Reproductive biology, post-fire succession dynamics and population viability analysis of the critically endangered Western Australian shrub Calytrix breviseta subsp. breviseta (Myrtaceae)

Abstract

Calytrix breviseta Lindl. subsp. breviseta is a critically endangered, obligate-seeder shrub within fire-prone kwongan of south-west Western Australia. Little is known about the species’ reproductive biology and how threatening processes, particularly altered fire regimes and exotic species invasion, will impact the long-term viability of the species. This study aims to elucidate the species’ reproductive biology and patterns of seedling recruitment during succession after fire. The effects of changes to the fire return interval and exotic species invasion on the long-term viability of the species is also described. The species exhibits abundant recruitment following fire and the application of a smoke treatment significantly improves germination, similar to many other Western Australian shrubs. However, significant inter-fire recruitment was observed up to 10 years following fire, leading to the presence of multi-aged subpopulations, although seedling recruitment was negligible >20 years after fire. The juvenile period is short at 3–4 years to first flowering. Population viability analysis (PVA) predicted that the optimal fire return interval to maintain C. breviseta subsp. breviseta was dependent on the carrying capacity (K) of the community and the number of individuals present. Carrying capacity will be related to site quality and competition from invasive species. PVA showed that if K remains high, then the optimal fire return interval is ~15–20 years, but under lower carrying capacity, (i.e. weed competition) fires decrease the likelihood of population survival.

Fine-scale temporal turnover of jarrah forest understory vegetation assemblages is independent of fire regime

“…In the absence of long-term field data, some scientists have modelled outcomes of various fire regimes on the persistence of plant populations, based on vital attributes and life histories (Bradstock et al 1997;Bradstock et al 1998;Enright et al 1998;Groeneveld et al 2008;Nield et al 2009). While modelling can provide valuable insights, the models necessarily make assumptions about fire behavior and plant responses (Ooi et al 2006;Burrows and Middleton 2016).…”

Germination Ecology and Seed Dispersal of a Critically Endangered Plant: A Case Study of Pomaderris vacciniifolia (Round-Leaf Pomaderris)

“…Mass germination follows heat shock, which seeds would experience during a fire, leading to greater population sizes, replenishment of the soil seed bank and greater resilience to impacts such as grazing. This recruitment strategy has been recognised for other post-fire recruiters [ 52 , 53 ]. Maturation of recruits germinating in the absence of fire may be affected by native and exotic herbivores, or competition from native and exotic plants; these factors may threaten populations persisting where fire has been absent, although this needs further attention.…”

Recovery of threatened plant species and their habitats in the biodiversity hotspot of the Southwest Australian Floristic Region

“…Recent research in shrublands, mallee-heaths and kwongan provide some support for this proposition with significant correlations between senescence and structural decline with time since fire (Gosper et al., 2012, Gosper et al., 2013). Furthermore, numerous studies have demonstrated that some threatened species are most abundant in the first decade after fire and gradually retreat from the plant community to persist as seeds in the soil until the passage of another fire (Yates and Broadhurst, 2002, Yates et al., 2003, Yates and Ladd, 2005; Nield et al., 2009).…”