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

A valley mire was sampled on the flanks of Swampy Hill, east Otago, New Zea land. It formed in a narrow valley, apparently originally comprising two ba sins. The end of the mire nearest the outlet contained species typical of f ens (i.e., rheotrophic mires). At the head of the valley there was a sectio n of the mire with mixed vegetation cover comprising the tussock grass Chio nochloa 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 inapplicab le here. It is not known whether New Zealand Sphagnum species are as effici ent at lowering the pH as those investigated elsewhere. Macrofosssil eviden ce indicates that some components of the bog, such as Sphagnum and epacrida ceous subshrubs, have remained constant, almost since the inception of the bog. However, Empodisma minus, currently absent from the bog and rare in th e region, was present at one stage. The change from cover with Empodisma an d Dracophyllum as significant components, to the present Chionochloa/Sphagn um/cushion composition, occurred a few hundred years ago, probably initiate d by fire. Comparison with preliminary information for other bogs suggests that those in the eastern part of the South Island vary considerably in spe cies composition, with individualistic assemblages of species. The site is seen as having high conservation values. To protect these values the bog ne eds protection from invasive exotic weeds, and from damage by wild pigs.