Dry sclerophyll forest
Dry Sclerophyll Forest In Tasmania
Sclerophyll means hard-leaf, and describes the leathery foliage of understorey plants in eucalypt forests generally adapted to dryer conditions, with a rainfall less than 1,000 mm per year. Dry sclerophyll forests are adapted to these dryer conditions and to high fire frequencies. They usually have a multi-levelled overstorey of eucalypts of different ages, relating to fires that occur once every 5 to 25 years in low rainfall areas, and a sparse understorey of small trees, hard-leaved shrubs and bracken fern or grasses. Trees are slower to grow in dryer conditions, and the overstorey of mature dry sclerophyll forests often does not reach more than 30 metres in height.
Recruitment to the canopy is a continuous process. Although most seedlings do not survive the cotyledon stage the many lignotuberous seedlings are able to withstand adverse seasons browsing and fires unless exhaustion of their food reserves leads to their death. Disturbance of the surrounding vegetation leads to their promotion to sapling status. The growth rates are slow compared to those of the wet eucalypt forest. In the dryer forests, water is often the limiting factor, so that much growth is directed to roots and survival organs such as lignotubers; while in the wetter forests, there is more necessity to compete with weeds for light and growth space, so that height growth is more important.
As well as having a greater number of levels, dry sclerophyll forests also have a wider range of vascular plant species in both overstorey and understorey. Of Tasmanias 29 eucalypt species, 25 can be found in dry sclerophyll forests. Various kinds of peppermint are most common, but ash and gum species are also widespread. Over 40 different dry sclerophyll communities have been described. Their names relate to the kinds of understorey plants the thrive in different soil and temperature conditions with further subdivision according to the dominant eucalypt species, height, structure and other special factors such as geology. These groups cover most vegetation of Tasmanias dry lowlands and subalpine areas which exrend over much of the state’s east.
The major dry sclerophyll forests include:
Grassy understorey dry sclerophyll forests
This type occurs on dry, fertile sites. The vegetation structure ranges from open-forest to open-woodland with tree heights from 15 to 41 metres. They have a sparse shrub layer and a dense, species rich, ground layer of grasses and herbs.
Heathy understorey dry sclerophyll forests
This type occurs on drier, infertile sites. It has a dense, medium (under 2 m) shrub layer of high species diversity. The ground layer may be dominated by bracken fern on frequently burnt sites. The tree canopy is usually 15 to 30 metres high.
Sedgey understorey dry sclerophyll forests
This type has a sparse to medium canopy over a tall to medium shrub understorey of variable cover, with a dense ground layer of sedges and cord rushes. The understorey is the result of the fire regime and drainage characteristics of the site. Higher fire frequencies favour the development of sedgelands because of their capacity for rapid vegetative recolonisation (sprouting from underground root systems). Many of the sedges are intolerant of low light levels and die out as the canopy closes during longer intervals between fires. On the typically poorly drained sites a shrubby component of tea-tree can be present.
Shrubby understorey dry sclerophyll forests
This type has a multi-layered shrubby understorey. It is widespread on comparatively fertile and well-drained sites, which often have a high surface rock cover. Structure varies from tall open-forest to woodlands. Members of the ash group of eucalypts tend to be dominant on moist or shady sites, which often support wet forest elements in the understorey. Peppermint species are common on exposed or dry sites. The tall shrub/small tree layer is generally sparse, with eucalypt regrowth often a major component.
Dry sclerophyll forests support a much wider range of mammals and birds than the other two main types of Tasmanian forest. This is partly because a greater diversity of plants occurs in, and also creates, a wider range of habitats, and partly because the structure of their sparser uunderstoreys, which includes grasses, can provide grazing for ground dwelling animals.