SOUTHERN-HEMISPHERE PATTERNED MIRES, WITH EMPHASIS ON SOUTHERN NEW-ZEALAND

Extensive patterned mires in valley heads and on glacial benches in southern New Zealand: (45 degrees 22'S; 1250-1400 m.a.s.l.), and valley floors in Tierra del Fuego (54 degrees 53'S; 60-100 m.a.s.l.) have developed under cool, moist climatic conditions favourable for peat accumulation. In southern New Zealand's tussock grassland landscape, aapa mire pools (often with peat islands) and ridges, are elongated (pools: mean 24.5 +/- 2.4 m x 7.5 +/- 1.0 m) and aligned 90 degrees to gentle slopes. Feat depths (0.3-2.5 m) are greatest on downslope margins of pools and sometimes associated with basement profile concavities. Pools up to 1.3 m deep have peat bases, are generally not fed by nor linked to surface streams, and have steep downslope, with more gentle upslope, margins. Pools may be incipient (occupying small pear depressions), fluctuating or permanent. In steeper headwater sections, surface and underground channels link small stream pools. On glacial benches, pools (to 1 ha) occupy basement rock depressions with up to 1.5 m of underlying peat. Vegetation displays a repeating basic pattern. On pool rims aquatic mosses (Acrocladium samzentosum and/or Sphagnum falcatulum) cover steep pool edges; S. squarrosum inner faces of rims; S. cristatum, Carex galldichaudiana and C. lachenalii on rims and declines. The tall, vertical peat pedestals support a similar vegetation pattern. Carer gaudichaudiana occupies shore margins prone to intermittent flooding with peat-forming Sphagnum mosses absent. Islands are produced from elongated peninsulas or sinuate mainland shores. These persist if peat formation exceeds water level rise. Snow tussocks of Chionochloa macra grow on localised elevated areas unrelated to subsurface topography. In Tierra del Fuego, raised (4-6 m) rain-fed aapa mires, bordered by intermittent lagg streams, develop amongst partially cleared Nothofagus pumilio forest. Elongated (3-60 m length), steep-sided and island (circular: c. 2 m diameter)- studded pools, form generally parallel crescentic lines with regular to sinuate margins associated with incipient islands. Occasional islands are either decadent, or submerged and moribund. Sphagnum magellanicum and Empetrum rubrum dominate above water level, amongst pure stands of Marsippospermum grandiflorum on higher ground. Sphagnum fimbriatum characterises a narrow zone at water line. Vegetation/peat development reinforces pool-vegetation boundaries. Until drained, vegetation/firm peat development is prevented in pools greater than or equal to 20 cm deep. Following localised subterranean drainage, non-wetland species may colonise. Underlying topography, differential peat formation, hydrological and drainage properties, plus vegetation development all influence patterning in the mires. Biotic factors are emphasised over physical processes in the origin and maintenance of the patterned wetland systems but are not mutually exclusive.