The Impact of the European Rabbit (Oryctolagus Cuniculus L.) on Diversity of Vascular Plants in Semi-Arid Woodlands
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The impact of the European rabbit (Oryctolagus cuniculus L.) on diversity of vascular plants 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 New South Wales 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 Plant 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 NSW Department of Land and Water Conservation 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 Nature Reserve ........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 NSW Department of Land and Water Conservation 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 Australia 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