The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular in semi-arid woodlands

NSW Department of Land and Water Conservation

The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands

A consultancy report for WEST 2000Plus

Prepared by: David Eldridge

NSW Department of Land and Water Conservation The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

Acknowledgments

I am grateful to the following people for their hard work and assistance with field data collection: James Val, Scott Jaensch, Ron Rees, Sharee Bradford, Daryl Laird and Peter Connellan. James Val and Bruce Cooper provided comments on an earlier draft. Special thanks are due to Ron Rees (WEST 2000Plus) who has worked tirelessly to promote rabbit control in the Western Division.

Published by: Centre for Natural Resources Department of Land and Water Conservation Parramatta

March 2002 ? NSW Government ISBN 0 000 0000 0 ISSN 0000 0000 CNR2002.006

NSW Department of Land and Water Conservation

ii The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

Contents

Page

Executive Summary...... v Terms of Reference ...... v

1. Background...... 1

2. Research approaches to a study of rabbits and biodiversity ...... 2

3. Methodology ...... 3 3.1 Selection of sites ...... 3 3.2 Selection of the warrens ...... 3 3.3 Detailed warren measurements at all sites ...... 4 3.3.1 Vegetation cover measurements...... 4 3.3.2 Additional measurements (conducted at Yathong only)...... 4 3.4 Statistical analyses ...... 5

4. Results...... 6 4.1 Floristics and species richness...... 6 4.2 Community vegetation structure...... 6 4.2.1 types...... 6 4.2.2 Community Plant Structure...... 6 4.2.2.2 Calcareous loams – Warrananga Bluebush...... 8 4.3.2.3 Non-calcareous loams – Warrananga Sandplain ...... 8 4.2.2.4 Non-calcareous sands– Morquong...... 9 4.3 Morphology of warren surface soils...... 10 4.4 Differential germination of plant species...... 10 4.5 Post-calicivirus warren reinvasion ...... 10

5. Discussion...... 16 5.1 Effects of rabbits on biodiversity ...... 16 5.2 Effects of rabbits on soil and ecological processes...... 17 5.3 Impact of rabbits on other fauna ...... 18

6. Recommendations ...... 19

7. References ...... 20

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iii The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

Figures

Page Figure 1. Mean soil cover for various surface components on the warren and non-warren microsites at Yathong...... 12 Figure 2. Percentage germination of the four plant species after 10 days on warren and non-warren microsites...... 14

Tables

Page Table 1. Description of the four study areas...... 3 Table 2. Floristics and ground cover measurements for the control and warren microsites for the four sites...... 6 Table 3. Mean cover-abundance of each of the 44 species recorded at Yathong ...... 7 Table 4. Mean cover-abundance of each of the 33 plant species recorded at the Warrananga Bluebush site ...... 9 Table 5. Species, mean cover and percent dissimilarity contributing to 82% of the dissimilarity between control and warren species at the Warrananga Bluebush site...... 10 Table 6. Mean cover of each of the 40 plant species recorded at the Warrananga Sandplain site ...... 11 Table 7. Species, mean cover and percent dissimilarity contributing to 75% of the dissimilarity between control and warren species at the Warrananga Sandplain site...... 12 Table 8. Mean cover of each of the 33 plant species recorded at the Morquong site ...... 13 Table 9. Species, mean cover and percent dissimilarity contributing to 78% of the dissimilarity between control and warren species at the Morquong site...... 15 Table 10. Mean (+ standard error of the mean SEM) numbers of active, inactive and total entrances for the ripped and unripped treatments...... 15

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iv The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

Executive Summary

The European rabbit (Oryctolagus cuniculus L.) occupies approximately 4.5 million square kilometres of southern and is regarded as Australia’s number one vertebrate pest. Rabbits markedly reduce the quality of the environment through their negative impacts on plant structure and composition, and soil and landscape health. Over much of their range in continental Australia rabbits live in large underground colonies or warrens. The process of burrow excavation leads to extensive and sustained soil disturbance in the vicinity of warrens.

Field survey results indicated that warrens of the European rabbit supported less than half of the number of species, significantly lower richness, and reduced cover of groundstorey plants compared with adjacent non-warren sites. Weedy plants such as Sisymbrium irio and Centaurea melitensis dominated the warren surfaces on the hard red soils (Yathong). At the other sites, the exotic weeds Carrichtera annua, Vulpia myuros, Schismus barbatus, Bromus rubens and Asphodelus fistulosus tended to make up the bulk of the plant cover on the warrens. Though they also occurred off the warrens (albeit at reduced cover), their dominance on the warrens makes them a suitable seed source for dispersal to other areas.

Warren surfaces generally comprised a greater proportion of bare ground, and significantly less litter compared with the non-warren surfaces. This difference in surface morphology helps to explain the significantly greater germination rates of the weedy forbs Marrubium vulgare and Brassica tournefortii, and the lower germination of the perennial native grass Austrodanthonia caespitosa on the warren compared with the non-warren surfaces. The study of warren reactivation after release of calicivirus indicates that ripping significantly reduces the number of warrens being reactivated compared with unripped warrens.

Taken together, these results confirm that rabbits have a marked negative effect on the diversity of woodland vegetation and the quality of soils. This report recommends that additional research is required to:

? examine the impact of rabbits on other taxa such as reptiles, small mammals and arthropods ? examine the impact of ripping on plants and animals associated with rabbit warrens ? examine changes in soil seed banks on rabbit warrens to determine their role as a harbor for weeds.

TERMS OF REFERENCE

The objectives of this project were to:

? review literature relevant to the European rabbit (Oryctolagus cuniculus) and its effect on the biodiversity of groundstorey plants

? undertake field work at a number of sites in south-western NSW to collect data on plant cover and floristics in relation to rabbit infestation, and

? produce a report.

The project was initiated in response to a request from WEST2000 Plus to provide information on the impact of rabbits on the diversity of native plants and animals in western NSW. Given constraints of time and money it was decided to concentrate on the impact of rabbit warrens on reductions in plant

NSW Department of Land and Water Conservation

v The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report diversity, and to collect data from a limited number of field sites in western NSW (three sites near Wentworth, one site near Cobar). A more detailed assessment of the influence of rabbits on other taxa (e.g. ground-dwelling arthropods, reptiles etc) was beyond the scope of this study.

A field survey was conducted near Wentworth to collect information on rabbits and the diversity of plants in relation to rabbit warrens. These data were compared with comparable data from Yathong Nature Reserve near Cobar. The limited literature relevant to diversity of plants in relation to rabbits was reviewed and incorporated into a report that includes the major findings and recommendations for further investigations.

