Tasmanian temperate rain forests

The Tasmanian temperate rain forests are part of the Australasia ecozone, which includes Tasmania and Australia, New Zealand, New Guinea, New Caledonia, and adjacent islands.^[1]

Rainforest communities in Australia are classified as closed forests in which the canopy comprises 70-100% cover.^[2] It can be divided into tropical, subtropical, monsoon and temperate rainforest.^[3] Tasmanian rainforest is classified and as cool temperate rainforest, it represents the most floristically complex and best developed form of this forest type in Australia.^[4] In Tasmania, they can be found in the West, Savage River National Park, South West, North East and in patches on the East Coast.^[5] On the mainland of Australia, cool temperate rainforest have a wide variety of woodland trees, Tasmania only has a limited number of woodland and vascular plants such as mosses, liverworts, lichen and fungi.^[6] Because of this, the definition of Tasmanian cool temperate rainforest was redefined in the 1980s to allow for communities that did not meet the canopy requirements and clearly separate cool temperate rainforest from mixed forest; The current definition states that cool temperate rainforest are those with trees usually greater than 8m in height and capable of regenerating in the absence of large scale catastrophic events such as fire.^[7] These forests are climax vegetation and are dominated by angiosperms (Nothofagus cunninghamii, Atherosperma moschatum and Eucryphia lucida) as well as gymnosperms (Athrotaxis selaginoides Lagarostrobos franklinii and Phyllocaldues aspleniifolius.^[8] The limited number of woody species is thought to be due to repeated glaciation.^[9]

Tasmanian cool temperate rainforest can be divided into four types: Callidendrous rainforest, Thamnic rainforest, Implicate rainforest and Open Montane.^[10] These four major types differ in many of their characteristics such as structure, floristics, distribution, level of endemism and ecology.^[11]

Community composition and descriptions

Tasmanian cool temperate rainforest is composed of two alliances, the myrtle-beech (Nothofagus cunninghamii) alliance and the pencil pine (Athrotaxis cupressoides). The former is made up of callidendrous, thamnic and implicate, whilst the latter is all open montane.^[12]

Callidendrous rainforest

This is the simplest rainforest community in Tasmania; It is represented typically by medium to tall forests dominated by Nothofagus cunninghamii and/or Atherosperma moschatum (sassafras), Leptospermum lanigerum or Acacia melanoxylon have also been found to accompany them.^[13] Typically, these forests are characterised as > 40m in height.

Trees are usually well formed and widely spaced, the understorey is open and often described as 'park like'.^[14] The diversity of woody species is low, they are usually sparse and inconspicuous throughout the understorey of most communities. However, at mid to low altitudes, the understorey may contain a few small trees or shrubs; Olearia argophylla, Pimelea drupacea, Pittsporum bicolor, Aristotelia peduncularis and Comprosma quadrifida.^[15] Fern diversity is usually high in many areas, in areas where tree ferns provide a suitable substrate epiphytes also flourish.^[16] The dominant tree ferns are commonly Dicksonia antarctica and/or Polystichum poliferum. Common epiphyte species include Rumohra adiantiformis, Asplenium bulbiferum, Asplenium terrestre, Microsorum diversifolium, Hymenophyllum flabellatum, Hymenophyllum australe, Hymenophyllum cupressiforme, Polyphlebium venosum and many more.^[17] Histiopteris incisa and Hypolepis rugosula occur in disturbed sites such as along roads where there have been breaks in the canopy.^[18] As altitude increases, the height of the forest decreases,^[19] Nothofagus cunninghamii becomes multi-stemmed, develops crooked leaning stems and abundant epiphytic bryophytes and lichens produces a patterned effect on the trunks.^[20] The typical understorey becomes dominated by Tasmannia lanceolata and Telopea truncata, the ground layer becomes host to Oxalis megellancia and Lagenifera stipitata. The pteridophytes diversity decreases and only small species such as Lycopodium fastigiatum, Hymenophyllum peltatum, Grammitits billardierei and Blechnum penna-marina persist.^[21] - occurs in the eastern half of the state and in the northwestern and central Tasmania.^[22]

