335 NORTON ET AL: INFLUENCE OF PASTORAL MANAGEMENT ON PLANT BIODIVERSITY New Zealand Journal of Ecology (2006) 30(3): 335-344 ©New Zealand Ecological Society Available on-line at: http://www.nzes.org.nz/nzje Published on-line: 9 October 2006 Infuence of pastoral management on plant biodiversity in a depleted short tussock grassland, Mackenzie Basin David A. Norton 1 *, Peter R. Espie 2 , Will Murray 3 and Jim Murray 3 1 School of Forestry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand 2 AgScience Ltd., PO Box 1475, Dunedin, New Zealand 3 Glenmore Station Ltd., PO Box 97, Lake Tekapo, New Zealand *Author for correspondence (E-mail: david.norton@canterbury.ac.nz) ___________________________________________________________________________________________________________________________________ Abstract: This study investigated the effects of different management inputs (fertiliser and seed) and grazing patterns on plant biodiversity in a short tussock grassland with a strong Hieracium pilosella component. Cover abundance of vascular and non-vascular plants and environmental variables were measured in 32 10×10-m plots located in fve blocks with different management treatments. Ordination of the foristic data separated the block with the highest management inputs from other blocks. Several adventive species were signifcantly more abundant in this block, while several native species were either absent or uncommon, but were signifcantly more abundant in other study blocks. H. pilosella was signifcantly more abundant in blocks with lower management inputs. Diversity was signifcantly higher in the block with the highest management inputs. The native tussock Poa colensoi had signifcantly greater cover abundance while Festuca novae-zelandiae tussocks were signifcantly taller in this block. Our results suggest that high management inputs reduce the abundance of H. pilosella and diversity of native species, but increase the abundance of other adventive species and the cover and vigour of native tussocks. Our results highlight an interesting management conundrum for short tussock grasslands. No-input management is likely to result in a decline in native biodiversity, as well as production values, as H. pilosella mats deplete soil nutrients and restrict regeneration of native species. However, input of fertiliser and adventive seeds to enhance production values, although resulting in an increase in the vigour and abundance of some native species (mainly tussocks) and a reduction in H.pilosella abundance, will also result in a decline in overall native species richness. ___________________________________________________________________________________________________________________________________ Keywords: short-tussock grassland; biodiversity conservation; farm management; Hieracium pilosella; high country Introduction Grasslands dominated by native tussock forming grasses from the genera Chionochloa, Festuca and Poa are the main vegetation cover of the inter-montane basins and ranges of the eastern South Island high country (Mark and McLennan, 2005 ). Although much of this area was forested prior to human settlement (McGlone, 2001), dramatic ecological transformations have occurred with both Polynesian and European settlement (Molloy et al., 1963; Connor, 1964; Scott, 1984; McGlone and Moar, 1998; Ledgard, 2001; O’Connor, 2003) due to human induced fres, grazing by sheep and cattle, and through the deliberate and accidental introduction of adventive species, resulting in large areas of induced grassland. As a result of these changes it is possible that some of these high country ecosystems are now crossing ecological thresholds that are unlikely to be readily reversed (Hobbs and Norton, 2004). These induced high country grasslands are used primarily for pastoral fne-wool production, but have recreation, conservation and other values and there is considerable debate over their appropriate long-term management, particularly the interaction between pastoralism and native biodiversity conservation (Swaffeld and Hughey, 2001; O’Connor, 2003; Mark and Dickinson, 2004; Mark and McLennan, 2005). Despite considerable ecological research on the interaction between pastoral farming and native biodiversity conservation in New Zealand tussock grasslands, most of this has focused solely on the effects on native biodiversity of excluding domestic stock with little consideration of other management effects (Walker, 2000; Meurk et al., 2002; Mark and Dickinson, 2003). It is, however, clear that the impacts of grazing on these grasslands is compounded by the infuence of invasive species, especially herbs from the genus Hieracium ( Treskonova, 1991; Rose et al., 1995;