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vi The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

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vii The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

1. Background

In 1788 five European rabbits (Oryctolagus cuniculus L.) arrived in Australia aboard the First Fleet, and escapees quickly became established in the vicinity of the new colony around Harbour (Rolls 1984). Within 100 years of their release, rabbits had spread to all States and Territories, quickly becoming Australia’s number one vertebrate pest (Coman 1999). Today the rabbit now occupies extensive areas of southern Australia, and a substantial industry has developed around its control.

Rabbits are selective feeders, but in dry times will eat plants, shrubs and grasses indiscriminately. Their overall impact on the environment is in reducing plant cover, altering the composition of groundstorey plants and shrubs, predisposing the soil to wind and water erosion, and altering the quality of the soil (Eldridge and Simpson 2002). Rabbits are also implicated in the displacement of native animals such as the burrowing bettong (Bettongia leseur) from much of eastern Australia (Myers et al. 1994).

The purpose of this report is to examine the role of the European rabbit in reducing the biodiversity of groundstorey plants.

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1 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

2. Research approaches to a study of rabbits and biodiversity

In order to examine the impacts of rabbits on biodiversity, three approaches can be taken. These are:

1. Exclosure studies where rabbit-infested areas are compared with rabbit-free areas. Unfortunately, very few rabbit-proof exclosures are available for study, as exclosures are costly and difficult to maintain. Further, the lack of replicate exclosures on comparable land and soil types means that often the data cannot be rigorously subjected to statistical analyses (e.g. Bath 1992).

2. Chronosequence (or time series) studies within areas where rabbits have been removed at different points in time. These might include, for example, sites where warrens (and rabbits) have been progressively removed, allowing a comparison of rabbit (warren)-free sites with areas currently occupied by rabbits and their warrens. These types of studies are again complicated by a number of factors. Differences between sites may be due to a variety of effects such as differential stocking rates by domestic or native animals, differences in rainfall, or differences in other unknown factors. Consequently, any observed differences may not be attributable to the presence (or absence) of rabbits per se.

3. In-situ warren studies whereby measurements on the warrens are compared with adjacent non- warren areas. Over much of their range in continental Australia rabbits live in large underground colonies or warrens which are typically 0.3 to 0.5 m above the general level of the landscape (Eldridge & Myers 2001). The warren mound is constructed by soil excavated by the rabbits. Warren excavation is an on-going process, with the mound being replenished by a buildup of freshly excavated soil (Parer et al. 1987, Myers et al. 1994). This process of burrow excavation and warren replenishment leads to extensive and sustained soil disturbance in the vicinity of warrens and therefore major effects on the vegetation. Further, these effects are intensified by circular grazing gradients radiating out from the warrens, with plants close to the warrens likely to be more heavily grazed than those at greater distances (Lange & Graham 1983). Palatable or desirable plants are likely to be less abundant close to the warrens than further away (Foran 1986, Leigh et al. 1989, Myers et al. 1994).

The third type of study was chosen for three reasons. Firstly, it was easiest and provided a greater number of independent samples than would have been possible using exclosures. Second, it allowed comparison between rangeland types and soils types to be made, and third, it was relatively rapid and cost-effective.

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3. Methodology

3.1 SELECTION OF SITES

The study was restricted to three sites in the West Darling and one site south of Cobar. The main features of these sites are described in Table 1. Sites were selected to encompass the main soil types in the area and those most influenced by rabbits. Final sites were selected based on the availability of intact (unripped) warrens, sufficient vegetation cover to allow detection of any possible differences in species, different soil types, and access to warrens. The Yathong site was located at Yathong Nature Reserve approximately 130 km south of Cobar near Mount Hope, in central-western New South Wales. The Warrananga sites were situated approximately 40 k west of Wentworth in south-western NSW, and the Morquong site was situated approximately 6 km east of Buronga (19 km east of Wentworth). The Yathong site was measured in February 2000 and the other sites in December 2001.

Table 1. Description of the four study areas.

Site Yathong Warrananga Bluebush Warrananga Sandplain Morquong Geomorphology Slopes and associated Extensive plains with Extensive plains with Plains of low sandy outwash colluvial plains scattered depressions scattered depressions rises and extensive and low, sandy rises sand sheets Soil type Hard red loams and clay Calcareous loams and Non-calcareous loams Loamy and clayey loams clay loam sand Slope <1 % 1-2 % 1-2 % 1-2 % Vegetation community Grassy and shrubby Chenopod shrubland Chenopod shrubland Open woodland semi-arid woodland Dominant vegetation Red box (Eucalyptus Pearl bluebush Pearl bluebush and Belah (Casuarina intertexta), poplar box (Maireana sedifolia) and black bluebush pauper) – rosewood (E. populnea) and pine black bluebush (M. (Alectryon oleifolius) (Callitris glaucophylla) pyramidata) Erosion Some gullying and rilling Moderate windsheeting, Moderate windsheeting Moderate on lower slopes some rilling windsheeting

3.2 SELECTION OF THE WARRENS

At all sites, 10 warrens were selected for detailed vegetation measurements. Warrens were located within an area of about 5 ha on the basis of three criteria. Firstly, warrens needed to be more than 150 m from the nearest adjacent warren in order to ensure than warren-free surfaces were not unduly influenced by nearby warrens. Second, only warrens present in open woodland sites were chosen for study. As warrens often occur under trees (Vine 1999), and Eucalyptus trees are known to influence soil physical and chemical properties (Tongway & Smith 1989, Chilcott et al. 1997), sites under trees were avoided. However, two of the warrens at Morquong were under trees. Third, only warrens of comparable size were selected.

Each warren is a complex of three distinct microsites; the mound, a disturbed area, and the adjacent undisturbed perimeter (control). The mound is the elevated section of the warren system and is generally heavily disturbed by the rabbits. The control is chosen to be away from the influence of the warren where no soil disturbance is evident. In areas where rabbits are extremely active, their effect on the vegetation may extend up to 100 m from the mounds (Leigh et al. 1989). At all four sites however, rabbits had been eliminated by calicivirus at least 12 months prior to field work, and control sites with little evidence of disturbance by rabbits were found within 20 m of the warren mounds. An intermediate area occurs between the mound and control microsites and is termed the ‘disturbed’ area.

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This exhibits characteristics of both microsites, and is characterised by scratchings, dung piles, small mounds of disturbed soil and undisturbed biological soil crust (Wood 1988, Eldridge & Myers 1999).

3.3 DETAILED WARREN MEASUREMENTS AT ALL SITES

3.3.1 Vegetation cover measurements

At each warren at each site, we selected an area of approximately 30 m by 30 m within the centre of the warren. For smaller warrens, the area selected was reduced to about 20 by 20 m.