Thamnic Rainforest

Characterised by well formed trees of medium height and a distinct shrub layer, the forest height is well below 40m. The canopy is commonly dominated by a mixture of 2-5 species, these include combinations of: Nothofagus cunninghamii, Eucryphia lucida, Atherosperma moschatum, Lagarostrobos franklinii, Eucryphia milliganii, Phyllocladus aspleniifolius, Athrotaxis selaginoides and Nothofagus gunnii (rarely).^[23] The shrub layer is more prominent and has an increased diversity of woody trees. Common species are: Anopterus glandulosus, Anodopetalum biglandulosum, Acradenia frankliniae, Archeria hirtella, Archeria eriocarpa, Cenarrhenes nitida, Trochocarpa cunninghamii, Trochocarpa gunnii, Orites diversifolia, Prionotes cerinthoides, Richea pandanifolia and Richea scoparia (at high altitudes only).^[24] The increase in understorey shrub for this rainforest type is due to the larger numbers of gaps in the canopy and the differing light requirements of competing species.^[25] Fern diversity decreases in this type because of the decrease in light from the understorey.^[26] Blechnum wattsii is the main ground fern and is able to survive as it prefers damp shaded areas on forest floor; it forms a very dense layer in some areas but can be absent in others.^[27] Small epiphytes are widespread, these include Hymenophyllum rarum and Grammitis billardierei, Apteropteris applanata can occur in areas containing Athrotaxis. Other larger epiphytes are usually present, but they are rarely prominent.^[28] At higher altitudes, the general appearance resembles that of a callidenderous rainforest, but the floristic differences remain the same. - occur mostly in western and southwestern Tasmania^[29]

Implicate rainforest

Low in stature, broken uneven canopies, height reduced below 20m. Dominance is usually shared between several species: Nothofagus cunninghamii, Nothofagus gunnii, Eucryphia lucida, Atherosperma moschatum, Lagarostrobos franklinii, Eucryphia milliganii, Phyllocladus aspleniifolius, Athrotaxis selaginoides, Diselma archeri, Leptospermum scoparium, Leptospermum glaucescens, Leptospermum nitidum, Leptospermum lanigerum, Acacia mucronata and Melaleuca squarrosa.^[30] Atherosperma moschatum is usually represented by small diameter depauperate plants. Understorey is tangled and barely distinguishable from the canopy layer.^[31] It can from a continuous layer from the ground to the canopy but some scattered emergents can occur. Species diversity is high for trees and shrubs in this community, but very low for ferns.^[32] Anopterus glandulosus, Anodopetalum biglandulosum,^[33] Cenarrhenes nitida, Telopea truncata, Agastachys odorata, Comprosma nitida, Archeria eriocarpa, Archeria serpyllifolia, Archeria hirtella, Olearia persoonioides, Trochocarpa cunninghamii, Trochocarpa gunnii, Richea pandanifolia, Richea scoparia, Dracophyllum milliganii and Prionotes cerinthoides are all typical shrubs or small trees that comprise these communities.^[34] The ferns are dominated by Blechnum wattsii but small epiphytes do prevail: Hymenophyllum rarum, Hymenophyllum marginatum, Grammitis billardierei and Apteropteris applanata occurs in communities where Athrotaxis are present.^[35] - occur mostly in western and southwestern Tasmania^[36]

Open montane rainforest

Low and dominated by Athrotaxis cupressoides or Athrotaxis selaginoides (less commonly).^[37] Open canopy, widely spaced trees allow bright light to penetrate the lower levels of the forest. In some communities, the canopy can be dense and instead resemble a high altitude callidendrous forest. Understorey may be dominated by either Poa (grasses) or Sphagnum (mosses) or commonly, low shrubs that are less than half the height of the forest. There is a high diversity of woody species but a low diversity of ferns. Multiple species from nearby treeless vegetation are present, but their classification as rainforest species is yet to be confirmed.^[38] Understorey shrubs include: Nothofagus cunninghamii, Nothofagus gunnii, Diselma archeri, Podocarpus lawrencei, Richea pandanifolia, Richea scoparia, Richea sprengelioides, Orites acicularis, Orites revoluta, Microstobos niphophilus, Tasmannia lanceolata, Epacris serpyllifolia and Baeckea gunniana.^[39] Ferns are usually poorly developed with larger ground species absent or confined to rocks, Gleichenia alpina is the exception to this observation.^[40] Small species such as Hymenophyllum peltatum and Apteropteris applanata can sometimes make an appearance. - occur on the Central Plateau but can extend as small outliners to the mountains further south.^[41]

Biological factors

Geology and soils are important factors in Tasmanian ecology:^[42] Callidendrous forest require good quality sites where fertile soils occur over rocks such as basalt, dolerite and the more nutrient rich granites;^[43] Implicate forests are at the other extreme and moslty grow in organic soils or mineral soils derived from nutrient poor rock types such as quartzites and silicous conglomerates, poorly drained areas are also suitable;^[44] The Thamnic forests tend to prefer an intermediate substrate.^[45] With the exception of Open Montane forests, altitude seems to have little to no effect on the floristic differences between the different community types.^[46][47]

Conservation

In 1982, the United Nations Educational, Scientific and Cultural Organization (UNESCO) designated the northern portion of the ecoregion a World Heritage Site.

See also

• Savage River National Park
• Tarkine
• Mount Field (Tasmania)

References

External links

• "Tasmanian temperate rain forests". Terrestrial Ecoregions. World Wildlife Fund.