Background Paper 1 of 3 The Ecology of Wild Horses and ...€¦ · The Ecology of Wild Horses and their Environmental Impact in the Victorian Alps May 2013 Table of Contents Introduction

The Ecology of Wild Horses and their Environmental Impact in the Victorian Alps May 2013

Background Paper 1 of 3

The Ecology of Wild Horses and their Environmental Impact in the Victorian

Alps

Wild horse exclusion plot, Native Cat Flat 2004 (source: Parks Victoria).

Parks Victoria

May 2013

This paper was written by: Joanna Axford1, Michelle Dawson2 and Daniel Brown3

1 Formerly Parks Victoria, Bright

2 Eco Logical Australia

3 Parks Victoria, Bright

Acknowledgements: Arn Tolsma and Nick Clemann (Arthur Rylah Institute for Environmental Research,

DEPI) provided content and reviewed this paper. Charlie Pascoe, Dave Foster and Mike Dower (Parks Victoria)

provided information on wild horse impacts in the Alpine National Park, and Malcolm Kennedy (formerly Parks

Victoria) reviewed this paper. Joanne Lenehan, PhD candidate (University of New England), provided

unpublished results of her study into wild horse impacts in Guy Fawkes River National Park. Alison Matthews

(Charles Sturt University), Associate Professor J. Gilkerson (Equine Infectious Disease Laboratory, University of

Melbourne) and H. Crabb (Principal Veterinary Officer-Intensive Farming Systems, DEPI Victoria) were

consulted on various sections of this paper.


Acronym List ABA: Australian Brumby Alliance

ABMA: Alpine Brumby Management Association

AALC: Australian Alps Liaison Committee

AANPs: Australian Alps National Parks

ANP: Alpine National Park

BAW: Bureau of Animal Welfare

COP: Code of Practice

DEPI: Department of Environment and Primary Industries

EPBC: Environment Protection and Biodiversity Conservation Act 1999

FFG: Flora and Fauna Guarantee Act 1988

KNP: Kosciuszko National Park

RSPCA: Royal Society for the Prevention of Cruelty to Animals

SOP: Standard Operating Procedure

VBA: Victorian Brumby Association


Table of Contents

Introduction to Wild Horse Background Papers ..................................................................................... 1

1. Introduction .................................................................................................................................... 2

2. Wild horse ecology in the Victorian Alps ........................................................................................ 2

3.1 Wild horse distribution ........................................................................................................... 2

3.2 Wild horse population trends ................................................................................................. 3

3.3 Wild horse demography .......................................................................................................... 6

3.4 Wild horse social organisation and movement ...................................................................... 6

3.5 Wild horse habitat and diet preferences ................................................................................ 7

3.6 Wild horse mortality factors ................................................................................................... 8

3. Wild horse environmental impacts ................................................................................................. 9

3.1 Environmental impacts of wild horses .................................................................................... 9

3.2 Impacts on soil and substrate ............................................................................................... 11

3.3 Impacts on vegetation .......................................................................................................... 14

3.4 Impacts on peatlands ............................................................................................................ 18

3.5 Impacts on waterways (streams and stream-banks) ............................................................ 20

3.6 Impacts on fauna .................................................................................................................. 22

4. Wild horse biosecurity issues ........................................................................................................ 25

5. Gaps in knowledge ........................................................................................................................ 26

References ............................................................................................................................................ 27

Appendix 1: Officially listed plant ecological communities at risk of severe damage from wild horse

activity ................................................................................................................................................... 36

Appendix 2: FFG-listed and EPBC-listed plant species potentially at risk from wild horse activity in the

eastern Victorian Alps ........................................................................................................................... 37

Appendix 3: Officially listed or threatened fauna species potentially at risk from feral horse activity in

the eastern Victorian Alps ..................................................................................................................... 39


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Introduction to Wild Horse Background Papers Horses (Equus caballus) living in unmanaged, wild populations in Australia are generally known by three terms;

feral horses, wild horses and brumbies. Any introduced domestic animal that lives in unmanaged, self

sustaining, wild populations is by definition a feral animal. However, some people are uncomfortable with the

term ‘feral’ being associated with horses and prefer the terms ‘wild horse’ or ‘brumby’. ‘Brumby’ is a colloquial

term often used in Australian folklore; however some people believe the term elicits a romanticised view of

horses and detracts from their environmental impacts. In this series of papers the term ‘wild horse’ will be

used, as it is a generally accepted term and clearly refers to un-domesticated horses living in the wild.

Horses were introduced to Australia by early European settlers and Australia now has the highest population

of wild horses in the world, with more than 300 000 (Dobbie et al. 1993). Wild horses are a pest species in

Australia, that is, an “animal that has, or has the potential to have, an adverse economic, environmental or

social/cultural impact” (Natural Resource Management Ministerial Council 2007).

Wild horses occur across the Australian Alps and have been identified as a high priority threat to natural

values of the region (Coyne 2001). The “degradation and loss of habitat caused by feral horses” is listed as a

potentially threatening process under Victoria’s Flora and Fauna Guarantee Act (1988).

In Victoria, wild horses occur within the Victorian Alps, with a smaller population present in the Barmah Forest

(Wright et al. 2006). This series of three Background Papers will focus on wild horses in the Victorian Alps

(Alpine National Park (ANP) and surrounding State forests).

The Background Papers investigate the ecology, environmental impacts, human dimensions and management

and control of wild horses in the Victorian Alps. They are arranged in the following order:

Background Paper 1: The Ecology of Wild Horses and their Environmental Impact in the Victorian Alps. The first

section of this paper considers the ecological dimensions of wild horses in the Victorian Alps including their

distribution, population trends, demography, habitat, diet and mortality factors. The environmental impacts of

wild horses within the region are then considered including their impacts on: soil and substrate, vegetation,

peatlands, waterways and fauna. Biosecurity issues are also discussed.

Background Paper 2: The Human Dimensions of Wild Horse Management in the Victorian Alps. This paper

provides the social context for wild horse management in the Victorian Alps. A brief history of wild horses in

the region and the major stakeholder groups involved is outlined. The socio-economic and cultural heritage

values of wild horses are then explored followed by a discussion on public perceptions about wild horses and

their management in the Victorian Alps. Research from national and international investigations into

perceptions towards wild horses is drawn upon to help unravel the complexity of this value-laden issue.

Background Paper 3: Wild Horse Management and Control Methods. This paper considers the management of

wild horses in the Victorian Alps and considers control methods for managing wild horses. An overview of how

wild horses have been managed in the Victorian Alps and the legislation and policy framework for wild horse

management is provided. The paper explores welfare issues and costs associated with wild horse control,

levels of control and control options.

This series of papers was prepared based on available literature and research, and, through consultation with

experts where possible. The papers provide a foundation for discussion concerning the future management of

wild horses within the Victorian Alps.


2

1. Introduction

In Victoria wild horses (Equus caballus) occur in the Victorian Alps with a smaller population present in the

Barmah Forest, on the Murray River (Menkhorst 1995; Wright et al. 2006). Wild horses are considered a

significant environmental threat to the Victorian Alps (including the Alpine National Park (ANP) and adjacent

State forests). The “degradation and loss of habitat caused by feral horses” is listed as a potentially threatening

process under Victoria’s Flora and Fauna Guarantee Act (1988). This paper will explore the ecological

dimensions of wild horses in the Victorian Alps and the extent to which they are affecting the natural values of

the region.

Several studies and reviews have been conducted on the ecology and environmental impacts of wild horses in

various parts of the Australian Alps, including: Dyring 1990; Thiele & Prober 1999a, 1999b; Walter 2002, 2003;

Walter & Hone 2003; Montague-Drake 2005; Prober & Thiele 2007; Nimmo & Miller 2007; Laake et al. 2008;

Dawson 2005, 2009a, 2009b; and Venn et al. 2009. To help unravel the significance of wild horses in the

Victorian Alps, information in this paper is also drawn from national and international literature as well as

anecdotal information on wild horses in the Victorian Alps.

2. Wild horse ecology in the Victorian Alps

3.1 Wild horse distribution

Wild horses in the Australian Alps are relatively isolated from populations elsewhere in Australia. The largest

populations in Australia occur in dry and tropical environments, mainly in the Northern Territory and

Queensland, but also Western Australia and South Australia (Dobbie et al. 1993). In much of Australia, drought

limits the distribution of wild horses (Dobbie et al. 1993). However, this is not evident in the Australian Alps

which occupy wetter bioregions with more consistent rainfall (Hobbs & McIntyre 2005). The distribution of

wild horses in Australia has also been strongly influenced by human intervention including farming

infrastructure such as fencing (McKnight 1976).

Wild horses were initially introduced into the Australian Alps by European settlers in the 1830s. Graziers

managed the distribution (and numbers) of wild horses to varying degrees from the mid-1800s up until cattle

grazing ceased early this century (Walter 2002; Foster 2004). Non-human influences on wild horse distribution

in the Alps include preferred habitat, geographical barriers and natural events such as severe snow storms, fire

and drought (Walter 2002). Between 1990 (Dyring 1990) and 2002 (Walter 2002) wild horse distribution

appeared to be relatively stable in the ANP, however, in the past ten years wild horse populations have

expanded their range in a number of locations, including spreading to new locations on the Bogong High Plains

(Dawson 2009). Dawson (2009) also suggests that there is suitable habitat for wild horses in Australian Alps

that is currently not occupied. Furthermore, it is predicted that with climate change, areas at higher elevation

will become more suitable for wild horses (Dunlop & Brown 2008; Green & Pickering 2002).

The largest population of wild horses in the Victorian Alps is in the eastern Alps (east of Omeo) and is

connected to a population in Kosciuszko National Park, NSW to the north (Figures 1 and 2). It extends south to

the Nunniong Plains, as far west as Mt Pinnibar and Buenba Creek, and to Deddick and Amboyne east of the

Snowy River. The second, smaller population is on the southern Bogong High Plains, between Falls Creek and

Mount Hotham, and in the headwaters of the Cobungra, Bundara and Victoria Rivers (Ethos NRM 2012). The

Bogong High Plains/Cobungra population is isolated from the Eastern Alps population by around 30km and

considered to have a lower density of horses than the east Alps population (Ethos NRM 2012) (figure 2). Both

populations, while situated predominantly within the ANP, extend into adjacent State forests and reserves

and, probably, private land.


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Records of small groups of horses have occurred at other disjunct locations across the Victorian Alps from time

to time, however these isolated records are considered not represent extant populations.

In spring 2009 a group of 18 wild horses was discovered in the headwaters of the Moroka River, near Mt

Wellington in the Alpine National Park and the adjacent Carey State Forest. This group of horses is suspected

to have been illegally introduced, but was gradually trapped and removed by Parks Victoria and DEPI over the

subsequent summer and autumn. In early winter 2010, another new group was discovered in State forest at

Connors Plain, north-west of Licola. This group was also trapped and removed. Monitoring continues in both

areas to ensure that all the horses have been captured.

