Native grasslands have few or no trees. Before European settlement native tussock grasslands occurred on many of the fertile plains between Launceston and Hobart. A superficial resemblance to European pasture made both the northern and southern Midlands and the lower Derwent Valley attractive to early settlers.
The lowland tussock grasslands have been heavily cleared and today only small patches remain in places like country cemeteries and road reserves. Some larger areas of lowland native pastures are still found on grazing properties where they are valued for the high quality wool produced by sheep grazing on them.
Lowland grasslands are of two types: lowland silver tussock grassland or kangaroo grass tussock grassland, both of which are endangered. Lowland silver tussock grassland
is generally found on alluvial river flats less than 600 m above sea level. It also occurs in coastal areas on sand ridges or next to wetlands, where it is usually the result of excessive burning of shrubby coastal vegetation. The dominant grass is silver tussock (Poa labillardierei
) which is a narrow-leaved species that forms dense tussocks up to 1 m in height. Lowland silver tussock grassland usually occurs in association with black gum (Eucalyptus ovata
) grassy woodland. Many farmers value these river flat grasslands for the shelter they provide newly shorn sheep or lambs. They are also important for erosion control during floods. Lowland grassland is probably the Tasmanian vegetation type that has undergone the most destruction since European settlement. The remnants of this community in the Midlands are of particularly high conservation significance as they have concentrations of rare and threatened species. Every remnant - no matter how degraded - is important. Kangaroo grass tussock grassland
is found on well-drained, fertile valley floors in low rainfall, low altitude areas. It is also found on shallow soils on well-drained hill tops and ridges on basalt, dolerite and deep sands. It is dominated by kangaroo grass (Themeda triandra
) which is a deep-rooted, summer-growing, perennial grass. It has a distinctly-shaped flowering head and its foliage is red-green during the non-growing season. Other common grasses of kangaroo grass tussock grassland include wallaby grass, weeping grass and tussock grass. Kangaroo grass tussock grasslands are often characterised by a rich variety of lilies, orchids, daisies and other herbs in the patches between the tussocks. They are rich in rare or threatened species. Kangaroo grass tussock grassland is one of Tasmania's most endangered vegetation types.
Where to see lowland grassland
Township Lagoon Nature Reserve at Tunbridge has good examples of both types of lowland grassland. The adjacent paddocks are cabbage gum (Eucalyptus pauciflora) grassy woodland. The best time to visit is spring when there is a profusion of wildflowers. The Tunbridge area has one of the highest concentrations of threatened plant species anywhere in Tasmania. Lowland silver tussock grassland is found on many river flats, including the Macquarie, South Esk, St Pauls and North Esk Rivers.
Biodiversity values of lowland grassland
Grasslands are some of the vegetation types that have been most extensively cleared and modified. They are an extremely high priority for conservation
, especially for threatened animal and plant species. A number of Tasmanian grassland plant species are extinct, as is the Tasmanian emu.
Management issues in lowland grasslands
Fire and grazing are the main tools used to maintain the health of native grassland. In many cases fire is not essential as grazing by stock or native animals performs a similar role of reducing the competition from dense grasses. One of the main aims of managing grassland is to retain a rich and diverse flora by maintaining the gaps between the tussocks. Once the grass becomes rank and dense the gaps between the tussocks disappear. As a result wildflowers fail to flower and set seed, and eventually they become sparse or disappear. Grassland may have over 50 different species in an area of 10 square metres but once the inter-tussock gaps close up this may drop to as low as 10-15 species. Both fire and grazing can be used to maintain the gaps between the tussocks.
Managing by condition
The best management regime for lowland grassland will depend on the condition of the vegetation. Management guidelines based on the condition of the habitat are given below. However, the specific needs of threatened plants may override these recommendations. If you are unsure what condition your bush is in refer to Condition of Your Bush
Grassy bush in excellent condition is characterised by:
- a rich diversity of species and a mixture of dominant grasses, including kangaroo grass, wallaby grass, weeping grass, tussock grasses and wheat grass. There is a rich variety of wildflowers
- inter-tussock spaces (gaps between the grass tussocks) that are important areas for the germination of trees, shrubs and wildflowers
- a cryptogamic mat (a mat of lichens and mosses) on the soil surface. This protects the soil from erosion, helps the infiltration of water, helps nutrient recycling, and plays a role in seed germination
- low levels of weed invasion
- young trees of different ages
Bush in excellent condition is an asset. Maintain your current management. There is no need to change your farming practices unless there is an obvious reason to do so.
Recommendations for grazing and fire management are given below. However, other aspects of your farm may affect what is practical and the particular requirements of threatened plants may override these recommendations.
Ungrazed native grasslands will need some form of regular management to reduce the growth of grasses and maintain the gaps between the tussocks. This can be achieved by occasional crash grazing so that the rank grasses are reduced to a short sward. Burning can also result in a healthy grassland. A hot burn in autumn is preferable. It will probably be needed about every three years to maintain the gaps. Mowing or slashing is an option in the short term but unless the grass clippings or hay are removed they will cover the inter-tussock gaps and suppress germination of the native species and favour the invasion of weeds.
An active weed control program, particularly of gorse, is vital for maintaining the integrity of grassland.
Tree planting is undesirable in grassland.
Grassy bush in good condition is characterised by:
- a lack of inter-tussock spaces
- weed invasion - native pastures and bush runs are occasionally top-dressed with superphosphate and aerially seeded with pasture grasses and clovers. As a result these sites are often weedy. Gorse can be a major problem, as can annual grasses and herbs.
- many areas of bare soil, especially on the warm north-facing slopes preferred by stock.
