Wildfire in wet sclerophyll forests: the interplay between disturbances and fuel dynamics

There are multiple pathways for vegetation to change following disturbances. Understanding those post-disturbance pathways is critical for managing wildfire risk since vegetation is fuel in a wildfire context. Across forest systems, there is considerable debate about disturbance-related changes to fuels and flammability. This study investigated post-disturbance fuel trajectories following three disturbance typeshigh severity wildfire, low severity wildfire, and clear-fell logging. Fuels were measured in a chrono-sequence of 141 sites in Mountain Ash (Eucalyptus regnans)-dominated wet sclerophyll forest in southeastern Australia, a particularly contentious forest system. Wildfires are an important part of the lifecycle of these forests, but too frequent fire can threaten post-fire regeneration. Large wildfires (in 2009, 1983 and 1939) and ongoing public and scientific debate over clear-fell logging highlight the need to better understand post-disturbance trajectories for fuel and flammability in wet sclerophyll forests. We used empirical data to test 10, sometimes contradictory, hypotheses from the scientific literature regarding post-disturbance pathways for fuel following wildfire and logging. Only five hypotheses were supported with surface fine fuels, fuel hazard, species composition, and vertical structure driving overall differences in post-disturbance fuel trajectories. The implications for flammability remain uncertain because the independent and interactive effects of many fuel components on overall flammability remain unquantified. Importantly, we found there were always high quantities of fuel, irrespective of disturbance history, which demonstrates that fire occurrence is not fuel-limited in wet sclerophyll forests. Under conditions of abundant fuel, fuel moisture could become critical to fire occurrence. Therefore, forest management should prioritize efforts to quantify not only the importance of individual fuel components to flammability but also fuel moisture dynamics in wet sclerophyll forests. As the climate (and fuels) becomes drier under climate change, it will be a major challenge to manage fire regimes in these highly valued forests.