Figure 1: Estimated wild horse distribution in the Victorian Alps, showing the two disjunct populations. This distribution

map is based on a report by Ethos NRM (2012) that used previous horse records and interviews with a broad range of

stakeholders (with knowledge and experience of wild horses in the Victorian Alps) to estimate the distribution of wild

horses in the Victorian Alps. NB: This map is based on anecdotal qualitative information and provides only a broad guide to

wild horse distribution.

3.2 Wild horse population trends

The most reliable estimates of wild horse population size have come from aerial surveys across the Australian

Alps National Parks (AANPs) conducted in 2001, 2003 and 2009 (Walter & Hone 2003; Dawson 2009). These

surveys were developed with the aim of providing a repeatable and robust method for monitoring wild horse

population size in parts of the AANPs (not including adjacent areas such as State forests and private land)

(Walter & Hone 2003). Surveys are conducted from a helicopter at a fixed-height and speed along east-west

transects at two kilometre intervals and analysed using line-transect techniques (Walter & Hone 2003). This

method was designed to minimise several potential sources of bias such as decreasing detectability of horses

with distance from the aircraft (Walter & Hone 2003), and counting horses more than once (see Linklater &

Cameron 2002).

Alpine National Park



Snowy River

National Park

Mount Buffalo

National Park


4

Figure 2: Estimated distribution and relative density of wild horses in the Victorian Alps. This map is based on a report by

Ethos NRM (2012) that used previous horse records and interviews with a broad range of stakeholders (with knowledge

and experience of wild horses in the Victorian Alps) to estimate the distribution and density of wild horses in the Victorian

Alps. NB: This map is based on anecdotal qualitative information and provides only a broad guide to wild horse distribution

and density.

Wild horse populations can increase at a maximum rate of 21-37% per annum, depending on local

environmental conditions (Eberhardt 1987; Garrott et al. 1991a; Linklater et al. 2004; Grange et al. 2009;

Scorolli 2010). Populations do not sustain these levels of growth indefinitely. Population growth slows, stops or

becomes negative when horses are removed from the population by people (e.g. Garrott & Taylor 1990); or

when populations become limited by resources such as food or water (Dobbie et al. 1993; Grange et al. 2009;

Scorolli & Lopez 2010). The wild horse populations in the Australian Alps were estimated to be increasing at

21% per annum between 2003 and 2009 after broad-scale, intense bushfires in the summer of 2002/3 reduced

populations by approximately 54 percent (Dawson 2009). In a study of three small wild horse populations in

the Australian Alps (one in Victoria and two in New South Wales) prior to the 2002/3 bushfires, Dawson and

Hone (2012) observed that the populations were either stable or increasing at a rate of up to nine percent per

annum. More stable rates were observed in long established unmanaged populations (including Cowombat

Flat) and a higher rate of increase in an area where human intervention had recently been reduced (Dawson

and Hone 2012).

Trends in the size of the wild horse population in parts of the ANP have been derived using aerial survey

results since 2001 (Figure 3). The population appears to have fluctuated between 2001 and 2009, primarily as

a result of the severe and extensive bushfires in 2002/3 (Dawson 2009). The estimates show a rapid growth

phase between 2003 and 2009 (with an annual growth rate of 21%) consistent with recovery post-fire. This

rapid population increase has occurred despite the removal of more than 700 horses by Parks Victoria during

this period. The size of the population in the surveyed portion of the ANP has been in the order of 1000 to

3500 horses between 1990 and 2009, with the highest estimates in the most recent 2009 survey (3442 horses

± 874 SE). However, these estimates are based on aerial surveys that cover less than half the area known to be

occupied by wild horses (ELA 2012) and there is no indication that the population has stopped growing since


5

2009. Thus, the true size of the wild horse population in the Victorian Alps is expected to be significantly

higher.

Population modelling has been undertaken to estimate the wild horse population size for the entire Victorian

Alps. This modelling involves using estimated wild horse density and distribution mapping to extrapolate the

population estimates derived from aerial surveys across the entire area occupied by wild horses. Wild horse

population growth is estimated using a logistic growth model that calculates population growth towards an

estimated carrying capacity (derived from field studies), which varies in response to environmental variability

(rainfall) (ELA 2012). This modelling suggests that the entire Victorian Alps wild horse population is now

approximately 9718 horses (SE: 8151 – 10 896) (ELA 2012) (figure 3). This represents an average wild horse

density of 3.4 per km2 across their current distribution in the east Victorian Alps. The highest documented

densities of wild horses in the Australian Alps is 6.4 km-2

at Cowombat Flat, Victoria, at a time when the

population was stable (Dawson & Hone 2012).

Figure 3: Estimates of wild horse population size ± SE derived from aerial surveys of the surveyed portion of the ANP

(Dawson 2009) (blue columns) and extrapolated for the whole area occupied by wild horses in the Victorian Alps (ELA

2012) (green columns). The 2012 estimate is derived from modeling wild horse population growth from 2009 towards

estimated carrying capacity (ELA 2012). The number of horses removed from the Victorian Alps through Parks Victoria

management programs since 2005 is also included (red columns).

The Bogong High Plains wild horse population remained relatively static at around 80 - 100 horses between

2005 and 2009 (Dawson and Miller 2008), despite the removal of 102 horses over the same period. However,

aerial surveys indicate that the population has decreased in the equivalent survey area between 2009 and

2012, from around 90 to 50 horses (figure 4). Seventy six horses were removed during this same period.

2159 1011 344249

02

22

93

70

87

97

18

88 95 121 185 193 150 122 145

0

2000

4000

6000

8000

10000

12000

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

Nu

mb

er

of

Ho

rse

s

Year

Estimated population size (aerial survey area only)

Estimated population size (extrapolated for whole Victorian Alps)

Horses removed

Bushfires


6

Figure 4: Estimates of wild horse population size ± SE for the Bogong High Plains population only. The number of horses

removed from these areas by Parks Victoria since 2005 is also included (red columns). Population estimates are derived

from aerial surveys (Dawson and Miller 2008).

3.3 Wild horse demography

Wild horses have an annual breeding season, producing one young at a time (Grange et al. 2009). The first

young are usually produced when females are three years of age. When wild horse density is low and food is

abundant they occasionally reproduce at two years of age (Berger 1986; Duncan 1992). During a three year

study from 1999 to 2002, the youngest mare observed with a foal in the Australian Alps was three years old

(Dawson & Hone 2012). Foaling rates increase up to the age of five and mares continue to have high foaling

rates until the onset of senescence at 15-18 years of age (Garrott & Taylor 1990; Garrott et al. 1991b; Duncan

1992; Linklater et al. 2004; Grange et al. 2009). Foals are usually born in the summer months when food

availability is at its highest (after an 11 month gestation) but can be born at any time of year (Dawson

unpublished data). Foaling rates observed for wild horses in three separate populations in the Australian Alps

between 1999 and 2002 were lower than those reported in other environments with 42-62% of adult females

observed with foals (Dawson & Hone 2012).

Between 1999 and 2002 survival rates of adult wild horses in the Australian Alps were generally high (91% per

annum) with little annual variation, while survival rates in the first three years of life are lower and more

variable (63-75% per annum) (Dawson & Hone 2012). This is similar to wild horse populations from around the

world (Garrott & Taylor 1990; Linklater et al. 2004; Grange et al. 2009; Scorolli & Lopez Cazorla 2010). There is

no data on the lifespan of wild horses in the Australian Alps, however studies of wild horses in Maryland,

United States of America (USA) found wild horses lived as long as 20 years (Kirkpatrick & Turner 2008).

3.4 Wild horse social organisation and movement

Wild horses live in small social units as harem or bachelor groups. Harem groups consist of a dominant male,

multiple females and their off-spring (Menkhorst 1995). Bachelors are non-dominant males that have been

92 95 88 51

106

11

55

37 38

31

7

0

20

40

60

80

100

120

140

2005 2006 2007 2008 2009 2010 2011 2012

Nu

mb

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of

Ho

rse

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Year

Estimated Horse Population

Horses Removed


7

forced out of their harems; they generally occur alone or in groups of two or three (Dobbie et al. 1993). The

average group size (harem and bachelor groups) from three sites across the Australian Alps was 5.65 (± 0.51

SE) (Walter & Hone 2003), while Drying (1990) found that harem group sizes in the Alpine region ranged from

two to 11 individuals, with groups typically consisting of one stallion, two mares and one foal. Wild horses

rarely have periods of social isolation during their lifetime except for bachelors in their pre-harem formation

stage (van Dierendonck 2006). Harem groups tend to be stable breeding units and generally favour permanent

locations around reliable water sources (Dobbie et al. 1993). Within harem groups, adult mares form a long-

term stable nucleus, while the breeding stallion is regularly replaced (van Dierendonck 2006). Bachelor groups

are more mobile and unstable (Dobbie et al. 1993).

Groups of wild horses are loyal to undefended home ranges with central core use areas (Linklater 2000). The

home ranges of groups overlap entirely with other groups and home range size increases with group size

(Linklater 2000). Home ranges of wild horses in the Australian Alps have not been studied but there is

information available from other environments. Home range sizes vary within a region and between regions. In

Queensland and central Australia wild horses were estimated to have a home range of approximately 100km²

and 70km² respectively (Dobbie et al. 1993). In contrast, wild horses at Kiamanawa in New Zealand, which has

a similar climate to the Australian Alps, had home ranges 0.96 to 17.7 km2 (Linklater 2000). Given the climatic

similarities, home range of horses in the Victorian Alps are likely to be similar to Kaimanawa.

As prey animals in their native environment, a horse’s primary defence mechanism is rapid flight away from

the threat of danger. It is therefore advantageous that they identify potential predators as quickly as possible

(van Dierendonck 2006). This is aided by their monocular and binocular vision, which enables them to have an

extensive view of their surrounds (Dobbie et al. 1993). With well developed hearing any movement is readily

detected (Dobbie et al. 1993).

3.5 Wild horse habitat and diet preferences

Wild horses occupy a range of habitats across Australia and the world. While they are best adapted to open

grassy plains they will also use rugged country (Norris & Low 2005). Wild horses are present from the highest

to the lowest elevations in the Australian Alps (Walter 2002). Some groups may migrate to lower elevations in

winter but many horses maintain a high elevation (1600 metres) home range throughout winter (Dawson,

unpublished data). Drying (1990) found that wild horses in Kosciuszko National Park (at a site in NSW six

kilometres from the Victorian border) made extensive use of heaths and grasslands for feeding, whilst

avoiding the forests at all times of the year; this preference for open areas was broad-based with no

discrimination between feeding and other activities. The preference for grasslands over forest is universal for

wild horses (Pratt et al. 1986; Keiper & Berger 1982; Berger 1986; Linklater et al. 2000). The only exception

has been observed in the middle of the day in summer when wild horses seek refuge from the heat and

horseflies (Tabanidae) in forested areas (Duncan 1983; Dyring 1990; Keiper & Berger 1982; Berger 1986).

