Australia: The Land Where Time Began
Nothofagus Southern beech, Antarctic beech
Nothofagus is considered by some to be the key genus in the evolution and biogeography of plants of the Southern Hemisphere (van Steenis, 1971, 1972).
This is based on 4 characteristics - It is confined strictly to the the Southern Hemisphere, though its closest relatives are in the Northern Hemisphere. This is believed to have been the case since the genus first evolved. Antarctica is the only landmass, of those that were formerly part of Gondwana, on which it does not occur, though there is an extensive fossil record. The present distribution of Nothofagus takes in east and southeast Australasia, Australia, including Tasmania, New Zealand, New Guinea and New Caledonia. It has never been found as an autogenous fossil in India or Africa. The dispersal of the fruit is very limited (Rodway, 1914). It does not survive long periods immersed in sea water, not being distributed in the ocean as is the coconut (Preest, 1963). There is consensus that long-distance fruit dispersal probably didn't occur to any great extent, though evidence has been presented that at least limited long-distance dispersal has occurred (McPhail et al., in Hill, 2007). There is a well-known, extensive fossil record.
The distribution of Nothofagus in the past, and its origins and migration routes, were formerly dependant on present distribution and interrelationships of Nothofagus. Many centres of origin have been proposed for the genus (Cranwell, 1963; Darlington, 1965; van Steenis, 1971,1972; Raven & Axlerod, 1972; Hanks and Fairbrothers, 1976; Schuster, 1976). A revision of the pollen record (Dettmann et al, 1990), as well as descriptions and reviews of the macrofossil record (Romero & Dibbern, 1985; Tanai, 1986; Hill, 1991) have led to a much more detailed knowledge of the distribution and evolution of the genus in earlier times, though there is not complete consensus on all aspects of the genus.
Nothofagus is usually assigned the the Fagaceae family, though there is evidence supporting its allocation to a monogeneric family, Nothofagaceae (Nixon, 1989). In spite of some contradictory evidence, summarised by Hill (1993), it has been suggested that Nothofagus is probably closer to the Betulaceae than to the Fagaceae, (Nixon, 1989).
3 infrageneric classifications have been suggested for Nothofagus (van Steenis, 1953; Philipson & Philipson, 1988; Hill & read, 1991). The pollen of Nothofagus displays 3 different distinct pollen morphologies among the extinct and extant species, which caused difficulty for the earlier classifications, as only 1 of the 3 correlated with formal infrageneric groupings. The deciduous or evergreen habit created a dichotomy that was the basis for the primary infrageneric division (van Steenis, 1953). In another of the classifications, 4 variation patterns are recognised (Philipson & Philipson, 1979, 1988). Combined with a number of other characteristics of the leaves and cupule morphology, these 4 variations of pattern led to the hypothesis that the evergreen habit is polyphyletic (Hill & Read, 1991). The most recent classification, that of Hill & Read (1991), correlates closely with the established and revised groupings (Dettmann et al., 1990).
The Fagaceae and Betulaceae are considered to be the most closely related families to Nothofagus, hence the migration routes and origin of Nothofagus must be compatible with the migration routes of those 2 families of plants. The possibility of plant interchange between Southeast Asia and Australia has been studied for the period covering the Late Cretaceous and the early Tertiary (Burger, 1981, 1990; Truswell et al., 1987). Their studies concluded that there may have been a fragmentary path between the 2 continental masses in the form of a complex of continental fragments since the Early Cretaceous, but especially in the Late Cretaceous to the early Tertiary. One study (Truswell et al., 1987), found evidence in the fossil pollen record of possible 2-way exchange, but their results exclude Nothofagus from these instances of exchange, as its distinctive pollen has not been found in the appropriate sediments. Macrofossils, leaves and wood, that are believed to be species of Fagaceae, that are not Nothofacus, as well as abundant Nothofagus fossils, have been found in sediments from the Southern Hemisphere dating to Late Cretaceous-early Tertiary (Romero, 1986; Romero & Dibbern, 1985; Birkenmajer & Zastawniak, 1989a). A leaf has been found in the Winton Formation of Queensland that is believed to possibly be fagaceous (Hill, 2005). Leaves have been found in New Zealand that show morphological similarity to those of the Betulaceae, in deposits dating to the Late Cretaceous (Pole, 1992). This suggests there may have been a fagalean complex in Gondwana in the Cretaceous, during, and possibly preceding, the early history of Nothofagus (Hill, 2007).
