How do drought and fire influence the patterns of resprouting in Australian deserts?
Rainfall is the key driver of woody cover and life-history attributes in arid grassy biomes where disturbance is mostly rare and of low intensity. However, relatively little is known about the causes of woody community assembly in arid systems that are subject to periodic intense fire disturbance. In the central Australian desert region, grassland and shrubland fire can occur following above average rainfall. Patterns of species regeneration response (resprouting vs. reseeding) are poorly documented in this region. We tested the effects of rainfall and fire on species' resprouting response across the latitudinal rainfall-fire gradient using constrained ordination of 385 sites and general linear models. A resprouting response was significantly greater in grassland habitat as well as at the high end of the rainfall-fire gradient. The frequency of epicormic stem resprouting also increased along the rainfall-fire gradient. We attribute this pattern to the combined effects of frequent fire and rapid gap closure on seedlings of slow-growing, fire-killed woody species in higher rainfall grasslands. In addition, we also demonstrated that rapidly maturing fire-recruiting species are similarly favoured by high fire disturbance. In arid grassy ecosystems, unlike in mesic savanna, flammable grassland supports a mix of resprouting and recruitment functional types, and habitat membership cannot be predicted by resprouting capacity. Regions, such as central Australia, that are characterised by grassland-shrubland mosaics of high and low fuel biomass, respectively, pose specific challenges to fire ecology research that are possibly best dealt with by focussing modelling at the habitat scale.
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 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.