An Assessment of Feral Horse Impacts on Treeless Drainage Lines in the Australian Alps (2015)

Geoff Robertson, John Wright, Daniel Brown, Kally Yuen and David Tongway | 2015

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Introduction

The Australian Alps are a place of outstanding natural and cultural significance. Containing the highest points in the Great Dividing Range and spanning over 600 km from Mount Donna Buang in Victoria to Piccadilly Circus in the Australian Capital Territory (ACT), the Australian Alps cover an area of more than 1.6 million hectares. They encompass the headwaters of many major rivers in south-eastern Australia and contain a diverse array of ecosystems that provide critical habitat for many threatened flora and fauna species. The significant value of the Australian Alps is reflected by their inclusion in Australia’s National Heritage List.

Feral horses have been present in the Australian Alps since the 1890s (Dyring, 1990). The environmental impacts of feral horses in the Australian Alps have been of concern since at least the 1950s (Costin 1954, 1957). Impacts on riparian and wetland ecosystems, especially those impacts associated with erosion and damage to streams, are of particular concern. Many of these ecosystems include the Commonwealth-listed Alpine Sphagnum Bogs and Associated Fens Endangered Ecological Community and synonymous communities listed under New South Wales and Victorian State legislation. These ecosystems also provide important habitat for a range of Commonwealth and/or State listed threatened species including the Alpine Water Skink, Guthega Skink, Alpine She-oak Skink and Alpine Bog Skink (Clemann et al. 2001; Clemann 2001; Meredith et al. 2003; Steane et al. 2005).

Streams, wetlands and adjacent riparian ecosystems are susceptible to damage through selective grazing, trampling, pugging, wallowing and crossing by feral horses and other hard- hoofed animals (Costin 1954; Whinam & Comfort 1996; Williams et al. 1997; Whinam & Chilcott 2002; McDougall 2007; Prober & Thiele 2007; Wild and Poll 2012). Impacts associated with feral horses include changes to soils, streams and vegetation (Dyring 1990); changes in stream structure and function, vegetation structure and composition (Prober & Thiele 2007; Wild and Poll 2012); and damage to peatland systems through track creation, compaction, trampling, pugging and stream bank slumping (Tolsma 2009).

Due to concerns about impacts on natural values, feral horse abundance across the Australian Alps has been monitored systematically since 2001. The feral horse population was reduced by large bushfires that affected much of the Australian Alps in 2002-2003 (Walter 2003). However, since then, the population has continued to grow, with the annual rate of increase for the Northern Kosciuszko area in New South Wales and the Southern Kosciuszko – Northern Victoria area estimated at 17% and 6% respectively (Cairns 2014).

Despite the long history of concern about impacts of feral horses and the substantial increase in horse abundance across the Australian Alps observed over the past decade, there has been little research to quantify the impacts of feral horses on natural values of the Australian Alps. Furthermore, those studies that have examined feral horse impacts have generally focused on localised areas. Such studies are very useful for understanding the nature of impacts at a site-scale, however for developing effective management strategies across the Australian Alps landscape, it is also important to understand how widespread these impacts are.

This study aims to address this knowledge gap. It compares various attributes of treeless drainage lines in sites with no sign of horse presence and sites that do show evidence of horse presence (observations of horses, horse dung, prints or trails). To our knowledge, this is the first study that has assessed the environmental impacts of feral horses across the Australian Alps landscape.