Snow tussock (Chionochloa) population responses to removal of sheep and European hares, Canterbury, New Zealand

  • Published source details Rose A.B. & Platt K.H. (1992) Snow tussock (Chionochloa) population responses to removal of sheep and European hares, Canterbury, New Zealand. New Zealand Journal of Botany, 30, 373-382.


In New Zealand, by the time of European settlement about 150 years ago, native tussock grassland had invaded many previously forested areas. Subsequent livestock grazing and burning has resulted in tussock grassland degradation. Although a consequence of human activity, such anthropogenic grassland-induced areas have conservation value. In this study, snow tussock (Chionochloa macra and C.flavescens brevis) regeneration in response to cessation of sheep Ovis aries and experimental restriction of brown hare Lepus europaeaus browsing were investigated in montane-subalpine grasslands in the Harper-Avoca catchment (43º10'S, 171º33'E), Canterbury (South Island).

The broad effects of cessation of sheep-grazing were assessed by surveying snow tussock distribution and basal area on two large north- and two south-facing management blocks (1,000-1,400 m altitude). In December 1988, 86 (4 m²) sampling plots were established: north aspect - sheep-grazing retired 1968, 26 plots, grazed 22 plots; and south aspect - grazing retired 1955, and grazed (19 plots each).
Ten representative stands were subsequently selected to assess snow tussock characteristics and population structure under different grazing regimes. In each, a sample plot of 24-900 m² (large enough to sample at least 30 Chionochloa plants) was established in January/February 1989. The stands represented:
1) hillslope, C.macra sheep grazed for about 80 years;
2) hillslope, C.macra retired from grazing in 1955;
3) terrace, C.macra retired from grazing in 1955 but intensively hare-browsed;
4) terrace, C.macra retired from grazing in 1955, exclusion of hares for10 years (i.e. in 1979, an exclosure was erected in a heavily hare-browsed area and compared with an adjacent unfenced stand);
5) hillslope, C.flavescens retired from grazing in 1968.

Chionochloa basal area, height (maximum leaf length), number of flowering culms and recent grazing damage were recorded. Population structure was assessed by assigning individuals to one of four age classes: seedling, juvenile tussock, mature tussock or senescent tussock. Seedling regeneration was assessed.

The initial survey indicated that snow tussock was significantly less abundant on slopes still grazed by sheep and that average basal area was low. Basal area (m²/ha) on the north aspect was: retired - C.macra 24, C.flavescens 151; grazed - 0 (both species); and on the south aspect: retired - C.macra 349, C.flavescens 0; grazed - C.macra 73, C.flavescens 0.
Basal area in the 10 representative stands ranged widely (14-1,672 m²/ha), cover (<5-45%), and density (500-37,200 tussocks/ha). On areas with 80 years of sheep grazing, most snow tussock had been lost, persisting tussocks were mostly senescent with few seedlings present. The lack of seedlings was reflected by scarcity and poor vigour of tussocks remaining as seed sources. In contrast, stands retired from sheep-grazing (for 21 or 34 years) had a low proportion of senescent tussocks and high proportion (>60%) of seedlings and juveniles, suggesting onset of increasing tussock abundance.
The exclosure experiment indicated that hare browsing inhibited C.macra recovery.
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