Mechanical Treatments and Prescribed Burning Can Reintroduce Low-Severity Disturbance in Southern Australian Temperate Sclerophyll Forests

Abstract

The establishment of sustainable, low-intensity fire regimes is a pressing global challenge given escalating risk of wildfire driven by climate change. Globally, colonialism and industrialisation has disrupted traditional fire management, such as Indigenous patch burning and silvo-pastoral practices, leading to substantial build-up of fuel and increased fire risk. The disruption of fire regimes in southeastern Tasmania has led to dense even-aged regrowth in wet forests that are prone to crown fires, and dense Allocasuarina understoreys in dry forests that burn at high intensities.Here, we investigated the effectiveness of several fire management interventions at reducing fire risk. These interventions involved prescribed burning or mechanical understorey removal techniques. We focused on wet and dry Eucalyptus-dominated sclerophyll forests on the slopes of kunanyi/Mt. Wellington in Hobart. We modelled potential fire behaviour in these treated wet and dry forests using fire behaviour equations based on measurements of fuel load, vegetation structure, understorey microclimate and regional meteorological data.We found that (a) fuel treatments were effective in wet and dry forests in reducing fuel load, though each targeted different layers, (b) both mechanical treatments and prescribed burning resulted in slightly drier, and hence more fire prone understorey microclimate, and (c) all treatments reduced  predicted subsequent fire intensity by roughly 3-5 fold. Our results highlight the importance of reducing fuel loads, even though fuel treatment make forest microclimates drier, and hence fuel more available to burn.Our finding of the effectiveness mechanical treatments in lower fire risk enables managers to reduce fuels without the risk of uncontrolled fires and smoke pollution that is associated with prescribed burning. Understanding the economic and ecological costs and benefits of mechanic treatment compared to prescribed burning requires further research.

Keywords: Mechanical thinning, Prescribed burning, Eucalyptus forests, wildfire, fire regime, fire behaviour modelling