Long-term survival of trees retained for hollow-using fauna in partially harvested forest in Tasmania, Australia

Impacts of changing fire regimes on hollow-bearing trees in south-eastern Australia

“…In the southern part of our study area, 0.5% of all trees collapsed within 2-5 years after harvesting and a low-severity slash-burn; and in the same forest type after harvesting and a high-severity slash-burn, the rate of collapse among all trees over the same period was 1.5% (Gibbons et al 2000a). In Tasmania, Koch et al (2018) examined collapse among trees in clumps retained within harvested areas treated with no post-harvest burning or a low severity post-harvest slash-burn. Over 8 years, 11.7% of all trees and 1.5% of hollow-bearing trees collapsed on harvested sites, compared with 2.8% of all trees and 0.3% of hollow-bearing trees in unharvested sites (Koch et al 2018).…”

“…In Tasmania, Koch et al (2018) examined collapse among trees in clumps retained within harvested areas treated with no post-harvest burning or a low severity post-harvest slash-burn. Over 8 years, 11.7% of all trees and 1.5% of hollow-bearing trees collapsed on harvested sites, compared with 2.8% of all trees and 0.3% of hollow-bearing trees in unharvested sites (Koch et al 2018).…”

“…where S is the proportion of trees surviving after t years, annual rates of collapse among trees in unburnt forests were between 0.04 and 0.9% per annum; and in the first 5 years after fire, annual rates of collapse were between 0.1 and 5.7% per annum (excluding estimates for montane ash forests, which do not occur in the study area and are more likely to be killed by fire than most of the tree species in our study area). Rates or mortality and/or collapse of trees after fire in different mixed-species Eucalyptus forest have been variously reported to be highest in the smaller DBH classes (Bennett et al 2016;Prior et al 2016), highest in the largest DBH classes (Forestry Corporation of NSW 2016) or not vary with DBH (Gibbons et al 2000a;Koch et al 2018). Given this uncertainty, we applied the same annual rates of collapse to all stems in each run of the model, although an additional rate of mortality is applied to reflect the maximum standing life of older stems as described in the next section.…”

“…Once trees reach the end of their life-span, they may remain standing and provide suitable hollows as dead trees. Although dead trees appear to collapse at higher rates than living trees (Parnaby et al 2010;Koch et al 2018), there are no published estimates of the longevity of dead trees, other than an www.publish.csiro.au/wf International Journal of Wildland Fire 33 (2024) WF23094…”

“…Given we found that the number of hollow-bearing trees was sensitive to the rate at which trees grow, form hollows and collapse, there should be a focus on improving these data. For example, rates of collapse for trees were derived from three published studies (Gibbons et al 2000a;Bluff 2016;Koch et al 2018), and rates of collapse were applied uniformly across all DBH classes and to living and dead trees, which is simplistic given we know from studies in other Eucalyptus-dominated forests and woodlands that rates of mortality and/or collapse of trees after fire can vary with DBH (Bennett et al 2016) and whether trees are living or dead (Lindenmayer and Wood 2010). We also used DBH to predict the proportion of trees with hollows that were visible from the ground.…”