Assessment of tree fern browsing by introduced Sambar Deer in south-eastern Australia

Abstract

Browsing on tree ferns (Cyathea australis and Dicksonia antarctica) was assessed at Mt Toolebewong, Victoria, Australia, where a population of Sambar (Rusa unicolor), a large deer species, is known to occur and compared with tree fern browsing at Tarra-Bulga National Park, Victoria, where Sambar are uncommon. At Mt Toolebewong, 52% of surveyed tree ferns had been browsed, with most damage occurring on individuals up to 130 cm high and typically involving removal of most or all of a frond to the base of the rachis. In contrast, only 7% of tree ferns had been browsed at Tarra-Bulga, with none browsed above 85 cm and only the frond tips removed. Browsing of whole fronds on mid-size tree ferns at Mt Toolebewong is attributed to the population of Sambar, and the lower intensity of browsing on smaller tree ferns at Tarra-Bulga to native herbivores. Populations of Sambar in wet forests of south-eastern Australia may, therefore, hinder recruitment of tree ferns into larger size-classes, at least at sites where tree ferns are favoured browse. The potential ecological consequences and management implications are discussed. Information is lacking on the severity and spatial scale over which deer impact tree fern populations. Tree fern browsing may be locally severe with site- and height-based browse evidence suggesting that this can largely be attributed to introduced Sambar. Browsing by deer has the potential to decrease growth, reduce survival and prevent recruitment of tree ferns into larger class sizes, with potentially detrimental implications for tree fern populations, associated species such as epiphytic flora, and the structure and function of wet forest ecosystems. Collection of appropriate field data will provide a better understanding of tree fern browsing and identify if and where management intervention is required.