Response of Resprouting Shrubs to Repeated Fires in the Dry Sclerophyll Forest of Gilbraltar Range National Park
Fire regimes affect survival and reproduction of shrub species in fire-prone vegetation such as occurs in Gibraltar Range National Park. The influence of fire regimes on resprouting shrubs is known for a range of species in coastal regions of Australia but is poorly known in montane sclerophyll communities. The fire responses of three Proteaceae shrubs ('Banksia spinulosa', 'Hakea laevipes', 'Petrophile canescens') and a grasstree ('Xanthorrhoea johnsonii') were measured after the wildfire of 2002 to determine whether: 1) storage organ size was related to post-fire growth and flowering response, 2) fire frequency influences postfire mortality and if survival was related to the size of plant; 3) fire frequency influences the resprouting ability of plants, and 4) fire frequency affects pyrogenic flowering in the post-fire environment. We found the size of storage organs was positively related to post-fire sprouting in the three shrubs and to flowering in the grasstree. However, high fire frequency only affected the survival of Banksia spinulosa and decreased flowering in 'Xanthorrhoea johnsonii'. Survival in all species ranged between 83 and 99% and it appears that the intervals between fires (7-22 years) had been sufficient for most adult plants to regain the ability to resprout. The ability of juvenile plants to develop the ability to resprout needs to be tested on seedlings that established after recent fires.
Post-fire response of shrubs in the tablelands of eastern Australia: do existing models explain habitat differences?
Fire is an important ecological factor that influences the distribution and abundance of plant populations of shrub species in fire-prone habitats. Comprehensive information about the fire-response syndromes and post-fire recruitment of seedlings in tableland habitats of eastern Australia is poorly known. In particular, data on shrubs occurring in grassy habitats are lacking for temperate regions of Australia. The post-fire response and recruitment patterns of shrub taxa were recorded from research burns and wildfires on the New England Tablelands over 4 years in the following four habitats: grassy woodlands and open forests, shrubby open forests, wet heaths and rocky outcrops. The ratio of obligate seeder to resprouter species differed among habitats, with the highest ratio occurring on rocky outcrops (90 : 10) and the lowest in grassy forests (19 : 81). Post-fire recruitment of seedlings was also highest on rocky outcrops whereas seedlings were rarely observed in the wet heaths and grassy forests. The following six models that explain these patterns were reviewed: fire and grazing frequency, soil nutrients and texture, habitat openness and environmental variability. No one model could uniformly explain differences in fire response across all habitats but a combination of disturbance-frequency and regeneration-niche models may provide a mechanism for the patterns observed. Field and laboratory experiments are needed to examine allocation to persistence (resprouting) and reproduction in species with different fire-response syndromes. These experiments also need to examine both disturbance-frequency and regeneration-niche factors in manipulative experiments.
Fire response syndromes of shrubs in grassy woodlands in the New England Tableland Bioregion
In fire-prone grassy woodlands, fire response and time to reach reproductive maturity are two traits that can be used to provide an indication of the minimum interval between fires needed to maintain biodiversity. This study examined the effects of fire intensity and adult size on shrub mortality together with the primary and secondary juvenile periods of shrub species in the New England Tableland (NET) Bioregion. Most shrub species resprouted via basal lignotubers following fire, irrespective of fire intensity and shrub size. The primary juvenile period of most species was found to be greater than four years and the secondary juvenile period for most resprouting species was less than four years. These results suggest that a minimal interval between fires of eight years may be needed to maintain shrub species in grassy woodlands in the NET Bioregion, and that repeated fires at intervals of less than 8 years should be avoided. The time taken for shrubs in the grassy woodlands of the NET Bioregion to reach reproductive maturity appears to be longer than conspecifics in other Bioregions. Caution is needed when using data collected from outside a Bioregion to determine minimum fire frequency thresholds.