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=Changes in plant community structure & species diversity with altitude at Mt Field= Mount Field National Park is very diverse in vegetation types which are rich in species and consist of many communities. The vegetation types are classified into altitudinal zones: a tall open forest in the lower zone, a closed rainforest in the middle zone and an upper zone of alpine to subalpine forests. There is a high level of plant variation due to the aspect, altitudinal difference, soil composition and geology. Along the altitudinal elevational gradient, many environmental factors (such as temperatures, growing season, humidity, wind velocity and atmospheric pressure) vary concurrently.

Description
The plant community varies in the composition of the vegetation species within the limited area which is distinguishable from the other vegetation types. The vegetation structure can be floristically differentiated by observing the presence of species in the different layers (emergent, dominant canopy, subdominant canopy, understory, shrub, and groundcover). Plant communities are formed based on vegetation types. Furthermore, the vegetation types are dependent on the ecological factors such as altitude, aspect, rainfall, geology, temperature, soil type, solar radiation, wind, humidity and frequency of disturbance.

At different altitudes, the vegetation type and environmental factors differs. Also, there is a big gradient of temperature in a short distance at the varying altitudes. Hence, this system is important to determine species diversity at the different altitude zones, the means of adaptation to their surroundings, the limitations and benefits of community structure.

Plant Community Structure
Mount Field National Park has an altitudinal transect operating from 150m to 1280m, which are classified into threefold altitudinal zones :
 * Low region (~150m - 650m)
 * Middle region (~670m - 840m)
 * Upper region ( ~880m - 1280m)

12 different community types at Mount Field at the respective altitudes (shown in the table below) surveyed by Field Botany students of University of Tasmania from 09/02/15 to 13/02/15:

Low region
The lower zone, from 150m to 650m, comprises of tall open forest dominated by Eucalyptus species.

There are two community types in this region:  Dry sclerophyll forest (site 1)
 * It is a marginal dry sclerophyll forest, possibly maintained by the interaction of the soil type, aspect and frequent disturbance by fire. It is an open forest with vegetation of Eucalyptus obliqua and Eucalyptus amygdalina in the canopy of the forest estimated up to 15m tall . It has an understory of Exocarpus cupressiformis and Banksia marginata, a shrub layer of Epacris impressa, Pultenaea juniperina and Daviesia latifolia and a sparse ground layer of Gonocarpus teucrioides with a high percentage of bare ground, rocks and litter.


 * It has low annual rainfall (~950mm) and more sun radiation, which increases the dryness of the soil, therefore water availability is a limited in this site. Many plants in this site are relatively short (~15m-20m), as they use their energy to get more depth in their roots or lignotubers to try to obtain more water. The soil is unable to retain moisture as it runs out of it which limits plant growth and when the soil is completely moist, erosion will happen.


 * However, there are multi-age trees in this site evident that there are regeneration after a fire (fire affects the soil and nutrient status).

 Wet sclerophyll forest (site 2)
 * Wet sclerophyll forest with gigantic emergent eucalypts 70m tall, with a typical closed understory of a variety of Acacia species, and the indicator species Olearia argophylla (musk).


 * It is mainly dominated by Eucalyptus obliqua and Eucalyptus regnanswhich are about 60m in height, with a 25-50% canopy cover. This site shows a discontinuing canopy of eucalypts, which suggests long intervals of fire events .When there is a fire, the ash bed introduces the next generation. Thus, species in this site encourages fire in their life cycle. The understory consists of three Acacia species: Acacia dealbata, Acacia melanoxylon and Acacia verniciflua, which are 25-30m in height and cover more than 75% of the area. Due to limited sunlight, there is a sparse ground cover with mostly fern species (Dicksonia antarctica). They have a similar structure as a mixed forest, but consisting of different species.

Middle region
The middle region has as an altitudinal zone between 670m to 840m and typically comprises of a closed rainforest or mixed forest dominated by Nothofagus cunninghamii and Atherosperma moschatum shown in site 4. This zone can also be characterized by the presence of Phyllocladus aspleniifolius which is similar to site 3.  Sphagnum bog (site 3)
 * Due to the underlying sandstone shelf, site 3 resulted in waterlogging (poor-drainage) which differs from site 4. The vegetation structure consists of implicate rainforest species, which includes Phyllocladus sp. and Anodopetalum biglandulosum, and Eucalyptus subcrenulata stunted, about 5-10m tall and more than 75% canopy coverage expected over the sphagnum bog. The understory usually contain the epacrid species with Richea pandanifolia with a height of 2.5m.

Mixed forest (site 4)
 * With the absence of fire, this site has emergent Eucalyptus delegatensis (up to 60m) with a closed understory of rainforest species as a wet sclerophyll forest replaced by a rainforest . The canopy is mainly dominated by rainforest species of Nothofagus cunninghamii and Atherosperma moschatum as these species are able to tolerate low light environments. The groundcover is mainly ferns and bryophytes. However, the understory has limited light which restricts growth of the species.


 * Fire needs to be present to open up the forest for regeneration. The lack of a fire event in the next 50-100 years will result in the extinction of eucalypts in this site.



