Variation in fire response traits of plants in mountainous plant communities of south-eastern Australia

Abstract

In fire-prone ecosystems, plant species exhibit a range of traits which allow them to persist under certain fire regimes. Two critical traits are resprouting and regeneration from seed. Resprouters and seeders can coexist within plant communities, but their relative proportion varies. This research investigated variation in patterns of community composition, in terms of fire response traits, across a mountainous region of south-eastern Australia. The relative importance of fire regimes, habitat, vegetation cover and resource gradients in influencing these patterns was tested. Associations between leaf traits and fire response types were also explored to investigate whether traits related to fire persistence can be considered as part of a broader spectrum of plant ecological strategies, and assist in explaining landscape patterns. In January 2003 unplanned fires burned through the region, creating the opportunity to investigate the responses of locally occurring plants. An initial study of observed field data demonstrated that some species varied in their response between sites. Furthermore, observed responses often differed from those reported in a fire response trait database. As such, the decision was taken to use observed site-specific data on fire response traits where possible to analyse community composition across the region. Data were subsequently collated from five post-fire surveys conducted across 284 sites in the study area. Resprouting was a dominant response of species in the region. However, woody obligate seeders, although infrequent, were often structurally important. Within-species variation was identified, with variability in post-fire seed regeneration particularly evident in trees. The results unexpectedly identified 'dataset' as the factor most strongly associated with the observed patterns, raising important questions about the use of data collated from different sources. Obligate resprouters were favoured at sites burned with no short intervals between fires, whereas several woody obligate seeding types were in higher proportions at sites burned with one or two short intervals. This suggests that some degree of fire is required for obligate seeder persistence. However, the possibility that woody obligate seeders had already been eliminated from the region prior to this study, due to short inter-fire intervals, could not be discounted. Significant differences between habitats were identified, with woody obligate seeders found in high proportions on rock outcrops and in wet grasslands. However, trends in the proportions of fire response types across habitats could not be reconciled with trends in habitat characteristics such as canopy height and understorey cover. Understorey cover was negatively associated with seeders and facultative resprouters, suggesting an important influence of competition post-fire. Leaf trait comparisons showed that facultative resprouters differed from obligate seeders and obligate resprouters, indicating that this strategy requires an investment into rapid acquisition of resources and fast growth to compete. Differences in leaf traits in species with a canopy seed bank were also identified, raising some important considerations regarding approaches to classifying species by fire response traits. This research illustrates the value of considering the relative importance of fire in relation to other factors for developing a thorough understanding of the processes governing community composition in fire-prone ecosystems. Importantly, the approaches taken in this thesis also revealed a range of issues regarding the application of trait data, which are discussed in relation to trait-based ecological research and management. Show more