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Slim-leaved snow tussock
Chionochloa macra



Diagnostic features for identification in the field

  • A medium sized tussock which varies in stature. It tends to be smaller at higher altitudes or in more exposed sites.

  • Leaves are usually 50 - 100cm with narrow flat or loosely rolled, which do not bend over or trail on the ground, so that exposed soil doesn't show that swept effect common under C. rigida or C. flavescens (Connor & MacCrae, 1969). The midrib is darkish in colour and isn't obvious.

  • The sheaths at the base of each bunch of leaves are a dull purplish brown, and do not break off with ageing. There is therefore little or no litter derived from leaves and sheaths.

References:
  • Mark, A.F and Adams, N. New Zealand Alpine Plants
  • Wardle, P. 1991. Vegetation of New Zealand. Cambridge University Press.
  • Connor, H.E. & Macrae, A.H. 1969. Montane and subalpine tussock grasslands in Canterbury. Chapter 9 In:Knox, G.A. (ed.) The Natural History of Canterbury, pp 167-204. Reed, Wellington.
  • Wilson, H. 1996. The wild plants of Mount Cook National Park, Manuka Press.


Description of community and habitat

Slim-leaved snow tussocks are found only to the east of the Main Divide.

East of the Main Divide, South Island
Slim-leaved snow tussock grasslands are found from western Marlborough to central Southland. In Otago and Southland, slim-leaved snow tussock grasslands are confined to alpine areas, while in north Canterbury and Marlborough, they also descend as low as 800m a.s.l. on deforested foothills. It is the main snow tussock species as far north as the head of the Awatere River. It is absent on the Kaikoura Range, north-west Nelson, western districts and the North Island.

Slim-leaved snow tussocks are usually associated with the narrow leaved snow tussock (C. rigida), and occupies the transition zone between it and the low open vegetation found at higher altitudes. Slim-leaved snow tussock may hybridize with C. rigida. At lower altitudes, it tends to be confined to the shaded south facing slopes, whilst at higher altitudes it spreads onto northerly slopes. At it's upper limit, the cover of slim-leaved snow tussocks becomes patchy and the tussocks small. This is a reflection of the harsher climate, and its sensitivity to fire and grazing which have lead to the fragmentation of once-continuous slim-leaved snow tussock belts.

Where modified, the cover of slim-leaved snow tussocks can be low, and it commonly occurs with Festuca matthewsii, Poa colensoi, Celmisia spp, Rytidosperma pumilum, and hawkweeds.

Reference:Wardle, P. 1991. Vegetation of New Zealand, Cambridge Press, Cambridge



Other species present

At high altitudes, few exotics are usually present, the common species being sheep's sorrel (Rumex acetocella) and catsear (Hypochaeris radicata). The presence of exotic species increases with decreasing altitude, although they can be common where sheep camp at any altitude. Hawkweeds (Hieracium spp)can be a problem at such locations.

Slim-leaved snow tussocks are commonly found with alpine fescue tussock (Festuca matthewsii). In drier locations, these grasslands are often modified by pastoral activity, and occur with blue tussock (Poa colensoi), Rytidosperma setifolia, R. pumilum, false spaniard (Celmisia lyallii), clubmoss (Lycopodium fastigiatum), Coprosma perpusilla, Luzula rufa and Celmisia sessilforum. Phormium cookianum may be present. Hebe lycopodioides and H. hectorii are common shrubs.

In wetter sites of Central Otago, slim-leaved snow tussocks are found with scattered narrow-leaved snow tussock, and herbs such as Aciphylla horrida, A. scott-thomsonii, Celmisia semicordata, C. prorepens, Brachyglottis revoluta, Hebe pauciramosa, and Schoenus pauciflorus.

In the Rakaia valley, Canterbury, subalpine shrubs e.g. Dracophyllum acerosa, D. pronum, and D. uniflorum are often abundant. False spaniard (Celmisia lyallii) is the most common companion in Canterbury, although C. angustifolia, C. spectabilis and C. viscosa are also abundant.

References:
  • Connor, H.E. 1965. Tussock grasslands in the middle Rakaia Valley, Canterbury, New Zealand. New Zealand Journal of Botany, 3: 261-276.
  • Wardle,P. 1991. Vegetation of New Zealand. Cambridge University Press, Cambridge.


Vegetation History

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. The grassland swept across low altitude valley bottoms. Subsequent modification of these tall tussock grasslands in subalpine and montane zones, through pastoral activities has lead to a transformation to short tussock grasslands. Slim-leaved snow tussock individuals can still be observed in these lower altitude short tussock grassland in Canterbury.

Connor and Macrae (1969) suggest that, although slim-leaved snow tussock grasslands were driven back upslope, the tussocks don't cease to attempt new colonisations as they may be found reinvading sites they previously occupied, or migrating into fescue tussock/copper tussock grasslands.

For those areas where forests were burnt in early European times, the evolution of tall tussock grasslands has not necessarily taken place.




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