Management will need to focus on reducing the stocking levels so that the bush can recover. Destocking may be the best option in some situations. This will also reduce the risk of soil erosion by restoring a perennial grass cover. You may decide to limit access to sensitive areas through strategic fencing. Sensitive areas include areas with highly palatable threatened species and north-facing slopes where soil erosion is a major problem.
Lowland grassland in poor condition is characterised by:
- little diversity in the ground cover
- many patches of bare ground
- no cryptogamic mat to protect the soil
- severe weed problems
- soil compaction with poor water infiltration
Threatened species are often found in grassland in poor condition. The species found tend to be those that need disturbance as part of their life cycle. For example, curly sedge (Carex tasmanica
) is often found where there has been digging or other soil disturbance and where there is only a handful of native species. Peppercress (Lepidium hyssopifolium
) is another threatened plant that thrives on disturbed soils with very low levels of stock grazing.
If your bush has threatened species it is best not to change your management regime without advice from DPIPWE's Threatened Species Unit
If your poor quality grassland does not contain threatened species you will probably need to change the pattern and intensity of stocking by spelling it over spring and summer. Weed control is a major management issue in degraded native pastures. In many cases it may be a matter of learning to live with most of the weeds and directing your management to favour the native species so that they eventually dominate.
Consider rehabilitating the area, including treating the eroded areas, direct seeding of native grasses, and controlling weeds.
Grazing management will depend on the management aims and the condition of the grassland. Some general guidelines are outlined below.
- Do not set stock or stock heavily for extended periods. Native grasslands tolerate moderate levels of grazing but their condition deteriorates at high stocking levels. The highly palatable kangaroo grass is eliminated from native pasture at high stocking levels and heavy cattle grazing can eliminate silver tussock grass. Do not stock at levels that cause the loss of tussocks and increase the amount of bare soil.
- Reduce the rank growth of grasses by crash grazing or burning. Crash grazing is a technique where a mob of sheep is put into an area to graze it heavily for a short period of time.
- If annual grasses and broad-leaved weeds are a problem stock heavily during early spring to reduce the seed set of weeds. Late winter and early spring is the main growing and flowering period for annual grasses and broad-leaved weeds. Burning in spring can achieve the same effect.
- Spell grasslands over late spring and summer. Some of the healthiest and most diverse areas of grassland are those that are spelled in late spring and summer. This allows grasses and herbs to flower and set seed.
- Stock grasslands after the autumn break. Use your native pastures and bush runs for autumn and winter grazing.
- Do not graze too soon after burning. Grazing stock too soon after a fire will eliminate the regenerating seedlings. Do not graze until the new plants are out of the reach of stock.
- Limit access to sensitive areas through strategic fencing. This includes areas with grazing-sensitive threatened species, north-facing slopes where soil erosion is a major problem, and where the regeneration of trees and shrubs is needed. Grazing-sensitive threatened species include austral thornbush (Discaria pubescens), Gunns mignonette (Stackhousia gunnii), young seedlings of Midlands wattle (Acacia axillaris), and peppercress (Lepidium hyssopifolium).
See Threatened Species
for more details on these species.
Fire is often used in lowland grassland to produce green-pick for stock. Fire can also be used to control silver wattle and prickly box if they become too dense. It is an important method of managing woody weeds.
- Autumn is the best season to burn for most species. Most of the plants and animals have completed their life cycle in autumn and conditions are more likely to be suitable for a controlled burn. Burning in spring and summer will stop flowering and seed set for that season. Spring burning could be useful for the control of weeds, particularly annual grasses.
- Burn lowland grassland when the gaps between the tussocks start to close up. Intervals of 2-5 years between fires are recommended in ungrazed native grasslands to maintain the inter-tussock gaps. Grassy woodlands and forests also need less frequent fires than grasslands. Recommended fire intervals are 4-10 years for grassy woodlands and 6-18 years for grassy forests. However, this is only a guide and the appropriate interval will vary from situation to situation.
- Fairly hot burns are better than cool burns in most situations. The fire should at least remove all the ground litter.
- Don't burn if fire-sensitive threatened species are present. If you have Midlands wattle (Acacia axillaris) on your property it can be eliminated by fire, unlike most wattles. The role of fire in the regeneration of austral thornbush (Discaria pubescens) is not clear. It re-sprouts after some fires but the young shoots are highly palatable and the resprouting stems and leaves are heavily browsed.
It is best to seek expert advice from DPWIE's Threatened Species Unit
if you wish to burn the riparian (i.e. riverside) grassy forests where austral thornbush is found.
Weed invasion is a critical issue for management of grassland, particularly for woody weeds such as broom, gorse and Spanish heath.
Gorse is widespread in white gum woodlands which are used extensively as bush run country in the Midlands. These woodlands are occasionally top-dressed with superphosphate and aerially seeded with pasture species. As a result these sites are often weedy and gorse can be a major problem.
In some districts gorse is tolerated by landowners because of the valuable shelter it provides for stock in the absence of native shrubs. It can also provide an important habitat for bandicoots by providing protection from cats and dogs.
Some native woody species such as prickly box and silver wattle can also become dense in native pastures and may be considered weeds by landowners. The invasion of native pastures by both native and introduced woody shrubs leads to changes in the structure of the vegetation. It can be a serious management issue because the quality of the pasture is reduced and wool can be contaminated by twigs, seeds and other woody material.
Annual weedy grasses and herbs are present even in remnants that are in excellent condition but they are only a problem when they are at high levels.
Introduced grasses such as browntop bent, Yorkshire fog-grass and cocksfoot are widespread in native grassy understoreys. A number of farmers have commented that hairs-tail grass has been invading aggressively in the past few years.
Horehound has become invasive in the past decade and is a serious problem for wool growers. It tends to establish where sheep camp. Other common herbaceous weeds include yellow daisies such as flatweed, hawkbit and dandelion.
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