A 50 m transect was placed along the longest axis of each warren so that the middle of the transect was aligned with the centre of the warren, defined as the location with the highest elevation. A second 50 m transect was placed perpendicular to the first transect through the centre. Quadrats, measuring 0.5 m by 0.5 m (Yathong) or 0.7 m by 0.7 m (Wentworth sites), were placed about every 5 m along both transects, and each quadrat was recorded as either warren or non-warren. Quadrats falling on intermediate surfaces i.e. showing characteristics of both warrens and non-mounds, were rejected, and additional quadrats were examined until a total of 10 warren and 10 non-warren quadrats was measured on each warren complex, resulting in a total of 200 quadrats for the 10 warrens at each of the four sites. In doing this the aim was to restrict the analyses to those microsites which were predominantly either mound or non-mound, though intermediate microsites are recognised as a common warren feature (Eldridge & Myers 1999). The cover of all species was assessed within each quadrat. As two different teams of recorders were used in this study, both teams worked on warrens at the same site, and constant checking and reassessment of cover values between teams ensured consistency of estimates between them.

3.3.2 Additional measurements (conducted at Yathong only) 3.3.2.1 Soil surface morphology

At the Yathong site, previous work from a smaller number of warrens used for a more detailed soil chemistry study (n = 5) revealed some differences in soil surfaces between the warren mounds and the non-warren surfaces (Eldridge & Myers 2001). At five of the 10 warrens (every second warren), soil surface morphology was assessed on both the mounds and adjacent control sites using the line intercept method. Along two 1 m transects per warren, micro-surfaces were classified into scarps, depressions and flats. The flats and scarps were each further subdivided into bare soil, litter, cryptogam, lag material and dung. Together these features can be used as an index of the degree to which the surface has resisted or undergone change through erosion processes (Eldridge 1998). The aim of this work was to determine the proportion of the soil surface comprising various microtopographical cover classes.

3.3.2.2 Classification of the vegetation community

At Yathong, we wished to test whether vegetation assemblages on the mound section of the warrens and the non-warren microsites differed on the basis of a unique set of morphological, reproductive or dispersal attributes. Thirty ecological and morphological attributes from 10 characters were scored for the 25 species which occurred in 25% (50) or more of the 200 quadrats. The choice of attributes was a compromise between what could easily be assessed in the field and their ecological relevance (sensu McIntyre et al. 1999). Consequently, attributes which could easily be measured in the field and/or supplemented from the literature were used. Measurements of field specimens were complemented by information obtained from the literature (Harden 1990-1995, Cunningham et al. 1992) as some characters such as seed ornamentation were difficult to find in field specimens at the time of this

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4 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report study. Plant attributes were generally binary or continuous, and generally easily quantifiable in the field.

3.3.2.3 Plant germination study

To test for possible differences in germination rate between the warren and non-warren microsites, a laboratory-based reciprocal germination trial was undertaken using two species commonly found on warren surfaces (Marrubium vulgare and Centaurea melitensis) and two species commonly found on non-warren surfaces (Austrodanthonia caespitosa and jerichoensis). Seeds of all species were collected from the vicinity of Yathong Nature Reserve between March 1998 and April 1999.

Previous studies indicated that warren mounds were characterised by bare, eroded soils whilst cryptogamic crusts dominated the control surfaces (Eldridge & Myers 1999). Undisturbed samples of surface soil dominated by either bare soil (from active mounds) or cryptogams (from control microsites) were collected in 80 mm diameter plastic Petrie dishes and transported intact to the laboratory. The germination experiment consisted of a fully orthogonal design of two surface types (cryptogam and bare soil) by four species, each with five replicates, resulting in a total of 40 Petrie dishes. Fifty seeds of each of the four species were placed on each of the 10 Petrie dishes. On the cryptogamic surface, seeds were placed in the cracks between individual lichens and mosses, as previous studies indicated significant differences in germination between different niches (i.e. surface vs cracks) within the cryptogamic crust community (Eldridge unpublished data).

The 40 Petrie dishes were illuminated for 12 h photoperiods with a flux of 50 ? mol m-2 s-1 using an array of fluorescent lights. Petrie dishes were watered ad libitum with distilled water. Seeds were counted daily and removed once they had germinated, i.e. when the shoot had emerged. The species chosen are not known to have dormant seeds, and previous studies (Eldridge unpublished data) indicated that the majority of seeds germinated within 10 days. Consequently, germination was assessed up until day 10 only.

3.3.2.4 Warren reactivation after calicivirus: ripped vs un-ripped warrens

Two areas, each approximately 2 ha in size, were chosen at Yathong Nature Reserve for detailed measurements of reinvasion of warrens which had either been ripped or left unripped. The unripped site was grassy woodland whilst the ripped site was grassland with scattered trees that had its warrens ripped between January 1995 and May 1996 using a winged tyned ripper. Warrens were located by systematically walking across the sites. At each warren, detailed measurements were made of the following: warren size (length and width) and shape, the number and activity of rabbit entrances. Active entrances were defined as showing recent evidence of rabbit activity including fresh rabbit tracks or scratch marks, a recently reworked entrance without debris (leaf litter, sticks or weeds), or faeces near the entrance.

3.4 Statistical analyses

One-way ANOVA was used to test for differences in soil surface cover composition and cover of each species between warrens and non-warrens after checking for homogeneity of variance (MINITAB 1997). Where transformation failed to improve the distribution of the data, the non-parametric Mann- Whitney U Test was used.

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5 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

4. Results

4.1 FLORISTICS AND SPECIES RICHNESS

Rabbit warrens contained less than half of the number of species, generally significantly reduced richness, and less cover of plants compared with the adjacent non-warren (control) sites (Table 2). Cryptogam cover was significantly less on the warrens compared with non-warrens at Yathong, but up to three times greater on the warrens compared with non-warrens at the sites near Wentworth (Table 2).

Table 2. Floristics and ground cover measurements for control and warren microsites for the four sites. For a given site, different superscripts within a row indicate a significant difference at P<0.05.

Yathong Warrananga Warrananga Morquong hard red calcareous sandplain sandplain Warren Control Warren Control Warren Control Warren Control Total number of species 14.2a 6.4b 15.3a 8.9b 16.4a 8.6b 20.9a 11.1b Richness 4.03a 1.53b 4.56a 3.14b 5.7a 3.9b 5.3a 5.4b Evenness 0.79a 0.74a 0.61a 0.58a 0.67a 0.71a 0.65a 0.74a Plant cover (%) 26.9a 26.7a 24.0a 13.4b 16.1a 9.3b 43.4a 8.1b Bare ground (%) 10.9a 46.2b 15.1a 29.1b 29.2a 40.3b 13.8a 45.7b Cryptogam cover (%) 32.4a 7.8b 37.0a 50.3b 10.3a 34.7b 13.8a 28.9b Litter cover (%) 29.8a 9.3b 20.7a 11.3b 24.5a 9.7b 28.1a 15.2a

4.2 COMMUNITY VEGETATION STRUCTURE

4.2.1 Plant types

At Yathong, a study of plant morphologies growing on the warrens compared with non-warren surfaces indicated that warrens contained significantly more exotic and tall (> 50 cm) species, and species with burrs compared with non-warren microsites. In general, non-warren species were erect or prostrate, low growing (< 30 cm tall), native perennials, with awns barbs or wings, and with fibrous or tap roots.

