Using herbarium specimens to determine the drivers of mast seeding in spinifex and hence the drivers of boom-bust growth in vertebrate populations of arid Australia

Spinifex (Triodia spp.) is a genus containing 64 species of long-lived perennial grasses endemic to Australia (Wright et al. 2014) and which dominate around 22% of the continent in arid and semi-arid regions (Griffin 1984; Lazarides 1997). Triodia germinates from the soil seed bank (Armstrong & Legge 2011) but the seed crops are highly episodic and synchronised in large crops or “masts” (Wright et al. 2014) that flood the local ecosystem and are thought to drive short-lived booms in vertebrate populations (Letnic & Dickman 2010). As a widespread and dominant genus, Triodia are also major contributors to the fixation of CO2 in the arid zone (Poulter et al. 2014) and therefore relevant to carbon accounting. Despite their central role in the ecology of Australia’s deserts, little is known about the seeding ecology of Triodia; most especially, how does the volume, distribution, and timing of rainfall influence mast seeding? The reasons for this knowledge gap are twofold. Firstly, the frequency of masting is episodic with long irregular intervals between seeding events making masting problematic to witness in the field without long-term study (Elliott et al. 2019). Secondly, Triodia are known to flower but their inflorescences frequently abort resulting in seed production that is highly variable (Wright et al. 2014). This has meant that flowering in Triodia, even when measured in the field, is not a good predictor of seed production (G. Wardle pers. com.)