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Management Information for Blue wheat grass and Rytidosperma grassland ( Elymus and Rytidosperma spp.)

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Developing management options

The majority of tussock grassland research has focussed on determining the vegetation history of the mountain lands, and how pastoral management practices have influenced vegetation succession patterns. Only recently has grassland research started to look at the issue of progressive successional changes occurring on retired land (i.e. what vegetation changes will take place when tussock grasslands are retired from grazing and burning). In addition, the majority of studies have focussed on determining the impacts of pastoral use on induced montane fescue tussock grasslands (Festuca novae-zealandiae), the most widespread type of short tussock grassland in the eastern parts of the Main Divide. There are many information gaps to be filled, some of which are currently addressed in the FRST-funded research programme "Improved Management Systems for Tussock Grasslands". For more information about this research programme and how to become involved, contact the programme leader Dr Ockie Bosch at boscho@landcare.cri.nz.

In the meantime, the suggested management options have to draw on broad principles and "best guesses" by ecologists, or observations made by people who live and work in the tussock grasslands. Such "best guesses" may be appropriate in some situations, but not others. They will be updated as and when more information becomes available.


High-altitude tussock grasslands

High-altitude tussock grasslands generally require less active management than such communities at lower altitudes. High-altitude areas tend to be less modified, as the more extreme growing environment makes such areas less attractive for pastoral development. Short tussock grasslands at high altitude are an exception. Although some occur naturally in zones of natural disturbance such as avalanche paths, most of those occurring east of the Main Divide have been induced from tall tussock grasslands as a result of pastoral management, and may be further modified by weeds.


Mid-altitude tussock grasslands

Mid-altitude tussock grasslands generally require more active management than such communities at higher altitudes, because there is a higher risk of weed spread and woody plant regeneration. These areas have been attractive for pastoral development because the combination of adequate rainfall and soil temperatures promotes moderately good plant growth.

Low-altitude tussock grasslands

Low-altitude areas have been the focus of farm development programmes, which may include cultivation, land drainage, tree planting, and exotic pasture establishment. The majority of lower altitude tussock grasslands have therefore already been partially modified or totally removed. Existing tussock grasslands are often at high risk of weed invasion from surrounding farmland. Such areas therefore generally require more active management than communities at higher altitudes.

Dryland low altitude tussock grasslands

Factors influencing the distribution and characteristics of tussock grasslands

for more information on environmental gradients that determine the distribution of tussock grassland types, or the management factors that have influenced the characteristics of tussock grasslands.

Vegetation change since human settlement

if you want further information on a generalised model for vegetation change, east of the Main Divide.

Evolution of short tussock grasslands

Before the arrival of humans in New Zealand, short tussock grasslands would have been restricted to frosty flats, riparian sites such as river flood-plains, and semi-arid areas where rainfall was less than 500mm, thereby preventing forest or tall tussock establishment (Connor & Macrae 1969, Wardle 1991). Wraight (1965) indicates that bristle tussocks are likely to have occurred naturally in Marlborough as a minor species in rocky high altitude creek beds. However, when the forest cover was reduced by Polynesian fires, the short tussock species migrated from these niches to colonise the slopes exposed by the fires. This was followed by a period of downslope migration of tall tussocks over a period of 200 years. European settlement saw an escalation of burning, both of tall tussock grasslands - to improve accessibility and palatability of tall tussock grasslands for sheep grazing- and remaining forest cover. The repeated burning and grazing depleted the tall tussocks, which were replaced in dominance by the short tussock species. This zone extended up to about 1000m for fescue and silver tussock, with bristle tussock to about 1500m in Marlborough.

More recently, these short tussock grasslands have undergone further modification through pastoral development, which involves the aerial application of fertiliser and pastorally important herbs and grasses. The spread of invasive exotic species has also modified these grasslands.

Short tussock grasslands are inherently unstable and prone to weed invasion due to their open cover, short stature of vegetation, thin cover of litter, presence of weed species, and their long history of management disturbance (e.g. grazing). Environmental stresses such as drought) accentuate the problems associated with managing short tussock grasslands.

Buffering

The relationship between an area managed for conservation purposes and its surrounding landscape is important. Ideally, the area should be surrounded by land, which will buffer it from external influences that may compromise its conservation values.

The buffer zone may:
  • act as a fire break, thereby protecting neighbouring land from wild fires occurring in dense tussock grasslands, or preventing controlled fires on pastoral land inadvertently burning an area managed for conservation;
  • protect the area from inadvertent drift of fertiliser and/or seed from neighbouring land (during aerial application);
  • help reduce the rate of spread of some weed species into the area, e.g. intensive grazing between a forest and an ungrazed tussock grassland helps reduce the establishment of wilding trees from that forest.


