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Heathland Heathland is found on flat to gently undulating, acidic, nutrient-poor sandy soils in southern and western Victoria. The altitude range is generally between 50 and 300 m above sea level and the rainfall varies from 600 to 1100 mm a year. Small areas in the sub-alps have a higher rainfall and experience snow in the winter. About 40% of the area once supporting Heathland in Victoria falls on public land while about a quarter is represented in conservation parks and reserves. About 55% of all Heathland has been permanently cleared for agriculture, urban development or mining. Heathland ecosystems are characterised by a dense layer of
small-leafed shrubs, usually 1-2 m tall, over a ground layer of sedges,
coarse lilies, rope-rushes, prostrate shrubs and herbs. In most
places there are occasional small, short-trunked, spreading trees, to 15m tall,
which may form a sparse canopy on deeper soils. The commonest tree
species is Eucalyptus viminalis subsp. pryoriana (Coast
Manna Gum) in the eastern part of the range, Eucalyptus
baxteri (Brown Stringybark),
Eucalyptus arenacea (Wimmera
Scentbark) and Eucalyptus willisii (Shining
Peppermint) in the west and south-east, and Eucalyptus
pauciflora (Snow Gum) along the
margins in the high country. Where the soils are relatively dry
the dominant shrubs are usually tea-trees (Leptospermum)
and stunted she-oaks (Allocasuarina);
where the soils are waterlogged, paperbarks (Melaleuca)
and large sedges (Gahnia, Lepidopserma)
form dense thickets with occasional small trees such as Eucalyptus
cephalocarpa (Mealy Stringybark)
and Eucalyptus conspicua (Silver
Swamp Stringybark). In the high country wet heathlands are
dominated by a range of heaths (Epacris)
and rope rushes (Restionaceae). |
| Heathland |
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Heathland is one of the oldest recognised ecosystems in the world. The name was first applied to the the treeless vegetation of Europe where Heather (Calluna vulgaris) and the spiny pea, Gorse (Ulex europaeus), often make up the bulk of the vegetation. The male and female names Heath and Heather are derived from the ecosystem and the term Heathen was originally coined to represent those people who lived in Heathland away from the major townships and hence shunned mainstream Christianity. When vegetation with a similar appearance was discovered in Victoria it was logical that the same term would be used to describe it, even if there were significant differences at the ecological level. It is therefore a little ironic that while Victorian Heathlands are natural ecosystems most of the European versions were probably created by removing the trees from a native woodland some time during the Bronze Age (about 3000 or more years ago) and the Heathland people maintained the treeless landscape so they could graze their livestock. The key ecological feature of Heathland is the extremely low nutrient status of its soils, a feature that affects almost everything about the way the ecosystem is inhabited. Every plant and animal that lives within Heathland must have some adaptive mechanism for dealing with the relative paucity of significant biological chemicals such as phosphates and nitrates. The most obvious physical adaptation is the small stature of most Heathland plants, which goes hand in hand with a slow growth rate. The slow growth often overrides periodic flushes of extra nutrients - for example, when an animal dies and decomposes or when masses of nutrients are released after a wildfire - which are stored in underground organs rather than utilised in increasing the size of above-ground plant parts. The presence of large underground woody storage organs (lignotubers) on many of the shrubs and large, carbohydrate-rich tubers, corms and leaf bases on sedges and herbs means that there is usually a greater mass of living tissue beneath the soil surface than above. Even slow growth cannot proceed unless there are mechanisms for extracting the small amounts of nutrients from the soils and to do this most species have adaptations associated with their root systems. Members of the Proteaceae (Banksia, Hakea, Grevillea) and at least one pea (Viminaria) have the ability to generate dense clusters of fine roots, covered with long root hairs, whenever the root system encounters pockets of nutrients. Some sedges (Gahnia, Lepidosperma, Schoenus) and rope rushes (Hypolaena, Empodisma) have analogous structures designed to maximise the root surface contact with the soil. Many other species, especially the shrubs and small trees, utilise a symbiotic relationship between soil fungi and roots (mycorrhizae) to access soil nutrients. The host plant provides the fungus with carbohydrates and in return gains access to a far-reaching network of fine nutrient-gathering fungal threads (hyphae). Another symbiotic relationship, this time between roots and soil bacteria, creates nodules on the roots of some species (bush peas, wattles, she-oaks) which can convert atmospheric nitrogen in the soil into a form suitable for uptake into the plant. Finally, some plants use insectivory to supplement their nitrate and phosphate intake (Drosera, Utricularia) while others simply resort to parasitism (Cassytha). Fires, which are a relatively frequent event in Heathland, are an important component of the ecosystem's ecology. They act as a means of returning nutrients to the soils and opening the canopy for regeneration of small, ground-layer species such as orchids, sundews, dampieras, lilies, goodenias and other herbs. The structure of Heathland vegetation encourages these events. As the larger shrubs age they present a greater quantity of dry branches and fine twigs with only a relatively thin veneer of small, hard