4.2.2 Community Plant Structure

4.2.2.1 Hard red soils – Yathong Nature Reserve:

Forty-four vascular plants comprising 33 forbs, 10 grasses and one shrub were recorded from the red earth soils at Yathong (Table 3). Twelve species accounted for about 80% of total cover-abundance, and of these, five species (Medicago laciniata , Centaurea melitensis, Erodium crinitum, Sclerolaena diacantha and Sysimbrium irio ) accounted for half (50.1%) of total cover-abundance. Some species were found primarily on mound microsites (Sysimbrium irio ), some on both mound and non-mound (Medicago laciniata ), and others primarily on non-mound microsites (Aristida spp). Ten species had

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6 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

Table 3. Mean cover-abundance of each of the 44 species recorded at the Yathong Nature Reserve. Species are arranged in order of decreasing cover-abundance averaged across the mound and non-mound microsites. F=forb, G=grass, S=shrub; - insufficient data to allow significance testing (see Methods); # cover-abundance < 1%, *exotic species.

Species Growth form Proportion of total cover- P value abundance (%) Medicago laciniata* F 16.92 >0.05 Centaurea melitensis* F 9.85 <0.01 Erodium crinitum F 8.71 0.02 Sclerolaena diacantha F 7.39 >0.05 Sisymbrium irio* F 7.26 0.02 Aristida jerichoensis G 6.69 <0.01 Tetragonia tetragonioides F 5.74 - Marrubium vulgare* F 3.66 >0.05 Austrostipa scabra subsp. scabra G 3.60 0.03 Rhodanthe corymbiflora F 2.97 >0.05 Paspalidium constrictum G 2.65 >0.05 Salsola kali var. kali F 2.65 0.01 Chamaesyce drummondii F 1.77 >0.05 Convolvulus erubescens F 1.70 >0.05 Maireana humillima F 1.52 >0.05 Vittadinia cuneata complex F 1.52 <0.01 Schismus barbatus* G 1.45 - Goodenia hederacea F 1.39 >0.05 Chenopodium melanocarpum F 1.33 - Ptilotus obovatus var. obovatus F 1.20 0.04 Hordeum leporinum* G 1.18 - Chenopodium curvispicatum F 1.14 >0.05 Austrodanthonia caespitosa G 1.01 - Sida cunninghamia F 1.01 0.03 Abutilon otocarpum F # <0.01 Actinobole uliginosum F # - Wahlenbergia sp. F # >0.05 Sclerolaena divaricata F # >0.05 Sonchus oleraceus* F # - Boerhavia dominii F # >0.05 Monachather paradoxa G # >0.05 Solanum esuriale F # - Carthamus lanatus* F # >0.05 Chloris truncata G # - Nicotiana velutina F # - Scaevola aemula F # - Alternanthera denticulata F # - Aristida behriana G # -

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Table 3. (continued)

Cheilanthes sieberi subsp. sieberi F # - Eremophila longifolia S # - Lomandra effusa F # - Oxalis perennans F # - Solanum ferrocissimum F # - Thyridolepsis mitchelliana G # - significantly different cover-abundance levels between the microsites (P<0.05; Table 3). For example, Centaurea melitensis had significantly higher cover-abundance on the mounds, and accounted for 17.1% of total cover-abundance. On the non-mound microsites however it accounted for only 2.1% of cover-abundance. Ten of the 44 species recorded on the warren complexes were exotics. As expected, exotics had significantly higher cover-abundance on the mounds (64.1% of total cover-abundance) compared with the non-mounds (21.7%, P<0.01). Cover-abundance of the naturalised legume Medicago laciniata was very high on both microsites (Table 3), and accounted for 86% of total exotic cover-abundance on the non-mound microsites.

4.2.2.2 Calcareous loams – Warrananga Bluebush

Thirty-three vascular plants comprising 25 forbs, seven grasses and one shrub were recorded from the calcareous soils at Wannananga (Table 4). Six species (Carrichtera annua, Sclerolaena obliquicuspis, Medicago minima, Zygophyllum sp., Maireana sclerolaeneoides and Austrostipa scabra subsp. scabra) accounted for about 85% of total cover (Table 4). Four species, three natives (Crassula colorata var. acuminata , Rhodanthe sp. and Tripogon loliiformis) and one exotic (Hordeum leporinum) were found only on the warrens. The cover of eight species (Austrostipa scabra subsp. scabra, Omphalolappula concava, Medicago minima, Limonium lobatum, Goodenia sp., Austrodanthonia caespitosa, Salsola kali var. kali and Carrichtera annua) was significantly higher on the non-warrens compared with the warrens (P<0.05; Table 4). Carrichtera annua accounted for 40% of the dissimilarity between the control and warren surfaces (Table 5).

4.3.2.3 Non-calcareous loams – Warrananga Sandplain

Forty vascular plants comprising 28 forbs, 11 grasses and one shrub were recorded from the non- calcareous loams at Warrananga (Table 6). Two species, both natives (Portulaca oleracea and Triraphis mollis) were found only on the warrens. The cover of eight species (Austrostipa scabra subsp. scabra, Goodenia sp., Calotis hispidula, Medicago minima, Alyssum linifolium, Rhodanthe pygmaea, Silene sp and Vittadinia cuneata complex) was significantly greater on the non-warrens compared with the warrens (P<0.05; Table 6). However, the cover of Tetragonia tetragonoides was significantly greater on the warrens compared with the non-warrens (P<0.05). Eight species (Schismus barbatus, Sclerolaena obliquicuspis, Austrostipa scabra subsp. scabra, Maireana pyramidata, Medicago minma, Salvia verbenacea, Goodenia sp. and Silene sp.) accounted for about 75% of the dissimilarity between warrens and non-warrens (Table 7).

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8 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

Table 4. Mean cover of each of the 33 plant species recorded at the Warrananga Bluebush site. Species are arranged in order of decreasing cover (averaged across the warren and non-warren microsites); *exotic species; F=forb, G=grass, S=shrub; n.s. no significant difference between warren and non-warren microsite. # for all significant species, cover is greater on the non-warren compared with the warren.

