Grassy/heathy woodland and forest has an understorey in which small-leaved shrubs and grasses make up more than 30% of the cover in the layer that is less than 2 m tall. Typical shrubs include heaths (Epacridaceae family), acacias, and legumes (Fabaceae family). Typical grasses include wallaby, plume, spear and tussock grasses. There may be a taller subsidiary layer in which wattles and she-oaks are prominent. However, this layer is sparser than the lower one. The canopy may be dominated by a range of eucalypts. The trees in woodland are spaced such that the gaps between their crowns are wider than the crowns. The crowns are closer together in forest. The terms woodland and forest are used interchangeably and the management guidelines apply to both.
The outstanding example of grassy/heathy forest is grassy/heathy black peppermint (
Eucalyptus amygdalina) forest. This occurs on sandy soils derived from Tertiary laterite, which are known locally as buckshot or ironstone gravels. It is found in the northern Midlands and near Swansea on the east coast. Some areas of grassy/heathy woodland and forest also occur within black peppermint forest on dolerite, highland cabbage gum (
Eucalyptus pauciflora) woodland and forest, and gum-topped stringybark (
Eucalyptus delegatensis) forest.
Where to see grassy/heathy woodland and forest
Some of the best examples of grassy/heathy woodland and forest lie within the Tom Gibson Nature Reserve on Barton Road, Epping Forest. The majority of the reserve is grassy/heathy black peppermint forest. Good examples can also be seen at Diprose Lagoon Nature Reserve. The Tom Gibson Nature Reserve also contains grassy white gum woodland and forest, sedgey black gum forest, and cabbage gum open forest on sand. Be sure to visit the reserve in early spring to see the prolific wildflowers, especially the orchids.
Biodiversity values of grassy/heathy woodland and forest
At least half of the original black peppermint forests in Tasmania have been cleared, largely for pasture. Considerable areas have been mined for gravel for roadworks. Grassy/heathy black peppermint forest contains threatened plants and is important habitat for the Tasmanian bettong. Grassy/heathy forests dominated by cabbage gum are poorly reserved. Grassy/heathy forest dominated by gum-topped stringybark are well reserved.
Refer to
Threatened Species for more information.
Management issues in grassy/heathy woodland and forest
Grassy/heathy woodland and forest is often marginal country for grazing in terms of its nutritional value. However, it is valuable country for shelter for lambing and off-shears. The carrying capacity is low. Many landowners use this type of bush only over the winter months.
Light grazing by sheep does not appear to harm woodlands and forests with grassy/heathy understories. Remnants that are lightly grazed over the winter months and spelled during spring and summer are largely in good condition, with a diversity of native species and few weeds.
However, some of the best remnants are those that have had stock excluded for more than 30 years. They have a greater diversity of species, a denser cover of grasses and wildflowers, and fewer weeds.
Overgrazing can lead to the elimination of the shrub and ground layers.
If your remnant is in excellent or good condition there is no reason to change its current management.
Grazing
Exclude stock if possible.
- Light grazing is preferable if the bush is to remain stocked. If bush with a grassy/heathy understorey is an important part of your grazing enterprise then grazing at low stocking rates is not damaging.
- If the area is grazed it should be grazed over winter, after the autumn break and before flowering of the native herbs and shrubs.
- Destock in spring and summer.
- If the autumn break has failed consider destocking or lowering the stocking rate. It could be tempting or even necessary to graze the bush but this is the time when seedlings, especially those of trees, are most vulnerable.
- Do not graze soon after burning. Stocking too soon after fire will impede the regeneration of trees and understorey shrubs and herbs.
- If annual grasses and broad-leaf weeds are a problem, stocking heavily during early spring can help to reduce the growth and seed set of weeds.
Fire
- Patch burn to favour target species. Fire should favour the persistence of rare and threatened plants and animals. In some cases the regime needed by different species will conflict. For example, the fire frequency required to maintain the subterranean fungi that are the food source for bettongs may conflict with the fire regime required to maintain some plant species.
- Choose a fire regime to suit the desired outcome. For example, shrubs will become dominant with infrequent fires so if you want to reduce the shrub layer burn frequently enough to suppress the growth of shrubs.
- A diversity of fire regimes is preferable. The maintenance of biodiversity is best served by having a mix of fire ages and intensities across the landscape. This is partly because the needs of many plants and animals are not known and having a range of fire ages lessens the risk of long-term damage. If you have an area of bush that has not been burnt for many years it may be best to continue to avoid fire.
- Use fire to manage weed species. After a fire most native species resprout or regenerate from seed stored in the soil. Research on the germination of both native and introduced species has shown that weeds do not germinate after relatively hot fires, thereby allowing better regeneration of the native species. If many annual weeds such as shivery grass or brome grass are present, spring burning before they set seed, for at least two years, may help to eliminate them by reducing their soil seedbanks. Fire can also be used to stimulate the germination of hard-coated weed seeds that persist in the soil, such as broom and gorse. This can then be followed by a chemical spraying program. A second burn 18-24 months later will germinate much of the remaining seed. The subsequent seedlings can be eliminated by follow-up chemical spraying.
- Use fire to stimulate the germination of trees and shrubs.
- Use fire in combination with herbicides to control woody weeds.
When and how to burn
- The timing of burns will vary according to circumstances. However, autumn burns are usually preferable as most plants and animals will have completed their life cycle. In autumn the vegetation is likely to be fairly dry giving a good burn while the humidity at night will help to control the fire.
- An interval of 8-20 years between fires is thought to be appropriate for grassy/heathy woodland and forest.
- Moderately hot burns are better than cool burns. Burns should be hot enough to at least remove all the ground litter. However, burns that are too hot will scorch the tree crowns and should be avoided.
- Burn small to medium patches, for example 1-5 ha.
When not to burn
- Don't burn during spring and summer.
- Don't burn if there is a gorse problem, unless you are able to apply herbicide following the burn.
- Don't burn when large amounts of seed have germinated recently. Mass germination is relatively rare and could be important for the growth of a new generation of trees, shrubs and understorey species.