, together with the break-up of the landscape by roads and areas of very young (1–4 year) regeneration, assisted the protection of adjacent older ash by breaking the continuity of high fuel loads and in some cases providing a basis for safe suppression. It is not a panacea, but protects some older stands and associated biodiversity, provides more options for control lines, and assists suppression when weather conditions allow.

The key issues about future meg fires are about: (i) reducing wildfire intensity and associated severity of impact on the ecosystem (ideally, allowing suppression); and (ii) being able to regenerate potential landscape traps, should they eventuate. More effective and better-equipped suppression services, more prescribed burning, and more resources for regeneration, if the worst occurs, are essential.