The Ecology of Wild Horses and their Environmental ... - Parks Victoria

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The Ecology of Wild Horses and their Environmental Impact in the Victorian Alps May 20133. Wild horse environmental impacts3.1 Environmental impacts of wild horsesAustralia's ecosystems have evolved without the grazing pressure and the physical impact of heavy, hardhoofedanimals (Carr & Turner 1959a; 1959b Ashton & Williams 1989; Green et al. 2006). Wild horse activity inthe Victorian Alps represents a type and intensity of impact to which native ecosystems and their componentsare not adapted. The environmental impacts of wild horses are recognised by Victoria’s environmentlegislation with “degradation and loss of habitat caused by feral horses” listed as a threatening process underthe Flora and Fauna Guarantee Act (1988).The social and behavioural habits of wild horses as well as their physical characteristics (i.e. hard hooves, largesize, dietary preferences and general requirements), impact on the environment directly and indirectly.Trampling and grazing are the most researched and known agents of change associated with wild horses (Loydi& Zalba 2009). However, other negative actions include: consumption of native plants, bark chewing,compaction of soils, pugging (trampling of wet soils leaving a dense mat of deep footprints), track formation,wallowing (rolling), and the redistribution of nutrients and plant seeds via dung and urine. The impacts ofthese actions are summarised in Table 1.Table 1: Summary of wild horse environmental impactsElement Impacts Australian Alps research General researchSoil & substrate • Exposed soil surface;Dyring 1990Berman & Jarman 1998• soil loss & erosion;Whinam et al. 1994 Beever & Herrick 2006• down-slope sedimentation;De Stoppelaire et al. 2004• soil pugging, drying & compaction;Rogers 1991, 1994• loss of soil structural compositionTurner 1987especially on wet soils; &Loydi & Zalba 2009• creation of nutrient hotspots(especially nitrogen).Peatlands (alsoknown as bogs ormossbeds)Waterways(streams &streambanks)Vegetation (&communities)• Drying out of bogs & potentialdraining of entire bog systems;• creation of bare pavements;• incision & soil erosion;• silt deposition downstream;• dominance of unpalatable species; &• loss of habitat for threatenedspecies.• Degradation of stream function;• incision & channelling;• soil compaction leading to decreasedinfiltration;• increased downslope sedimentation;• increased nutrient loads;• lateral erosion;• streambank disturbance & slumping;• fouling of waterholes; &• changes in water flow & drainagepatterns.• Removal of native vegetation cover;• dispersal of weed seeds;• changes to the vegetation structure& species composition of the groundstratum;• native tree mortality;• increase vulnerability of threatenedvegetation; &• increased nutrient loads.Dyring 1990Whinam & Chilcott 2002Whinam et al. 2003Tolsma 2008a, 2008bProber & Thiele 2007Dyring 1990Whinam & Comfort 1996Whinam & Chilcott 2002Prober & Theile 2007Wild & Poll 2012Dyring 1990Whinam & Chilcott 2002Whinam & Comfort 1996Whinam et al. 1994Prober & Theile 2007Walter 2002McKay 2001Leigh et al. 1991Thomas 2010Wild & Poll 2012Rogers 1991, 1994Beever & Brussard 2000Rogers 1991, 1994Beever & Brussard 2000Beever et al. 2003Beever et al. 2008Rogers 1991, 1994Turner 1987Loydi & Zalba 2009De Stoppelaire et al. 2004Bridle & Kirkpatrick 1999Cambell & Gibson 2001Schott 20029
The Ecology of Wild Horses and their Environmental Impact in the Victorian Alps May 2013Native fauna • Competition for resources;• altered food availability;• habitat modification & loss;• increased vulnerability of threatenedspecies; &• competitive exclusion.Clemann et al. 2001Clemann 2002Brown et al. 2007Berman & Jarman 1998Lenehan 2010Zalba & Cossani 2009Beever & Herrick 2006Beever et al. 2008Nano et al 2003The degree of wild horse related degradation in the Victorian Alps will depend on:• wild horse density;• scale of activity (extent);• topography – including slope;• elevation;• climate;• recent weather;• local drainage;• access to suitable areas;• timing (i.e. seasonality of grazing);• the resilience of the vegetation community;• soil type (i.e. fineness and/or wetness);• the frequency and intensity of use;• effects of other sympatric species; and• the longer-term disturbance history of the site (Whinam etal. 1994; Beever et al. 2003; Beever et al. 2008).These factors vary throughout the Victorian Alps but some generalisations can be made.Concerns about the environmental impacts of wild horses in the Australian Alps were first raised in the 1950s(Costin 1954). While there is extensive evidence of wild horse impacts in the Victorian Alps, relatively fewstudies have been undertaken to quantify these impacts. Research includes:• Dyring (1990) conducted research on the effects of wild horses on sub-alpine and montaneenvironments in Australia. Wild horse impacts on soils, vegetation and streams were quantified infour small catchments in the southern Snowy Mountains. Seasonal habitat usage and the abundanceof wild horses were also investigated. Wild horses were found to either initiate or perpetuate changesin sub-alpine and montane environments. Rates of environmental change could not however beinvestigated in the short time-frame of the study.• In 1999 an experimental program was established in the East Alps Unit of the ANP to determine theeffects of wild horse activity on grasslands and stream margins (Prober & Thiele 2007; Wild and Poll2012). Exclosure plots, that prevent horses from accessing a defined area but allow access for otheranimals, were established at Cowombat Flat and Native Cat Flat. Detailed vegetation monitoring ofthese exclosure plots, as well as monitoring of stream bank condition, disturbance and erosion wasundertaken in 1999, 2005 and 2012 (Prober & Thiele 2007; Wild and Poll 2012). The results show thatchanges to stream structure and function as a result of wild horses are clear and substantial, withsignificantly more incision and damage in the wild horse occupied area (outside the wild horseexclosures). Exclosure from horses has led to clear increases in vegetation height and increased littercover (Wild and Poll 2012). The effect of wild horses on vegetation structure and composition wasless consistent; however there was a trend for the recovery of dense swards of sedges and grassesassociated with the competitive exclusion of some lower stature species inside horse exclosures (Wildand Poll 2012). In contrast, horse occupied areas tended to be characterised by low herbfield turfs,likely to be maintained by the preferential grazing of grasses and sedges by horses (ibid).• In 2008 Arn Tolsma from the Arthur Rylah Institute assessed the status and needs of 105 individualmossbeds (also commonly termed peatlands or bogs) in the Victorian Alps (Tolsma 2008a; 2008b).This work supplemented broad-scale post-fire assessment of mossbeds that have been conducted bythe Arthur Rylah Institute since 2004. The aims included: to assess the current state of sub-alpinemossbed communities, estimate potential threats to mossbeds and determine restoration and othermanagement needs. Tolsma found that most systems show signs of contraction over a decadal scale,and few systems could be considered in relatively good condition. Evidence of wild horse activity10
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