Weed control

Weed spread is less likely to be a problem at high altitudes, except where significant disturbance has taken place e.g. sheep camps, or at sites which are downwind of conifer stands (plantation or wilding forests). Periodic monitoring of the area is necessary to determine whether weed species are coming into the area, and whether they are reaching problem levels. An assessment of the feasibility of controlling the weeds will then have to be made.

The need to control weed species is dependent on the characteristics of the weed (e.g. will it overtop the tussocks; does its' dispersal mechanism make it an aggressive invader?) and their impact on the indigenous ecosystem in question. Tall woody weeds are considered to be the most troublesome weed in tussock grasslands, as they have the potential to overtop and shade-out the tussocks. Wilding trees are a growing problem in Otago and inland Canterbury.

for more specific information on weed control

The spread of Hieracium in short tussock grasslands

Irrespective of whether managed for pastoral use, or soley for conservation purposes, many short 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, and associated trends on vegetation composition. However, no studies have focussed specifically on alpine fescue tussock grasslands.

More information on hawkweeds:

Summary of study findings Hieracium Management Information Module


Succession in short tussock grasslands in general

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

Most research in the tussock grasslands has focussed on the vegetation changes which have taken place as a result of man-induced disturbance (grazing and burning). 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, especially in small lowland patches of native vegetation may well result in successional pathways away from desired native stable communities. At a Conservation Workshop, Dr Alan Rose outlined five interacting factors which influence the rate and direction of plant invasion in short tussock grasslands. Short tussock grasslands (especially those in modifed environments) are highly predisposed to invasion by weeds for a number of reasons, which are detailed here.

At a conservation workshop in 1996, ecologists and land managers developed a broad brush model to show the possible successional pathways that silver tussock grasslands could take following destocking. Participants suggested that this model could be applied to other types of short tussock grassland. 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).

Suggested successional pathways after destocking of silver tussock grasslands under different environmental conditions

Allowing a bristle tussock (Rytidosperma setifolia) grassland to succeed towards a community dominated by native species (composition determined by seed bank)

Little work has been done which can help determine the successional pathways of tussock grasslands under a no burn and no grazing regime. However, where an adequate seed source for snow tussocks or shrub species is present- either from adult plants or the seed bank in the soil- it is likely that the bristle tussock grassland would gradually be overtopped and dominated by these other plants. The rate of succession will be dependent, in part, on the quantity, viability and type of seed in the seed bank, and the climatic characteristics of the area (the rate of woody plant invasion generally increases with increasing soil moisture).

Impacts of grazing on short tussock grasslands in general

Short tussock grasslands occur where disturbance (e.g. grazing, burning) or environmental stress (e.g. soil moisture deficit) prevents the short tussocks from being out-competed by taller, more stable vegetation types, such as tall tussocks and woody species. Grazing therefore plays an important role in preventing such succession.

Short tussock grasslands usually have some exotic plants growing within the community. In moist sites where the intertussock spaces are dominated by exotic plants, grazing will keep the palatable exotic plants at bay, thereby reducing competition (Lord 1990). Grazing can also control palatable woody weeds.(Meurk et al. 1989). This not only benefits the native plants present in the grassland, which are easily smothered by such competitive grasses, but native insect fauna may also benefit (White 1991). Grazed short tussock grasslands therefore generally have greater species diversity of both native and exotic vascular and non-vascular plants (Meurk et al.1989).

Grazing adversely effects short tussock grasslands by reducing the cover of palatable native plants (Lord 1990). Meurk et al.(1989) suggested that in some situations, it may be feasible to reduce competition of exotic species by mowing, cutting, weeding or burning. These methods may be preferable to grazing as they do not discriminate against palatable native species. Tussock size can also be reduced when over-grazed.

Short tussock grasslands dominated by native plants, in dry areas do not benefit from being grazed. For example, Meurk et al. (1989) noted that the grazing of a dryland Rytidosperma sp. tussock grassland on the Canterbury Plains, resulted in a reduction of native vascular plant species in favour of non-vascular species. The presence of stock results in increased nutrient cycling (i.e. through the urine) which favours the more competitive adventive intertussock grasses.

A reduction in grazing pressure results in an increase in tall statured vegetation, including snow tussocks and native scrub species (Hunter and Scott 1994; Rose 1983).

Impact of grazing on blue wheatgrass and Rytidosperma grasslands

Little information is available regarding the impacts of management on dryland blue wheatgrass and Rytidosperma grasslands. Observation made in the Manuherikia Valley indicate that intense grazing pressure (e.g. deer grazing) can severely reduce the size and cover of tussocks. This trend is also apparent at Flat Top Hill, near Alexandra, where palatable native grasses, such as blue wheatgrass tend to be restricted to inaccessible rocky areas (Walker et al. 1995) in response to heavy grazing pressures in the past.

