Australia – Types of Vegetation
The brush corresponds to the tropical and subtropical forest. It is found in moist, sheltered and rich soils, in the coastal area and in the tables of eastern Australia and reaches its greatest development in Queensland and in the basalt areas of New South Wales. It contains few Australian types but many Malaysians. It consists of forests made up of vigorous trees, climbing and scent plants, including lianas, and many undergrowth shrubs. The genus Eucalyptus it is rarely found there and the trees are mainly Meliacee, Sapindaceae, Saxifragacee, Cunoniacee, Lauracee, Monimiacee, Conifere and Taxaceae. The pillar stems are a feature; often long aerial roots form support for the long trunks that run upwards towards the light. Among the most notable species are the Ficus spp., Iloanea, Cryptocarya, Araucaria Cunninghamii (hoop pine), Cedrela toona (red cedar), Gmelina Leichardti (beech), Doryphora sassafras, Melia azedarach (white cedar), Elaeocarpus grandis (blue fig) and many others. Some of the finest woods in the world are found in these forests.
The brush contains a large number of epiphytes, including various ferns (Platycerium alcicorne, Asplenium nidus) and orchids (Dendrobium sarcochilus, Bulbophyllum). In the undergrowth there are also varieties of beautiful ferns among which stand out Alsophila excelsa, Australia australis and Dicksonia antartica. In the north, the undergrowth is very dense, often impenetrable due to the intricate masses of vines, including some species of Rubus spinosi. La Palma-Advocate (Calamus Muelleri) forms dense, impenetrable layers with lower undergrowth.
In strong contrast to the vegetation described are the various xerophilous formations, so widespread as to give a particular character to the Australian vegetation as a whole. Under this title the Eucalyptus forest should be mentioned first of all, which is especially developed in extension and density. in southeastern and southwestern Australia, where most of the rain falls in winter. The Eucalyptus forest is open, well lit, always green, composed of large trees of Eucalyptus, Acacia, Casuarina, Grevillea, with undergrowth of xerophilous shrubs (especially Leguminosae, Proteacee, Myriacee, Rutaceae).
According to top-mba-universities, Xerophilia naturally increases with the accentuation of the continental character of the climate and then proceeding inland. A first passage occurs, in the north and east, from the Eucalyptus forest to vast areas of savannah (prairies tree-lined especially by acacias) and to the scrubs already described, characterized by a vegetation of shrub-like acacias. Elsewhere, especially in the south, there is a shrub formation based on Eucalyptus nano (mallee). In general, these shrubby associations recall certain traits of the Mediterranean and Californian scrub and like this they show considerable variations in a more or less xerophilic sense, in some cases being reduced to true steppes with scarce woody vegetation, in others to relatively dense mesophytic scrubs. A further accentuation of xerophilia leads to the mulga type, steppe surfaces resulting from grasses (Andropogon, Sporobolus, Stipa, Aristida, Triodia) and by shrubs of phillodinic acacias (mulga). A final progress towards the desert can be found both in the expanses of dunes fixed only by a scarce herbaceous vegetation, and in coincidence with the saline areas, where the saltbush, a vegetation of Atriplex and other halophilous species develop.
The leaves of all this xerophilic vegetation are hard, leathery and show numerous adaptations for the reduction of transpiration: such as the rolling up of the margins, the sinking of the stomata, the development of hair covering the surface, the thickening of the cuticle, the large development of sclerenchyma, reduction of intercellular spaces.
Spinescence is a common peculiarity (see the acacias and, among the herbaceous plants, the very widespread Spinifex), and thus the development of glandular hairs that secrete resin in abundance and are frequently encountered in the Sapindaceae (Dodonaea) and Mioporinee families (Eremophila) and hence the smoothing of the surface in older leaves. As for the shape, the leaves are mainly of the long and narrow type as in Eucalyptus and in the Fillodinica Acacias. They are then either vertical or hanging and acquire a position parallel to the incident rays of light, a position commonly found in xerophile floras.
Leaf reduction and fillodinia are found in certain species, while aphillia is found in the genera Viminaria, Exocarpus, Casuarina, Bossiaea, Tetratheca juncea, Daviesia alata, Amperaea spartioides, etc.
The protection of the buds is carried out above all with the covering of the young leaves by stipules which are often secretory. Woolly hairs develop in a considerable number of genera, including Newcastlia, Dicrastylis and Lachnostachvs. A layer of gum covers the young leaves in Angophora and Eucalyptus species. The scales that cover the buds are missing, but often the young leaves are glued together and completely enveloped in a layer of resin or mucilage.
Succulence is a feature of low-lying flora in xerophilous formations of arid inland regions. It is found mainly in Chenopodiacee, Zigofillacee, Ficoidee, Crassulacee, Portulacaceae. There are no gigantic succulent plants as they are found in America and Africa.
Aquifers fabrics are also developed in woody plants, especially in the roots of Eucalyptus dumosa (mallee), E. oleosa, Hakea leucoptera and Casuarina Decaisneana: they also characterize certain singular trees such as the north-west gouty stem (Adansonia Gregorii) and various Sterculiaceae such as the “bottle” tree (Brachychiton rupestris).