Wild horses spend most (55-65%) of their time feeding (Duncan 1980). They are generalist grazers with a

strong preference for the greatest concentrations of high quality food (green plant matter); when green plant

matter becomes sparse, the horses’ tactic is to search out areas with the greatest concentrations of perennial

herbaceous plants, green or dead (Duncan 1983). Their diet mainly includes herbaceous plants (grasses, reeds,

sedges and forbs), but they will also eat roots, bark, buds and fruit (Csurhes et al. 2009). Due to their forward-

cut front incisors they are able to graze close to the ground (Dobbie et al. 1993). Horses have a different

digestive system to most ungulates (hoofed mammals), which enables them to consume large quantities of

low quality food and survive on a lower quality diet than cattle (Janis 2007). Cattle require time to chew their

cud so cannot consume such large quantities but tend to select higher quality food (Janis 2007).

Horses must drink at least once a day in summer and at least every second day during winter (Norris & Low

2005). If food is plentiful horses will graze near water sources (Dobbie et al. 1993).


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3.6 Wild horse mortality factors

With few predators, unmanaged wild horse populations may increase in size and distribution until they

approach carrying-capacity; at this point the population size stabilises as a result of a decrease in birth rates

and survival rates caused by limited food availability (Grange et al. 2009; Scorolli & Lopez Cazorla 2010). For

example, in the Camargue in France, Grange et al. (2009) found that a decrease in available food resources, as

a result of increasing density, caused a loss of body condition and the survival of foals and adult females

decreased with increasing density.

In sub-alpine and montane environments of the Australian Alps, there is evidence that between 1999 and

2002, the growth of three wild horse populations was limited by food availability (Dawson & Hone 2012). The

density of horses at the three sites was higher than the average determined from aerial surveys (see above).

The Cowombat wild horse population had the highest density (6.4 km²), adult horses had the poorest

condition, recruitment (from birth to 3-years-old) was low, pasture biomass was low and population growth

was zero. In general however, unlike the Camargue example above, wild horses in the Australian Alps are not

contained and do not currently occupy their entire potential range (Dawson 2009). Therefore there is scope

for the wild horse population to spread.

It is not clear whether wild horse populations across the Australian Alps would reach ‘carrying capacity’

because the ability to reach equilibrium density depends on the variability of environmental conditions. In

stochastic environments characterised by a high degree of unpredictable environmental variance (e.g. rainfall),

an equilibrium is not reached (McLeod 1997). There are several examples of environmental events, in

particular drought, snow and fire, which have lead to dramatic declines in wild horse populations (thus

preventing the population from reaching carrying capacity). The eastern side of the AANPs (e.g. Buchan River,

Lower Snowy, Suggan Buggan) lies in a rain-shadow and has limited available water. The drought in 1982-83

was reported to have led to a dramatic decline of most wild horses in this area (Walter 2002), similar patterns

are observed in central Australia (Dobbie et al. 1993). Drought can affect horses through thirst, starvation and

ingestion of poisonous plants (Dobbie et al. 1993).

At higher elevations wild horse mortality occurs as a result of severe snow events or long periods of snow

cover in the alpine area (Walter 2002). In winter wild horses at higher elevations, such as those on the Bogong

High Plains, have to dig through snow to access food for many weeks of the year which leads to a loss of body

condition in the horses (Dawson unpublished data). In some cases severe snow events have resulted in

mortality and in one historic event in the Brindabella’s (Australian Capital Territory (ACT)) an entire population

was wiped out (Walter 2002).

The 2003 fires had a substantial impact on the wild horse population of the Australian Alps, with a sharp

decrease in the wild horse population size following the fires (Figure 2). After the fires, Walter (2003) indicated

that when wild horse numbers were low, that there was great potential for the population to increase

dramatically due to the increased availability of high quality food and reduced population pressure. This was

demonstrated by the results of the 2009 aerial survey which showed that the population had increased by

224% since 2003 (Dawson 2009a). In a slightly different context, Catling (1991) predicted that wild horses

would be advantaged by frequent low intensity fires due to a simplification in forest structure.

Additional wild horse mortality factors that should be considered include wild dogs and parasitism. There have

been reports of wild dogs chasing foals in the Victorian Alps (Walter 2002). Parasitism and disease may also be

causes of mortality and/or reduced health. However, neither of these factors has been formally investigated or

quantified.


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3. Wild horse environmental impacts

3.1 Environmental impacts of wild horses

Australia's ecosystems have evolved without the grazing pressure and the physical impact of heavy, hard-

hoofed animals (Carr & Turner 1959a; 1959b Ashton & Williams 1989; Green et al. 2006). Wild horse activity in

the Victorian Alps represents a type and intensity of impact to which native ecosystems and their components

are not adapted. The environmental impacts of wild horses are recognised by Victoria’s environment

legislation with “degradation and loss of habitat caused by feral horses” listed as a threatening process under

the Flora and Fauna Guarantee Act (1988).

The social and behavioural habits of wild horses as well as their physical characteristics (i.e. hard hooves, large

size, 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 of

these actions are summarised in Table 1.

Table 1: Summary of wild horse environmental impacts

Element Impacts Australian Alps research General research

Soil & substrate • Exposed soil surface;

• soil loss & erosion;

• down-slope sedimentation;

• soil pugging, drying & compaction;

• loss of soil structural composition

especially on wet soils; &

• creation of nutrient hotspots

(especially nitrogen).

Dyring 1990

Whinam et al. 1994

Berman & Jarman 1998

Beever & Herrick 2006

De Stoppelaire et al. 2004

Rogers 1991, 1994

Turner 1987

Loydi & Zalba 2009

Peatlands (also

known as bogs or

mossbeds)

• Drying out of bogs & potential

draining of entire bog systems;

• creation of bare pavements;

• incision & soil erosion;

• silt deposition downstream;

• dominance of unpalatable species; &

• loss of habitat for threatened

species.

Dyring 1990

Whinam & Chilcott 2002

Whinam et al. 2003

Tolsma 2008a, 2008b

Rogers 1991, 1994

Waterways

(streams &

streambanks)

• Degradation of stream function;

• incision & channelling;

• soil compaction leading to decreased

infiltration;

• increased downslope sedimentation;

• increased nutrient loads;

• lateral erosion;

• streambank disturbance & slumping;

• fouling of waterholes; &

• changes in water flow & drainage

patterns.

Prober & Thiele 2007

Dyring 1990

Whinam & Comfort 1996


Prober & Theile 2007

Wild & Poll 2012

Beever & Brussard 2000

Rogers 1991, 1994

Vegetation (&

communities)

• Removal of native vegetation cover;

• dispersal of weed seeds;

• changes to the vegetation structure

& species composition of the ground

stratum;

• native tree mortality;

• increase vulnerability of threatened

vegetation; &

• increased nutrient loads.

Dyring 1990


Whinam & Comfort 1996

Whinam et al. 1994

Prober & Theile 2007

Walter 2002

McKay 2001

Leigh et al. 1991

Thomas 2010

Wild & Poll 2012

Beever & Brussard 2000

Beever et al. 2003

Beever et al. 2008

Rogers 1991, 1994

Turner 1987

Loydi & Zalba 2009

De Stoppelaire et al. 2004

Bridle & Kirkpatrick 1999

Cambell & Gibson 2001

Schott 2002


10

Native fauna • Competition for resources;

• altered food availability;

• habitat modification & loss;

• increased vulnerability of threatened

species; &

• competitive exclusion.

Clemann et al. 2001

Clemann 2002

Brown et al. 2007

Berman & Jarman 1998

Lenehan 2010

Zalba & Cossani 2009

Beever & Herrick 2006

Beever et al. 2008

Nano et al 2003

The 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 et

al. 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 few

studies have been undertaken to quantify these impacts. Research includes:

• Dyring (1990) conducted research on the effects of wild horses on sub-alpine and montane

environments in Australia. Wild horse impacts on soils, vegetation and streams were quantified in

four small catchments in the southern Snowy Mountains. Seasonal habitat usage and the abundance

of wild horses were also investigated. Wild horses were found to either initiate or perpetuate changes

in sub-alpine and montane environments. Rates of environmental change could not however be

investigated 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 the

effects of wild horse activity on grasslands and stream margins (Prober & Thiele 2007; Wild and Poll

2012). Exclosure plots, that prevent horses from accessing a defined area but allow access for other

animals, were established at Cowombat Flat and Native Cat Flat. Detailed vegetation monitoring of

these exclosure plots, as well as monitoring of stream bank condition, disturbance and erosion was

undertaken in 1999, 2005 and 2012 (Prober & Thiele 2007; Wild and Poll 2012). The results show that

changes to stream structure and function as a result of wild horses are clear and substantial, with

significantly more incision and damage in the wild horse occupied area (outside the wild horse

exclosures). Exclosure from horses has led to clear increases in vegetation height and increased litter

cover (Wild and Poll 2012). The effect of wild horses on vegetation structure and composition was

less consistent; however there was a trend for the recovery of dense swards of sedges and grasses

associated with the competitive exclusion of some lower stature species inside horse exclosures (Wild

and 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 individual

mossbeds (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 by

the Arthur Rylah Institute since 2004. The aims included: to assess the current state of sub-alpine

mossbed communities, estimate potential threats to mossbeds and determine restoration and other

management 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 activity


11

(tracks, compaction, trampling, pugging and stream bank slumping) was observed in 67% (70 of 104)

of the mossbeds assessed that year. Tolsma argued that on-going activity by wild horses is of great

concern in the east Alps of Victoria. In the East Alps Unit of the ANP, 97% (63 of 65) of peatland

systems were found to be impacted (i.e. compacted, trampled or pugged) by wild horses (Tolsma

2008b).

• In 2011 the AALC commenced a project that aims to quantify the impacts of wild horses on upland

streams and wetlands in the Australian Alps. The results of this study will be available in autumn 2013

and will provide further evidence of the impacts of wild horses on sensitive environments.

A number of protected areas regionally, nationally and internationally recognise that wild horses have a

negative impact on the environment and have developed strategies to address these impacts (Table 2).

Table 2: Examples of wild horse management plans and strategies and their ecological rationale

Region Wild horse strategy Rationale for the plan (ecological)

AANPs Kosciuszko National Park Horse

Management Plan.

The National Parks & Wildlife Service has legislative responsibility to

protect native habitats & wildlife within its reserves & a responsibility

to minimise the impact of introduced species, including wild horses.

The 2006 Plan of Management called for a wild horse management

plan & the exclusion of wild horses from key areas. (NSW NPWS 2008).

Namadgi National Park Feral horse

Management Plan.

The plan aims to minimise the negative impact of wild horses including

grazing on sensitive vegetation, trampling of streambanks, trail

formation & erosion. These can lead to draining of entire bog systems,

loss of habitat for threatened species & silt deposition downstream.

(ACT Government 2007).

National Guy Fawkes River National Park:

Horse Management Plan.

