Thinning forests no defence against fires

8 October 2020

Having logging machines "thin" forest for fire reduction is largely ineffective, a new peer-reviewed, scientific study has found.

The study, led by researchers at The Australian National University and published in the journal Conservation Letters, compared fire severity in unthinned versus thinned forest burned in the 2009 wildfires. It covered two forest types - mixed species forest and ash forest.

The scientific evidence showed that across almost every forest age and type, thinning made little difference. It actually increased the likelihood of a crown burn in older, mixed species forests, and slightly reduced the chance of crown burn in younger aged, mixed species forest. 

Lead author Dr Chris Taylor, from the ANU Fenner School of Environment and Society, said thinning made very little difference to fire severity.

"The impact of thinning varied with forest type, the age of the forest and fire conditions," Dr Taylor said.

"Across most forest types and ages, thinning had little impact on forest fire severity, although it did worsen severity in mixed species forest aged 70 years plus and did reduce it in mixed species forest aged 20-40 years.

"Overall, the evidence indicates thinning forests does not reduce fire risk."

The study also found 20- to 40- year old forest was more likely to suffer crown burn than 70-year-old forest. It also suggested more study could still be done on the topic.

"A previous report found thinning of forests increased fire risk," Dr Taylor said. "And multiple previous studies have also found fire severity is lower in older, undisturbed and unlogged forests."

Dr Taylor also noted previous Silvicultural Guides to control forest growth for Victoria and Tasmania have stated thinning would produce an "increase in fire hazard" due to "high fuel loads".

Read the full study in Conservation Letters.