Comparative effects of logging and wildfire on carbon and fire dynamics in resprouting and non-resprouting eucalypt forests

The tall (>30 m) eucalypt forests of south-eastern Australia are valued for their carbon storage and sequestration. However, they may also act as a carbon source given that they are prone to large wildfires and subject to commercial logging. Logging may reduce carbon stocks, but the relative losses compared to wildfire have not been quantified in many types of these forests. There is also growing evidence that logging may make carbon stocks in affected forests less resistant to fire and increase the risk of wildfire. These dynamics may also vary between eucalypt forest types. Carbon and fire dynamics in forests dominated by eucalypt species that cannot resprout new foliage after fire may be more sensitive to antecedent disturbance than the more widespread resprouting eucalypt forests. Non-resprouting eucalypt forests are often subject to stand replacing wildfires, but such a response is inherently absent in resprouting eucalypt forests. Non-resprouting eucalypt forests are also subject to clearfell logging, while logging practices in resprouting eucalypt forests are often less intense. Hence, a thorough comparative assessment of the effects of logging, wildfire and carbon dynamics across these broad forest types is needed to inform ongoing management of tall eucalypt forests. In this thesis, I compare how logging and wildfire affect forest carbon stocks, carbon stability (the capacity for carbon stocks to persist through, and recover after likely disturbances) and the risk of fire. The effects of logging and wildfire are compared between resprouting and non-resprouting eucalypt forests. I measured above ground carbon stocks and fuel characteristics (using a terrestrial laser scanner) along approximately 80-year chronosequences of logging and wildfire. Most sites in the resprouting forest study area were subsequently burnt by a mixed severity fire during the 2019-2020 fire season, enabling me to measure the change in carbon stock associated with wildfire and how it was affected by antecedent disturbance and fire severity. I also assessed the effects of variations in fuel characteristics on the severity of the 2019-2020 wildfires. To determine the effects of logging and wildfire on fire weather conditions, I measured fire weather conditions below the canopy across approximately 70-year chronosequences of logging and wildfire in the resprouting study area.