Abundant post-fire recruitment and rapid seedling maturity emphasise regular burning is beneficial for conserving the Vulnerable Purple-flowered Wattle (Acacia purpureopetala)

Abstract

Purple-flowered Wattle (Acacia purpureopetala) has a Vulnerable status under the Queensland Nature Conservation Act (1992) and is listed as Critically Endangered under the Environment Protection and Biodiversity Conservation Act (1999). It grows in eucalypt woodlands of North Queensland. Its post-fire response was examined to better understand its ecology and management requirements. Before and after fire surveys found Purple-flowered Wattle is a fire-killed ‘obligate seeder’ with abundant fire-promoted germination, but limited recruitment in the absence of fire, highlighting the importance of regular burning for generating new plants. Nearly half of Purple-flowered Wattle seedlings began producing seed in their second year, indicating a population tolerant of frequent burning. Combined, the abundant fire-promoted recruitment and rapidly maturing seedlings suggest regular patchy fires that allow some mature plants to survive unburnt while promoting recruitment in burnt areas would benefit the population. A laboratory trial found percentage germination after 3 weeks was significantly higher for seeds treated by soaking in hot water for 5 minutes (31% germination), compared with those soaked in ambient temperature water (4% germination). However, by 5 weeks, germination differences between seed treatment were not statistically significant. The apparent discrepancy where unheated seeds eventually germinated in a laboratory setting, yet in situ germination was almost completely restricted to the post-fire environment, warrants further investigation. It may be that successful germination and seedling establishment in woodlands requires the rapid removal of physical dormancy, or perhaps keeping unheated seed constantly moist for 5 weeks in a laboratory trial is simply an unnatural treatment producing a germination response not relevant to ecosystem function. The abundant fire-triggered germination and rapid maturity of seedlings, combined with the known population number (>4,000 plants) and distribution range (850 km²), support existing recommendations that Purple-flowered Wattle warrants a Vulnerable rather than Critically Endangered Environment Protection and Biodiversity Conservation Act (1999) status, as is current at the state level. Management that includes regular patchy burning with good soil moisture that reduces the extent and intensity of individual fires is likely to benefit the long-term preservation of this restricted species and associated species of its ecosystems.