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Succession after Disturbance in Tasmanian Lowland Vegetation

The after disturbance in vegetation is the continuous change of plant community after a drastic shift caused by a temporal environmental event. In Tasmanian lowland, in which altitude 0-600m above sea level, the shifts are mainly due to fire and they are thought to be temporal. However, when the fire is intense or more frequent the succession process is prone to accompany a long-run community shift. Among the 6 representative vegetation community types in the area, only the rainforest community mainly locating west Tasmania can have a climax of secondary succession, and other community types, which are wet sclerophyll, dry sclerophyll, hearth, coastal and their mixture, are thought to show cyclic successions.

Disturbance of ecosystem in the lowland

In ecosystems there are two factors, which are stress and disturbance, trigger change in the system. The latter is more temporal and prone to cause abrupt shift. While in the monsoon area and the tropics the disturbance consist flooding, erosion, strong wind and landslides, fire is widely known as the common disturbance all over the world. In Tasmanian lowland, frequent fire is predominant disturbance, while gap generation by fallen trees is major disturbance in climax rainforests in the west and anthropogenic impact is common in forestry and coastal areas. The common strong wind and drought in summer are thought no to be disturbance but stress.

Succession patterns

Frederic Clements (1916) redefined ecological succession, primary succession, secondary succession, sere and climax. With a few exceptions such as volcanic disturbance, secondary succession after fire is common in Tasmania.

Drift model

The progression of succession in Tasmania can be understood basically by an ecological drift model, relating both vegetation and soil development to fire, proposed by Jackson (1968). According to the model, the community can be predicted by intervals between successive fires. From shorter to longer successional fire interval, the community changes from heathland, sclerophyll forest, mixed forest and rainforest. For example, while short interval area can only develop heathland, the one longer than 200 years in the interval can have mixed forest, which contains rainforest and sclerophyll species, may succeed to pure rainforest if no successive fire would come. Since every fire consume most of stored nutrient materials into air, frequent fire in prone to cause poor nutrient soil rapidly.

Other key factors

However, a better explanation needs more factors such as intensity of fire, burned area and nutrient richness as proposed by Brown and Podger (1982). Intense fire burns not only surface litter but also peat layer in soil, which gives moisture and nutrient in the ecosystem. Even the fire generate inorganic nutrient chemical materials on the surface ground, they including fine soil particles are washed away in a short time, which cause the following succession more like primary one taking longer time for recovery. On the other hand moderate and light fire leaves soil as it has been and seed bank as well. Suckering also accelerates succession processes. Moderate fire can make germination of Eucalyptus capsules, so that broader biodiversity than that of other intensities can be expected.

Width of the burnt area is also essential to the recovery succession especially in closed rainforest with tall crown trees. To have enough advantage against other spices, Eucalyptus requires more than 30 by 30 m open area.

Richness in nutrient and drainage of soil are other key factors in the progressive succession. Since vegetation in poor soil is not able to grow fast and the same in too good or too poor drainage , the longer fire interval is required for each community to establish, which sometimes cause fixation of interim stage of succession like a climax. Local micro-climate and slope aspect affect recovery speed as well.

Important species

Other than the representative vegetation spices in each community type, nitrogen fixation plant such as Fabaceae, Mimosaceae, Lichens and Bryophytes are playing essential function for recovery process especially in poor land such as mudstone area and acidic moor/lagoon.ref to be cited.

Further information: [[:geologic time scale]]

Bryophyte diversity and ecological role

A diverse range of cool temperate rainforest bryophyte species in Mt Field

Bryophytes are ancient true land plants that consist of mosses, liverworts and hornworts and are found in a huge range of enviroment from deserts, artic, antarctic, rainforest, caves, acidic bogs, urban areas, decomposing animal bodies, dung and even on old cars. Bryophytes are called "non-vascular plants" because of the lack internal vessels(xylem and phloem) for conducting fluids however many bryophyte species have conducting structures; hydroids, within the stems and sometimes leaves, often bryophytes have leaves that are one cell thick, hence the need for complex transport systems. They do not have roots but are anchored by fine, hair-like rhizomes.

Further information: [[:Bryophytes]]

There are at about 13,000-22,000 or so species of bryophytes in the world today with a variable 10,000 - 15,000 species of mosses, 5,000 - 7,500 species of liverworts and 100 - 236 species of hornworts. Although it does not compare to the minimum 223,300 species of flowering vascular plants About 643 species are recognised in Tasmania with about 230 bryophyte species recorded in Tasmanian rainforest alone, For any given site, the difference in species richness between vascular plant (3-6 species) and bryophyte (30-70 species) diversity is huge ). It occurs throughout the forest mainly in moist and very shady enviroment, from ground level to canopy with it being the most abundant in the understory as epiphytes on living wood, dead wood, leaves of plants and exposed rocks.