The National Parks & Wildlife Service has legislative responsibility to

protect native habitats & wildlife within its reserves & a responsibility

to minimise the impact of introduced species, including wild horses

(NSW NPWS 2006a). Wild horses are an introduced species that have

adverse impacts on Australian ecosystems with particularly severe

consequences for native fauna & flora (English 2001).

Feral horse Management Plan for

Oxley Wild Rivers National Park

Wild horses have been identified as posing a threat to the conservation

values of the park & water quality. (NSW NPWS 2006b).

Protecting the natural & cultural

values of Carnavon National Park:

A plan to manage wild horses &

other pest animals

Queensland Parks & Wildlife Service has a legal obligation to conserve

& protect the natural values of Canarvon NP & control threatening

processes caused by pest species including wild horses. Destructive

impacts by wild horses have led to: the deterioration of aquatic

ecosystems & serious landscape dysfunction (losses in biomass,

accelerated erosion, soil compaction, altered species composition &

vegetation structure & altered fire ecology). (Weaver 2007).

New

Zealand

Kaimanawa Wild Horses Plan. Horses have been shown to adversely affect nationally significant

ecological values. There is a need to eliminate the impacts of horses on

important conservation values. (DOC 2006).

In addition to these wild horse plans and strategies, a series of workshops on wild horse impact and

management in the Australian Alps (see: Walters & Hallam 1993; O’Brien & Solomon 2004) and a national

workshop (see: Dawson et al. 2006) have demonstrated widespread concern from scientists and practitioners

about the impacts of wild horses in alpine and sub-alpine environments.

The impacts that wild horses have on the soils and substrate, peatlands , waterways, vegetation and fauna of

the Victorian Alps is considered below in greater detail.

3.2 Impacts on soil and substrate

It is generally accepted that alpine areas are more susceptible to damage by hard hooved animals such as wild

horses than most other environments, due to their wet fragile soils and slow vegetation growth rates (Whinam

et al. 1994). Wild horse trampling and grazing can lead to major changes to the soil, including: pugging, drying,


12

compaction and erosion (Berman & Jarman 1988; Dyring 1990; Beever & Herrick 2006; De Stoppelaire et al.

2004).

Some of the immediate effects of wild horses include the creation of tracks and bare patches due to trampling,

wallowing and horse camps (see Photo 1, 2 and 3). Trampling and wallowing have been found to cause

localised damage by reducing organic matter and exposing and compacting the soil surface (Dyring 1990).

Track networks are formed by the movement of wild horses. Dyring (1990) found that wild horses produce

extensive track networks in the Australian Alps. Continual trampling by wild horses can increase soil

compaction and therefore reduce aeration and pore space of soils and subsequently decrease water

infiltration and moisture content of soils. In addition, trampling and wallowing reduce plant cover and diversity

(Dyring 1990). The loss of vegetation cover means a reduction in shading for soils and less organic matter

inputs, resulting in greater erosion and a reduced ability of the soil to retain moisture (Beever & Herrick 2006).

Beever and Herrick (2006) found in western Great Basin sites (USA), three to 15 times lower penetration

resistance (a measure of soil compaction) in the soil surfaces of sites without wild horses (compared to those

with wild horses).

Photo 1: Trampled area at Cowombat Flat (source: Arn Tolsma 2008).

Photo 2: Wild horse camp, Davies Plain (Source: Arn Tolsma 2008)


13

Photo 3: Trampling at The Playgrounds, ANP (Source: Arn Tolsma 2008)

In the Australian Alps wild horse tracks have been found to result in a loss of plant cover, erosion (averaging

between 40-156cm³/m²), soil compaction, and a loss of soil structural composition (Dyring 1990). Drying

(1990) found that the soil on tracks was significantly compacted compared with off-track areas. Compaction

was found to be most severe on dry soils, where 20-50 passes by wild horses resulted in significantly

compacted soils. Compaction was found not to increase substantially with subsequent passes. Therefore an

average group of four wild horses using a new track twice daily for less than a week will result in significant

compaction. Wild horses were found to have similar usage of sub-alpine and montane areas, with no

difference in compaction or track width demonstrated between these sites (Dyring 1990). Whinam et al.

(1994) in their study of horse riding in Tasmanian Alpine environments found that 20-30 passes by horses has

substantial immediate as well as delayed effects on the soils of shrubland, herbfield and bolster heath

communities, however effects on dry grassland soils were less evident. Wild horse exclosure experiments in

the eastern Victorian Alps have shown that continued grazing and trampling by wild horses has maintained low

herbfield turfs, where the soil surface is more susceptible to trampling impacts than the grasslands found in

the horse exclosure plots (Wild & Poll 2012; Whinam et al. 1994).

Dyring (1990) found that wet soils were less prone to compaction but more susceptible to structural damage

than dry soils. This is supported by Rogers (1994) who demonstrated that dry areas are more resistant to

fracturing than wet areas, which were more easily broken up by trampling. The loss of soil structural

composition is most pronounced on wet soils because horse trampling and grazing fractures saturated soils

(Rogers 1994; Turner 1987; Dyring 1990). Fracturing of water saturated grassland can result in downslope

sedimentation, water ponding, and opportunities for the establishment of weeds (Rogers 1994). The gradient

of the slope has been found in other studies to directly correspond to the level of erosion. The steeper the

slope the more prone it will be to erosion (Dyring 1990).

Disturbances to the substrate caused by actions such as wild horse trampling, wallowing and grazing increase

the exposure of soils to the elements (such as wind, rain and needle ice), leads to the removal of vegetation

and alters drainage conditions hence increasing susceptibility to erosion (Dyring 1990). In central Australia,

wild horses were linked to aggravated gully erosion in areas close to water (Berman & Jarman 1988). Wild

horses caused considerable erosion in a sandy environment in the USA: over a five to seven year period fenced

plots (excluding horses) were on average 0.63 m higher than unfenced plots in sand dunes habitats (De

Stoppelaire et al. 2004).

Pugging of soil (trampling of wet soils leaving a dense mat of deep footprints), in particular around wetlands

and waterways, can change soil nutrient status, and increase water turbidity and sediment loads in adjacent

waterways (O’Connor 2005). Dyring (1990) found that wild horses in the Australian Alps can create nutrient


14

hotspots due to the high levels of nutrients (especially nitrogen) in their dung and urine. Manure in dung piles

increases the availability of soil nutrients, especially nitrogen and phosphorous, thus creating microhabitats

suitable for weed invasion (Loydi & Zalba 2009).

3.3 Impacts on vegetation

The level of impact wild horses have on native vegetation is dependent on the amount and type of use, and,

the resilience of the vegetation (Whinam et al. 1994). The most obvious impact wild horses have on vegetation

is a reduction in vegetation cover and height, however they may also alter plant species composition, richness

and diversity, and contribute to weed invasion (Turner 1987; Dyring 1990; Rogers 1991; Beever & Brussard

2000; De Stoppelaire et al. 2004; Loydi & Zalba 2008; Wild and Poll 2012). Trampling by wild horses also alters

vegetation, particularly along tracks and at watering points (Turner 1987; Dyring 1990; Rogers 1991; Beever &

Brussard 2000).

3.3.1 Removal of native vegetation by grazing, trampling and wallowing

Vertebrate grazers can negatively affect the cover of herbs in alpine and subalpine regions of Australia (Bridle

& Kirkpatrick 2001). Dyring (1990) found that wild horses preferentially graze grasslands and healthlands.

Studies in the greater alpine region have demonstrated that a decrease in grazing pressure from introduced

herbivores has led to an increase in plant cover or flower stem production (Carr & Turner 1959a; 1959b;

Wimbush & Costin 1979a; 1979b; 1979c; Leigh et al. 1991; Wahren et al. 1994). Bridle and Kirkpatrick (2001) in

their study of Tasmanian alpine and subalpine plains found the impacts of domestic stock (i.e. cows, horses,

sheep), rabbits and native herbivores on treeless subalpine vegetation were much greater than the effects of

natives herbivores and rabbits alone (Bridle & Kirkpatrick 1999).

McKay (2001) conducted a survey of the impacts of horse-riding and walking on the alpine vegetation of

Mount Bogong. Trampling was found to reduce the height, cover and abundance of both shrub and ground

flora within track areas and to result in greater exposure of bare ground. Beever et al. (2008) argue that the

loss of connectivity in shrub canopy due to rubbing and trampling may increase rates of isolation,

evapotranspiration and soil loss at small spatial scales.

Results from the Cowombat Flat and Native Cat Flat horse exclosure plot monitoring program have shown that

horse trampling and grazing has resulted in the removal of vegetation and increased bare ground in horse

occupied areas (Wild & Poll 2012). In contrast, fenced horse exclosure plots showed a trend for increasing

vegetation cover and decreasing bare ground as they recovered from past horse disturbance over a thirteen

year period (ibid).

It is argued that grazing may have an impact on the reproductive success of some flora species by impacting on

the dispersal opportunities of wind-dispersed species as well as their ability to attract pollinators; both of

these functions are affected by flower height (Bridle & Kirkpatrick 1999). For example, on the Assateague

Barrier Island (USA), a small herbaceous annual, Amaranthus pumilus was once abundant and is now limited to

a couple of individuals; its decline is linked to wild horse grazing and trampling (De Stoppelaire et al. 2004).

Bridle and Kirkpatrick (1999) found decreased fecundity of herbs with increasing grazing pressures. In

Australia, clipping experiments on alpine herbs have shown that flowering success may be retarded if plants

are clipped early in the growing season or if they are cut more than once (Leigh et al. 1991).

3.3.2 Change in vegetation composition and structure

Grazing by introduced herbivores can alter the appearance, productivity and composition of vegetation

communities (Dyring 1990; Hobbs & Hyeneke 1992). This may be due to reduced regeneration/recruitment as

a direct result of selective grazing or the physical impacts of trampling and erosion. Wild horses selectively

graze palatable species and have the potential to change the composition of threatened vegetation


15

communities (Dyring 1990). Redistribution of nutrients through dung can also contribute to the changes in

vegetation patterns (Dyring 1990).

Trampling can create openings in vegetation that provide opportunities for new plants to become established.

Different vegetation types demonstrate differing levels of resistance (tolerance) to trampling. Within some,

non-tolerant vegetation types, trampling can slow the growth of dominant species sufficiently to allow the

persistence of less vigorous species (Hobbs & Hyeneke 1992).

Dyring (1990) found trampled sites (and areas adjacent to track systems) had lower native plant diversity and a

higher abundance of exotic species. Plants found on wild horse tracks were characteristically non-woody

prostrate fast-growing annuals and grasses, with hemicryptophitic life-forms (species with renewal buds near

the surface), which tolerated trampling better than upright plants (Dyring 1990). Similarly, horse occupied sites

at Cowombat Flat and Native Cat Flat exhibited a predominance of hemicryptophitic species in contrast to

horse exclosure plots, which were dominated by grasses and sedges (Wild & Poll 2012). Grasslands are more

resilient to the impact of wild horses than other communities where ferns, mosses and shrubs are important

components of the vegetation (Whinam et al. 1994; Venn et al. 2009). Whinam and Chilott (1999) found that

shrubs and shrubland communities were more vulnerable to trampling than other life-forms or vegetation

types in central Tasmanian alpine vegetation.