Release from grazing appears to improve both the size and cover of blue wheatgrass and Rytidosperma tussocks on free-draining gravelly sites in the Manuherikia valley, where the exotic component of the grassland is of low stature. Destocking of dryland grasslands results in an increase in perennial plants (Orr, 1981; Allen et al.) 1996), which may include an increase in palatable species previously sought out by stock. On Flat Top Hill at moister cooler sites with 'deep' fine textured soils, such as on westerly, south and east-facing slopes, destocking is forecast to result in an increase in perennial grasses such as cocksfoot and shrubs (e.g. thyme). Walker et al. (1995) suggest that any increase in palatable native herbs and grasses (including blue wheatgrass) will be dependant on their ability to compete with such vigorous exotic plants. These studies indicate that destocking of dryland grasslands also results in an overall decline in species richness.

Fertiliser Amendment

Many short tussock grasslands in the high country have received fertilizer and pastoral seed inputs, applied by plane (AOSTD). Where these inputs have not been maintained, or at best, have been intermittent, Fan and Harris (1996) suggest that the grassland becomes predisposed to invasions by hawkweed. They suggest that when the introduced grasses and clovers die during times of stress e.g. drought, over-grazing, the bare patches of soil between the tussocks, which are rich in nutrients, favour hawkweed ingression.

Fescue tussock density and growth are increased where fertiliser containing phosphorus and nitrogen are applied (FRI 1990). However, the application of fertiliser creates an environment better suited to competitive exotic herbs and grasses, than the slower growing native tussocks and associated plants.


Native woody plant regeneration

The regeneration of native subalpine shrubland species is dependent on the seed source and presence of adult plants in the grassland.

Animal Pests

The historical as well as present day degradation of tussock grasslands has been attributed in part, to high rabbit numbers (see Cockayne 1919). Some species that are presumed extinct and for which rabbits have been implicated in their demise include Logania depressa, Myosotis laingii, and Stellaria elatinioides (P. De Lange, pers. comm. in Norbury 1996). Other species once widespread in the short tussock grasslands e.g. the highly palatable Gingidia montana, are restricted to rocky refugia that are inaccessible to grazing mammals (Allen et al. 1995).

In a short term exclosure study on degraded short tussock grasslands of Earnscleugh Station where rabbit numbers were high (30-76 rabbits/spotlight km), it was found that after one growing season, the exclosure of rabbits resulted in a six fold increase in pasture yield (Rose 1996). Most of the biomass consisted of exotic grasses and herbs, but a significant increase in hard tussock and blue tussock also occurred. It was also noted that with protection from grazing, both grasses and hawkweed flowered prolifically, whereas no flowering was observed in the grazed plots. Norbury and Norbury (1996) suggest that rabbits were probably restricting the spread of exotic grasses and hawkweed, and the regeneration of palatable native tussocks.

In coastal silver tussock grassland on Motunau Island, Canterbury, areas with high rabbit numbers were characterised by dead tussock stumps, bare ground and barley grass. Areas with low rabbit numbers had healthy tussocks with a diversity of intertussock species, and a dense litter layer. After rabbit control, existing tussocks recovered and tussock seedlings were evident (Mason 1967).

In Central Otago, rabbit grazing has undermined and destroyed silver tussocks growing at the Cromwell Chafer Beetle Reserve (Barratt and Patrick 1992).

On Molesworth Station, Marlborough, Moore (1976) observed rabbits killing fescue tussocks (Festuca novae-zelandiae) by eating tillers and physically uprooting plants. With rabbit control, the palatable blue tussock recovered well, as did fescue tussock. Similar observations have been made by more recently some farmers in the Mackenzie Basin following intensive rabbit control during the Rabbit and Land Management Programme (1990 - 1995).

Some native plants appear to thrive in the open disturbed ground induced by grazing. At Flat Top Hill, Alexandra, Walker et al. (1995) noted that the rare native annual herbs- Myosurus minimus subsp. novae-zelandiae, Ceratocephalus pungens and Myosotis pygmaea var. minutiflora were present despite a history of high stocking rates and high rabbit numbers. Rabbit grazing here is likely to be beneficial to the conservation of these species by suppressing the spread of exotic grasses and herbs which might otherwise colonise the bare ground that these native annuals require.

Rabbit grazing appears to beneficial in controlling some woody weeds, including thyme in Central Otago (Wilkinson et al. 1979; Fraser 1985; Walker 1994), sweet briar (Moore 1976; Ogle 1990) and broom (Moore 1976).

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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