Prescribed burning of thinning slash in regrowth stands of jarrah (Eucalyptus marginata) following bauxite mining in south-west Australia

Abstract

Prescribed burning of regrowth jarrah stands established after bauxite mining is key to their integration into standard jarrah forest management, but fire management in thinned regrowth stands has not been studied. Fuel loads in 10- to 13-year-old thinned regrowth increased exponentially with thinning intensity, doubling from 18 t ha–1 in untreated stands (1500–2500 stems ha–1) to 37.4 t ha–1 in the heaviest treatment (400 stems ha–1 retained); however, litter and standing dead vegetation were concentrated within 60 cm of the ground. Intensities of subsequent autumn prescribe-burns increased with increasing fuel loads, but all burns were typically of low to moderate intensity <1800 kW m–1. Three months post-burn, total fuel loads averaged 5 t ha–1, recovering after 4.5 years to 75% of pre-burn levels across all thinning treatments owing mostly to dense understorey regeneration. Where no burning occurred after thinning, total fuel loads declined to be comparable to the unthinned control after 4.5 years, averaging 20 t ha–1. Prescribed burns in autumn following thinning are not recommended because a dense well-aerated and elevated fuel layer is reinstated, posing a future fire risk. Burning 1–2 years before thinning may be an appropriate alternative strategy.