The ecological role of bryophytes in Tasmania rainforest isn't well studied as compared to other fields of study, hence the suggestion is that

• Bryophyte increase water holding capacity of vegetation which might other wise be lost as run-off
• Reduces evaporation from soil, preventing or reducing erosion of soil
• Slow releases of water during dry spells which influences and reduces fluctuations in humdity
• Maintain a stable environment for other cryptogams and invertebrate animals
• May play an important role in nutrient cycling
• pioneering plants on converting unfavourable substrate into suitables ones for other plants

Anthocerotophyta (Hornworts)

Hornworts are a group of bryophytes comprising the division Anthocerotophyta. The common name refers to the elongated horn-like structure, which is the sporophyte. The flattened, green plant body of a hornwort is the gametophyte plant. There are about 100 known species so far but new species are still being discovered. A common example of hornwort found in tasmania is Phaeoceros carolinianus

Further information: [[:Hornwort]]

Bryophyta (Moss)

Mosses are a group of bryophytes comprising the division Bryophyta. Commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems. At certain times mosses produce spore capsules which may appear as beak-like capsules borne aloft on thin stalks. There are about 12,000 species of moss at the moment. A common example of moss in tasmania is Thamnobryum sp.

Further information: [[:Moss]]

Marchantiophyta (Liverworts)

Liverworts or hepatics are a group of bryophytes comprising the division are a division Marchantiophyta. Like other bryophytes, they have a gametophyte-dominant life cycle. Leafy liverwort specuies can be mistaken for a moss, however liverwort do not posses a costa in their leaves and may bear marginal cilia which are rare in mosses. Other differences are not universal for all mosses and liverworts, but the occurrence of leaves arranged in three ranks, the presence of deep lobes or segmented leaves, or a lack of clearly differentiated stem and leaves all point to the plant being a liverwort. There are about 9000 species of liverworts. A common example of liverwort in tasmania is Marchantia sp

Further information: [[:Liverwort]]

Bryophyte examples spotted in Mt. Field

Liverwort

• 
  Liverwort, Tylimanthus pseudosaccatus
• 
  Liverwort, Riccardia sp

Moss

• 
  Moss, Dicranoloma menziesii
• 
  Moss, Hypnodendron comosum & Hypnodendron vitiense
• 
  Moss, Ptychomnion aciculare

Further Reading

Kantvilas, G., & JARMAN, S. J. (2012). Lichens and bryophytes in Tasmanian wet eucalypt forest: floristics, conservation and ecology.

Kantvilas, G., & Jarman, S. J. (2008). The cryptogamic flora of an isolated rainforest fragment in Tasmania. Botanical journal of the Linnean Society, 111(2), 211-228.

Pharo, E. J., & Beattie, A. J. (2002). The association between substrate variability and bryophyte and lichen diversity in eastern Australian forests. The Bryologist, 105(1), 11-26.

Pharo, E. J., & BEATTIE, A. J. (2006). Bryophyte and lichen diversity: a comparative study. Australian Journal of Ecology, 22(2), 151-162

Tng, Y.P.D., Dalton, P.J. & Jordan, G.J., (2009). Does moisture affect the partitioning of bryophytes between terrestrial and epiphytic substrates within cool temperate rain forests? A Journal of Bryology and Lichenology, The Bryologist, vol 112, pp.506–519.

Turner, P. A., & Pharo, E. J. (2005). Influence of substrate type and forest age on bryophyte species distribution in Tasmanian mixed forest. The Bryologist, 108(1), 67-85.

Williams J.E. (2012). The Evolutionary Significance of Tasmania’s Rainforests and Associated Vegetation. A report to the Independent Verification Group, Tasmania, February 2012.

External links

B.Goffinet (2012), Australian Mosses Online 53. Splachnaceae. Australian Biological Resources Study, Canberra. Version 22 June 2012.

McCarthy, P.M. (2006), Checklist of Australian Liverworts and Hornworts. Australian Biological Resources Study, Canberra. Version 6 April 2006.

Key to Tasmanian Dicots. 2011 http://www.utas.edu.au/dicotkey/dicotkey/key.htm Viewed on March 9 2013

Glime, Janice M. 2007. Bryophyte Ecology. Volume 1. Physiological Ecology. Ebook sponsored by Michigan Technological University and the International Association of Bryologists. accessed on March 9 2013 at <http://www.bryoecol.mtu.edu/>.

References used

A diverse range of cool temperate rainforest bryophyte species in Mt Field