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A geothermal streamside at Spa (Otumuheke) Stream, Taupo, with native ladder fern ([Nephrolepis flexuosa]), Christella ‘thermal’, inkberry ([Dianella nigra]), and adventive blackberry ([Rubus fruticosus]) (Bruce Burns)

A geothermal streamside at Spa (Otumuheke) Stream, Taupo, with native ladder fern ([Nephrolepis flexuosa]), Christella ‘thermal’, inkberry ([Dianella nigra]), and adventive blackberry ([Rubus fruticosus]) (Bruce Burns)

Geothermal streamsides are steam-influenced microhabitats created by hot springs and streams that allow species (particularly those with tropical origins) to exist in areas that would otherwise be too cold. For example, harakeke (Phormium tenax) and pukio (Carex secta) grow beside the hot pools in the Copland Valley at 450 m, a higher altitude than elsewhere in Westland.

Notable flora and fauna

Threatened plants include the nationally vulnerable Machaerina complanata, the declining Cyclosorus interruptus and native ladder fern (Nephrolepis flexuosa), and the naturally uncommon giant hypolepis (Hypolepis dicksonioides). Indeterminate species include the declining Christella aff. dentata (’thermal’).

These systems contain two species of macroinvertebrates confined to high-temperature, low-pH waters: the ephydrid fly Ephydrella thermarum and an endemic mosquito (Culex rotoruae).

Threat status

Critically endangered (Holdaway et al. 2012)

Threats

Wilding pines (e.g., Pinus pinaster, P. radiata), blackberry (Rubus fruticosus), Scotch broom (Cytisus scoparius), buddleia (Buddleja davidii), and some exotic grasses can be problematic in marginal areas where the soils are sufficiently cool for their establishment. Geothermal areas are generally too unstable for urbanisation; however, they have been used as dumping grounds. In more stable areas, stock may trample vegetation when unfenced. Geothermal fluid extraction for energy can affect surface activity and change soil temperatures with consequent impacts on plant communities. Geothermal fluid extraction can also cause subsidence. There are some impacts from tourism, but usually these impacts are well controlled.Some trampling occurs where people access hot streams for bathing.

Where do they occur?

Geothermal streamsides are common in the Taupo Volcanic Zone on the North Island Volcanic Plateau and also occur in association with the Alpine Fault in the South Island as far south as the Copland Valley. Unfortunately many of these streamsides no longer support native vegetation.

Further reading

Boothroyd IKG 2009. Ecological characteristics and management of geothermal systems of the Taupo Volcanic Zone, New Zealand.  Geothermics38: 200-209.

Burns BR 1993. Bryophytes and lichens of Te Kopia Scenic Reserve geothermal vegetation.  New Zealand Botanical Society Newsletter 34: 8-9.

Burns BR 1997. Vegetation change along a geothermal stress gradient at the Te Kopia steamfield . Journal of the Royal Society of New Zealand 27: 279-294.

Duggan IC, Boothrod IKG, Speirs D 2007. Factors affecting the distribution of stream macroinvertebrates in geothermal areas: Taupo Volcanic Zone, New Zealand . Hydrobiologia 592: 235-247.

Given DR 1980. Vegetation on heated soils at Karapiti, central North Island, New Zealand and its relation to ground temperature . New Zealand Journal of Botany 18:1-13.

Wardle P 1991. Vegetation of New Zealand. Cambridge University Press. Pp. 400-404.

Wildland Consultants 2011. Geothermal vegetation of the Waikato Region - An update based on 2007 aerial photographs . Wildland Consultants Ltd Contract Report No. 2348. Prepared for Waikato Regional Council. 515 pp.

Links

NZ's Thermal Hot Pools and Hot Springs, New Zealand - Your Online Guide

Geothermal plant communities and ecosystems  (NZ Plant Conservation Network)

New Zealand Geothermal Association

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