Species Growth Proportion of P value # form total cover (%) Carrichtera annua* F 45.52 0.047 Sclerolaena obliquicuspis F 18.30 n.s. Medicago minima* F 13.14 0.008 Zygophyllum sp. F 2.68 n.s. Maireana sclerolaeneoides F 2.65 n.s. Austrostipa scabra subsp. scabra G 2.23 0.001 Rhodanthe pygmaeum F 1.66 n.s. Maireana pyramidata S 1.51 n.s. Schismus barbatus* G 1.36 n.s. Salvia verbenacea* F 1.35 n.s. Calotis hispidula F 1.25 n.s. Brachycome linearloba F 1.22 n.s. Limonium lobatum* F 1.12 0.009 Austrodanthonia caespitosa G 1.12 0.019 Maireana turbinata F 1.00 n.s. Goodenia sp. F 0.79 0.010 Omphalolappula concava F 0.54 0.001 Tetragonia tetragonoides F 0.48 n.s. Silene sp.* F 0.33 n.s. Actinobole uliginosum F 0.32 n.s. Alyssum linifolium F 0.27 n.s. Salsola kali var. kali F 0.24 0.029 Vittadinia cuneata complex F 0.24 n.s. Tripogon loliiformis G 0.16 n.s. Erodium crinitum* F 0.13 n.s. Myriocephalus stuartii F 0.08 n.s. Bulbine semibarbata F 0.05 n.s. Crassula colorata var. acuminata F 0.05 n.s. Enneapogon avenaceas G 0.05 n.s. Rhodanthe sp. F 0.05 n.s. Bromus rubens* G 0.03 n.s. Hordeum leporinum* G 0.03 n.s. Maireana georgii F 0.03 n.s.

4.2.2.4 Non-calcareous sands– Morquong

The site at Morquong supported 38 species, including eight grasses, 29 forbs and one shrub (Table 8). Nine species (Austrostipa scabra subsp. scabra, Vulpia myuros, Bromus rubens, Schismus barbatus, Sclerolaena diacantha, Asphodelus fistulosus, Hordeum leporinum, Actinobole uliginosum and Sclerolaena obliquicuspis) accounted for 82% of total cover (Table 8). Only one species, the native shrub Enchylaena tomentosa, was found only on the warrens. The cover of 14 species

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9 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

(Omphalolappula concava, Schismus barbatus, Brachycome lineariloba, Sclerolaena diacantha, Goodenia sp., Vulpia myuros, Medicago minima, Actinobole uliginosum, Hypoc haeris glabra, Austrostipa scabra subsp. scabra, Bromus rubens, Crassula colorata var. acuminata, Mollugo cerviana and Sonchus oleraceus) was significantly higher on the non-warrens compared with the warrens (P<0.05; Table 8). Eight species accounted for 78% of the dissimilarity between warrens and non-warrens (Table 9).

Table 5. Species, mean cover and percentage dissimilarity contributing to 82% of the dissimilarity between control and warren species at the Warrananga Bluebush site. Average dissimilarity = 57.27.

Mean abundance Dissimilarity Species Control Warren Percent Cumulative % Carrichtera annua 11.51 5.45 40.3 40.3 Sclerolaena obliquicuspis 2.93 3.88 15.6 55.9 Medicago minima 3.47 1.43 10.1 66.0 Maireana sclerolaeneoides 0.93 0.06 4.4 70.4 Austrostipa scabra subsp. scabra 0.73 0.10 3.2 73.6 Zygophyllum sp. 0.71 0.29 3.1 76.7 Rhodanthe pygmaeum 0.47 0.15 2.7 79.4 Maireana pyramidata 0.23 0.33 2.5 81.9

4.3 MORPHOLOGY OF WARREN SURFACE SOILS

At all four sites, warren surfaces were characterised by significantly more bare ground, and significantly less litter (except for Yathong) compared with the control surfaces (P < 0.01, Figure 1). Detailed measurements of the morphology of warren soils at Yathong indicated significantly more gravel (P = 0.04) and dung (P = 0.02), and significantly less cryptogam cover (P < 0.01) on the warrens compared with the non-warren surfaces (Figure 1).

4.4 GERMINATION OF PLANT SPECIES

A reciprocal germination study was carried out on soils from the hard red rangetype (Yathong). Germination of the weeds Marrubium vulgare and Brassica tournefortii at 10 days was significantly greater on the bare warren surfaces compared with the cryptogamic non-warren surfaces (F1,32 = 24.82 and 20.62, P<0.001 for Marrubium and Brassica respectively; Figure 2). Germination of Austrodanthonia caespitosa was significantly greater on the cryptogamic surface (F1,32 = 22.82, P<0.001). Aristida failed to germinate substantially on either the warren or non-warren surface (<2%), and was not significantly different between the two surfaces (Figure 2).

4.5 POST-CALICIVIRUS WARREN REINVASION

Both study sites were exposed to the release of rabbit calicivirus disease (RCD) in October 1996. Averaged over both sites, there was no significant effect of warren ripping on the total number of entrances at each warren (Table 10). However, when only active entrances were considered, there were significantly more active entrances at the unripped site compared with the ripped site (F1, 98 = 328.18, P<0.001; Table 10).

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10 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

Table 6. Mean cover of each of the 40 plant species recorded at the Warrananga Sandplain site. Species are arranged in order of decreasing cover (averaged across the warren and non-warren microsites); *exotic species; F=forb, G=grass, S=shrub; n.s. no significant difference between warren and non-warren microsite. # for all significant species (except Tetragonia tetragonoides), cover is greater on the non-mound compared with the mound.

Species Growth Proportion of P value # form total cover (%) Schismus barbatus* G 23.41 n.s. Sclerolaena obliquicuspis F 12.42 n.s. Salvia verbenaca* F 10.75 n.s. Maireana pyramidata S 6.76 n.s. Actinobole uliginosum F 2.51 n.s. Bromus rubens* G 2.25 n.s. Crassula colorata var. acuminata F 1.26 n.s. Chthonocephalus pseudevax F 1.19 n.s. Maireana sclerolaenoides F 1.15 n.s. Tripogon loliiformis G 1.14 n.s. Hordeum leporinum* G 1.05 n.s. Brachycome lineariloba F 0.82 n.s. Danthonia caespitosa G 0.75 n.s. Vulpia myuros* G 0.51 n.s. Rhodanthe sp. F 0.43 n.s. Zygophyllum sp. F 0.27 n.s. Carrichtera annua* F 0.24 n.s. Hypochaeris glabra* F 0.24 n.s. Omphalolappula concava F 0.16 n.s. Daucus glochidiatus G 0.12 n.s. Erodium crinitum* F 0.12 n.s. Rhodanthe moschata F 0.12 n.s. Salsola kali var. kali F 0.12 n.s. Maireana turbinata F 0.08 n.s. Airea sp*. G 0.04 n.s. Convolvulus erubescens F 0.04 n.s. Enneapogon avenaceus G 0.04 n.s. Limonium lobatum* F 0.04 n.s. Myriocephalus stuartii F 0.04 n.s. Portulaca oleracea* F 0.04 n.s. Triraphis mollis G 0.04 n.s. Austrostipa scabra subsp. scabra G 7.68 0.001 Goodenia sp. F 1.77 0.006 Calotis hispidula F 1.42 0.007 Medicago minima* F 13.11 0.014 Alyssum linifolium* F 0.98 0.014 Rhodanthe pygmaea F 1.62 0.020 Silene sp.* F 2.35 0.023 Vittadinia cuneata complex F 0.43 0.027 Tetragonia tetragonoides F 2.53 0.029

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11 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

Figure 1. Mean soil cover for various surface components on the warren and non-warren microsites at Yathong. Bars indicate one standard error of the mean. Different letters within a component indicate a significant difference at P < 0.05 between warren and non-warren.

