Comment on ‘Self-thinning forest understoreys reduce wildfire risk, even in a warming climate’

Abstract

In this comment we examine a recent study published in Environmental Research Letters that analysed fire history data from forests in Western Australia to suggest that changes in forest structure result in a long-term reduction of fire risk after 56 years since last fire. We examine the data underpinning this study and find that its strongly skewed sample size distribution creates a bias to the extent that the analytical approach would find a pattern of declining fire risk even when there was no decline. Moreover, the very small sample sizes of the longest unburned forests mean that fire mapping errors as small as 1–2 ha can reverse key findings. With documented mapping errors orders of magnitude larger, the dataset is not robust to analysis at this level of precision. An appropriate conclusion, taking into account these detection and sensitivity issues, would be that likelihood of subsequent wildfire is reduced in the first ∼6 years following fire, and remains fairly consistent at a higher level for at least the next 3 decades, with no evidence for a long-term reduction of fire risk. This is relevant given that many fire and forest management decisions are made based on scientific literature. Rather than wildfire risk reducing with increasing time since fire, our projections indicate that ceasing active fire management in the sampled forests could result in landscape wildfire extent 25%–65% above current levels. We recommend further steps that would help provide sound, evidence-based knowledge to inform science, management, and policy.