Understanding the spatiotemporal dynamics of understorey biomass in semi-arid woodlands of south-eastern Australia
Linda Riquelme
A * , Libby Rumpff A , David H. Duncan A and Peter A. Vesk A
+ Author Affiliations
- Author Affiliations
A School of Ecosystem and Forest Sciences, The University of Melbourne, Vic. 3010, Australia.
* Correspondence to: lriquelme@student.unimelb.edu.au
The Rangeland Journal 44(1) 47-59 https://doi.org/10.1071/RJ21060
Submitted: 9 December 2021 Accepted: 7 March 2022 Published: 19 April 2022
© 2022 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the Australian Rangeland Society. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)
Abstract
When managing grazing pressure for conservation, understanding forage dynamics is essential. In south-eastern Australia, ongoing grazing is inhibiting regeneration in several semi-arid woodland communities. Western grey kangaroos (Macropus fuliginosus (Desmarest, 1817)) have been identified as a key component of total grazing pressure. They are thought to switch from grass to lower-quality browse, including tree seedlings, when grass biomass falls below 400 kg ha−1. One static threshold may not adequately capture the spatial and temporal hazard associated with kangaroo grazing, and this study aimed to explore how grassy biomass varies across a case-study landscape. Understorey biomass and species composition data were collected in the field on seven occasions between December 2016 and May 2019. We used Generalised Linear Mixed Models (GLMMs) to describe the influence of environmental and herbivory variables on total (live and dead) understorey, live understorey, and grass (live and dead) biomass. Canopy cover showed the strongest influence on understorey biomass, with more biomass found in open sites than in woodland. Understorey biomass levels were lowest in summer and autumn. Grass biomass, in particular, fell below the 400 kg ha−1 forage-switch threshold in wooded areas during this time. We anticipate that an increased understanding of understorey biomass dynamics will inform managers as to when and where to focus management efforts to promote regeneration and sustained recovery of these semi-arid woodlands. Results of this study suggest that conducting management efforts before the summer/autumn decline in understorey biomass, particularly in woodlands, is critical in reducing the browsing risk to seedlings.
Keywords: grazing management, grazing pressure, herbage mass, herbivory by kangaroos, regeneration, semiarid rangelands.
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