70

non-warren b 60 warren a 50

40 a 30 b Cover (%) 20 a b b 10 a a a a b 0 Dung Vegetated Gravel Bare Litter Cryptogam

Table 7. Species, mean cover and percentage dissimilarity contributing to 75% of the dissimilarity between control and warren species at the Warrananga Sandplain site. Average dissimilarity = 71.62

Mean abundance Dissimilarity

Species Control Warren Percent Cumulative % Schismus barbatus 1.72 4.24 20.0 20.0 Sclerolaena obliquicuspis 2.50 0.66 12.8 32.8 Austrostipa scabra subsp. scabra 1.95 0.01 12.3 45.1 Maireana pyramidata 1.32 0.40 8.3 53.4 Medicago minima 2.38 0.96 8.1 61.5 Salvia verbenacea 1.24 1.50 7.1 68.6 Goodenia sp. 0.45 0.00 3.1 71.7 Silene sp. 0.59 0.01 3.0 74.7

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12 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

Table 8. Mean cover of each of the 33 plant species recorded at the Morquong site. Species are arranged in order of decreasing cover (averaged across the warren and non-warren microsites); *exotic species; F=forb, G=grass, S=shrub; n.s. no significant difference between warren and non-warren microsite. # for all significant species (except Schismus barbatus), cover is greater on the non-mound compared with the mound. Species Growth Proportion of P form total cover (%) value # Austrostipa scabra subsp. scabra G 34.53 0.001 Vulpia myuros* G 12.31 0.018 Bromus rubens* G 8.39 0.001 Schismus barbatus* G 5.34 0.027 Sclerolaena diacantha F 5.32 0.021 Asphodelus fistulosus* F 4.51 n.s. Hordeum leporinum* G 4.10 n.s. Actinobole uliginosum F 3.91 0.012 Sclerolaena obliquicuspis F 3.24 n.s. Silene sp.* F 2.51 n.s. Dissocarpus paradoxus F 1.99 n.s. Crassula colorata var. acuminata F 1.97 0.001 Calotis hispidula F 1.84 n.s. Medicago minima* F 1.68 0.013 Brachycome lineariloba F 1.61 0.027 Tetragonia tetragonoides F 1.58 n.s. Goodenia sp. F 1.01 0.019 Zygophyllum apiculatum F 0.80 n.s. Mollugo cerviana F 0.68 0.001 Brassica tournefortii* F 0.66 n.s. Rhodanthe pygmaea F 0.41 n.s. Salsola kali var. kali F 0.29 n.s. Medicago laciniata* F 0.23 n.s. Hypochaeris glabra* F 0.22 0.005 Sonchus oleraceus* F 0.21 0.001 Omphalolappula concava F 0.10 0.038 Digitaria sp. G 0.08 n.s. Erodium crinitum* F 0.08 n.s. Daucus glochidiatus G 0.06 n.s. Tripogon loliiformis G 0.06 n.s. Vittadinia cuneata complex F 0.06 n.s. Chenopodium desertorum subsp. anidiophylum F 0.04 n.s. Chthonocephalus pseudevax F 0.04 n.s. Enchylaena tomentosa S 0.04 n.s. Medicago truncatula* F 0.04 n.s. Alyssum sp.* F 0.02 n.s. Carthamus lanatus* F 0.02 n.s. Lactuca serriola* F 0.02 n.s.

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13 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

Figure 2. Percentage germination of the four plant species after 10 days on warren and non-warren microsites. Bars indicate one standard error of the mean (sem); different letters indicate a significant difference for a particular species at P < 0.05.

100 b 90 non-warren warren 80

70

60

50 a

40

30 a b 20

10 b

Germination by day 10 (%) a a a 0

Aristida Marrubium Brassica

Austrodanthonia

Statistical analyses of the results showed that the more than 70% of the warrens measured at the unripped site were found under the protection of trees or fallen timber, presumably for protection, and ease of digging. Larger warrens tended to have a greater number of active entrances. This trend was very apparent at the unripped site. The results showed that more trees on a warren were also correlated with more active entrances, and hence larger warrens. However, larger warrens were not consistently found to be under large trees, but rather more trees.

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14 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

Table 9. Species, mean cover and percentage dissimilarity contributing to 78% of the dissimilarity between control and warren species at the Morquong site. Average dissimilarity = 85.2

Mean abundance Dissimilarity Species Control Warren Percent Cumulative % Austrostipa scabra subsp. scabra 17.22 0.56 37.1 37.1 Vulpia myores 5.82 0.52 11.5 48.6 Bromus rubens 4.23 0.09 9.8 58.4 Sclerolaena diacantha 2.61 0.13 6.6 65.0 Schismus barbatus 0.65 2.10 3.9 68.9 Actinobole uliginosum 1.87 0.14 3.2 72.1 Sclerolaena obliquicuspis 0.99 0.68 3.0 75.1 Hordeum leporinum 1.76 0.35 2.7 77.8

Table 10. Mean (± standard error of the mean SEM) number of active, inactive and total entrances for the ripped and unripped treatments. Different letters within a column indicate a significant difference at P<0.05.

Active warrens Inactive warrens All warrens Treatment Mean SEM Mean SEM mean SEM Ripped 0.43a 0.26 10.81a 1.22 11.24a 1.22 Unripped 4.01b 0.43 9.55a 1.05 13.56a 1.33

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15 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

5. Discussion

This study reinforces the view that rabbits are a major land management problem in the semi-arid woodlands. Rabbits, by constructing their warrens, reduced the diversity of groundstorey plants, made the soil more erodible, and produced a soil surface which was more suitable for the germination of weedy plants. Rabbits also damage woody vegetation, reducing seedling establishment and influencing the population structure of many species (Crisp & Lange 1976, Lange & Graham 1983, Leigh et al. 1989). Long-term, continuous grazing by rabbits results in increased total grazing pressure, reduced pastoral productivity (Williams et al. 1995), and eventually leads to increased landscape degradation (Cooke 1991). Given its marked negative impact on ecological processes, the European rabbit has been nominated as a Key Threatening Process under Schedule 3 of the Threatened Species Conservation Act (1997).

