Spatially variable recruitment response to fire severity in golden-top wattle (Acacia mariae, family: Fabaceae), a thicket-forming shrub of semi-arid forests

Boyd R. Wright; Damien D. Andrew; Michael Hewins; Claire Hewitt; Roderick J. Fensham

doi:10.1071/BT24023

RESEARCH ARTICLE (Open Access)

Previous Contents Vol 73(1)

Spatially variable recruitment response to fire severity in golden-top wattle (Acacia mariae, family: Fabaceae), a thicket-forming shrub of semi-arid forests

Boyd R. Wright

^A ^B ^C ^* , Damien D. Andrew

^A , Michael Hewins ^A , Claire Hewitt ^A ^D and Roderick J. Fensham ^E ^F

+ Author Affiliations

- Author Affiliations

^A Department of Botany, School of Environmental and Rural Science, The University of New England, Armidale, NSW 2350, Australia.

^B School of Agriculture and Food Sustainability, University of Queensland, Saint Lucia, Qld 4072, Australia.

^C The Northern Territory Herbarium, Department of Lands, Planning and Environment, Alice Springs, NT 0871, Australia.

^D Environmental Resources Management Australia Pty Ltd, Level 14, 207 Kent Street, Sydney, NSW 2000, Australia.

^E Queensland Herbarium, Mt Coot-tha Road, Toowong, Qld 4066, Australia.

^F School of the Environment, University of Queensland, Saint Lucia, Qld 4072, Australia.

^* Correspondence to: bwright4@une.edu.au

Handling Editor: Ben Gooden

Australian Journal of Botany 73, BT24023 https://doi.org/10.1071/BT24023

Submitted: 13 April 2024 Accepted: 16 December 2024 Published: 24 January 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Context

Investigations into the life history strategies of organisms in ecosystems prone to fires are essential for effective fire impact management. In Australia, fire severity is expected to increase under anthropogenic climate change (ACC), therefore understanding plant responses to this fire regime element is essential for developing conservation-focused burning practices.

Aims

Assess the recruitment response of golden-top wattle (Acacia mariae) to varying fire severities (high, low and unburnt) in the semi-arid Pilliga forest in Northern Inland New South Wales. Investigate seedbank dynamics and germination biology to inform post-fire recruitment patterning.

Methods

Longitudinal seedbank studies were performed to understand seedbank dynamics and the associated influence on post-fire regeneration. A laboratory trial was conducted to assess the effects of heat shock and incubation temperature on seed germination. Field surveys were conducted at four sites to assess fire severity impacts and evaluate spatial variability in post-fire recruitment after the 2018 Gibbican Rd wildfire.

Key results

Recruitment varied among sites but was highest in shrubs burned by high-severity fire (5.8 seedlings/shrub), followed by low-severity fire (0.8 seedlings/shrub) and unburnt shrubs (0.1 seedlings/shrub). Over 5 years, seedbank densities fluctuated markedly, peaking in 2021 following a major seeding event but declined rapidly thereafter. Germination was optimised when seeds underwent heat shock at temperatures between 100 and 140°C and incubated at warm temperatures.

Conclusions

Acacia mariae germination is promoted by heat stimulation, explaining why high intensity burns with higher soil temperatures enhance recruitment. Differences in seedbank densities at the time of fire may account for varied recruitment across landscapes. Overall, A. mariae regenerates well after high-severity fires but poorly after low-severity fires, indicating that the species may be resilient to increased fire severity under ACC but struggle under current widespread low-severity prescribed management burning regimes.

Keywords: Acacia, burn severity, climate change, fire regime, granivore, recruitment, seedbank, semi-arid.

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