Adaptive management of shrub-encroached woodlands: assessing the short-term impact of alternative mastication techniques on fuel and biodiversity

Woody shrub encroachment is a growing problem in many ecosystems across the globe, causing declines in biodiversity and elevated fire risk. Mastication can be used to remove the dense shrub layer, however decisions regarding the optimal mastication technique are hampered by a lack of information about how different mastication techniques influence fuel, vegetation structure and floristic composition. We applied an adaptive management approach to trial various mastication techniques. The trial was co-designed with land managers and conducted in eucalypt woodlands of southeastern Australia which have a dense understorey of Coast Wattle (Acacia longifolia var. sophorae). We tested two techniques, a high intensity (greater mechanical processing) and low intensity (less mechanical processing) treatment. We measured surface fuel, vegetation structure and floristic diversity pre-mastication, then 1-, 6- and 12-months post-mastication. The high intensity technique produced higher surface fuel loads compared to the low intensity technique. By 12-months post-mastication, cover of short (<0.3 m tall) vegetation had recovered to pre-treatment levels, with no difference between techniques. Both techniques yielded higher native species richness and diversity than the control, driven mainly by increases in native forb species. The low intensity technique was faster and less expensive and had similar impacts on floristic diversity but had lower surface fuel load. Therefore, we recommend the application of the low intensity technique to manage shrub encroachment. Our study used adaptive management to understand the short-term (1-year) impacts of different mastication techniques. Future trials (with additional treatments) and ongoing monitoring are planned to further improve our understanding of how to best to manage shrub encroachment.