Does rapid utilization of elevated nutrient availability allow eucalypts to dominate in the tropical savannas of Australia?

Abstract

Northern Australia's savannas are among the most fire‐prone biomes on Earth and are dominated by eucalypts (Eucalyptus and Corymbia spp.). It is not clear what processes allow this group to dominate under such extreme fire frequencies and whether a superior ability to compete for nutrients and water might play a role. There is evidence that eucalypts are adapted to frequent fires; juvenile eucalypts escape the fire trap by growing rapidly in height between fires. However, non‐eucalypts are less able to escape the fire trap and tend to have stand structures strongly skewed toward suppressed juveniles. The mechanisms that drive these contrasting fire responses are not well understood. Here, we describe the results of a controlled glasshouse seedling experiment that evaluated the relative importance of nutrient and water availability in determining height growth and biomass growth of two eucalypt and one noneucalypt tree species, common in northern Australian savannas. We demonstrate that growth of eucalypt seedlings is particularly responsive to nutrient addition. Eucalypt seedlings are able to rapidly utilize soil nutrients and accumulate biomass at a much greater rate than noneucalypt seedlings. We suggest that a seasonal spike in nutrient availability creates a nutrient‐rich microsite that allows eucalypt seedlings to rapidly gain height and biomass, increasing their likelihood of establishing successfully and reaching a fire‐resistant size. Our results extend our understanding of how eucalypts dominate northern Australian savannas under extremely high fire frequencies.

A Hollow Argument: Understory Vegetation and Disturbance Determine Abundance of Hollow-Dependent Mammals in an Australian Tropical Savanna

“…The impacts of which are also likely exacerbated by high feral herbivore densities (Legge et al, 2019). There needs to be a greater exploration of how frequent fires, even those of low intensity, influence vegetation structure and diversity, especially in relation to the shrub and grass layers, which provide critical shelter from predators and also provide food resources (e.g., fruits, flowers, and seeds; Bowman, 1988;Fensham, 1990;Paramjyothi et al, 2020). In the relatively intact savannas of northern Australia, such as Melville Island, management should aim to conserve hollow-bearing trees while retaining dense and complex under-and mid-story vegetation, which appears to be essential for the conservation of hollow-dependent arboreal mammal species.…”

Taxonomic revision of Australian <i>Erythrophleum</i> (Fabaceae: Caesalpinioideae) including description of two new species

“…Germination is reasonably straightforward for Erythrophleum species because the seeds behave like most legumes (Missanjo et al 2017). Stem survival following fire is low (often <10%), although survival of lignotubers is high (88%; Williams et al 1999b) because greater resource allocation is made to root mass relative to co-occurring eucalypts (Paramjyothi et al 2020). Interestingly, both smaller (DBH < 20 cm) and larger (DBH > 30 cm) trees are most likely to die following fire, with mid-aged trees being most resilient (Williams et al 1999b).…”

“…Interestingly, both smaller (DBH < 20 cm) and larger (DBH > 30 cm) trees are most likely to die following fire, with mid-aged trees being most resilient (Williams et al 1999b). This is directly related to bark thickness (Lawes et al 2011), so they may be useful indicators of recent fire history (Paramjyothi et al 2020). Whitau et al (2018) provided evidence for the fluctuation in abundance of Erythrophleum related to long-term fire regimes in the northern Kimberley on the basis of campfire deposits spanning a 45 000-year occupation sequence.…”