Year

2021

Degree Name

Bachelor of Conservation Biology (Honours)

Department

School of Earth, Atmospheric and Life Sciences

Advisor(s)

Katarina Mikac

Abstract

Wildfires are prevalent across Australian landscapes and their effects on plants are highly variable. Climate change has already caused an extensive fire season in 2019-20 in eastern Australia and frequency and intensity of fires is predicted to further increase into the future. These dynamic changes in the fire regime places plant species, even those with fire-adapted traits, at risk of population decline or extinction. A fundamental aspect of fire-plant relationships is understanding the plant-responses and processes that cause change when related to fire. This hinges on the species, size and age specifics of individual plants. Plants can be broadly categorised as resprouters or seeders. Resprouters are able to survive fire through resprouting new shoots, while seeder species are typically more sensitive to fire and persist through recruitment. However, time between fire events must be sufficient to allow these species to reach reproductive maturity. Thus, it is critical to highlight that plants are not adapted to a single fire, but the fire regime itself. The fire regime is made up of a combination of factors such as the season of occurrence, intensity and length between fire events (fire frequency). The recent fire season provides researchers with a unique opportunity to investigate changing fire regimes impacts on vegetation and provide baseline data for future comparison. Therefore, this study aimed to assess the impact of a large mixed-severity wildfire in Monga National Park and evaluate vegetation recovery across different fire severities (low, moderate, and extreme). The overall objectives of this thesis were to: 1) classify the floristic composition of Monga National Park after the most recent fire event; 2) assess the effect of previous fires and fire severity on the current composition of vegetation; and 3) evaluate the recovery rates of fire resilient forests dominated by eucalypts. Standard 20 x 20 m plot sizes were used to obtain information on plant foliar cover and abundance. 50 x 20 m plot sizes were used to obtain detailed measurements of eucalypt tree epicormic growth rates and sizes. This was achieved by firstly assessing the effect of fire history and fire severity on the current composition of Monga National park and secondly evaluating the fire resilience of the dominant eucalypt species through recruitment and mortality rates. The findings of the study indicate strong effects of fire history on the composition of plants, regardless of fire severity. Sites with past fires were dominated by resprouter species, while seeder species were more abundant in sites with no previous fire. This may be explained by the inter-fire interval being long enough to allow seeder species to reach sexual maturity. The composition of Monga National Park 10 months post fire showed characteristic growth of post fire environments with an initial rise in resprouter species. The results overall indicate a good levels of recovery 10 months post fire and show that the effects of previous fire significantly influenced community composition. Strong effects of eucalypt resilience was also observed through high rates of seedling recruitment. Probability of stem damage and mortality rates revealed a strong size class effect of eucalypts ability to withstand fire. This is consistent with many other studies and highlights their resilience to high severity wildfires. However, research suggests that this resilience will be reduced following subsequent fires. Further, trees need to reach a sufficient size to be able to withstand fire. Thus, the impact of this fire may not be evident until subsequent fire and the degree of impact will depend upon the timing and severity of the next fire event.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.