Determining the effects of drought and fire on tree regeneration in the Northern Jarrah Forest

Travis Rasmussen

Forest ecosystems in fire-prone regions globally have a high level of resilience. However, as the climate changes, the level of frequency and severity of disturbances is expected to increase. This may influence the likelihood of multiple disturbance events occurring and impeding the ability of a forest to regenerate. Tree regeneration has been previously examined, although evidence-based data assessing tree regeneration following multiple disturbances are rare, limiting the capability to predict forests recovery and persistence once a disturbance occurs. This study expanded upon two earlier studies to quantify the regeneration of overstorey and midstorey species ten years after drought-induced canopy die-off and three years following a mixed-severity wildfire that burnt under extreme fire weather. The effects of prescribed burning were also examined by including prescribed burning activity of the same time since fire as the wildfire event. This study investigated three main questions. (1) How is tree regeneration affected by drought and fire? (2) How do growth stages of tree regeneration vary by drought and fire severity? Lastly, (3) How does tree regeneration respond to fire over time? The study found that firstly, under a drought and fire interaction, regeneration density significantly increased, secondly, lignotuberous seedlings and seedling coppice were the most dominant growth stage identified with significantly higher densities following moderate severity fire. Thirdly, moderate severity fire displayed higher densities over the three years since wildfire, however, prescribed burning and high severity fire showed less regeneration abundance by comparison. This study highlights the need for future research in prescribed burning techniques and an increase in forest management practices due to the increased risk of higher fire severities. Furthermore, it illustrates the necessity of understanding the long-term trajectory of tree regeneration following multiple disturbance events.

Determining the effects of drought and fire on tree regeneration in the Northern Jarrah Forest

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