As well as affecting vegetation community composition, wild horse activity can affect the physical structure of

vegetation communities. Exclosure experiments have shown that vegetation cover and height is far greater in

horse free sites (Turner 1987; Beever & Brussard 2000; De Stoppelaire et al. 2004; Prober & Theile 2007; Wild

& Poll 2012). Lower plant biomass was found in the Australian Alps where wild horse densities were higher

(Walter 2002). In the Cowombat Flat and Native Cat Flat wild horse exclosure plot monitoring program, the

following results occurred in the wild horse exclosures (see also Photo 4):

• a significant increase in the average height of vegetation;

• a significant increase in litter cover;

• no significant effect in species richness at Cowombat Flat;

• significantly lower native species richness at Native Cat Flat, due to the gradual competitive exclusion

of some lower stature species by dense swords of sedges and grasses;

• no indication of an increase in weed richness/abundance due to exclosure (Prober & Theile 2007,

Wild & Poll 2012).

While the effect of wild horses on vegetation structure and composition was less consistent than the effect of

horses on vegetation height, plots inside horse exclosures were often characterised by dense swards of sedges

and grasses associated with the competitive exclusion of some lower stature species (Wild & 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). Wild and Poll (2012) suggest that the

resurgence of dense sedges and grasses and competitive exclusion of some lower stature species may indicate

restoration to a previous, more natural state and possibly towards a peatland environment.

Studies in the USA have shown that wild horses can lower vegetation cover, abundance and flora species

richness as well as alter the species composition and structure of the vegetation (by increasing the

predominance of grazing resistant forbs and exotic plants and creating a less continuous shrub canopy)

(Beever et al. 2003; Beever and Herrick 2006; Stoppelaire et al. 2004; Beever & Brussard 2000). Using a series

of monitoring and exclosure plots in the Kaimanawa Mountains, New Zealand, Rogers (1991; 1994), found that

wild horses severely disrupted the composition of the native vegetation. In the grazed plots, species biomass

and stature was low for all potentially taller, palatable grasses (Rogers 1991).


16

Photo 4: Cowombat Flat wild horse exclusion plots from the air (source: Geoff Robinson).

3.3.3 Threatened vegetation

In the Victorian Alps, wild horses are considered to be one of the major threats to alpine ecosystems (Tolsma

2008b). Wild horses are considered to be a serious threat to at least five plant communities listed in the

Victorian Flora and Fauna Guarantee Act 1988 (FFG) (Appendix 1), and numerous plant species (Appendix 2).

The threat that wild horses pose to threatened species and communities is recognised in the listing of

“degradation and loss of habitats caused by wild horses” as a potentially threatening process under the FFG

Act. It is likely that wild horses threaten many other species or communities not yet identified or investigated.

Trampling by ungulates (hoofed animals) has been considered one of the major threats to several FFG listed

alpine vegetation communities. Within the Caltha introloba Herbland Community, cushions of tuft-rush

(Oreobolus), which play an important role in reducing the erosive forces of flowing water, may be dislodged by

trampling, or their regeneration disrupted (McDougall 1982; McDougall & Walsh 2007). Similarly, the Alpine

Snowpatch Community, situated on steep sheltered slopes, is subject to constant irrigation during the thaw

which renders them particularly susceptible to soil loss following damage to the vegetation by trampling

(McDougall 1982; Wahren et al. 2001a; McDougall & Walsh 2007). Montane Swamp, because of its position in

the landscape, is another listed community likely to be susceptible to the impact of wild horses (Dawson 2009).

Ecological communities which have been listed under the Federal Environment Protection and Biodiversity

Conservation Act 1999 (EPBC) and/or the Victorian FFG Act 1988, and that are potentially at risk from wild

horses, are presented in Appendix 2.

In order to mitigate the threat that wild horses pose to threatened flora species in the Victorian Alps, Parks

Victoria has established three wild horse exclusion fences around particularly threatened and sensitive


17

communities. In 2002 two wild horse exclusion fences were established on Davies Plain around sub-alpine

bogs known to contain several threatened plant species and the threatened Alpine Water Skink. In 2010 an

exclusion fence was established at The Playgrounds to protect a population of threatened Marsh Leek Orchid

(Prasophyllum niphopedium) (see Photo 5). The aim of all exclusion fences is to protect these species (and their

habitat in the case of the Alpine Water Skink) from trampling and grazing by wild horses.

Photo 5: The Playgrounds wild horse exclusion fence, established to protect a population of threatened Marsh Leek Orchid,

an alpine bog community and habitat for the endangered Alpine Water Skink (source: Parks Victoria 2012).

3.3.4 Weed dispersal and encouragement

Wild horses can facilitate weed invasion through dispersal and the creation of a favourable environment for

weeds through disturbance. Weed species are dispersed through attachment to the body of the wild horse

(epizoochory) or by being ingested and later excreted (endozoochory) (Cambell & Gibson 2001). Therefore

wild horses have the potential to disperse weeds both long and short distances and can subsequently

contribute to the establishment of weed species across several spatial scales (Nimmo & Miller 2007). Weaver

and Adams (1996) argue that within their home range, horses are a potentially significant vector in the

dispersal of a range of weed species.

While wild horses are less likely than domestic horses (i.e. recreational riding horses or horses illegally released

into the region) to introduce new weeds into the Victorian Alps, there is potential for this to occur, especially

considering their increasing range and the potential for wild horses to occur across tenures (i.e. farms, state

forests and national park). Many species of seed are transported in the dung of wild horses. Dung can be a

source of viable seed taxa not otherwise found in a community (Campbell & Gibson 2001). Campbell and

Gibson (2001) found that horses pass large numbers of seeds through their digestive tract generally within

48hours of consumption (but sometimes longer), and many of these seeds remain viable (Weaver & Adams

1996). In some cases the process of digestion scarifies the seed coat, enhancing germination (Campbell &

Gibson 2001). Weaver and Adams (1996) investigated the spread of environmental weeds into areas of native

vegetation along horse-riding tracks in three national parks in Victoria (including the ANP). Twenty-nine

species of weeds were found to be dispersed via horse manure.

Wild horse disturbance (i.e. dung, soil disturbance and pugging) can provide favourable environmental

conditions for the germination and colonisation of weed species (Dyring 1990; Rogers 1991; Loydi & Zalba

2009). Wild horse dung can result in significant changes in vegetation and can introduce and encourage some

invasive weed species that could eventually colonise more pristine areas (Loydi & Zalba 2009). Nutrients in

dung can favour weed establishment, with weeds establishing more vigorously in areas both trampled and

subject to deposition of dung. In a study of the potential for horse dung to act as an invasion window in

montane pampas grasslands, Loydi and Zalba (2009) found that the cover of introduced species was higher in

dung piles than in control plots. Dyring (1990) speculated that the redistribution of nutrients through uneven


18

dung deposits and selective grazing would lead to exotic plants such as White Clover (Trifolium repens) and

Cats Ears (Hypochoeris radicata), which readily colonise dung and disturbed areas, becoming established in

disturbed grassland and healthlands.

Wild horse disturbance was found to enhance the spread of smothering weeds in New Zealand’s Kaimanawa

Mountains (Rogers 1991; 1994). In the Australian Alps, exotic species were found to colonise the disturbed

area of wild horse tracks but did not tend to expand into untrampled areas (Dyring 1990). Dyring (1990)

argued that the maintenance of tracks by wild horses enables the continued survival of exotic weeds.

Horse occupied areas at Cowombat Flat were found to be characterised by a higher abundance of Yorkshire

fog grass (Holcus lanatus, an invasive grass species native to Europe) and red fescue grass (Festuca rubra, an

exotic grass species native to North America) than adjacent fenced horse exclosure areas (Wild & Poll 2012).

In a weed assessment of the peatlands within the Eastern Alps Unit of the ANP for Parks Victoria (Thomas 2010

unpublished report) Thomas (2010) made a series of assessments regarding wild horses and their relationship

with weeds. These observations are unquantified so are only mentioned briefly here:

• White clover (Trifolium repens) were found growing out of dung piles;

• the spread of Birds foot trefoil (Lotus uliginosus) into peatlands from culverts on Davies Plain Track

appeared to be associated with wild horses;

• there was evidence of wild horses grazing on Brown top bent grass (Agrostis capillaris), which may be

aiding the spread of this weed; and

• wild horses appear to avoid Yorkshire fog grass (Holcus Ianatus), providing this species with a

competitive advantage.

3.3.5 Native tree mortality

Wild horses have been found to affect native tree mortality in Australia. The chewing and stripping of bark by

horses can reduce regeneration of seedlings and may result in the death of mature trees. A significant negative

relationship was found between bark chewing damage and overall tree health in Guy Fawkes River National

Park (Schott 2002). Impact assessments identified bark-chewing damage was most severe along drainage-lines

and in close proximity with other water sources that are heavily used by wild horses. Schott (2002) found that

wild horses chew bark most intensely during summer and favour particular trees (Eucalyptus amplifolia and E.

saligna and E. Moluccana).

3.4 Impacts on peatlands (also known as mossbeds, peats, bogs, Sphagnum bogs, wet heathlands &

mires)

In Australia, peatlands are a rare ecological community, largely restricted to the highlands of Tasmania and the

south-east corner of the mainland (Tolsma 2008b). “Alpine Sphagnum bogs and associated fens” are listed as

an endangered ecological community under federal legislation (Environmental Protection and Biodiversity

Conservation Act 1999). Alpine bogs are also protected by Victorian legislation, where they are listed as a

threatened community under the Flora and Fauna Guarantee Act (1988). These ecosystems are of national

importance due to their significance in providing critical habitat for several endemic flora and fauna species

(many of which are threatened and several risk extinction) and the important role they play in the regulation

of water release and flow downstream to major river systems, such as the Murray (DEWHA 2009a).

Sphagnum moss is an important component of peatlands, integral to their structure and function. Wild horses

are known to have a detrimental impact on Sphagnum growth and integrity, with the resulting vegetation loss

ultimately leading to degradation of this ecological community (Dyring 1990; TSSC 2009). Wild horses are

therefore a major threat to Alpine Sphagnum peatland communities (Whinam & Chilcott 2002; Tolsma 2008b;

TSSC 2009; DEWHA 2009a).


19

Bogs and peatlands are highly sensitive to damage by trampling and grazing. Preferential grazing of palatable

herbs and grasses in Sphagnum bogs, combined with browsing of new growth of shrubs can lead to increased

dominance by unpalatable species (Whinam & Chilcott 2002). Sphagnum is easily crushed and broken up by

wild horses trampling the delicate vegetation, selectively grazing and wallowing in pools and waterways (TSSC

2009). Trampling may lead to the drying out of bogs, the loss of Sphagnum cover as well as changes to other

vegetation, and creation of bare pavements (Theile & Prober 1999a; TSSC 2009). Once Sphagnum cover is lost,

alpine soils and peat environments are very susceptible to desiccation, incision and soil erosion (TSSC 2009).

