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Calcareous cliffs, scarps and tors

Calcareous cliffs on Ben More, Marlborough, with silver tussock ([Poa cita]) and [Myosotis arnoldii] (Peter Williams)

Calcareous cliffs on Ben More, Marlborough, with silver tussock (Poa cita) and Myosotis arnoldii (Peter Williams)

Cliffs are high steep faces and scarps are cliffs along the edge of a plateau, while tors are mounds of glacial eroded bedrock with steep sides. Together, they provide many varied habitats - from bare rock that can be colonised only by mosses and lichens to deeper soils supporting woody vegetation, from highly exposed situations to heavily shaded and sheltered habitats, and from very dry to permanently wet surfaces. Hebes, some heath-like shrubs, flaxes and native grasses are important on cliffs. Plants seldom grow on the massive cliff faces but are rooted within the instices of ledges, crevices, and cracks. Long tap-like roots are a noteable trait of limestone cliff plants such as cheesemanias and pachycladons. Many native shrubs, grasses, and herbs that have been lost from neighboring habitats find refuge on cliffs, scarps and tors. Some limestone outcrops are important sites of both ancient depositional fossils and New Zealand biota that has become extinct since humans arrived.

Notable flora and fauna

Threatened and rare plants include, the nationally critical Pachycladon exileCardamine magnifica, Mt Burnett sedge (Carex dolomitica), pink broom (Carmichaelia carmichaeliae), Holloways broom (Carmichaelia hollowayi), Chaeropyllum basicola, Convolvulus verecundus forma glaberrimus, Gentianella calcis subspecies calcis, manahune, taiko and waiparaGeranium socolateumGingidia haematitica, Kawarau cress (Lepidium sisymbrioides), Myosotis saxosa, Pachycladon fasciarium, Poa spania, Simplicia buchananii, Simplicia laxa, kakabeak (Clianthus maximus), Ranunculus aff. royi (CHR 513327; Waihao), Ranunculus callianthus, koheriki (Scandia rosifolia), and the nationally endangered Canterbury limestone wheat grass (Australopyrum calcis subsp. optatum), Veronica maccaskillii, and Melicytus (a) (CHR 355077; Matiri Range). Nationally vulnerable species include Carex cremnicola, dwarf broom (Carmichaelia astonii), North-west Nelson marble clematis (Clematis marmoraria), and trailing bindweed (Convolvulus verecundus forma verecundus). Species in decline include Anisotome patula, Mt Burnett matipo (Myrsine argentea), Awaroa koromiko (Veronica scopulorum), and relict species include Melicytus obovatus. The naturally uncommon species include Carex calcis, Carex impexa, Chionochloa flavicans f. temata, Craspedia (t) (CHR 365392; Chalk), Gingidia grisea, Chalk Range Gentian (Gentianella astonii subsp. arduana), Astons Gentian (Gentianella astonii subsp. astonii), Fiordland limestone hebe (Veronica arganthera), Veronica stenophylla var. hesperia, Veronica townsonii, Fiordland snow tussock (Chionochloa spiralis), fierce lancewood (Pseudopanax ferox), Geranium (a) (CHR 518296; Pareora River) and Veronica aff. albicans (AK 252966; Mt Burnett).

Threatened fauna include the nationally vulnerable black-eyed gecko (Mokopirirakau kahutarae) which is rare on the Arthur Range.

Threat status

Vulnerable (Holdaway et al. 2012)

Threats

Limestone areas are particularly favoured by grazing animals because of the high mineral content of the foliage. Grazing is a major threat, particularly where goats, and even possums are present, because they can often access cliffs. Exotic weeds are less of a threat on extremely steep slopes because instability ensures fresh sites for native species colonisation. However, stability combined with sufficient fine material can allow exotic thistles, nutrient demanding grasses such as Chewing’s fescue (Festuca rubra), Scotch broom (Cytisus scoparius) and old mans beard (Clematis vitalba) to establish. Introduced pest and diseases of Brassicaceae (cabbage family) threaten some native members of this family, e.g. Pachycladon cheesemanii although weeds are a greater threat. Some sites are threatened by quarrying for agricultural lime and road gravel, e.g., dolomite mining at Mt. Burnett in North West Nelson. Steep limestone habitats are also vulnerable to development for wind farms, as at Mt. Cass, Canterbury.

Where do they occur?

Calcareous cliffs occur within most limestone, marble, and dolomite outcrops throughout the North and South Islands. Significant locations include: western Waikato, Hawke Bay (Te Mata Peak); Wairarapa (in the Ruamahanga Valley); Marlborough (on the Chalk Range, Sawcut gorge in the Waima valley, and in the Leatham Valley); western Nelson (on Mt. Burnett, the Matiri Range, and Mt. Owen); Canterbury (in the Castle Hill basin and Pareora River); Otago (throughout north Otago and south Canterbury either side of the Waitaki River in the Waitaki Valley at the Awahokomo Karstland).

Further reading

Brown JA, Smith ANH, Robinson TJ 2008. The response of rare herbaceous plants to the removal of weeds in an unproductive environment . Community Ecology  9: 53–58.

Druce AP, Williams PA 1989. Vegetation and flora of the Ben More - Chalk Range area of southern Marlborough, South Island.  New Zealand Journal of Botany 27: 167-199.

Ford KA 2007. Carex (Cyperaceae)—two new species from the calcareous mountains of North‐West Nelson, New Zealand . New Zealand Journal of Botany 45: 721-730.

Heenan PB, Molloy BPJ 2019. Five new and Nationally Threatened taxa of Brachyscome, Cardamine, Convolvulus, Geranium and Ranunculus obligate to vulnerable limestone habitats, eastern South Island, New Zealand . Phytotaxa 415: 32–48.

Heenan PB, Rogers GM 2019. Conserving the plants of eastern South Island limestone Ngā tipu ō te pākeho . Canterbury Botanical Society, Christchurch. 224 p.

Martin W 1969. New Zealand Lichens and their Habitats . Tuatara 17:20-26.

Molloy BPJ 1994. Observation on the ecology and conservation of Australopyrum calcis (Triticeae: Gramineae) in New Zealand . New Zealand Journal of Botany 32: 37-51.

Peat N, Patrick B 2001 Wild Rivers: Discovering the Natural History of the Central South Island . Dunedin, University of Otago Press. Pp. 88-90.

Rogers GM, Courtney SP, Heenan, PB 2018. The calcicolous vascular flora of New Zealand: life forms, taxonomy, biogeography and conservation status . Science for Conservation 331. Wellington, Department of Conservation.

Smissen RD, Heenan PB 2011. Interspecific hybridization among indigenous New Zealand Convolvulus (Convolvulaceae) and the affinities of the Awahokomo limestone population . New Zealand Journal of Botany 49: 329-338.

Wardle P. 1991. Vegetation of New Zealand. Cambridge University Press. Pp. 375-396.

Links

Mineral commodity report 21 - limestone, marble and dolomite  (New Zealand Petroleum & Minerals)

The rocks of Castle Hill  (New Zealand Geographic)