leaves (which may themselves contain flammable oils) in the upper canopy. After 30 to 50 years without fire the understory is largely shaded out and is less diverse, the leaf litter (which may help reduce the numbers of other species by releasing growth inhibitors into the soil) becomes dense and the vegetation is extremely susceptible to burning. Heathland fires are seldom 'hot', in the sense that the explosive crown fires in forests can be, and they flare up and die down very rapidly because the fuel load is never large, at least when compared to the massive quantities of logs, dry tree trunks and oil-laden eucalypt leaves that make up a forest. A Heathland fire, in old vegetation during the summer, is an almost perfect regeneration burn. The larger shrubs have most of their branches removed but few of them die and most regenerate directly from rootstocks and lignotubers. Those that are killed will reproduce from seed that was held on the plant in woody capsules until after the fire (Hakea, Banksia, Leptospermum, Allocasuarina, Melaleuca) or from hard-cased, soil-stored seed (wattles, bush-peas). Similarly, grass trees (Xanthorrhoea) will sprout from their bases within days of the fire passing and the following spring will display a uniform mass of new flowering spikes, attracting sometimes huge flocks of parrots, lorikeets and honeyeaters. Most sedges, coarse lilies and many herbs will regenerate in the same manner as the grass trees providing post-fire forage for wombats and wallabies. The real excitement, however, will be the wide range of small plants that no longer have to contend with the inhibiting effect of a dense shrub layer and now can put up shoots, often from semi-dormant tubers, and flower in great numbers. Chief amongst the small plants that flourish after fires are the ground orchids. Heathland supports a greatest proportion of orchids of all Victorian ecosystems and many species respond quickly to fire, indeed some are fire specialists (Pyrorchis, Burnettia) and seldom flower under other conditions. The first spring after a fire will usually yield the greatest flowering events, provided there have been adequate winter rains. In subsequent years the shrub, sedge and rope-rush recovery will be greater and the vegetation starts to take on a more uniform look. Nevertheless, the botanical diversity of Heathland is greatest in the first decade after a fire and this seems to be critical to the survival of some small mammals such as native mice (Pseudomys) and bandicoots. These species forage on a range of seeds, tubers, fruits, invertebrates and fungi which become fewer and more difficult for the animals to find as the vegetation ages. Consequently these animals will move around the ecosystem seeking out the younger vegetation, without which local extinctions are likely. Human use of Heathland, since European settlement, has been minimal; in most cases the ecosystem has either been cleared or left alone. In areas where the soils are deeper and slightly more fertile there has been widespread clearing for marginal agriculture where application of phosphate and nitrate fertilisers and sowing of pasture grasses has enabled sheep grazing. In most other areas the vegetation has been left undeveloped and, over time, many of these have been incorporated into the park system. There are now substantial parks with Heathland as a major component (Grampians, Croajingolong, Little Desert) as well as many smaller reserves. Management of the vegetation has been been a straightforward affair as weed eradication programs are often unnecessary because of the inability of most northern hemisphere species to invade the infertile soils. Fire management features high on the list of priorities for Heathland reserves perhaps because they are easy to control, due to their relatively low intensity. A problem that has arisen from the application of fire to Heathland is that the botanical composition of the vegetation has changed, in some areas quite radically. Bracken (Pteridium esculentum) often comes to dominate the understory in areas where high-frequency burning (less than 5 years) has been applied and especially when this has taken place during spring or autumn rather that the, more natural, summer season. Today Bracken and Prickly Tea-tree (Leptospermum continentale) are the two most widespread and abundant species of Heathland, the former because of its ability to regenerate from underground rhizomes, the latter because of its prolific seed production and rapid germination after fire. Both species grow in such dense thickets that much of the understory is shaded out and the overall diversity of the ecosystem is diminished. The European Heather is a member of the Ericaceae and it, along with other members of the family, including the dry-seeded Erica (European Heath) and the fleshy-fruited Vaccinium (Cranberry), are small-leafed, tubular-flowered shrubs with an unusual, fine root system that develops a mycorrhizal association peculiar to the family. In Victorian Heathland the analogous family is the Epacridaceae (Epacris, Leucopogon, Astroloma, Acrotriche, Monotoca, Richea, Styphelia, Brachyloma) which has similar tubular flowers, root systems and mycorrhizae, and also has both dry-seeded and fleshy-fruited species. Recently, some botanists have determined that the similarities between the two families are so great that they should both be merged into the older classification - that is, all should be considered to be members of the Ericaceae. While there are undoubtedly sound taxonomic and ecological reasons for this amalgamation it does seem a little disappointing to lose an Australian plant family which is characteristic of a distinctive, species-rich ecosystem. © Paul Gullan, Viridans Biological Databases |