Geothermally heated ground (dry) with prostrate kanuka scrub at Karapiti/Craters of the Moon, north of Taupo (Susan Wiser)
Geothermally heated soils result from heat flow through the ground (in contrast to heat losses from water sources or fumaroles, overflow from geysers and springs, or seepages to nearby lakes or rivers). The heat flowing through the heated ground is released at the surface as steam. Karapiti/Craters of the Moon (Given 1980), for example, is a steamfield that includes areas of heated ground as well as fumaroles. At Karapiti, there are no streams or areas of standing water. Soil temperatures at 15 cm depth in areas that support plants (including mosses) range from 40°C to 85°C. Prostrate kanuka (Kunzea ericoides var. microflora - a true-breeding form) is the most characteristic species.
Notable flora and fauna
Threatened and rare plants include the declining native ladder fern (Nephrolepis flexuosa), the taxonomically indeterminate and declining Christella aff. dentata (‘thermal’) and the naturally uncommon Dicranopteris linearis, Fimbristylis velata, giant hypolepis (Hypolepis dicksonioides), prostrate kanuka (Kunzea ericoides var. microflora), and red-bearded orchid (Calochilus robertsonii).
Threat status
Critically endangered (Holdaway et al. 2012)
Threats
Wilding pines (Pinus spp.) and blackberry (Rubus fruticosus) can be problematic in marginal areas where the soils are sufficiently cool for establishment. Although other weed species are present in most geothermal areas, geothermally heated soils mostly have few naturalised species. Stock can trample vegetation when areas are not fenced. The areas are generally too unstable for urbanisation, but some areas have been used as dumping grounds. Rabbits and hares are present in many geothermal ecosystems. Geothermal fluid extraction for energy can affect surface activity, changing soil temperatures, which can influence vegetation dynamics. Geothermal fluid extraction can also cause subsidence. In places where these areas are used for recreational activities, e.g., motocross riding, considerable damage can result. There are some impacts from tourism, but usually these are well controlled.
Where do they occur?
Heated ground primarily occurs in the Taupo Volcanic Zone on the Volcanic Plateau, in the central North Island.
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 1994. Botanical notes on a trip to White Island (Whakaari), 27 November 1993. New Zealand Botanical Society Newsletter 35: 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.
Cody AD 2007. Geodiversity of geothermal fields in the Taupo Volcanic Zone DOC Research & Development Series 281. Wellington, Department of Conservation. 70 p.
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.
van Manen SM, Reeves R 2012. An assessment of changes in Kunzea ericoides var. microflora and other hydrothermal vegetation at the Wairakei-Tauhara geothermal field, New Zealand. Environmental Management 50:766-86.
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
Geothermal resources (Environment Waikato)
Geothermal systems (New Zealand Geothermal Association)
Rotorua Geyserfields and Geothermal sites (DOC consultation on World Heritage Status)
Rotorua’s Geothermal Treasures (DOC factsheet)