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Management Information for Open canopied tall tussock grasslands and mixed short/tall tussock grasslands

|| about these grasslands || grazing || hieracium || vegetation succession || botanical information || monitoring ||

About mixed short/tall tussock grasslands

Where tall tussock grasslands have been significantly modified through pastoral disturbance, a mixed short/tall tussock grassland develops. They have at least 5% cover of tall tussocks , which usually consist of narrow-leaved snow tussock (Chionochloa rigida), but can be slim-leaved snow tussock (C. macra), copper tussock (C. rubra subsp. cuprea), or broad leaved snow tussock (C. flavescens). The short tussock component is usually dominated by fescue tussock (Festuca novae-zelandiae), but may include blue tussock (Poa colensoi), bristle tussock (Rytidosperma setifolium) or silver tussock (Poa colensoi). These grasslands tend to be located in drier areas, with rainfall around 600mm.

Mixed short/tall grasslands generally have greater diversity of species growing between the tussocks than grasslands with a more intact canopy. It is inevitable that patches of mixed grasslands will occur within larger areas of tall tussock grassland. These open patches may provide a seed source for intertussock species which get out-competed when tussock cover becomes too dense elsewhere.

The characteristics of a mixed short/tall grasland which can no longer regenerate to a tall tussock grasland are not understood. However, ecologists have suggested that a grassland with the following "minimum" characteristics will regenerate to a tall tussock grassland:

  • As long as there were 'some' tall tussocks present, the grassland will, given time, have some capacity for regeneration.
  • 20% cover of tall tussock is necessary for a grassland to regenerate towards a tall tussock grassland.
The presence and stage of invasion of exotic plants within mixed grasslands will play an important role in determining the response of a mixed grassland when grazing or burning disturbance ceases.

Role of grazing in maintaining a mixed short/tall grassland

For areas managed primarily for nature conservation, ecologists can see a role for light sheep grazing. The stocking rate would depend on the rainfall. In dry areas, tall tussock regeneration has been observed where stocking rates are less than 0.2su.ha.yr (Lee et al., 1993). In wetter areas, sheep could be stocked at slightly higher rates.

The benefits of grazing are that they prevent the out-right succession by more competitive vegetation types e.g. ingress of tall tussocks, shrubs, or exotic grasses. Grazing therefore maintains the open canopy, and the diverse range of intertussock species associated with it.

In reality, some areas in a paddock will receive greater grazing pressure (e.g. sunny faces where merinos like to camp), while others will hardly be touched. Over-grazing can prevent tussock regeneration (through browsing of flowerheads or young seedlings) and stress out adult tussocks, while palatable intertussock species are preferentially grazed. To minimise these adverse impacts, ecologists suggest that grazing should be managed, as far as possible, so that it occurs evenly across the block. To achieve this, the following options were suggested:

  • fence each landscape unit
  • identify the vegetation condition of the worst area in a block, and stock the whole block accordingly
  • some farmers shepherd their sheep round a block to prevent them from concentrating in one location
The natural and induced patchiness of vegetation cover within a block make grazing management difficult. If none of these options are feasible, the area should be destocked. Where mixed grasslands are being managed as part of a pastoral system, it may not be economic or practical for the farmer to attempt to achieve even-grazing pressure.


The spread of Hieracium in mixed short/tall tussock grasslands

Irrespective of whether managed for pastoral use, or soley for conservation purposes, many mixed tussock grasslands have a significant component of hawkweed. A large number of studies have been conducted to investigate the relationship between grazing management and rate of Hieracium spread in fescue tussock grasslands, and associated trends on vegetation composition.

More information on hawkweeds:

Summary of study findings Hieracium Management Information Module


Succession in mixed short/tall tussock grasslands

if you want general information on factors influencing vegetation succession (includes model for vegetation succession).


Most research in the tussock grasslands have focussed on the vegetation changes which have taken place as a result of natural and man-induced disturbance (grazing and burning). Obviously, future research will need to address information gaps relating to the direction and rate of vegetation change under a minimal disturbance regime. It seems likely, however, that even if burning and grazing cease, succession can be slow and uneven, because of inadequate seed sources and composition from the resident vegetation (Wardle 1991). The prevalence of exotic plants, espeically in small lowland patches of native vegetation may well result in successional pathways away from desired native stable communities.

At a conservation workshop in 1996, ecologists and land managers developed a broad brush model to show the possible successional pathways that mixed short/tall tussock grasslands could take following destocking. The direction and rate of vegetation change depends on rainfall and altitude. The most problematic weeds were considered to be those that can overtop the tussocks, especially wilding pines and broom (gorse can serve as a nurse crop).

Botanical information

Where tall tussock grasslands have been significantly modified through pastoral disturbance, a mixed short/tall tussock grassland develops. They have at least 5% cover of tall tussocks , which usually consist of narrow-leaved snow tussock (C .rigida), but can be slim-leaved snow tussock (C. macra), copper tussock (C. rubra subsp. cuprea), or broad leaved snow tussock (C. flavescens). The short tussock component is usually dominated by fescue tussock (Festuca novae-zelandiae), but may include blue tussock (Poa colensoi), bristle tussock (Rytidosperma setifolium) or silver tussock (Poa colensoi). These grasslands tend to be located in drier areas, with rainfall around 600mm.


Monitoring

The management guidelines suggested are based on the best available information, and are often only "best guesses". To ensure that the management practices are achieving the desired management goal, it is crucial that the vegetation condition and composition, weed status, and animal pests are monitored. Management may have to be changed in response to the findings of such on-going monitoring.

for more information on monitoring in tussock grasslands

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