5.1 EFFECTS OF RABBITS ON BIODIVERSITY

This study has confirmed that the activity of rabbits (through warren construction and digging alone) results in reduced diversity of vascular plants. Grazing by rabbits also produces major impacts on shrubs and trees through reduced recruitment, though we were unable to measure this in the present study. Rabbit grazing reduces survival and recruitment of several species of threatened plants including Acacia carneorum, Grevillea kennedyana, Cynanchum elegans, Thesium australe and Lepidium hyssopifolium (Cropper 1987, Auld 1990, Griffith 1992, Auld 1993, Matthes & Nash 1993, NPWS 2002).

Rabbits are selective grazers, eating plants, shrubs and grasses that they know are palatable, more nutritious, have a higher water content and are low in fibre and sodium (Gooding, 1955, Blair-West et al. 1968, Cooke 1982a, Friedel 1985, Foran 1986, Catling & Newsome 1992). Small shrubs and forbs, perennial grasses, and succulents are eaten first (Gooding 1955, Lange and Graham 1983, Foran et al. 1985, Friedel, 1985, Foran, 1986, Leigh et al. 1989), reducing their biomass and resulting in replacement by less desirable species which are often more resistant to grazing pressure. This may explain the commonly held view that warrens become dominated by Mediterranean weeds (Eldridge & Simpson 2002).

By preferentially eating the seedlings and young stems of small shrubs, rabbits often prevent the regeneration of these species (Cooke 1982b, Lange & Graham 1983, Foran 1986, Myers et al. 1994). Rabbits can alter the age structure of the vegetation community (Myers et al. 1994) and the species may be exposed to extinction threats if there is no successful recruitment. The lack of successful recruitment events in western myall (Acacia papyrocarpa) has been attributed to grazing of seedlings by rabbits in arid South Australia (Lange & Graham 1983). Thus grazing by rabbits could cause species, populations or ecological communities that are not threatened to become threatened (NPWS 2002).

A number of long-lived tree and shrub species have their recruitment prevented or severely limited by rabbit grazing in arid and semi-arid Australia, including NSW (Crisp & Lange 1976, Lange & Graham 1983, Chesterfield & Parsons 1985, Auld 1990, 1993, 1995a, 1995b, Woodell 1990, Pickard 1991, Tiver & Andrew 1997, Auld & Denham 2001). Continued rabbit impacts could cause some of these species (or populations of them) to become threatened. In places where they are the dominant species in the community, the community may become threatened. Examples include Acacia spp., Hakea spp., Callitris gracilis, and the belah (Casuarina pauper) – rosewood (Alectryon oleifolius) and boree (Acacia pendula) communities (NPWS 2002). Grazing by rabbits appears also to alter the structure and composition of sub-alpine, semi-arid and arid vegetation communities (Williams et al. 1995), and

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16 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report is a significant problem within the Acacia loderi community which has been listed as an Endangered Ecological Community.

The present study also identified the fact that the exotic weeds Carrichtera annua, Vulpia myuros, Schismus barbatus, Bromus rubens, Asphodelus fistulosus. Centaurea melitensis and Sisymbrium irio tended to make up the bulk of the plant cover on the warrens (Tables 3-4, 6 & 8). Although these also occurred on the non-warren soils (and the Wentworth sites were dominated by Carrichtera annua for example right across the landscape), their presence on the warrens acts as a continual seed source ensuring that the species are available for dispersal. There are abundant data to demonstrate that prolonged, small-scale disturbance created by mammals in a range of vegetation communities results in a decline in the relative abundance of perennial grasses at the expense of annual forbs (Friedel et al. 1988, Noy-Meir et al. 1989, Dean et al. 1994, Boeken et al. 1995, Gomez-Garcia et al. 1995, Milton et al. 1997). Research results from other areas suggests that, given the elimination of rabbits, it is unlikely that the original perennial grasses would return to the warrens due to the abundant soil seedbank of annual forbs in the mound soils (Lunt & Morgan 1999), and the fact that many perennial grasses are unable to reestablish in disturbed, unstable sites (Walker et al. 1995). Suppression of germination of perennial grasses such as Austrodanthonia caespitosa on the warrens (at Yathong) may explain some of the observed difference in cover between warrens and non-warrens. Compared with the non-warrens at Yathong, there were more species dispersed by burrs on the warrens. Thus warrens are likely to act as satellite sites for dispersal of weeds to other areas.

5.2 EFFECTS OF RABBITS ON SOIL AND ECOLOGICAL PROCESSES

One of the major effects of rabbits is to reduce ground cover, resulting in exposure of the topsoil, and subsequent soil erosion (Coman 1997). By removing above-ground and below-ground vegetation, rabbits contribute to a winnowing of the finer particles out of the soil by wind. This form of land degradation reduces the chance of successful establishment of native plants.

The long-term effect of disturbance by rabbits is to create a surface with a patchy arrangement of vegetated, bare or eroded soils, often with a layer of coarse gravel. Material excavated during warren construction is deposited near the burrow entrances (Myers et al. 1994, Eldridge & Myers 1999), and this not only covers the vegetation, but is richer in silts and clays (Eldridge & Myers 1999). Given the high clay content of the Yathong and Warrananga soils, mounds are highly susceptible to physical crusting, hardsetting and even wind and water erosion when unvegetated, largely through the re- organisation of silts and clays under the action of raindrops (Eldridge & Greene 1994, Walker & Koen 1995). Continued rabbit activity is likely to result in a continuation of surfaces with a degraded morphology.

Because warren surfaces however tend to be convex-shaped as well as smooth and bare, they tend to shed water. Lower levels of favourable soil nutrients such as nitrogen and carbon on the warrens compared with the non-warrens (Eldridge & Myers 1999, Eldridge & Myers 2001), suggest that either these nutrients are being eroded from the mounds, or that the rabbits are depositing less fertile soils at the surface. At the Yathong site, a significant impact of rabbits was to destroy the cryptogamic crust either directly by disturbance, or indirectly by smothering it with excavated soil. The marked differences in morphology between the warren and non-warren surfaces were reflected in large differences in germination in three of the four species tested. Germination of the weedy Marrubium vulgare and Brassica tournefortii was significantly greater on the disturbed, warren surface compared with the non-warren, cryptogamic surface, and conversely germination of the grass Austrodanthonia caespitosa was significantly greater on the cryptogamic crust

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17 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

Compared with the non-warren surfaces, the warren soils were typically dispersed (eroded), smooth, and contained large amounts of embedded gravel and coarse sand, but sparse litter. In general, reduced germination on these surfaces is likely to have resulted from poor soil-seed contact, high solar radiation, rapid moisture depletion and therefore poor soil moisture storage and a lack of suitable niches for seed entrapment (Peart & Clifford 1987). The close soil seed contact probably accounts for the ability of these species to readily germinate on degraded mound surfaces. In the case of Marrubium vulgare, the mucilaginous sheath around the seed may also have assisted in water retention (Gutterman 1986).

