School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemImpacts of short-interval wildfires on tree demography and forest structure in temperate Australia( 2019)Fire is a powerful agent of disturbance in terrestrial ecosystems, and it shapes vegetation composition and patterns globally. This is particularly true in south-eastern Australia where forests are dominated by species of the genus Eucalyptus, many of which have the capacity to recover from high-severity fire by resprouting from epicormic or basal buds. Climate change is predicted to yield more severe fire weather and lengthen fire seasons in temperate Australia, leading to increased wildfire frequency in these forests. While increased fire frequency – resulting in wildfire intervals of under a decade – are known to negatively affect fire-sensitive eucalypts (obligate seeders which have a juvenile period of 10 – 15 years) less is known about how such changes impact fire-tolerant, resprouting eucalypts. This Thesis examines the impacts of recent wildfires in south-eastern Australia, where a series of large wildfires burned over four million hectares of land, leading to the burning of different types of fire-tolerant eucalypt forests (basal resprouters, epicormic resprouters) by high-severity wildfires once, twice, and sometimes three times between 2003 and 2013. In the context of this massive natural experiment in the landscape, my overarching aim was to quantify the impacts of short-interval wildfire on eucalypt tree demography and regeneration, to improve understanding of potential fire-related changes to the structure and resilience of fire-tolerant forests. Short-interval high-severity wildfires significantly increased whole-tree mortality and decreased the abundance of both resprouts and seedlings in basally resprouting eucalypt forests. In these sub-alpine forests, dominated by snow gum (E. pauciflora), more frequent wildfire (two and particularly three short-interval fires) also increased the cover of grasses at the expense of shrubs. In mixed-species eucalypt forests, which occupy extensive tracts of low elevation landscapes in south-eastern Australia, resprouting occurs from both basal and epicormic buds. In these forests, the dynamics of both topkill (i.e. stem, but not whole-tree, mortality) and whole-tree mortality have important ramifications for forest structure. After a single high-severity wildfire, small-diameter stems were typically topkilled; after two short-interval wildfires, the diameter of stems topkilled increased. Additionally, the overall likelihood of either basal or epicormic resprouting decreased after two short-interval wildfires. This decline in resprouting capacity indicated that the size class most vulnerable to ‘resprout failure’ after multiple wildfires was intermediate sized stems (in the vicinity of 20 - 30 cm DBHUB), rather than smaller or larger stems. Seedling regeneration also decreased in these forest types after short-interval wildfires, suggesting that, as for fire-sensitive forests, immaturity risk may be a relevant factor for fire-tolerant forests. Short-interval wildfires reduced the total and aboveground carbon stocks of mixed-species forests, while also increasing the proportion of carbon mass in the dead pool, indicating that resprouter forests might not be perpetually secure carbon stocks under emerging fire regimes. My Thesis highlights that fire-tolerant forests may not be as invulnerable to changes in fire frequency as widely assumed, and that management interventions will likely be required to counteract increasing tree mortality and decreasing tree regeneration if predictions of more frequent and severe wildfires in temperate Australia are realised.
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ItemLong-term effects of frequent burning on fungal communities and the role of fungi in fire-prone forests( 2007)Bushfire is an integral part of the Australian environment. Animals and plants show adaptations to and dependence on fire and prescribed burning is an important management tool in eucalypt forest ecosystems. Responses of flora and fauna to fire regimes have been extensively examined in Australian forests, however one aspect of the biota abundant within all forest types that has received little consideration is fungi. Despite their undoubted ecological significance, little is known regarding the taxonomy, biology and ecology of fungi, let alone the impact of fire upon fungal communities. Knowledge of the responses of fungi to fire is of intrinsic interest and is essential for effective forest management. Fungi have significant roles in transporting, storing, releasing and recycling nutrients. Consequently, disturbances such as fire that impact upon fungi and their ability to perform these ecosystem processes may be of importance to forest structure, health, productivity and sustainability. The aim of this study was to investigate the effects of repeated low-intensity prescribed burning on various aspects of the fungal community in two Australian eucalypt forests. Such research was deemed necessary to fill a significant gap in current knowledge regarding fungal ecology and to provide forest managers with recommendations for use of prescribed burning to enhance fungal biodiversity. Current knowledge of fungal community structure, function and contributions of fungi to forest ecosystem processes was explored, with a range of traditional and new techniques used to assess quantitative, qualitative and functional aspects of above- and belowground fungal communities. The diverse methods used enabled comprehensive assessment of numerous community dynamics and their application throughout the study was evaluated. Cost analysis showed that assessment of diversity and functional diversity of aboveground sporocarps was far more expensive than analysis of belowground fungal diversity. It was therefore suggested that future research should consider the relevance of aboveground sporocarps in the overall fungal community and that more attention should perhaps be given to diverse, abundant and functionally significant soil fungi. Assessment of fungal communities was undertaken in relation to experimental burning treatments within eucalypt forests and the influence of fire on vegetation, fuel and soil characteristics. Little overall difference was observed in richness and diversity of sporocarp morphotypes and functional groups among treatments in the Wombat Forest. No significant differences were observed among soil fungal biomass as indicated by ergosterol concentration in either Bulls Ground or Wombat Forest soils. In addition, molecular data showed that richness and diversity of soil fungi among treatments were similar and that no specific fungal community was associated with soils of any particular treatment in the Wombat Forest. Such findings suggest that low-intensity prescribed burning has little long-term effect on these aspects of the fungal communities investigated in Wombat Forest and Bulls Ground study areas. However, given the critical roles of fungi within ecosystem processes it could be assumed that even minor changes in community dynamics may be of functional significance within forests. It was therefore considered too presumptuous for the current study to offer management recommendations based on these findings and was suggested that further understanding of relationships between fungal diversity, functional groups and ecosystem function is necessary for appropriate management decisions and development of sustainable forests.