In New Zealand wild horses have been found to severely degrade bog and wetland areas through trampling

and grazing, irrespective of local variations in horse density and habitat abundance (Rogers 1991). The

vulnerability of bogs in New Zealand was also found to increase with wetness (Rogers 1991). Whinam and

Chilcott (2002) found most Sphagnum peatland communities investigated in the ACT and New South Wales

(NSW) were degraded by wild horses and other agents (i.e. fire, feral pigs, grazing and clearing). In 2008 the

status of peatland systems in the Victorian Alps was investigated by Tolsma (2008a; 2008b). In the East Alps

Unit of the ANP, 97% (n=63) of peatland systems were found to be impacted (i.e. compacted, trampled or

pugged) by wild horses (Tolsma 2008b). Only two peatlands assessed by Tolsma (2008b) in this unit of the ANP

did not show any signs of current wild horse activity: a fenced peatland at Davies Plain and an isolated system

on the south-east edge of the Unit. Whinam and Chilcott (2002) argue that wild horses are one of the greatest

threats to the survival of peatlands.

Channelling is a form of erosion and water diversion which can result from wild horse activity. Trampling and

wallowing cause channels to form in the disturbed Sphagnum. Channelling leads to changes in water flow, as

water exits the disturbed bog more rapidly. This action may completely alter the drainage pattern and result in

drier conditions (Whinam & Chilcott 2002; TSSC 2009). The formation of channels is detrimental to the fens

associated with the bogs because the fens drain directly into the stream system and dry-up (TSSC 2009).

Due to the access provided to peatlands following extensive bushfires throughout the Victorian Alps (primarily

in the 2003 fires) Tolsma (2008b) found that wild horse activity in burnt sub-alpine to alpine peatlands in the

Victorian Alps varied from minor trampling at peatland margins to extensive pugging across almost the entire

burnt peatland surface. On average, 25% of all peatland surface area assessed in the East Alps Unit of the ANP

and 16% of peatland area assessed in State forest to the south was impacted by trampling (Tolsma 2008a)1

(see Photo 6). Trampling by wild horses restricts Sphagnum recovery in naturally-regenerating peatlands, and

may impact on some peatlands where restoration work is occurring (Tolsma 2008b). Tolsma (2008b) argues

that in the Victorian Alps, many areas of burnt peatland, particularly in the East Alps Unit, are unlikely to

completely recover while wild horses remain in the area (Tolsma 2008b).

Peatland communities are likely to face further strain as climate change further alters their functioning

(Dawson 2009b). At the same time it is suggested that the importance of the functional role that Alpine

Sphagnum peatlands play in water release and flow downstream will increase (DEWHA 2009a).

1 'Area impacted' is the estimated proportion of the peatland system that was compacted, trampled or pugged by wild

horses.


20

Photo 6: Wild horse trampling of a bog area at The Playgrounds (source: Parks Victoria 2010)

3.5 Impacts on waterways (streams and stream-banks)

Wild horse activity can lead to the degradation of waterways and a reduction of water quality in streams,

water holes and springs due to the trampling of stream banks and fouling of water holes (Csurhes et al. 2009).

Wetlands, waterways and their adjacent riparian ecosystems generally have very high diversity and

productivity (Dawson 2009b), but are typically fragile and susceptible to damage by wild horses (and other

large hoofed animals) from selective grazing, trampling, pugging, wallowing and crossing (Costin 1954;

Whinam & Comfort 1996; Williams et al. 1997; Evans 1998; Whinam & Chilcott 2002; McDougall 2007; NPWS

2007; Prober & Thiele 2007; Dawson 2010). Streambanks are easily churned up and broken down by wild

horse hooves sinking into wet soils (Dyring 1990). Grazing by large hard-hooved herbivores can affect

streamside vegetation, stream channel morphology, shape and quality of the water column and the structure

of the soil portion of the streambank, which has flow on effects for aquatic and terrestrial wildlife (Kauffmann

& Krueger 1984; Rogers 1994; Beever & Brussard 2000).

In the Victorian Alps, grazing and trampling within the vicinity of streams has been found to result in bank

slumping and breakdown, vegetation disturbance and increased soil compaction (see Photos 7, 8 and 9). This

can lead to a decrease in infiltration, increased run-off as well as further drainage channel development,

lateral erosion and stream incision (Dyring 1990).

The Cowombat Flat and Native Cat Flat monitoring program has revealed significant changes to stream

function and structure as a result of wild horse exclosure fencing. The unfenced stream areas had more bare

ground, were more entrenched and had distinct, open water channels, whereas areas within the exclosures

had indistinct channels, a more or less complete vegetation cover across the channel and no or little visible

open water (Prober & Thiele 2007, Wild & Poll 2012). There was a significant increase in stream depth over

time in unfenced plots at Native Cat Flat while stream depth within the exclosures remained stable, suggesting

accelerated erosion in horse occupied areas (Wild & Poll 2012). Stream condition was better and consistently

improved over time in the horse exclosure plots which exhibited less pugging, stream slumping (collapse of the

stream bank) and bare ground than unfenced areas (Wild & Poll 2012). The extra vegetation and lack of bare

ground have led to slower water flow along the stream in the horse exclosures (Prober & Thiele 2007, Wild &

Poll 2012). In contrast the increased bare ground and lack of vegetation in unfenced areas is contributing to

faster flows and accelerated erosion of the stream channel, particularly at native Cat Flat where steep banks

with undercutting were observed (Wild & Poll 2012). Subsequently Prober and Thiele (2007) and Wild and Poll

(2012) argue that at a catchment level, wild horse trampling and grazing may be impacting significantly on

stream and catchment hydrology and water quality.


21

In 2011 the AALC commenced a project that aims to quantify the impacts of wild horses on upland streams

and wetlands in the Australian Alps. The results of this study will be available in autumn 2013 and will provide

further evidence of the impacts of wild horses on sensitive stream and wetland environments.

Photo 7: Wild horse pugging of waterway resulting in bank slumping, Murray Headwaters (source: Parks Victoria 2006).

Photo 8: Wild horse damage to Murray River water source (source: Parks Victoria 2006)

Photo 9: Wild horse trampling at the head of Moscow Creek, Cobberas Range, ANP (source: Parks Victoria 2006).


22

3.6 Impacts on fauna

Wild horse populations can alter the composition of bird, fish, crustacean, small mammal, reptile and ant

communities (Nimmo & Miller 2007) and have been identified as a major threat to a range of native wildlife

species in the Victorian Alps. The 2001 AALC Natural Heritage Working Group Workshop of field staff and

scientists, ranked wild horses as one of the top five priority fauna threats to the Australian Alps (Coyne 2001).

Wild horses can affect native fauna through causing habitat modification or loss, and also through competition

for resources (i.e. food, water, shelter and space) (Olsen & Low 2006; Nimmo & Miller 2007).

3.6.1 Competition and altered food availability

Wild horses compete for resources with native herbivores, especially macropods, including: grey kangaroos

(Macropus giganteus), red-necked wallabies (M.rufogriseus) and swamp wallabies (Wallabia bicolour). Various

studies have demonstrated that high densities of wild horses correspond with reduced densities of macropods.

Berman and Jarman (1988) found few signs of macropods in the Northern Territory in areas heavily grazed by

wild horses. A study of wild horse impacts in Guy Fawkes River National Park by Lenehan (2010) provides

evidence of wild horses displacing kangaroos from prime feeding habitats. Dung transects conducted in the

national park showed a strong negative relationship between wild horse dung and macropod dung. As wild

horses were removed from the transect area (as part of NSW National Parks and Wildlife Service (NPWS) horse

capture program, where 250 wild horses were removed) there was a significant progressive decline in horse

dung and increase in macropod dung. Indicating that macropods were responding positively to decreases in

horse abundance (Lenehan 2010).

Although it has not been investigated to date, it is possible that wild horses also compete with other native

mammals such as wombats (Vombatus ursinus). Wombats also feed primarily on grasses (such as Poa and

other grass species and some shrubs) and like wild horses, dig below the snow to reach low vegetation during

winter (Matthews 2010).

Wild horse activity may constrain resources for many species and may increase the vulnerability of threatened

species (Nano et al. 2003). A reduction in the density of wild horses in Finke Gorge National Park and

surrounding area correlated with a striking increase in black-footed rock wallabies (Petrogale lateralis) and

small fauna populations (Matthews et al. 2001). In 1990 no fresh black-footed rock wallaby dung was

recorded, however after approximately 6000 wild horses were removed (and the population kept at low

numbers), the amount of fresh dung recorded steadily increased over the following ten years. It is suggested

that the wild horse population may also have suppressed the endangered stick-nest rat (Zyzomys

pedunculatus) in the West MacDonald ranges (Nano et al. 2003). Despite numerous surveys the species was

not recorded between 1960 and 1996 and it was concluded the species was extinct. However in 1996 it was

rediscovered at numerous sites, a finding that corresponded with the removal of 30 000 wild horses (Nano et

al. 2003). The major food plants identified in the diet of the stick-nest rat were also palatable to wild horses

and other introduced ungulates (ibid.).

3.6.2 Habitat modification

Wild horse grazing can result in a more open shrubland and increased area of bare ground, which in turn

causes changes for associated wildlife (Zalba & Cozzani 2009). The removal of vegetation through grazing,

trampling, wallowing and rubbing can result in a loss of shrub and ground vegetation connectivity. The habitat

value of a site for animal species that require shrubs for shade, food or protection from predators and other

threats may be reduced by the loss of this connectivity (Beever et al. 2008).

Simplification of habitat by wild horses can lead to a reduction in foraging, nesting and roosting opportunities

for native animals, such as ground dwelling, foraging and roosting birds (O’Connor 2005). Zalba and Cozzani

(2009) investigated the impact of wild horses on different bird communities in the Pampas grasslands in


23

Argentina. The presence of wild horses was associated with an increase in the rate of egg predation, which

varied from 12.5% within exclosures to 70% in grazed areas. This was directly related to increased visibility of

the nests and subsequent exposure to predators, nest trampling and reduced nesting sites. In Victoria’s

Barmah Forest wild horses are listed as a threat to some ground nesting birds including the Australasian

Bittern and Little Bittern (SAC 1997a; 1997b). Due to a lack of research it is unknown if wild horses pose a

threat to any birds in the Victorian Alps.

Wild horses may potentially cause the collapse of wildlife burrows (Theile & Prober 1999a). In the Victorian

Alps many medium and small mammals, such as the bush rat (Rattus fuscipes), swamp rat (R. lutreolus) and

broad-tooothed rat (Mastacomys fuscus), use burrows that may be susceptible to trampling damage. Wombat

burrows that, for example are dug in open ground with little protective cover over the burrow may be

susceptible to damage by wild horses. In the USA, exclosure plots around springs exhibited more small-

mammal burrow entrances than plots at horse-grazed springs (Beever & Brussard 2000).

