Impact of intense disturbance on the structure and composition of wet-eucalypt forests: A case study from the Tasmanian 2016 wildfires

Abstract

Fire is a key process in eucalypt communities, exerting a strong influence on the composition, structure and functioning of forests. Much of the research on the fire response of temperate, wet-sclerophyll trees in Australia comes from Victoria, where the dominant eucalypt is Eucalyptus regnans. In contrast, central and northern Tasmanian forests, dominated by Eucalyptus delegatensis, are relatively understudied. There is a need to determine whether Tasmanian wet-sclerophyll forests, though the same forest type in name, are functionally different in floristics and response to fire. Here we document the forest community response to a natural wildfire event in Tasmania—using opportunistic before/after control/impact (BACI) data from pre-existing monitoring plots. Uniting pre- and post-fire floristic data, we quantified mortality and regeneration of eucalypt, acacia and other dominant tree species, and tree ferns, Dicksonia antarctica, in response to wildfire. We also evaluated the density of eucalypt and acacia seedling establishment between burnt and unburnt forests, and quantified faunal responses to fire. Despite moderate-to-high intensity burning in patches across the plot, mortality of eucalypts, acacias and tree ferns due to fire were low. By contrast, fire-sensitive rainforest species showed low survival, though were able to persist in unburnt refugia. Eucalypt and acacia seedling regeneration was high in the burnt plot, suggesting that E. delegatensis forests regenerate without stand-replacing fire events. This contrasts to Victorian E. regnans forests, whose persistence is dependent on high-severity stand-replacing events. We also found some group-specific avifaunal and invertebrate responses to the fire event, which are broadly reflective of responses documented in other Victorian-based studies. Our results have implications for Tasmanian wet-forest silvicultural practices, which are based on the principle of stand-replacement after fire. The broader relevance of this work to forest ecology is in demonstrating the serendipitous opportunities that can arise with baseline monitoring plots.

Measuring a Fire. The Story of the January 2019 Fire Told from Measurements at the Warra Supersite, Tasmania

“…Accordingly, we expected to see similarities between the Riveaux Road and Lake MacKenzie fires in their impact in comparable areas of tall eucalypt forests. High survivorship of the overstorey eucalypts and the treeferns (D. antarctica) recorded at the Warra Supersite were also recorded at the Lake MacKenzie AusPlot Forests plot [41]. In contrast to [41], however, where most understorey trees survived, the Riveaux Road fire resulted in the death (from crown scorch) of the majority of the understorey trees.…”

“…High survivorship of the overstorey eucalypts and the treeferns (D. antarctica) recorded at the Warra Supersite were also recorded at the Lake MacKenzie AusPlot Forests plot [41]. In contrast to [41], however, where most understorey trees survived, the Riveaux Road fire resulted in the death (from crown scorch) of the majority of the understorey trees. As the weather conditions were similar when the fires burnt through the forest plots [34], the contrasting effects on the understorey trees may have been due to differences in fuels-Warra Supersite had higher fine and coarse fuel loads and higher density of manferns than Lake MacKenzie [34] and thus may have supported a higher intensity of ground fire.…”

Stand boundary effects on obligate seeding Eucalyptus delegatensis regeneration and fuel dynamics following high and low severity fire: Implications for species resilience to recurrent fire

“…While the Tasmanian variant E. delegatensis subsp. tasmaniensis has been observed to regenerate in the absence of stand-replacing wildfire (Lunn et al 2018), E. delegatensis subsp. delegatensis populations in Victoria have been suggested to require stand-replacing fire to establish new age cohorts (O'Dowd & Gill 1984;Prior et al 2016).…”