Upper region
There are two categories in the upper zone: sub-alpine and alpine. Sub-alpine (consists of sites 5-7)
 * The low canopy of the subalpine forests and woodlands on Mt Field typically consist Eucalyptus subcrenulata and conifers such as Athrotaxis cupressoides, Athrotaxis selaginoides, Podocarpus lawrencii, Microcachrys tetragona, Diselma archeri and Microstrobos niphophilus.
 * >>> Subalpine woodland near Lake Fenton (site 5)
 * This site has a wide range of shrub species (mainly Asteraceae, Proteaceae and Ericaceae). It is species rich low woodland with Eucalyptus coccifera or Eucalyptus subcrenulata up to 10-15m tall . Also, it has an understory layer up to 3m high consisting of Proteaceae and Epacridaceae.


 * The vegetation is prevalent on sheltered slopes to enable cold air drainage and water availability.


 * >>> Subalpine sclerophyll woodland (site 6)
 * Site 6 is located at the boundary between an open subalpine sclerophyll woodland and a moorland community . The subalpine community is a closed herbland with a 10m height canopy of Eucalyptus coccifera and Eucalyptus subcrenulata (covering more than 40%), a 1.5m of understorey of shrubs with Bauera rubioides and Richea scoparia while the moorland community consists of shrubs (Leptospermum rupestre and Boronia citriodora) and a more than 95% groundcover of Gleichenia alpina and Astelia alpina.


 * >>> Subalpine woodland near Lake Dobson (site 7)
 * Site 7 has a wide variety of shrubby species which mainly consists species of the Proteaceae and Epacridaceae family. It is a Eucalyptus coccifera or Eucalyptus subcrenulata woodland to Athrotaxis cupressoides closed forest with Eucalyptus subcrenulata.

Alpine (consists of sites 8-12)
 * The alpine sites are located beyond 1000m on Mount Field. There are a range of coniferous shrubs, sclerophyll heath, herbfield and microshrubbery communities. These communities are distributed depending on soil drainage, wind protection, snow and frequency of disturbances such as fire. Pineapple grass bogs, cushion plants typically occur on the unprotected sites.


 * >>>Coniferous shrubbery and sclerophyll heath above the ski huts (site 8)
 * They contain alpine coniferous closed heath or sclerophyll open heath . It is a changeable and harsh environment with a woody vegetation of Eucalyptus coccifera. Glazing storms can happen here and it is wind prone but it follows the contours of the rocks for protection.


 * >>> Coniferous shrubbery and sclerophyll heath of Roberts Tarn (site 9)
 * This site is either an alpine coniferous closed heath or open montane rainforest . Residual species of the Nothofagus sp. are present which have branches that can withstand snow and are protected under the snow for a period of time. Thus, Nothofagus sp. dominates the bottom of the Tarn (but fire also plays a role here).


 * >>> Coniferous microshrubbery/herbfield halfway along Tarn shelf (site 10)
 * This site consists of alpine herbfield or microshrubbery with full exposure to its surroundings and have a range of species less than 10cm in height (a mat of continuous cover) . The main species are Gymnosperms with many epacrids.


 * >>> Coniferous shrubbery and sclerophyll heath after fire at Backhouse Tarn (site 11)
 * It consists of slow recovering alpine vegetation or microshrubbery due to a fire that happened 30 years ago. The vegetation lacks adaption to fire, causing the soil to be thin and subject to erosion after fire.


 * >>>Microshrubbery (cushion plant community) at the top of Newdegate Pass (site 12)
 * It is an alpine bolster heath with compactly-packed cushion plants with many different species present in a small area at this site . It is a wind funnel and a harsh environment with ice, the cushion plant species here are good with frost so they do not usually freeze. Therefore, the plant community at this site are in the form of cushion plants to prevent severe abrasion.



Conclusion
There are a lot factors that change through the altitudnal zones, such as air pressure (direct), water availability, soil nutrients, geology, wind exposure. However, the characteristic that plays a major role in altitude changes is temperature. With the increase in altitude every 100m, the community environment gets colder by one degree. It is thought that vegetative richness would decline as altitude increases due to the colder climate at the top. The harsh cold condition, higher wind and solar radiation exposure of the higher altitudinal areas were speculated to have a lesser species diversity when compared with the warm lowland areas. However, it is evident in many studies that species richness increases with altitude and will peak at a certain point which is at mid-elevation. After the optimum, diversity will decrease as plant communities have to undergo harsh ecological factors such as temperature, wind, snow, sun radiation and atmospheric pressure.

As shown in many academic journals and further surveyed by the students of University of Tasmania, species richness does increase with the altitude elevation on Mount Field. There were lesser species diversity at low regions. Species diversity increased and reached optimum at subalpine communities which is 1000m in the upper region and eventually decreased altitudes beyond 1100m.

In conclusion, the peak of species diversity was at 1000m on Mount field is due to the probability that an overlap between lowland and highland plants exist. Hence, the ecological factors at the peak could be at adequate levels enabling both lowland and highland plants to coexist.