5.3 IMPACT OF RABBITS ON OTHER FAUNA

European rabbits are known to be eaten by introduced predators such as red foxes (Vulpes vulpes) and feral cats (Felis catus), and can maintain populations of these species at artificially high levels (Reid & Bowen 2001). Dietary switching of these predators from rabbits to indigenous species can occur following declines in rabbit populations, such as those caused by rabbit calicivirus disease, causing ‘hyper-predation’ impacts on indigenous species (Dickman 1996, Newsome et al. 1997, NPWS 2002). The influence of rabbits on other fauna e.g. reptiles and ground-dwelling arthropods is unknown. It is likely however that warrens may support a unique suite of invertebrate taxa (probably beetles, ants and spiders) which are well-represented in semi-arid areas. For example, large numbers of tenebrionid beetles normally found in litter and vegetation have been recorded from wombat burrows at Brookfield Conservation Reserve in arid South Australia (Tom Weir, pers. comm. 2002), and it is likely that warrens will yield unique faunal assemblages as well.

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18 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

6. Recommendations

This research and literature review has identified a number of issues relating to the influence of the European rabbit on biodiversity.

1. Little is known about the impact that rabbit activity (digging, scratching etc) has on other taxa such as reptiles, small mammals and arthropods. Further studies utilising pitfall trapping in areas with and without rabbits should be considered.

2. Results from Yathong Nature Reserve support data in the literature that warren ripping is a highly effective control method (Vine 1999). Results also show that rabbit calicivirus disease (RCD) is not effective enough as a sole method of rabbit eradication. Thus RCD needs to viewed not as a single control technique, but rather as a technique to establish low population numbers in order to make follow-up techniques such as ripping, cheaper and more effective. However, the effect of ripping on plants and animals associated with rabbit warrens may be an issue of concern, as is the question of whether ripping is likely to lead to a more or less stable surface than existed had the warrens been left intact.

3. Studies should focus on an examination of soil seed banks on warrens and non-warrens to examine the role of warrens as harbor for weed seeds. Similarly, inventories of other taxa (as 1 above) should proceed in order to examine the influence of ripping.

Apart from the warren-based study used here, it would be useful to be able to use a network of exclosures for studying the impact of rabbits over longer time frames. Many studies involving rabbits have been conducted in association with various Department of Land and Water Conservation (Soil Conservation Service), NSW Agriculture, and Rural Lands and Protection Board trials in the drier areas of NSW. There is a need to collate this information as part of a larger study to assess the importance of control measures such as RCD and ripping.

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19 The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants in semi-arid woodlands report

7. References

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Auld, T.D. (1993). The impact of grazing on regeneration of the shrub Acacia carnei in arid Australia. Biological Conservation 65, 165-76.

Auld, T.D. (1995a). Seedling survival under grazing in the arid perennial Acacia oswaldii. Biological Conservation 72, 27-32.

Auld, T.D. (1995b). The impact of herbivores on regeneration in four trees from arid Australia. The Rangeland Journal 17, 213-227.

Auld, T.D. and Denham, A.J. (2001). Flora conservation issues at Kinchega National Park, western NSW. Cunninghamia 7, 27-41.

Bath, R.K. (1992). Rabbits in the rangelands. In: Australian Rangelands in a Changing Environment. 7th Biennial Conference of the Australian Rangeland Society, Cobar NSW. pp. 350-351.

Blair-West, J.R., Coghlan, J.P., Denton, D.A., Nelson, J.F., Orchard, E., Scoggins, B.A., Wright, R.D., Myers, K., and Junqueira, C.L. (1968). Physiological, morphological and behavioral adaptation to a sodium deficient environment by wild native Australian and introduced species of animals. Nature 217, 922-8.

Boeken, B., Shachak, M., Gutterman, Y. and Brand, S. (1995). Patchiness and disturbance in plant community responses to porcupine diggings in the Central Negev. Ecography 18, 410-422

Catling, P.C. and Newsome, A.E. (1992). A new technique to determine the seasonal changes in the quality of food selected by free ranging rabbits. In: C.A. Thanos (ed.) Proceedings of the Sixth International Conference on Mediterranean –type ecosystems, Meleme, Crete, Sept 23-27, 1991. pp. 177-82. University of Athens, Greece.

Chesterfield, C.J. and Parsons, R.F. (1985). Regeneration of three tree species in arid south-eastern Australia. Australian Journal of Botany 33, 715-732.

Chilcott, C., Reid, N.C.H. & King, K. (1997). Impact of trees on the diversity of pasture species and soil biota in grazed landscapes on the , NSW. In: P. Hale & D. Lamb (eds.) Conservation Outside Nature Reserves, pp. 374-386. Queensland: University of Queensland Press.

Coman, B.J. (1999). Tooth and nail: the story of the rabbit in Australia . Text Publishing, Melbourne.

Cooke, B.D. (1982a). A shortage of water in natural pastures as a factor limiting a population of rabbits, Oryctolagus cuniculus (L.), in arid, north-eastern South Australia. Australian. Wildlife Research 9, 465-76.

Cooke, B.D. (1982b). Reduction of food intake and other physiological responses to a restriction of drinking water in captive wild rabbits, Oryctolagus cuniculus (L.). Australian Wildlife Research 9, 247-52.

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Cooke, B.D. (1991) Rabbits: indefensible on any grounds. Search 22: 193-194

Crisp, M.D. and Lange, R.T. (1976). Age structure, distribution and survival under grazing of the arid- zone shrub Acacia burkittii. Oikos 27, 86-92.

Cropper, S. (1987). Ecological notes and suggestions for the conservation of a recently discovered site of Lepidium hyssopifolium. Biological Conservation 41, 267-278.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. Inkata Press, Sydney.

Dean, W.R.J., Milton, S.J., Ryan, P.G. and Maloney, C.L. (1994). The role of disturbance in the establishment of indigenous and alien plants at Inaccessible and Nightingale Islands in the South Atlantic Ocean. Vegetatio 113, 13-23.

Dickman, C.R. (1996). Overview of the impacts of feral cats on Australian native fauna. Australian Nature Conservation Agency: Canberra.

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