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Blue tussock
Poa colensoi

Diagnostic features for identification in the field

  • Blue or green tussocks or forming low green turf. Tussocks vary in height from 5 to 40cm long.

  • Leaves are fine rolled with a long obtuse ligule, which wraps round the stem.

  • Prominent pale sheaths which are smooth, persistent and membranous.

  • Dead leaves comes away easily when you pull your fingers through the tussock.

  • Flowering stem is short (5-10cm) and smooth.

  • The flower panicle is open; awns are not present.

References:
  • Wilson, H.W. 1996: Wild plants of Mount Cook National Park. Manuka Press, Christchurch.
  • Jane, G. 1995. Field guide to grasses. 1. Alpine grasses. Description of community and habitat

Description of community and habitat

Blue tussock is widespread in lowland to high alpine regions throughout New Zealand (to 2100m a.s.l.). It has a wide range of habitats, and is one of the most common species in the alpine zone.

East of the Main Divide, South Island
Blue tussock has a wide altitudinal range being found in low valley floors to peaks in the high alpine zone. However, it forms a dominant cover only at high altitudes, above the limit of alpine fescue tussock grassland. It frequently dominates ridges near the upper limit of the continuous C. rigida zone, in Central Otago. Towards the upper limits of continuous vegetation on eastern mountains, blue tussock occurs with Celmisia viscosa, and other generally fire resistant plants. On the Old Man Range, blue tussock grassland occupies a well defined but only 100m wide zone, near the upper altitudinal limit of narrow-leaved snow tussock at about 1300m. The presence of isolated or small patches of snow tussock indicate that these are relics from an earlier snow tussock cover (Mark), which has been depleted by pastoral activities (grazing and burning). Blue tussock can also be a co-dominant with alpine fescue tussock (Festuca matthewsii).

In Central Otago, the dwarfed blue tussock is the sole dominant grass in late-snow hollows, where snow patch grass (Chionochloa oreophila) is absent.

West of the Main Divide, South Island
Blue tussock swards occupy alpine sink-holes in Arthur Ecological District in Western Nelson.

In Westland, browsing by feral deer, thar and chamois prior to 1968, resulted in large areas of mid-ribbed snow tussock grassland (C.pallens) being replaced by a grassland dominated by blue tussock and other grazing-tolerant plants (e.g. Microlaena colensoi and Celmisia walkerii). However, the subsequent effective control of feral animals has seen the re-establishment C.pallens in these areas.

This information was largely taken from :Wardle, P.; 1991. Vegetation of New Zealand, Cambridge Press, Cambridge.

Other species present

 East of the Main Divide, South Island
Blue tussock is a common species found in a wide range of communities. However, where it occurs as a blue tussock dominated sward, it is associated with Celmisia sessiliflora, Aciphylla hectori, Kelleria dieffenbachii, Luzula rufa, Anisotome flexuosa, and Raoulia grandiflora.

This information was taken from: Wardle, P.; 1991. Vegetation of New Zealand, Cambridge Press, Cambridge.

Vegetation History

 Alpine blue tussock grasslands
Much of the mountainlands to the east of the Main Divide were covered in forests prior to 700 - 900 years ago. These were largely destroyed by fire prior to European settlement, leading to a migration of tussock species into previously forested areas.

In Canterbury, slim-leaved snow tussock (together with C. rigida) naturally occupying alpine areas above the timberline, migrated downslope into penalpine, subalpine and even montane environments. Presumably, blue tussock naturally occurred within these snow tussock communities.

These snow tussock communities have subsequently been modified by grazing and burning, resulting in the opening up and depletion of the snow tussocks. Where repeated burning has taken place, snow tussock cover has become minimal, and in it's place is an induced short blue tussock grassland. This grassland occurs at altitudes above the induced alpine fescue tussock grasslands.

References:
  • Wardle, P. 1991. Vegetation of New Zealand, Cambridge Press, Cambridge.
  • Connor, H.E. and Macrae, A.H. 1969. Montane and subapine tussock grasslands in Canterbury, Chaper 9 In: Knox, G.A. (Ed.) The Natural History of Canterbury, pp 167-204. Reed, Wellington.





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