The affect that wild horses have on invertebrate eco-engineers such as ants in the Victorian Alps is currently

unknown. Beever and Herrick (2006) found a greater abundance of ant mounds in sites where wild horses had

been removed over ten years ago. This may have a substantial influence on ecosystem health and the survival

of other species.

Extensive damage to the structural complexity of ground-level vegetation and habitat caused by wild horses

threatens the reptile and amphibian species of the Victorian Alps. Structural complexity of habitat is a critical

requirement for many reptile species and communities (Clemann et al. 2001). Litter cover, ground cover and

the degree of soil compaction are all important elements for reptiles (e.g. Brown 2001; Jellinek et al. 2004).

Similarly, most amphibian species in the Australian Alps rely on the structural complexity formed by vegetation

along the margins of streams and ponds, especially for male calling and female egg laying sites (Osborne 1990;

Green & Osborne 1994). Grazing and trampling by ungulates such as wild horses in the alpine region affects

habitat complexity through: direct removal of vegetation; destruction of structural components in the ground

layer; and, soil compaction (Clemann et al. 2001). For example, the alpine water skink (Eulamprus kosciuskoi)

(photo 10), alpine she-oak skink (Cyclodomorphus praealtus) and alpine bog skink (Pseudemoia cryodroma) are

threatened by wild horse impacts on peatlands, wet heath and riparian areas, which provide vital habitat for

these species (Clemann et al. 2001; Clemann 2001; Meredith et al. 2003; Steane et al. 2005).

As discussed, peatland habitats are extremely vulnerable to wild horse activity. Horse damage to peatlands has

immediate effects on habitat structure, and leads to hydrological consequences such as deteriorating water

quality and loss of landscape structure. Damage to habitat caused by wild horses is specifically identified as a

threat to the federally endangered alpine she-oak skink, which occurs in close proximity to bogs, streams and

wet heaths. Recommended actions to mitigate this threat include the development and implementation of a

management plan for the control of wild horses (DEWHA 2009b).

Historically, the threatened alpine tree frog (Litoria verreauxii alpine) was widespread and abundant across

most of the high country of mainland south-eastern Australia (Clemann & Gillespie 2004). The species has

since retracted from much of its previous habitat. Populations of the alpine tree frog are known to be subject

to a number of threatening processes, including the trampling of habitat by wild horses (Clemann & Gillespie

2004). The threat of further population declines is likely and remains a cause for concern (Brown et al. 2007).

Small mammal communities may be affected by grazing ungulates such as wild horses indirectly through

alteration in vegetation structure, water quality and other site characteristics (Giuliano & Homyack 2004).

Removal of ungulates (mostly cattle) grazing from streams and associated riparian zones led to an increase in

mammalian species richness and abundance within two years in a study in south west Pennsylvania (USA)

(Giuliano & Homyack 2004). A similar result was shown in the central Kimberley across several habitats after


24

the removal of cattle (Legge et al. 2007). In a study of horse impacts using exclosures in the USA, qualitative

differences were observed in small mammal activity (Beever & Brussard 2000).

There are a limited number of small mammal species in the Australian Alps, and complexity of vegetation

structure is associated with habitat quality for these species (Carron 1985). The habitat of small mammals in

Alpine regions is extremely sensitive and threatened by climate change (Green et al. 2008). A species of

particular concern is the broad-toothed rat Mastacomys fuscus (Green & Osborne 2003 and references within)

whose habitat is shrinking and is likely to face a further declines with climate change (Green et al. 2008). The

broad-toothed rat inhabits areas of moderate-to-dense grass and/or sedge cover (Green et al. 2008). This

environment is favoured by wild horses for grazing and the habitat can be broken-up through wild horse

activity. O’Brien et al. (2008) found populations of broad-toothed rats that existed in isolated patches were

likely to suffer local extinction due to low levels of success emigrating through unsuitable habitat to reach

suitable habitat.

3.6.3 Threatened fauna in the Victorian Alps

Herpetofauna (reptiles and frogs) are central components of the vertebrate fauna of the Victorian Alps and

several threatened species are endemic to alpine areas (Clemann et al. 2001). A large proportion of this group

are officially listed as threatened at the federal and state level (Appendix 3). Herpetofauna in this region are

generally dependent on bog, grass and wet heath habitats (Clemann et al. 2001). As previously mentioned,

most alpine herpetofauna are intimately linked with habitat structure, particularly close to ground level

(Clemann et al. 2001). Wild horses are believed to be one of the processes directly or indirectly threatening

these species (Clemann et al. 2001). For example, the alpine water skink (Eulamprus kosciuskoi) (photo 10) is

listed as critically endangered in Victoria and is only found in the high altitude areas of south-eastern Australia

(Steane et al. 2005). Steane et al. (2005) found the preferred habitat of alpine water skinks to be mossbeds in

good condition (i.e. high cover of live Sphagnum and low cover of bare-ground, rock and non-mossbed

vegetation). Any threat to Sphagnum cover, such as that posed by wild horse grazing and trampling, severely

threatens the habitat of the alpine water skink (Steane et al. 2005). Horses have impacted much habitat that

was previously occupied by the alpine water skink on Forlorn Hope Plain in the Buchan headwaters.

Consequently, to protect threatened alpine water skink populations from trampling by wild horses, wild horse

exclusion fences at Davies Plain around two sub-alpine bogs have been constructed (see section 3.3.3).

Photo 10: The alpine water skink (Eulamprus kosciuskoi), an endangered species whose habitat is threatened

by wild horses (Source: Nick Clemann).


25

4. Wild horse biosecurity issues

Wild horses are a prominent reservoir for exotic and endemic diseases and parasites that can affect native

wildlife, domestic horses, stock and humans (Bradshaw et al. 2007). The spread of pests and disease by feral

animals is considered by the federal government of Australia to be a major biosecurity risk (DAFF 2010).

Wild horses in the Victorian Alps have the potential to be a biosecurity risk through harbouring and

transmitting disease. Diseases of concern are either those that have the potential to establish or exist already

within Australia. Diseases are highly variable, for example they may be equine specific or they may affect

several species, transmissibility varies, and symptoms range from minor ailments to mortality. The wild horse

population in the Australian Alps poses a potential risk to other species that may co-habit with them such as

native species, pigs, deer and cattle.

Wild horses have the potential to transport the Amphibian Chytrid fungus (Batrachochytrium dendrobatidis)

between waterbodies and between catchments. This pathogenic and highly transmissible fungus, results in the

disease chytridiomycosis, that has caused the decline or extinction of up to 200 species of frogs (Skerratt et al.

2007). Skerratt et al. (2007, p.125) refer to the impact of this fungus as the, “most spectacular loss of

vertebrate biodiversity due to disease in recorded history”. As well as being a potential vector of this disease,

horses may introduce novel strains of the fungus to new areas. Some fungus free frog populations remain in

places such as Grey Mare in Kosciusko National Park and keeping them fungus free is a critical biodiversity

priority.

Wild horses can play a potential role in a disease outbreak of a newly imported disease (Biosecurity Australia

2009). There are many steps involved in the outbreak of a new disease. Wild horses must first be exposed to

the disease, once exposure occurs, a range of outbreak scenarios are possible from no spread to widespread

establishment. Outbreak scenarios are dependent on the epidemiology of each disease agent. The role that

wild horses play in a potential disease outbreak scenario for a newly imported disease was considered in a risk

assessment by Biosecurity Australia (2009). In general, wild horses were thought to have a limited ability to

affect domestic horse populations because of their remoteness. Equine Influenza received the highest risk

assessment (moderate). There was an outbreak of Equine Influenza in 2007, which led to prohibitions on horse

movements in Victoria to control the spread of the disease, however, it was eliminated (Animal Health

Australia 2009).

There is little known about the incidence and prevalence of many existing diseases of domestic horses in

Australia, and much less is known about the frequency of disease in wild horses. There are a range of zoonotic

diseases (diseases that horses can share with humans and other livestock) which are present in Australia and

may be of concern including anthrax, Hendra virus disease, Murray Valley Encephalitis, leptospirosis,

Australian bat lyssavirus, Salmonellosis, Tetanus and ringworm. It is not known how these diseases may affect

native species.

Hendra virus is a relatively new and emerging disease, first reported in 1994 in Queensland (Equine Species

Working Group n.d). Subsequently there is not a great deal known about the disease, however, horses are

likely to be dead-end hosts. It causes severe respiratory illness in horses and is frequently fatal. Humans can

contract the disease if they have direct contact with blood or saliva of an infected horse (Equine Species

Working Group n.d).

Murray Valley Encephalitis is a virus spread by mosquitoes that can infect many animals, including horses and

humans (DPI 2012). The virus causes swelling of the brain and is potentially fatal for humans (DPI 2012).

Outbreaks in south eastern Australia are generally associated with wet conditions. In 2011 a widespread

outbreak infected domestic horses in north and north western Victoria (DPI 2012).


26

Humans, domestic animals and wildlife are susceptible to the bacterial disease Leptospirosis and infected

animals may become sick or show no symptoms at all (Equine Species Working Group n.d). Salmonellosis is a

bacterial disease that can infect horses and humans and is of concern because some strains exhibit resistance

to multiple antibiotics (Equine Species Working Group n.d). Salmonella may impact upon many species

(including native wildlife) particularly if they are under stress. Australian bat lyssavirus is the only type of rabies

in Australia; however, there have been no reports of horses being affected by this disease. Tetanus can be a

fatal disease and its spores are widely distributed, usually in soil, dust and manure; horses and humans are the

most susceptible of all of the animal species to tetanus (Equine Species Working Group n.d). Ringworm is a

fungal skin disease. Numerous species can transmit ringworm to humans (Equine Species Working Group n.d).

5. Gaps in knowledge

There has been a limited amount of research into wild horse biology, behaviour and ecological impacts in the

Alpine region to-date. An important area for investigation that will aid in guiding effective management is the

relationship between wild horse density and damage (Dawson et al. 2006). Quantification of the relationship

between density, impact and population control has been identified as a priority research area for the

management of wild horses by the AALC. The AALC has initiated a project that aims to address this gap by

developing a protocol for determining horse density at the local scale and investigating the influence of horse

density on impacts. Site-specific research using experimental trials to determine local levels of resistance to

impact would also provide important information (Venn et al. 2009).

Previous aerial surveys of wild horse populations have not covered the whole area occupied by horses and are

likely to significantly under-estimate the total population size. There are large areas known to be occupied by

wild horses that have been excluded from previous aerial surveys, including Byadbo and adjoining areas of the

Alpine National Park and adjacent State Forests (Dawson 2009). There are plans to cover a larger portion of

the area occupied by wild horse in future aerial population surveys in order to obtain a more accurate estimate

of the total Victorian Alps wild horse population size. Wild horses do not currently occupy all suitable habitat

within the Victorian Alps. Mapping potential horse habitat that could potentially be colonised by wild horses is

required and work has commenced to address this gap (Dawson 2009).

