The characteristics of healthy bush vary with the different vegetation types. For example, bush is often considered to be in good condition if there is a diversity of tree and shrub species, habitat provided by old trees and logs, and a rich ground layer of twigs and small branches. In grasslands and wetlands, where there are no trees, these components will not be present but the bush may still be in excellent condition. Similarly, you may wish to maintain the grassiness of your understorey and reduce the number of shrubs. Their absence does not mean that the bush is in poor condition. Rather, its condition is the result of the management option you have chosen. Nevertheless, healthy bush generally has a number of characteristics that are described below.
Health bush is made up of layers
Healthy bush is usually made up of a number of layers.
A thin layer of mosses and lichens on the ground is considered to be an important component of healthy bush, particularly in grasslands and grassy woodland. This layer, known as the cryptomatic mat, appears as a fine speckling of white, brown and green on the soil surface.
A litter layer helps protect the soil from rain and wind, and provides important habitat for invertebrates, spiders and reptiles. This layer is made up of twigs, sticks and leaves. In treeless grassy vegetation there is still usually a thick litter layer of dead grasses. Bacteria and fungi are important components of the litter layer as they break down the litter and release nutrients. Larger branches, limbs and logs are other important components of the litter layer because they provide habitat for a range of species. Old fence posts left lying on the ground along the edges of paddocks can also provide valuable habitat.
A rich and diverse ground layer made up of grasses, lilies, sedges and wildflowers is usually considered to be an indicator of healthy bush, particularly in grassy bush. Bush with a healthy and diverse grassy understorey is relatively rare - the understorey is often reduced to a few species such as wallaby grass and spear grass. In bush where shrubs and heaths dominate the understorey the ground layer may be less developed. In some situations such as in the saline herb fields that fringe wetlands only one or two species may be dominant. The absence of a diverse ground layer does not necessarily indicate poor condition. In some bush types the ground layer may be dominated by ferns, particularly in wet forests along creek lines and in damp gullies, or a dense layer of bracken may be prominent. This is not necessarily a problem and may reflect the use of frequent cool burns as a management tool. Dense bracken can protect young seedlings from grazing and in some bush it is the only place where young saplings can grow. It can also be important in preventing soil erosion.
An understorey of native shrubs is an important component of many bush types. This layer can be in poor condition in bush that is heavily grazed, particularly by cattle or goats. It may also be in poor condition in bush that has been burned so frequently that the shrubs have been eliminated because they were unable to flower and set seed between fires. Even shrubs that resprout after fire will eventually be weakened and killed by too many fires in quick succession. A shrub layer is less prominent in grassy vegetation although some low shrubs are still present. Shrubs are important as a nectar and food source for many insects and some birds. On a warm day species such as ants delight are covered in ants, flies, beetles, wasps, moths and spiders. Shrubs also offer habitat for small animals. Prickly shrubs help protect some species, such as wrens, from predators. They are also important structural components for web-building spiders, particularly in heavily-grazed areas.
The tree canopy in most Tasmanian bush consists of an upper layer of a dominant eucalypt and a few co-dominant eucalypts. A lower layer of small trees and shrubs such as wattles, native cherry and she-oak is often also present.
Range of habitat
Healthy bush provides a range of habitat for small mammals, birds and invertebrates. Types of habitat found in remnant bush include:
- large old trees
- tree hollows for nesting
- bush of different fire ages
- areas of dense vegetation - even gorse patches can be important habitat for bandicoots
- riparian vegetation
- logs and branches on the ground
- twigs and leaves
- thin soils on rock plates, particularly on dolerite
- rocky areas
Healthy bush regenerates itself spontaneously. The bush is likely to be in good condition if the ground layer, the understorey of shrubs and small trees, and the tree canopy are being replaced by young seedlings and saplings. This is particularly important in long-lived vegetation. The lack of regeneration is a major concern in the Midlands where rural tree decline is killing the eucalypts and no young trees are replacing them.
The nature of the surrounding landscape will affect the health of a patch of bush. If it is surrounded by bushland or is adjacent to a neighbour's bush it is likely to be in better condition than if isolated. If bush is surrounded by cropping land or pasture it is more likely to suffer from weed invasion and other problems.
Links to other bush
Bush that has a compact shape is more likely to be in good condition than bush that is long and thin with a high perimeter to area ratio. Long thin strips of bush are more prone to weed invasion, disturbance, accidental fertiliser drift, and the effects of wind. However, such strips can remain in good condition with appropriate management.
The habitat value of a patch of bush may be enhanced if it is linked to or is close to other patches, particularly if it is small. Small patches of bush close to each other provide an opportunity to establish vegetation buffers through strategic planting. These can also act as shelterbelts. There is much potential for landowners to work together to jointly manage their bush.