New Zealand Journal of Ecology (2001) 25(1): 39- 52

A Chionochloa/Sphagnum/cushion valley bog in east Otago, New Zealand

Research Article
Susan Walker 1
John B. Steel 1
G. L. Rapson 2
Stephen H. Roxburgh 3
Warren McG. King 4
Anni J. Watkins 1
Tom E. Myers 5
Jonathon A. Keogh 6
Amelia A. M. McQueen 1
J. Bastow Wilson 1,*
  1. Botany Department, University of Otago, P.O. Box 56, Dunedin, New Zealand
  2. Ecology Group, Institute of Natural Resources, Massey University, Private Bag, Palmerston North, New Zealand
  3. Ecosystem Dynamics Group, RSBS, Institute of Advanced Studies, Australian National University, Canberra, ACT 0200, Australia
  4. NSW Agriculture, Agricultural Research and Veterinary Centre, Forest Road, Orange, NSW 2800, Australia
  5. Dunedin Botanic Garden, Dunedin City Council, P.O. Box 5045, Dunedin, New Zealand
  6. Portobello Marine Laboratory, University of Otago, P.O. Box 8, Portobello, New Zealand
*  Corresponding author

A valley mire was sampled on the flanks of Swampy Hill, east Otago, New Zealand. It formed in a narrow valley, apparently originally comprising two basins. The end of the mire nearest the outlet contained species typical of fens (i.e., rheotrophic mires). At the head of the valley there was a section of the mire with mixed vegetation cover comprising the tussock grass Chionochloa rubra, Sphagnum species, and cushion/herb/shrub cover. Ombrotrophic status of this section was indicated by a slightly raised profile, greater acidity, lower exchangeable Na and K, and lower substrate cation exchange capacity, identifying it as a bog. Total Ca:Mg molar ratios were generally above 1.0, but this rule-of-thumb for ombrotrophic status may be inapplicable here. It is not known whether New Zealand Sphagnum species are as efficient at lowering the pH as those investigated elsewhere. Macrofosssil evidence indicates that some components of the bog, such as Sphagnum and epacridaceous subshrubs, have remained constant, almost since the inception of the bog. However, Empodisma minus, currently absent from the bog and rare in the region, was present at one stage. The change from cover with Empodisma and Dracophyllum as significant components, to the present Chionochloa/Sphagnum/cushion composition, occurred a few hundred years ago, probably initiated by fire. Comparison with preliminary information for other bogs suggests that those in the eastern part of the South Island vary considerably in species composition, with individualistic assemblages of species. The site is seen as having high conservation values. To protect these values the bog needs protection from invasive exotic weeds, and from damage by wild pigs.