The maintenance of Poa cita grassland by grazing


In New Zealand, much short tussock grassland is semi-natural because of a history of anthropogenic disturbance. Management such as grazing or burning is often considered necessary for short tussock grassland conservation. Previous short-tussock grassland studies provide conflicting evidence as to the impact of grazing on native plant species abundance. A study was undertaken in strongly modified silver tussock Poa cita grassland in the Port Hills of Canterbury (South Island). It focussed on the role of sheep grazing in the conservation of native plants.

The study area has been subject to low-intensity sheep grazing for over 100 years. Vegetation was predominantly Poa cita short-tussock grassland with fescue tussock Festuca novae-zelandiae. Inter-tussock areas were dominated by introduced invasives, primarily cock’s-foot Dactylis glomerata and sweet vernal Anthoxanthum odoratum, with Yorkshire fog Holcus lanatus and cats-ear Hypochoeris radicata.

Seven pairs of sites (adjacent grazed and ungrazed areas of similar slope, aspect and altitude (160-546 m)) were selected. Sheep stocking rate (1.4 to 0.6/ha) decreased towards the ‘lower rainfall end’ of the Hills. Ungrazed areas were formerly sheep grazed, but fenced to exclude them from four to more than 24 years ago. European rabbits Oryctolagus cuniculus and hares Lepus sp. were present throughout.
In late February to April 1988, vegetation at each site was sampled in 52, 4.5 m x 0.5 m belt transects. Percentage cover was estimated for each species in five alternate (0.5 x 0.5 m) quadrats (260 in total) along each transect.

A total of 63 species were identified; 23 were natives (some natives were only identified to genus thus several more ‘species’ were in fact present).

Ungrazed sites had fewer total species, lower native species cover and lower tussock density than adjacent grazed sites. Invasive dominanace (particularly cock’s-foot) in ungrazed sites was a main contributory factor.
The average number of invasive and native species per transect was:
Invasives - grazed 10.7, ungrazed 7.2; Natives - grazed 5.7, ungrazed 2.6.
The average percentage cover of invasive and native species per transect was:
Invasives - grazed 57.0%, ungrazed 84.1%; Natives - grazed 32.6%, ungrazed 13.5%.
Results indicate that low intensity sheep grazing maintains native species in this modified short tussock grassland.

Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at:


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