Flora of Tasmania - Flora

Flora

The most ancient communities in Tasmania have an ancestry that extend back to a time when the Earth's continents were all joined as single landmass known as Pangea which existed beyond 200 million years ago. Pangea split from east to west into Laurasia, compressing North America and Eurasia, and Gondwana, the two remaining connected at Gibraltar with the Tethys Sea separating them. The presence of closely related organisms in both the northern and southern hemispheres cannot be accounted for by migration.

The Tarkine, located in island's far North West, is the largest temperate rainforest area in Australia covering approximately 3,800 square kilometres (1,500 sq mi). The temperate rainforest has a high diversity of non-vascular plants: mosses, liverworts and lichens representing Australia's largest remaining single tract of Gondwanan rainforest and is the largest wilderness dominated by rainforest in Australia. It contains approximately 1,800 km² of rainforest, around 400 km² of eucalypt forest and a mosaic of other vegetation communities, including dry sclerophyll forest, woodland, buttongrass moorland, sandy littoral communities, wetlands, grassland and Sphagnum communities.

The Antarctic flora is a distinct community of vascular plants which evolved millions of years ago on the supercontinent of Gondwana, and is now found on several separate areas of the Southern Hemisphere, including southern South America, southernmost Africa, New Zealand, Australia and New Caledonia. Based on the similarities in their flora, botanist Ronald Good identified a separate Antarctic Floristic Kingdom that included southern South America, New Zealand, and some southern island groups. Good identified Australia as its own floristic kingdom, and included New Guinea and New Caledonia in the Paleotropical floristic kingdom, because of the influx of tropical Eurasian flora that had mostly supplanted the Antarctic flora.

Millions of years ago, Antarctica was warmer and much wetter, and supported the Antarctic flora, including forests of podocarps and southern beech. Antarctica was also part of the ancient supercontinent of Gondwanaland, which gradually broke up by continental drift starting 110 million years ago. The separation of South America from Antarctica 30-35 million years ago allowed the Antarctic Circumpolar Current to form, which isolated Antarctica climatically and caused it to become much colder. The Antarctic flora subsequently died out in Antarctica, but is still an important component of the flora of southern Neotropic (South America) and Australasia, which were also former parts of Gondwana.

Some genus originated in Antarctic Flora are still a recognized major component of New Caledonia, Tasmania, Madagascar, India, New Zealand, and southern South America.

There are three species of Nothofagus in Australia. Stands of Nothofagus cunninghamii (Myrtle beech) exist in the Tarkine Forest. There are also some small stands of this species in the Great Otway National Park, in Victoria.

The deciduous Antarctic beech (Nothofagus gunnii) also occurs in Tasmania. The related Antarctic beech (Nothofagus moorei) is found in Australia but it is not present in Tasmania.

Australia drifted north and became drier as well; the humid Antarctic flora retreated to the east coast and Tasmania, while the rest of Australia became dominated by Acacia, Eucalyptus, and Casuarina, as well as xeric shrubs and grasses. Humans arrived in Australia 50-60,000 years ago, and used fire to reshape the vegetation of the continent; as a result, the Antarctic flora, also known as the Rainforest flora in Australia, retreated to a few isolated areas composing less than 2% of Australia's land area.

The woody plants of the Antarctic Floristic Kingdom include conifers in the families Podocarpaceae, Araucariaceae and the subfamily Callitroideae of Cupressaceae, and angiosperms such as the families Proteaceae, Griseliniaceae, Cunoniaceae, Atherospermataceae, and Winteraceae, and genera like southern beech (Nothofagus) and fuchsia (Fuchsia). Many other families of flowering plants and ferns, including the tree fern Dicksonia, are characteristic of the Antarctic flora. In the past Tasmania was omitted since its plant species are more closely related to those found in the Australian Floristic Kingdom. Good noted, as had Joseph Dalton Hooker much earlier, that many plant species of Antarctica, temperate South America and New Zealand were very closely related, despite their disjunction by the vast Southern Ocean. Tasmania and New Caledonia share related species extinct in Australia mainland.

Investigations of Upper Cretaceous and Early Tertiary sediments of Antarctica yield a rich assemblage of well-preserved fossil dicotyledonous angiosperm wood which provides evidence for the existence, since the Late Cretaceous, of temperate forests similar in composition to those found in present-day southern South America, New Zealand, Australia and Tasmania. It is suggested a paleobotanical habitat similar to the extant cool temperate Valdivian rainforests.

Tasmania has extremely diverse vegetation, from the heavily grazed grassland of the dry Midlands to the tall evergreen eucalypt forest, alpine heathlands and large areas of cool temperate rainforests and moorlands in the rest of the state. Many flora species are unique to Tasmania, and some are related to species in South America and New Zealand through ancestors which grew on the super continent of Gondwana in the Paleotropical Kingdom, 50 million years ago.

Wet eucalypt forests grow mostly in the south, west and north west, the Tasman Peninsula, and higher altitude areas of north east. Dry eucalypt forests grow where there is little rainfall and droughts are common. Areas such as the east coast, midlands and north east, i.e. the Bass Strait Islands.

Tasmania is also home to some of the tallest and oldest trees of the world. For example, some individual Huon pines are believed to be more than 2,000 years old, and a stand of male Huon pines at Mount Read which has maintained itself by vegetative reproduction is estimated to be more than 10,000 years old.

The tallest trees in Australia, more than 90 metres (300 ft) tall, are Eucalyptus regnans found in the Styx Valley. As these are still growing, they may surpass the tallest tree ever measured in the country, a mountain ash growing at Thorpdale, Victoria that measured more than 112 metres (367 ft) before it was felled in 1884. Tasmania hosts endemic plant genera as well as plant genera of restricted distribution; an example of such a genus is Archeria.

Over millions of years, these type of vegetation present in the island, covered much of the tropics of Earth. The species of Tasmania are relicts of a type of vegetation disappeared, which originally covered much of the mainland of Australia, South America, Antarctica, South Africa, North America and other lands when their climate were more humid and warm. Although warm Cloud forests disappeared during the glaciations, they re-colonized large areas every time the weather was favorable again. Most of the Cloud forests are believed to have retracted and advanced during successive geological eras, and their species adapted to warm and wet gradually retreated and advanced, replaced by more cold-tolerant or drought-tolerant sclerophyll plant communities. Many of the then existing species became extinct because they could not cross the barriers posed by new oceans, mountains and deserts, but others found refuge as species relict in coastal areas and Islands.

When the large landmasses became drier and with a harsher climate, this type of forest was reduced to those boundaries areas. Although some remnants of archaic rich flora still persisted in their coastal mountains and shelter sites, their biodiversity were reduced. The location of Tasmania in the Pacific Ocean moderated these climatic fluctuations, and maintained the relatively humid and mild climate which has allowed these communities to persist to the present day.

The ecological requirements of many of the species, are those of the laurel forest and like most of their counterparts laurifolia in the world, they are vigorous species with a great ability to populate the habitat that is conducive. The geographical isolation and special edaphic conditions helped to preserve it too.

Many members of the late Cretaceous - early Tertiary Gondwanan flora survived in Tasmania and New Caledonia's equable climate but were eliminated in Australia mainland due to increasingly dry conditions.

Plants have limited seed dispersal mobility away from the parent plant and consequently rely upon a variety of dispersal vectors to transport their propagules, including both abiotic and biotic vectors. Seeds can be dispersed away from the parent plant individually or collectively, as well as dispersed in both space and time.