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Change in plant diversity with elevating altitude at Mt Field
Change in plant diversity with increasing altitude in Mt Field was found closely accordance with the Mid-elevational peak pattern (Figure 1.).

Theory in species diversity changes with increasing altitude
It was established that vegetation richness decreases with elevating altitude long time ago (Bruun, et al., 2006; McCain & Grytnes, 2010). People used to think the warmer the climate, the greater must be the number of growing plants (Lomolino, 2001). Alpine habitat is far from ideal condition for plants to live. Low temperature directly results in plants low growth rate and regenerate capacity. Increasing radiation exposure is also found harmful to plants. In Tasmania, alpine vegetation often live on dolerite soils, which are shallow with frequent rock fragments. Water supply is not constant which usually results in inadequate water availability. Furthermore, due to lack of long-standing snow protection, plants are more prone to frost and wind damage (Reid, et al., 1999). The interactions of these environmental factors prohibit plant species richness in high altitude habitat.

Alpine vegetation is found to have less diverted morphological and physiological characters than those live at lower altitude (McCain & Grytnes, 2010; Reid, et al., 1999 ). Because highland species have developed convergent characters in order to survive in the extreme habitat. Lomolino (2001) has also pointed out alpine communities should have relatively high extinction rates and low immigration rates. Therefore, species richness should be lower than those of lowland communities.

However, after further studies, McCain and Grytnes (2010) have found there are 4 types of patterns in species richness along increasing altitude: decreasing, low plateau, low plateau with a mid-elevational peak and mid-elevational peak. Most plants displayed a mid-elevational peaks with increasing altitude in their studies ( Bruun, et al., 2006; Lee et al., 2013; McCain & Grytnes, 2010; Vetaas & Grytnes, 2002). Mid-elevational peak means plants has a unimodal (hump-shaped) peak in diversity at intermediate elevations.

Findings at Mt Field
Based on our group collection of plants and observation of vegetation at four different altitudinal sites, I have found species diversity is quite poor at lowland dry sclerophyll forest but increased with elevating altitude and reaches a peak at 1000m above sea-level around lake Dobson but then decreased significantly at altitude of 1300m near Newdegate Pass.

Site 1. Altitude: 185m. Dry sclerophyll forest with large areas of bare ground and litter coverage. In our 10m x 10m quadrate, vegetation is dominated by Eucalyptus amygdalina and Eucalyptus obliqua with emergent understory of Daviesia latifolia and Exocarpus cupressiformis and scattered shrubs of Epacris impressa and Pultenaea juniperina. The plant variety is quite limited in this area.

Site 2. Altitude:680m. Mixed forest with little bare ground and litter coverage. In our 10m x10m quadrate, vegetation is dominated by Eucalyptus delegatensis and Atherosperma moschatum. Understory is mainly composed of Anopterus glandulosus and Nothofagus cunninghamii. Variety of ferns, Ericaceae, Fabaceae and Epacridaceae families can be found in shrubs. Obviously, the plant diversity has increased here compared to Site 1.

Site 3. Altitude: 1000m. Subalpine woodland around lake Dobson, vegetation is dominated by Eucalyptus coccifera and Eucalyptus subcrenulata. Various species of Asteraceae, Ericaceae, Mrytaceae, Proteaceae, Rutaceae and much more are crowded together here. This is where plants richness peaked.

Site 4. Altitude: 1280m. Near Newdegate Pass, cushion plant community dominates vegetation. 4 major cushion plant species were identified: Abrotanella forsteroides, "Donatia novae-zelandiae", "Dracophyllum minimum" and "Pterygopappus lawrencii". Here the variety of plants has decreased significantly compared to Site 3.

Possible explanations of the Mid-elevational peak pattern
One of theories to explain the cause of a Mid-elevational peak in plants richness is called Mid-domain effect (MDE). MDE predicts a uni-modal diversity curve with maximum diversity at the mid-height of the mountain simply because lowland communities overlap with highland species towards the intermediate altitudinal region ( McCain & Grytnes, 2010). Lee et al. (2013) have also found MDE supports a hump-shaped plants richness distribution in the mountain ecosystem. Because optimal climatic conditions exist at intermediate altitudes with moderate temperature and radiation as well as sufficient water which significantly promotes plants growth and development. Further more, Bruun, et al. (2006) have found in their study that there is a positive impact of relaxing competition of nutrients and water resources at mid-height altitude. The favorable climate condition and higher living resources may allow the co-existence of more species, which leads to higher plant species richness at intermediate region.

Another theory to explain the change pattern in plants diversity was stated by Vetaas and Grytnes (2002), that a mid-elevation peak in species richness may result from hard boundaries. Hard boundaries are defined as a plant’s maximum degree of physiological resistance to unfavorable living conditions. With gradual increasing altitude, plants start developing diverse strategies and features to adapt to changing climate. However, once the altitude reaches a certain height with a challenging habitat exceeds the physiological tolerances of a species, it places constrains on the plant’s development directly, which usually results in slow growth and low dispersal rates.

Limitations
As shown in Figure 1, the change in plant diversity at Mt Field does not distribute a typical hump-shaped pattern. The peak in richness was found at 1000m instead of 680m which is the mid height of the mountain. This is probably due to limited plants collection sites and sizes of our group. Also, other limiting factors contributed to less species variety at lower altitude areas were not considered such as low water availability at dry sclerophyll forest and low sun light penetration at the mixed rainforest. Last but not least, in order to verify the Mid-elevational peak pattern in plants diversity at Mt Field, further comprehensive collections and studies are needed.