Limestone erosion pavements

Erosion pavements scattered amongst grassland Matiri Range, western Nelson (Peter Williams)

Erosion pavements are flat to gentle slope areas that have been bared of topsoil formed through chemical weathering. They may or may not have large cracks and fissures, depending on rock type, that do not support gravel or colluvium and occur on ridges, mountain tops and plateaux rather than on tors or rock stacks. They do not include coastal turfs, even where these occur on coastal erosion pavements. They range in size from small inter-tussock spaces to patches many metres across. They commonly support only small appressed herbs, e.g., Craspedia spp., Epilobium spp., Raoulia spp.

Synonyms

Alvar

Notable flora and fauna

Threatened and rare plants include nationally critical moonwort (Botrychium lunaria), Chaerophyllum basicola, Mt Burnett sedge (Carex dolomitica), Castle Hill forget-me-not (Myosotis colensoi), simplicia (Simplicia buchananii), Gentianella calcis subsp. calcis, Melicytus improcerus and Ranunculus (a) (AKU 19876; Hope); nationally endangered Crassula multicaulis, Melicytus (a) (CHR 355077; Matiri Range); nationally vulnerable Tetrachondra hamiltonii and range restricted Craspedia sp. (f). Naturally uncommon species include Poa sudicola, New Zealand anemone (Anemonastrum tenuicaule), Carex calcis, Enys sedge (Carex enysii), Myosotis spathulata, and limestone cushion poa (Poa acicularifolia subsp. acicularifolia).

No information is available on threatened and rare fauna.

Threat status

Not threatened (Holdaway et al. 2012)

Threats

Introduced gasses and flatweeds can be invasive, especially along fissures and cracks. Grazing by deer or large mammals is likely to be a problem only where there is sufficient foliage, but hares have been noted eating even individual plants in the middle of pavements. Ironically, as described above, farming and stock grazing have probably increased the overall area of limestone erosion pavement. As with all limestone features, mining can be an issue.

Where do they occur?

They are scattered through the South Island lowlands in association with Amuri limestone from south Marlborough to north Otago, wherever the regolith has been stripped by water and wind. They have probably dramatically increased in frequency and area since humans arrived, due to grazing and burning. Most lowland limestone escarpment in dry eastern South Island have their upper margin, convex creep slopes stripped of their previous regolith to expose an underlying pavement They are particularly common on the subalpine limestone plateaux of western Nelson.