Factors determining shrub abundance on uncultivable hill country


  • G.B. Douglas
  • A.D. Mackay
  • M.B. Dodd
  • C.M. Lloyd-West
  • R.A.J. Gray




Development of mÄnuka (Leptospermum scoparium) and gorse (Ulex europaeus) is a widespread problem on pastoral hill country and is associated with reduced fertiliser inputs and grazing pressures. Using mÄnuka as a source for specialty products offers a potentially new, profitable enterprise alongside livestock and forestry. However, there is a lack of quantitative information on the optimum soil nutrient status and associated fertiliser programme to encourage presence and growth of this species. In a survey across 324 grazed sites, mÄnuka had greatest presence on steep slopes (>25o) and soils with Olsen P <10 μg/ml. MÄnuka presence was three times greater on steep than medium slopes (13- 25o) and 12 times greater than on low slopes (<13o). Annual fertiliser inputs did not appear to change this outcome provided Olsen P remained low. MÄnuka was virtually absent where Olsen P approached 50 μg/ml. At other grazed sites, mÄnuka and gorse were most likely to occur where Olsen P was <15 μg/ml. This study provided insights to underpin a set of nutrient guidelines for mÄnuka under grazing conditions to maximise its establishment and growth. It remains to be determined what the optimum Olsen P level is for this plant when managed in regimes without grazing and treading pressure. Keywords: mÄnuka, gorse, soil fertility, hill country


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How to Cite

Douglas, G., Mackay, A., Dodd, M., Lloyd-West, C., & Gray, R. (2015). Factors determining shrub abundance on uncultivable hill country. Journal of New Zealand Grasslands, 77, 239–244. https://doi.org/10.33584/jnzg.2015.77.454



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