@article {bnh-7977, title = {Bioclimatic drivers of fire severity across the Australian geographical range of giant Eucalyptus forests}, journal = {Journal of Ecology}, year = {2021}, month = {04/2021}, abstract = {

The relationships between productivity, fire frequency and fire severity shape the distribution of plant communities globally. Dry forests are expected to burn frequently and wet forests to burn infrequently. However, the effect of productivity on intensity and severity of wildfire is less consistent and poorly understood. One productive ecosystem where this is especially true is the Australian tall wet Eucalyptus-dominated forest (TWEF), which spans wet areas across the continent. This study aims to characterise how climate shapes the likelihood of low- and high-severity wildfire across Australian TWEF.

We performed a continental-scale analysis of fuels in 48 permanent plots in early-mature stage TWEF across four climate regions in Australia. We estimated fuel loads and measured understorey microclimate. We then obtained historical fire-weather observations from nearby meteorological stations and used fuel moisture and fire behaviour equations to predict the historical frequency with which TWEF could burn and what fire severities were expected. We investigated how this varies across the different TWEF climate regions. Lastly, we validated our approach by remeasuring eight plots that burned unexpectedly post-measurement.

We found that surface fuels in cooler, moister regions were available to burn 1{\textendash}16\ days per year historically, with only low-severity, surface fire possible most of these days: high-severity fire was only possible under rare, extreme fire-weather conditions. However, in warmer, drier regions, fuels were available to burn 23{\textendash}35\ days annually, and high-severity fire was more likely than low-severity fire. Validation showed that we slightly overestimated flame heights, inflating high-severity risk estimates. If we used elevated fuel loads to predict flame heights, however, high-severity fire was more likely than low-severity fire everywhere. Lastly, the likelihood of high-severity fire increased with increasing temperature and worsening fire weather.

Synthesis. Fire activity in early-mature TWEF is limited by climatic constraints on fire weather and availability to burn, with high-severity fire more likely in warmer, drier regions than in cooler, wetter ones. This indicates a particularly worrisome vulnerability to climate change, given TWEF{\textquoteright}s diminished ability to recover from disturbance in a warmer world. The occurrence of both low- and high-severity fire means the fire regimes of TWEF are best described as mixed severity.

}, keywords = {biogeography, Climate change, ecological disturbance, fire ecology, fire severity, macroecology, mixed-severity fires, tall wet Eucalyptus forests}, doi = {https://doi.org/10.1111/1365-2745.13663}, url = {https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.13663}, author = {Furlaud, James M. and Lynda Prior and Grant Williamson and David Bowman} } @article {bnh-7344, title = {Variation in Eucalyptus delegatensis post-fire recovery strategies: The Tasmanian subspecies is a resprouter whereas the mainland Australian subspecies is an obligate seeder}, journal = {Forest Ecology and Management}, volume = {473}, year = {2020}, month = {10/2020}, abstract = {

Eucalyptus delegatensis\ is native to the Australian Alps (subsp.\ delegatensis) and montane Tasmania (subsp.\ tasmaniensis).\ Post-fire regeneration mechanisms of the obligate-seeder subspecies on the Australian mainland are well-known, but less is known about the resprouter Tasmanian subspecies. In January 2016, large tracts of\ Eucalyptus delegatensis\ forests in central Tasmania, logged at different intensities, were burnt by low- and high-severity fire. We used statistical modelling to understand how tree survival, vegetative regeneration and seedling recruitment differed according to understorey type, fire severity, logging intensity and tree size (DBH). Fire severity, defined as unburnt, low-severity (fire scarring on the stem and/or lower canopy burnt) and high-severity (full canopy burnt), affected tree survival: 84\% of trees were alive in unburnt transects, compared with 43\% in low-severity transects and 36\% in high-severity transects. Epicormic resprouting was the dominant mode of vegetative recovery, with\ \<\ 1\% of total trees recovering solely by basal resprouting. Fire severity significantly affected epicormic resprouting, with 70\% of live stems resprouting post-fire in low-severity transects and 99\% in high-severity transects, compared with 4\% in unburnt transects. Tree survival was strongly influenced by tree size: in high-severity transects, 24\% of trees with DBH\ \<\ 20\ cm were alive, compared with 88\% of trees with DBH\ >=\ 20\ cm. These differences in survival were primarily because large trees were more likely to resprout epicormically, with epicormic shoots present on 24\% of live trees with DBH\ \<\ 20\ cm, compared with 79\% of live trees with DBH\ >=\ 80\ cm. The strong effect of tree size renders clear-felled forests especially vulnerable to fire during the several decades when all the regenerating trees are small (DBH\ \<\ 20\ cm). Seedling recruitment was uncommon, independent of understorey type and logging intensity, but with higher occurrence on high-severity (54\%) than low-severity (19\%) or unburnt (15\%) transects. When present, seedling densities were typically low: median\ =\ 400 and maximum\ =\ 4{\textperiodcentered}104\ seedlings ha-1. This study highlights that mature forests of\ Eucalyptus delegatensis\ in Tasmania are more resilient (able to return to pre-disturbance conditions) to single high-severity fires than their mainland counterparts, because they can recover more quickly through epicormic resprouting. However, clear-felling reduces this resilience for several decades because it decreases median tree size and, hence, leads to higher post-fire mortality. It is difficult to predict how the Tasmanian subspecies will respond to an increased frequency of high-severity fires associated with a projected warmer and drier climate.

}, keywords = {Clear-felling, Epicormic resprouting, Eucalyptus delegatensis, fire severity, Seedlings, Tasmania, Tree size, Tree survival, Understorey type}, doi = {https://doi.org/10.1016/j.foreco.2020.118292}, url = {https://www.sciencedirect.com/science/article/abs/pii/S0378112720310616}, author = {Dario Rodriguez-Cubillo and Lynda Prior and David Bowman} } @article {bnh-5426, title = {Relicts at Risk: Impacts of the 2016 Tasmanian Fires on Pencil Pine (Athrotaxis Cupressoides)}, number = {459}, year = {2019}, month = {03/2019}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

The main goal of this study is to obtain empirical measurements of fuel loads within the first year after a fire to complement the measurements of fuel loads taken directly before the fires.\  This will not only allow us to precisely quantify the fuel loads consumed by these relatively low-severity fires, but it will also give us a baseline measurement of fuel loads.\  We can use this baseline to anchor measurements of fuel accumulation in mature wet eucalypt forests that are part of related TERN and BNHCRC studies attempting to measure both the effects of climate and stand age on fuel accumulation in wet forests.\ 

}, keywords = {fire impacts, fire management, post-fire recover}, author = {Aimee Bliss and Lynda Prior and David Bowman} }