DIFICULTADES, NIVELES DE LECTURA Y COMPRENSIÓN

The Brandy Creek flora is moderately diverse with 18 leaf morphotypes and 36 pollen and spore taxa recorded at the locality. Many have affinity with extant families and genera found in rainforests of northeastern Queensland including the Lauraceae genera,Cryptocarya, Endiandra and Litsea; and Proteaceae, Sapindaceae,

Arcauariaceae and Podocarpaceae,Restionaceae, Dicksoniaceae and Cyatheaceae; Leaf litter sampling of modern forests shows that depositional sites close to or within streams can give results of high diversity that are, reflective of the local plant

population (Greenwood 1992 and Greenwood and Christophel 2005). The fine

siltstone and sandstone found at Brandy Creek, plus the presence of partial and entire leaves suggest that the Brandy Creek depositional environment was likely to have been a small lake or oxbow with the flora reflective of the local area (Greenwood, 1991).

The results document a peak in macrofossil diversity near the middle of the stratigraphic sequence. Lauraceae expands its dominance in both abundance and diversity. There is also an increase in abundance of Cunonicace/Elaeocarpaceae, which maintains its presence throughout the outcrop, whilst many Lauraceae genera

disappear and then reappear at different times.

Selective sampling of partial or entire leaves at Brandy Creek may have resulted in a bias towards families whose leaf material is more robust or of families more prominent in the landscape, increasing the chances of partial or entire leaves being fossilised. The selective sampling may have unintentionally limited diversity of the Brandy Creek macroflora. Many of the families that are recorded at the other Eocene localities are recorded as palynomorphs at Brandy Creek (figure 5.6).

The cluster analysis shows adjacent strata at the locality are not usually more similar to each other than to other strata. This is interpreted as the outcrop representing a single community type that did not experience significant shifts in composition for the time interval represented by the outcrop. Nevertheless relative

abundances varied.

The palynomorph results show that there is no movement in species

composition over time. Cyatheacidities spp, maintains it dominance throughout the outcrop and Nothofagus type pollen counts remain fairly stable through the section. Palynomorphs have been shown to reflect both local flora and regional vegetation depending upon depositional type. For example, pollen sequences from soil profiles tend to record population changes within a radius of less than 50 m (Odgaard 1999), however if the depositional environment is a medium to large lake then this can represent an area up to 5km from the depositional site (Odgaard 1999).

The Brandy Creek pollen and spore results show that Cyatheacidities spp. was present on the landscape, which can be said with some certainty. However, the abundance of Cyatheacidities spp. Spores could have more to do with the large volumes produced by a single frond, and not indicative of plant abundance on the landscape (Page, 1979). Other families may be under -representation in the palyoflora.

Pollen with affinity to Proteaceae was documented at Brandy Creek. It is likely that the Proteaceae pollen reflects local rather than regional presence, particularly as it occurs in the macrofossil samples from nearby Hotham Heights (Carpenter et al. 2004). Analysis of Proteaceae modern pollen rain has shown that Proteaceae can often be under represented in the pollen counts. Martin (1978) records 4% Proteaceae pollen from a modern study site having 13 Proteaceous species, and Hassell (2000) had similar results with less than 3% Proteaceae making up the pollen count. These low counts do not reflect the dominance of Proteaceae on the landscape today.

Under-representation in the pollen count can be attributed to its structural position in the plant community. For example, Proteaceae is typically an understory plant leading to low dispersal of pollen. Proteaceae pollen is large and heavy making transport difficult. Furthermore the family are also pollinated by insects, birds or other animals and do not produce large amounts of pollen which contributes to under- representation in the palynological count (Itzstein – Davey 2003).

Rare taxa are important elements in the vegetation and should be considered part of any plant community analysis. In most cases the occurrence of rare taxa in the pollen count is a result of the pollination mechanism and pollen productivity rather than rarity in the community. Some taxa produce few pollen grains to be carried by animal vectors rather that wind and water. Entomophilous taxa with low pollen productivity are more likely to reflect local vegetation (Weng et al. 2006; Metlsov et al. 2011). Large numbers of rare taxa among a few dominant taxa may signal a recent change in floristic composition, with the conditions favouring the dominant and common genera. These changes may include rainfall, temperature or competition for ground space to allow the expansion of the population.

The absence of Nothofagus from the macrofossil record of mainland Australia until the early Miocene indicates that the high proportion of Nothofagus pollen (Nothofagidites) at the Brandy Creek flora is more likely to reflect regional rather than local vegetation (Paull and Hill 1993; Christophel and Greenwood1989). Pollen from regional sources can dominate a pollen sum without contributing substantially to the local vegetation (Walker and Sun 2000; Rowe 2012). Nothofagus macrofossil have been recorded from Tasmania during the Eocene and it is likely that the presence of Nothofagus pollen in fossil localities from southeastern Australia, including Brandy Creek, is a result of long distance dispersal (Hill 1991, 1994; Hill et al. 1999 and Jordan and Hill 1999).