Granite sand plain on the Lookout Range, NW Nelson (Susan Wiser)
Granitic sand plains are indistinguishable from granitic gravel fields and they occur together on very exposed sites above treeline, where erosion-prone granite bedrock is close to the surface. Typically, 80% of the site cover is bare ground and bedrock. Due to their chemistry and structure, these granites crumble and rot to form angular gravels (2-64 mm) and ultimately sands. Relative to other alpine granite ranges in New Zealand, rainfall is relatively low and the terrain is flatter, differentiating them from screes on steeper slopes. Soils are well-drained and excessively nutrient-poor.
Vegetation is sparse and very species poor, and is characterised by low shrubs (e.g. Dracophyllum pronum, D. prostratum), grasses (e.g. Poa colensoi), cushion plants (e.g. Veronica pulvinaris) and small herbs (e.g. Anisotome imbricata and Notothlaspi australe). Vegetation height rarely exceeds 30 cm, with many plants being prostrate and woven among the granite particles.
Notable flora and fauna
Only one rare plant, the naturally uncommon cream gentian (Gentianella luteoalba), is known from this system and it is endemic to the Lookout Range.
The NW Nelson sites support a rare carabid beetle (Mecodema integratum) and screefields adjacent to the plains provide habitat for the range-restricted giant scree weta (Deinacrida connectens). In Fiordland the new moth species (Hierodoris extensilis) Hoare (Lepidoptera: Oecophoridae) can be found in granite sand plains and gravel fields.
Threat status
Not threatened (Holdaway et al. 2012)
Threats
This system does not appear to be threatened, however, invertebrates are threatened by mammalian predation.
Where do they occur?
The extent of granite sand plains is not well known, but they may be confined to the Lookout Range, NW Nelson, and Mt Titiroa in eastern Fiordland. They may also occur in the NE Paparoas where suitable granites occur above treeline, but this area has not yet been surveyed.
Further reading
Bell CJE 1973. Mountain Soils and Vegetation in the Owen Range, Nelson 2. The Vegetation. New Zealand Journal of Botany 11: 73-102.
Glenny D 2004. A revision of the genus Gentianella in New Zealand. New Zealand Journal of Botany 42: 361-530.
Hoare RJB 2012. A new species of Hierodoris Meyrick (Lepidoptera: Oecophoridae) with a telescopic ovipositor, from granite sand plains in Fiordland. New Zealand Entomologist 35: 51-57.
Hoare RJB, Millar IR, Richardson SJ 2016. The insect fauna of granite sand plains: a naturally rare ecosystem in New Zealand. New Zealand Entomologist, DOI:10.1080/00779962.2015.1108159
Richardson SJ, Williams PA, Mason NWH, Buxton RP, Courtney SP, Rance SP, Clarkson BR, Hoare RJB, St. John MG, Wiser SK. 2012. Rare species drive local trait diversity in two geographically disjunct examples of a naturally rare alpine ecosystem in New Zealand. Journal of Vegetation Science. Published Online 27 Feb 2012. DOI: 10.1111/j.1654-1103.2012.01396