Detecting the effects of logging and wildfire on forest fuel structure using terrestrial laser scanning (TLS)

Recent logging and wildfire have been linked to increased fire severity in forests around the world. The mechanisms driving this association are uncertain but increased vertical fuel connectivity in recently disturbed forests is often suggested as a possible cause. These suggestions often assume that the forest canopy is lost after logging and wildfire. However, the resprouting Eucalypt forests of south-eastern Australia may differ as the canopy can rapidly recover after wildfire, and some of the canopy is retained after logging to reflect this ecology. By contrast, stand replacement is common after wildfire in non-resprouting Eucalypt forests, which are also typically subject to clear-fell logging. Vertical fuel connectivity is not routinely measured in Australian forests due to the difficulty in reliably measuring tall elements of the fire fuel array. Here, we quantify the connectivity of understorey and canopy fuel using terrestrial laser scanning, to determine if it is affected by logging and wildfire history. We compare these findings between forests dominated by resprouting and non-resprouting Eucalypt species. The connectivity between the understorey vegetation and the canopy decreased with time since logging in both forest types, but only increased with time since wildfire in non-resprouting forests. These changes were largely driven by the increasing canopy base height. These findings support suggestions that logging and wildfire increase fire severity by increasing the vertical connectivity of fire fuel. However, this is only applicable where the canopy is replaced after disturbance, which does not happen after fire in resprouting Eucalypt forests. This research provides new insights into species dependent disturbance and fuel dynamics that are applicable to fire prone forests around the world.