Seedbank dynamics after masting in mulga (Acacia aptaneura): Implications for post-fire regeneration

Abstract

Members of the arid Australian mulga (Acacia aneura) complex are fire-sensitive shrubs that produce mast seed crops after exceptionally high rainfall years. Such years also drive widespread wildfires in inland Australia, as high rainfall causes grassy fuels to accumulate, thereby enabling fuel contiguity to occur. Despite seedling regeneration playing an important role in mulga post-fire recovery, a dearth of information exists on the dynamics of its seedbanks. Here we examine the temporal and spatial dynamics of mulga seedbanks after a region-wide masting event at Laycock's Sandplain, central Australia. Masting had a profound effect on seedbanks, producing massive but short-lived pulses of seed in upper soil layers. After seed fall, seedbanks declined rapidly, and within 18 months had been reduced by predator depredations to low pre-mast levels. Our results suggest that mulga masting should enhance resilience to burning by providing transient seed pulses during periods of high flammability (i.e. after heavy rainfalls). The results also suggest that burn intensity will influence post-fire regeneration, by interacting with seed germination biology and post-mast seedbank dynamics. In our discussion, we examine possible evolutionary drivers behind mulga seeding periodicity, and hypothesize that rain-driven masting in mulga is a fire-related form of environmentally predictive masting.