Flammability dynamics in the Australian Alps

Abstract

Forests of the Australian Alps (SE Australia) are considered some of the most vulnerable to climate change in the country, with ecosystem collapse considered likely for some due to frequent fire. It is not yet known, however, whether increasing fire frequency may stabilize due to reductions in flammability related to reduced time for fuel accumulation, show no trend, or increase due to positive feedbacks related to vegetation changes. To determine what these trends have been historically, dynamics were measured for 58 years of mapped fire history. The 1.4 million ha forested area was divided into broad formations based on structure and dominant canopy trees, and dynamics were measured for each using flammability ratio, a modification of probability of ignition at a point. Crown fire likelihood was measured for each formation, based on satellite-derived measurements of the 2003 fire effects across a large part of the area. Contrary to popular perception but consistent with mechanistic expectations, all forests exhibited pronounced positive feedbacks. The strongest response was observed in tall, wet forests dominated by Ash-type eucalypts, where, despite a short period of low flammability following fire, post-disturbance stands have been more than eight times as likely to burn than have mature stands. The weakest feedbacks occurred in open forest, although post-disturbance forests were still 1.5 times as likely to burn as mature forests. Apart from low, dry open woodland where there was insufficient data to detect a trend, all forests were most likely to experience crown fire during their period of regeneration. The implications of this are significant for the Alps, as increasing fire frequency has the potential to accelerate by producing an increasingly flammable landscape. These effects may be semi-permanent in tall, wet forest, where frequent fire promotes ecosystem collapse into either the more flammable open forest formation, or to heathland.

Climatic and edaphic gradients predict variation in wildland fuel hazard in south‐eastern Australia

“…Time since fire has limited capacity to explain variation in the plant diversity of south‐eastern Australia (Penman et al , Kasel et al 2017). Other components of the fire regime, such as fire severity, appear to have a stronger influence on the recruitment and distribution of species (Vivian et al , Cawson et al , Swan et al ). Different vegetation communities follow variable flammability pathways following fire (Moritz et al 2004, Zylstra , McColl‐Gausden and Penman 2019).…”

“…We used the results of past models (Hageer et al 2017) to select an initial set of predictor variables that included nine soil and climate variables and one variable relating to time since fire. We downloaded climate data from Worldclim at a resolution of 1 km 2 (accessed March <http://worldclim.org/version2>), and obtained soil data from CSIRO Data Access Portal at a resolution of 3 × 3 arc‐seconds (~90 m 2 ; accessed March <http://www.clw.csiro.au/aclep/soilandlandscapegrid/index.html>Viscarra Rossel et al 2015). The raw soil data were provided for three depths (0–5, 5–15, 15–30 cm); however, due to high correlations among the depths (Hageer et al 2017), we only included the top‐most layer for each soil variable.…”

“…For example, in tropical savannas, the high frequency (every one to three years) of low‐intensity fires means there is insufficient time for wildland‐fuel loads to accumulate to levels capable of producing high‐intensity fires (Murphy and Bowman , Archibald et al , Murphy et al ). In this system, fire behaviour is influenced more by fuel accumulation and structure than fire weather (Krawchuk and Moritz , Levi and Bestelmeyer ). In contrast, temperate eucalypt forests often are characterised by low‐frequency, high‐intensity wildfire (Murphy et al ).…”

Shoot flammability is decoupled from leaf flammability, but controlled by leaf functional traits

“…Flammability can influence the fitness, survival, reproduction and distribution of plants, as seen by the evolution of flammability strategies in fire‐prone environments (Bond & Midgley, ; Mutch, ; Pausas et al, ). Recently, there have been renewed efforts in plant flammability research to tackle fundamental topics such as the evolution of plant flammability (Archibald et al, ; Battersby, Wilmshurst, Curran, McGlone, & Perry, ; Pausas et al, ), and in an applied context to provide information useful for fire management (Krix & Murray, ; Wyse et al, ; Zylstra, ), building on past work in such areas (Bond & Midgley, ; Gill, ; Kerr, Schwilk, Bergman, & Feldman, ; Mutch, ). However, there is still considerable debate on how best to measure plant flammability and therefore, how to appropriately quantify this important plant trait (Schwilk, ; Varner, Kane, Kreye, & Engber, ).…”

Re‐evaluating pattern and process to understand resilience in transitional mixed conifer forests

“…The short fire intervals we found cast doubt on widespread assumptions that fuels accumulate over time and result in higher disturbance probability with increasing forest age, which appears to be at best overly simplistic (Zylstra ) or more likely not applicable in the red‐pine‐dominated stands we evaluated. Similarly, there may be a tendency to view frequent fire (every 10–50 yr) as the driving force in creating savanna, as opposed to forest structural conditions (Heinselman , Radeloff et al.…”