Bushfires and logging: Crusading ecologists eroding public trust in science

Unfortunately, those who work in the native forestry sector have become all-too-familiar with ‘academic credibility’ being mobilised as an existential threat against them. The latest example is the determination of a cohort of crusading ecologists, aided by unquestioning and supportive media outlets, to push the concept that “logging causes bushfires” at the very time that a Royal Commission and several state inquiries are examining last summer’s catastrophic fire season.

Since the start of May, three peer-reviewed scientific papers have been published citing timber harvesting (ie. logging) as a significant factor in causing and/or exacerbating bushfires. All have been written primarily by ecologists, with only one paper also co-authored by a known bushfire scientist (albeit a controversial one).

Two of the papers have been published in low tier international online or open access journals with quick turn-around from manuscript to published paper, including highly questionable peer review. The other was published in an international journal where peer review is also unlikely to have been conducted by anyone with local knowledge of the Victorian forests in question.

Because these papers have been so recently published, there has been no time to formally contest them through the scientific literature. Nevertheless, a cursory glance at them (and their supportive media) by forest scientists with a more practical appreciation of southern Australia’s forests and their relationship with fire, has unearthed some alarming errors and exaggerations. These include:

That parts of the forest industry are supposedly ‘now calling for increased logging’ within both burnt and unburnt forests;

• That logging supposedly increases subsequent wildfire severity by leaving ‘large amounts of debris’ on the forest floor, even though it is standard forestry practice to remove this debris by burning it during the post-harvest regeneration process;
• That East Gippsland’s forests have a natural fire interval of from 50 – 150 years, despite the region being one of the three most fire-prone regions on the planet;
• Categorising 3.25 million hectares (ie. 46%) of Victoria’s public forests as ‘productive native forests’ thereby implying that it is available for logging – an almost 8-fold overstating of the reality;
• Combining two burn severity classes together to substantially overstate the proportional area of ‘crown fire’ in Tasmania’s 2019 bushfires; and
• Alleged mislabelling of Tasmanian forest and plantation types in which fire severity had been remotely surveyed (from imagery).

The “logging causes bushfires” concept has an element of truth in that regrowth, whether resulting from timber harvesting or wildfire, naturally goes through several decades where its dense stocking and low canopy height can, after about age 8, make it more vulnerable to crown damage or even crown fire, especially if fires burn under severe to extreme weather conditions during an extended drought. The research suggests that this fire-vulnerable period extends to about age 35 years after stand-replacing bushfires or timber harvesting in wet Mountain Ash forests, and that it may well apply in other wet forest types. The ‘Black Saturday’ fires showed that regrowth younger than 8 years is least likely to be impacted by bushfire.  

The key point is that most of this fire-vulnerable regrowth would have resulted from past wildfires rather than timber harvesting. For example, between 2003 and 2009, bushfires burnt through almost half of Victoria’s public forested lands. The 2009 ‘Black Saturday’ bushfires burnt around 430,000 hectares of forest in just a few days. While not all of this burnt area would have sparked a mass regrowth event, it is nevertheless an area equivalent to about 140 years of timber harvesting at Victoria’s current annual rate.

The alarmist message being promoted by the three above-mentioned papers through the media, that “logging is likely to have exacerbated the country’s catastrophic summer bushfires” ignores the area of post-timber harvesting regrowth and its spatial arrangement through a vast and mostly unharvested forested landscape.  Only one of the three above-mentioned papers attempted to provide this context, but it grossly overstated the area available for timber harvesting. 

In reality, only a minor portion of forest is available for timber production in most states, and this is typically widely scattered. For example, only 6% of Victoria’s public forest is currently available for timber production, although a larger proportion was used in the past. At the present time, perhaps 2 to 3% of Victoria’s public forest area would be comprised of fire-vulnerable logging regrowth. But it would be widely spread from the far south-west of the state, through the central north, and the south-east through to the far east, given that 20 to 35 years ago, many areas had timber industries that now no longer exist. It barely plausible that such small and spatially scattered areas of regrowth could be driving any significant impact at the landscape level of the recent mega-fires.

At Victoria’s current annual rate of timber harvesting, the area of fire-vulnerable post-harvesting regrowth (of 8 – 35 years of age) would only ever comprise about 1.1% of the state’s public forests into the future. This would make it even less likely to have any significant impact on the extent and severity of future large bushfires.

It is important to note that although this fire-vulnerable regrowth is more likely to be severely burnt compared to an older, mature forest; fire severity is a post-burn parameter assessed by degree of tree crown scorch or loss. It does not reflect a greater intensity of fire, despite the ‘logging causes bushfire’ concept strongly implying that the presence of regrowth makes bushfires bigger and less controllable.