The effects of wild horse grazing on vegetation have been investigated at small spatial scales; however have

not been investigated at a broad spatial scale. The effects of chronic disturbance over broader areas is

subsequently not well understood within the Victorian Alps, greater Alpine area, Australia or internationally

(see Beever et al. 2003; Beever et al. 2008). To-date only studies at a small single spatial scale have been

considered. These studies are important; however they may not be representative of the Victorian Alps system

more broadly and may not represent the conditions prevalent on a landscape scale (Nimmo & Miller 2007)

Finally there is a need to further investigate how the environmental impact of wild horse’s changes through

time as the environment varies (e.g. drought, fire, climate change etc). The environmental impact of wild

horses may be exacerbated in drought years, as they tend to concentrate around watering points (Dawson

2010). Impacts are also likely to increase substantially after fire (such as those that occurred in Victoria in 2003

and 2006/07) when Alpine environments such as peatlands are particularly susceptible. Climate change is

likely to influence the magnitude of the impacts of wild horses in future years. Alpine species and communities

are amongst the most vulnerable to the effects of climate change and therefore their resilience to climate

change requires that they be protected and maintained in as healthy a condition as possible (DSE 2010). This

pressure combined with the impact of wild horses requires further investigation.


27

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36

Appendix 1: Officially listed plant ecological communities at risk of

severe damage from wild horse activity

Floristic Community or

Ecological Vegetation Class EPBC FFG Main consequences

Alpine Bog Community Endangered* Listed Disruption of plant regeneration, selective grazing

leading to compositional changes, weed invasion,

severe trampling, soil loss, and loss of hydrological

function.

Fen (Bog Pool) Community Endangered* Listed Disruption of plant regeneration, selective grazing

leading to compositional changes, weed invasion,

severe trampling, and loss of hydrological function.

Alpine Snowpatch

Community

Listed Severe trampling, soil loss, displacement of

vegetation, weed invasion, selective grazing

leading to compositional changes.

Caltha introloba Herbland

Community

Listed Soil loss, displacement of vegetation, weed

invasion

Montane Swamp Complex

Community

Listed Severe trampling, soil loss, displacement of

vegetation, weed invasion, smothering by dung

piles, selective grazing leading to compositional

changes.

* Alpine Bog and Fen Pool communities are combined in the EPBC listing


37

Appendix 2: FFG-listed and EPBC-listed plant species potentially at

risk from wild horse activity in the eastern Victorian Alps AROT = Australian

Rare or Threatened status, VROT = Victorian Rare or Threatened status. e = endangered (Victoria), r =- rare

(Victoria), v = vulnerable (Victoria), V = Vulnerable (EPBC, Australia).

Species Listed

AROT,

VROT Main consequences

Bogong Eyebright (Euphrasia

eichleri)

FFG,

EPBC

V, v May be selectively grazed - more common in ungrazed open heath

& grassland.

Snow Pratia (Lobelia gelida) FFG,

EPBC

V, v Trampling & loss of habitat - ephemeral pools in wet alpine

grasslands & creek margins

Austral Toad-flax (Thesium

australe)

FFG,

EPBC

V, v Trampling of habitat - grasslands & grassy woodlands. Considered

to be palatable to stock.

Tasmanian Bladderwort

(Utricularia monanthos)

FFG v Trampling & loss of habitat - Caltha introloba Herbland Community

& stream edges

Allied Bent-grass (Deyeuxia

affinis)

FFG e Trampling & loss of habitat - Caltha introloba Herbland Community

Cushion Rush (Juncus

antarcticus)

FFG v Trampling & loss of habitat - Caltha introloba Herbland

Community, Alpine Snowpatch Community & bog margins

Rock Poa (Poa saxicola) FFG v Trampling & loss of habitat - Alpine Snowpatch Community, open

heath & grassland. Palatable, & rare in grazed areas.

Marsh Leek-orchid

(Prasophyllum niphopedium)

FFG e Trampling & loss of habitat - alpine wet heathlands & bogs.

Observed to be directly impacted.

Mountain Daisy (Brachyscome

sp. 3)

FFG v Trampling & loss of habitat - alpine wet grasslands & herbfields

Slender Parrot-pea (Almaleea

capitata)

FFG v Trampling of habitat - sub-alpine heathlands & stream fringes

Wire-head Sedge (Carex

cephalotes)

FFG v Trampling & loss of habitat - alpine herbfields

Bogong Apple-moss

(Bartramia subsymmetrica)

FFG e Trampling & loss of habitat - wet grasslands & bog margins

Austral Moonwort

(Botrychium australe)

FFG v Trampling & loss of habitat - subalpine grassland & margins of bogs

& streams. Intolerant of disturbance.

Rough Eyebright (Euphrasia

scabra)

FFG e Trampling & loss of habitat - grassy edges of wetlands

Felted Buttercup (Ranunculus

muelleri)

v Trampling & loss of habitat - alpine herbfields, wet grasslands &

bog margins. Observed to be directly impacted.

Olive Mallee (Eucalyptus

elaeophloia)

v Trampling of habitat - sub-alpine woodlands. Observed to be

directly impacted.

Star Sedge (Carex echinata) v Trampling & loss of habitat - alpine wet heathlands & bogs

Snow Wort (Abrotenella

nivigena)

v Trampling & loss of habitat - alpine wet heathlands, bogs & moist

herbfields

Alpine Marsh Marigold

(Psychrophila introloba)

r Trampling & loss of habitat - Caltha introloba Herbland Community

Carpet Sedge (Carex jackiana) r Trampling & loss of habitat - moist alpine herbfields

Turquoise Coprosma

(Coprosma moorei)

r Trampling of habitat - alpine wet heathlands, bogs & grasslands

Dwarf Coprosma (Coprosma

pumila)

e Trampling of habitat - alpine woodlands, heathlands & grasslands

Snow Pennywort (Diplaspis

nivis)

r Trampling of habitat - alpine wet heathlands, bogs, grasslands &

herbfields

Sky Lily (Herpolirion novae-

zelandiae)

r Trampling & loss of habitat - alpine wet heathlands, bogs &

herbfields

Tuft-rush (Oreobolus

oxycarpus subsp. oxycarpus)

r Trampling & loss of habitat - alpine wet heathlands & bogs

Alpine Tuft-rush (Oreobolus

pumilo subsp. pumilio)


Parantennaria (Parantennaria

uniceps)

v Trampling & loss of habitat - Caltha introloba Herbland Community

Snow Aciphyll (Aciphylla

glacialis)

r Selective grazing in open heath & grassland. Highly palatable &

most common in ungrazed areas.


38

Mountain Aciphyll (Aciphylla

simplicifolia)

r Selectively grazed in grasslands & bog margins. Highly palatable,

most common in ungrazed areas.

Native Wintercress (Barbarea

grayi)

v Trampling & loss of habitat - bogs & stream margins. Highly

palatable to stock.

Grassy Moonwort

(Botrychium lunaria)

v Trampling of grassy habitat. Intolerant of disturbance.

Baw Baw Daisy (Brachyscome

obovata)


Marsh Daisy (Brachyscome

radicans)

r Trampling & loss of habitat - alpine wet heathlands & bogs.

Spreading Bitter-cress

(Cardamine astoniae)

v Trampling of habitat - wet grasslands and bog margins. Palatable

to stock.

Star Sedge (Carex echinata) v Trampling & loss of habitat - alpine wet heathlands & bogs.

Palatable to stock.

Raleigh Sedge (Carex raleighii) r Trampling & loss of habitat - alpine wet heathlands & bogs.

Palatable to stock.

Marsh Tree-moss (Climacium

dendroides)

v Physical damage to habitat - within streams

Creeping Coprosma

(Coprosma perpusilla)


White Billy-buttons

(Craspedia alba)

v Trampling & damage to habitat - Caltha herbfields & valley

bottoms. Palatable to stock.

Tufted Hair-grass

(Deschampsia caespitosa)

r Trampling & loss of habitat - Caltha introloba Herbland Community

& fens

Skirted Bent-grass (Deyeuxia

talariata)

v Trampling & loss of habitat - alpine wet heathlands & bogs.

Tailed Eyebright (Euphrasia

caudata)

r Trampling & loss of habitat - Alpine Sphagnum bogs

Slender Gingidia (Gingidia

harveyana)

v Trampling & loss of habitat - stream margins. Highly palatable,

hence selectively grazed.

Alpine Holy-grass (Hierochloe

submutica)

v Trampling & loss of habitat - alpine wet heathlands & bogs.

Tussock Woodrush (Luzula

alpestris)

r Trampling & loss of habitat - grassy edges of wetlands

Slender Woodrush (Luzula

atrata)

v Trampling & loss of habitat - damp grasslands

Spreading Clubmoss

(Lycopodium scariosum)


Hump Moss (Meesia muelleri) r Trampling & loss of habitat - boggy grasslands

Branched Caraway

(Oreomyrrhis brevipes)

v Selective grazing in rocky habitat. Palatable, and now extremely

rare in grazed areas.

Wedge Oschatzia (Oschatzia

cuneifolia)

r Trampling & loss of habitat - alpine wet heathlands and bogs.

Matted Rice-flower (Pimelea

biflora)

r Possible selective grazing in open heath & grassland. Rare in

grazed areas.

Hard-head Bush-pea

(Pultenaea capitellata)

r Trampling & loss of habitat - margins of alpine wet heathlands

Southern Sheep-grass

(Rytidosperma australe)

e Trampling & loss of habitat - Caltha introloba Herbland Community


39

Appendix 3: Officially listed or threatened fauna species potentially at

risk from feral horse activity in the eastern Victorian Alps

Species EPBC FFG DSE2 Main consequences

Alpine Water Skink

(Eulamprus kosciuskoi)

Listed Critically

Endangered

Loss and degradation of habitat - alpine bog

and alpine fen (bog pool) communities

Alpine Bog Skink

(Pseudomoia cryodroma)

Listed Endangered Loss and degradation of habitat - alpine bog

and alpine fen (bog pool) communities,

woodlands and heathlands

Alpine She-oak Skink

(Cyclodomorphus

praealtus)

Endangered Listed Endangered Loss and degradation of habitat - alpine

tussock grasslands, alpine low heathlands

Guthega Skink (Liopholis

guthega)

Under

consideration

Listed Critically

Endangered

Loss and degradation of habitat - alpine

heathlands

Mountain Skink (Liopholis

Montana)

Data Deficient Loss and degradation of habitat - alpine

woodlands

Alpine Tree Frog (Litoria

verreauxii alpina)

Vulnerable Listed Critically

Endangered

Loss and degradation of habitat - alpine and

subalpine wetlands, riparian zones and

ephemeral pools.

Documents

Background Paper 1 of 3 The Ecology of Wild Horses and ...€¦ · The Ecology of Wild Horses and their Environmental Impact in the Victorian Alps May 2013 Table of Contents Introduction