Year

2002

Degree Name

Master of Science (Honours)

Department

Department of Biological Sciences - Faculty of Science

Abstract

There is a lack of understanding of the ecology of many Australian plant species. In fire prone habitat, natural fire regimes have shaped the evolution, and subsequently the demography and life history traits, of the associated flora. Critical life history stages, like germination and recruitment, are often linked to fire in species that occur in fireprone habitats. Knowledge of plant demography in relation to fire is important, particularly for threatened species. Management decisions are based on understanding the effect of factors such as fire frequency and season of bum and ensuring that the fire regimes implemented do not have a negative impact on the vegetation community. The Epacridaceae are a large family of plants confined mainly to Australasia. Although common and widespread in fire-prone systems, epacrid ecology is poorly understood. Leucopogon is the largest genus within the Epacridaceae. The aims of this study were designed to improve the understanding of the demographic processes of Leucopogon in relation to fire. I addressed these aims by focussing on the threatened species L. exolasius. and some common congeners, L. setiger, L. esquamatus and L. ericoides, in the fire-prone vegetation of the Sydney region in south-eastern Australia. Specifically, the questions asked were: (i ) What is the fire response of established plants? (ii) Is there a delayed or seasonal component to seedling emergence? (iii) Are germination cues linked to the passage of fire? Fire response and seedling emergence patterns were compared between species. Data were collected after four fire events between August 1999 and September 2002. To determine fire response of the four study species, individuals were tagged and measured, then subsequently burned. Survivorship was monitored post-fire for up to 12 months. All four study species were fire sensitive (classified as mortality after 100% leaf scorch). However, some plants survived in areas that remained unburnt after the low intensity bums. The proportion of established plants that survived was therefore dependent on fire patchiness. Topography, such as rocky outcrops, contributes to patchy fuel conditions and represents a mechanism for adult plant survival. This finding supports some studies that suggest that rare species, particularly obligate seeders, are concentrated in parts of the landscape where fires are less frequent. The rare species, L. exolasius, occurs almost exclusively on rocky sandstone riparian hillsides where some individuals are likely to remain unburnt during low intensity burns. In areas like the Sydney region, where large wildfires are a common event, recruitment from the seed bank would still be essential for the long term persistence of a species. In the event of two fires occurring in quick succession, a dormant seed bank could represent a buffer to population decline. The role of fire on germination cues and seedling emergence was examined in three of the species (L. ericoides excluded) by monitoring the numbers of newly emerged Leucopogon seedlings over time. Permanent quadrats were established under mature plant canopies. After fire, quadrats were monitored approximately every three months, and the number of seedlings counted. Quadrats were also established in unburnt L. exolasius and L. esquamatus habitats. All three Leucopogon species displayed a flush of seedling emergence after fire. Time elapsed until the onset of emergence differed between fires but not between Leucopogon species. Seedling emergence was restricted, in all Leucopogon species and after all fires, to the autumn (primarily late autumn) and winter period. The same seasonal pattern was found in unburnt habitat, though at much lower seedling densities. Emergence of Leucopogon species was delayed when compared with other fire sensitive species that co-occurred in the habitat These results indicate that the magnitude of delay to the onset of emergence is dependent upon the timing/season of the fire event. Also, combinations of fire-related and seasonal factors are necessary to maximise germination. A residual seed bank is left after fire, with germination timing still linked to season, and some inter-fire recruitment may occur. Seasonal dormancy in Leucopogon is likely to have developed over evolutionary time scales, and although fire has provided a strong influence on germination cues, variable rainfall patterns in the Sydney region may have allowed the persistence of seasonal dormancy traits. Results from the study were combined with data collected on species distribution, historical decline and threats, to make an assessment of the threatened species, L. exolasius, using a modified version of the IUCN Red List Criteria. The conclusion reached was the recommendation that the threat status of the species should be upgraded from vulnerable to endangered. This research has several implications for the management of L. exolasius. Firstly, hazard reduction bums should primarily be conducted outside of the late autumn/winter period in L. exolasius habitat, to reduce the magnitude of delay of emergence after fire. Secondly, inter-fire intervals of greater than 10 years are recommended for the longterm persistence of L. exolasius populations. Primary juvenile periods are thought to be relatively long, and this amount of time is required for individuals to mature and replenish the seed bank. Finally, the threat status of the species on the Schedules of the NSW Threatened Species Conservation Act (1995) and the Commonwealth Environment Protection and Biodiversity Conservation Act (1999) should be changed from vulnerable to endangered.

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