Fire regimes in arid hummock grasslands and Acacia shrublands

The flammability of arid Triodia hummock grasslands and Acacia habitats (shrublands and woodlands) was highlighted when wildfires swept across central Australia in the summers of 2001 and 2002 (Allan 2009) (Figure 9.1). These conflagrations constituted the most extensive ‘fire event’ in inland Australia since the mid-1970s, burning more than 500 000 km2 in the southern Northern Territory alone. Such fires go largely unnoticed by the mostly urban Australian population and concern for potential ‘environmental disaster’ has not resonated with the general public. Since the last synthesis of fire in these landscapes (see Allan and Southgate 2002; Hodgkinson 2002) a steady flow of new research has focused on fire regimes and their impacts on species and habitat structure. Uncertainty still remains about how to manage fire regimes for biodiversity benefits, but we recommend a trait-based framework as a way forward. This approach differs from the overly simplistic dichotomisation of arid biota as ‘fire tolerant’ or ‘fire sensitive’ and moves towards the circumscription of demographic tolerance thresholds for focal species groups, with explicit emphasis on the interactions of climate and fire.Catherine EM Nano, Peter J Clarke and Chris R Pave

A synthesis of postfire recovery traits of woody plants in Australian ecosystems

Postfire resprouting and recruitment from seed are key plant life-history traits that influence population dynamics, community composition and ecosystem function. Species can have one or both of these mechanisms. They confer resilience, which may determine community composition through differential species persistence after fire. To predict ecosystem level responses to changes in climate and fire conditions, we examined the proportions of these plant fire-adaptive traits among woody growth forms of 2880 taxa, in eight fire-prone ecosystems comprising ~. 87% of Australia's land area. Shrubs comprised 64% of the taxa. More tree (>. 84%) than shrub (~. 50%) taxa resprouted. Basal, epicormic and apical resprouting occurred in 71%, 22% and 3% of the taxa, respectively. Most rainforest taxa (91%) were basal resprouters. Many trees (59%) in frequently-burnt eucalypt forest and savanna resprouted epicormically. Although crown fire killed many mallee (62%) and heathland (48%) taxa, fire-cued seeding was common in these systems. Postfire seeding was uncommon in rainforest and in arid Acacia communities that burnt infrequently at low intensity. Resprouting was positively associated with ecosystem productivity, but resprouting type (e.g. basal or epicormic) was associated with local scale fire activity, especially fire frequency. Although rainforest trees can resprout they cannot recruit after intense fires and may decline under future fires. Semi-arid Acacia communities would be susceptible to increasing fire frequencies because they contain few postfire seeders. Ecosystems dominated by obligate seeders (mallee, heath) are also susceptible because predicted shorter inter-fire intervals will prevent seed bank accumulation. Savanna may be resilient to future fires because of the adaptive advantage of epicormic resprouting among the eucalypts. The substantial non-resprouting shrub component of shrublands may decline, but resilient Eucalyptus spp. will continue to dominate under future fire regimes. These patterns of resprouting and postfire seeding provide new insights to ecosystem assembly, resilience and vulnerability to changing fire regimes on this fire-prone continent

Appraising widespread resprouting but variable levels of postfire seeding in Australian ecosystems: The effect of phylogeny, fire regime and productivity

Postfire resprouting (R+) and recruitment from seed (S+) are common resilience traits in Australian ecosystems. We classified 2696 woody Australian taxa as R+ or not (R−) and as S+ or not (S−). The proportions of these traits in Australian ecosystems were examined in relation to fire regimes and other ecological correlates, and by trait mapping on a phylogeny scaled to time. Resprouting mapped as an ancestral trait. Postfire reseeding recruitment, while ancient, is more taxonomically restricted and has evolved independently several times. Nevertheless, both R+ and S+ are common in most clades, but negatively correlated at the ecosystem level indicating an evolutionary trade-off related to differences in the severity of fire regimes, determined in part by ecosystem productivity. Thus, R+ was associated with persistence in ecosystems characterised by higher productivity and relatively frequent surface fires of moderate to low severity (fire-productivity hypothesis). S+, the fire-stimulated recruitment by seed, occurred in ecosystems characterised by infrequent but intense crown-fire and topkill, reducing competition between postfire survivors and recruits (fire-resource-competition hypothesis). Consistently large proportions of R+ or S+ imply fire has been a pervasive evolutionary selection pressure resulting in highly fire-adapted and fire-resilient flora in most Australian ecosystems