The generalised pollen type associated with the fagalean complex is believed to have possibly been present in Southeast Asian and Australian regions during the Cretaceous, possibly giving rise to the Fagaceae and Betulaceae in the more northern parts of the region, an area where the diverse fossil pollen of Betulaceae occurs at an early period (Crane, 1989). It has been suggested that part of this complex may have migrated to high southern latitudes by a route suggested by Burger (1981) and Truswell et al., (1987), where it evolved into Nothofagus. This would be compatible with the presence of 'betulaceous-fagaceous-like' microfossils in the Southern Hemisphere during the Late Cretaceous-early Tertiary, and would explain the lack of previous geographical links between the Nothofagus pollen and that of closely related taxa (Hill, 2005). It is also compatible with the hypothesis that Nothofagus arose at high latitudes in the Southern Hemisphere (Dettmann et al., 1990). The extensive pollen record indicates that Nothofagus originated in high southern latitudes, within the Weddellian Province, some time in the early Campanian of the Late Cretaceous (Dettmann et al., 1990). In the northern Southeast Asian-Australian region the pollen record is sparse during the Cretaceous, allowing some to suggest the lack of pollen may mask a centre of origin for Nothofagus in the region. Whether or not this is case requires the discovery of a more complete pollen record in the region (Hill, 2005).
The Weddellian Zoogeographic Province has been extended to a 'biogeographical province' (Case, 1988, 1989) and an hypothesis has been put forward that, during the Late Cretaceous and Tertiary, is was a diversification centre of the evolving biota, that included Nothofagus. The region involved is in the form of a band from southern South America, the Antarctic Peninsula, West Antarctica to Tasmania and southeast Australia and New Zealand. According to Case, this was a region in which many species arose and survived. The main reason for this may have been the low extinction rates that are characteristic of environments at high latitudes (Hickey et al., 1983; Jablonski et al., 1983). This hypothesis is consistent with the pollen record for Nothofagus in this region.
Pollen is the most complete record of Nothofagus. 2 of the 8 known pollen types associated with extinct and extant Nothofagus species are regarded as ancestral, being found first in the fossil record (Dettmann et al., 1990). A single fossil species, Nothofagus senectus, represented by ancestral type 'a' pollen, has been found in sediments dated to the early Campanian, over wide areas of southern Gondwana. A fossil species from southeast Australia, Nothofagus endurus, and N. kaitangensis, from New Zealand, have both been assigned to ancestral type 'b', both first occurring in the mid Campanian. It is believed ancestral type 'a' pollen is most closely related to the Nothofagus subgenera Fuscospora, and the ancestral type 'b' pollen with the Nothofagus subgenera Nothofagus.
Events of rapid diversification, that were spatially and temporarily distinctive, occurred after the first appearance of Nothofagus. The first known appearance of pollen types of extant subgenera has been found in deposits on the Antarctic Peninsula dating from the Campanian, and from deposits of Maastrichtian age in southern South America, a centre of diversification of Nothofagus in the Late Cretaceous (Dettmann et al. 1990). A migrational lag, and by routes across western Antarctica, is implied by occurrences of Nothofagus in southern Australia and New Zealand that are significantly younger, the subgenera Nothofagus in the Palaeocene, subgenus` Lophozonia from the Eocene, subgenus Brassospora, from the Eocene of new Zealand and the late Maastrichtian of Australia (Dettmann et al., 1990). The origin of the subgenus Brassospora in western Antarctica-southern South America region is indicated by the earliest appearance of B. spp in this region. Evidence against this possibility is the low diversity of this pollen type in this region, as well as its complete lack after the Oligocene (Dettmann et al., 1990). During the Eocene-Oligocene, a time of rapid diversification of subgenus Brassospora, it is found in the Australian-New Zealand region (Dettmann et al., 1990), pollen assemblages being dominated by its pollen type, especially in southeastern Australia at this time (Martin, 1978; McPhail et al., in Hill, 2005; Kershaw et al., in Hill, 2005). In southern Australia and New Zealand, most species with subgenus Brassospora type pollen went extinct during the late Tertiary, most likely in response to the changing climate, with the exception of Tasmania, where some species survived until the Pleistocene (Hill & McPhail, 1994).
The most common macrofossils of Nothofagus are leaves, of evergreen and deciduous forms (Romero & Dibbern, 1985; Tanai, 1986; Birkenmajer & Zastawniak, 1989a,b; Hill, 1991). Good organic preservation of Nothofagus leaves is not common in areas other than Tasmania, and to some extent in the southeastern part of the mainland. Based on only gross morphology and pattern of venation of Nothofagus leaves, it is difficult to determine infrageneric affinities (Hill, 1991). Macrofossil don't often include reproductive structures, Tasmania is the only part of Australia from which woody cupules, occasionally containing fruits, have been found (Hill, 1987, 1991), apart from a single site in southeast of the mainland (Christophel, 1985).
Most of the good macrofossils of Nothofagus are found in Tasmanian deposits, sediments from the Oligocene containing all 4 subgenera, and are found in small sedimentary units associated with restricted catchments, indicating they probably all coexisted (Hill, 1991). Of the 4 extant subgenera, 2, Lophozonia and Fuscospora, occur in Tasmania, with Brassospora restricted to New Guinea-New Caledonia and Nothofagus to South America (Hill, 1991).
The most significant Tasmanian macrofossils, biogeographically, are leaves of N. cethanica (Hill, 1984), the leaves, cupules and fruit of Nothofagus (Hill, 1987, 1991), leaves and cupules of multiple species of Nothofagus (Hill, 1987, 1991). Nothofagus cethanica is very simular to the extant New Zealand endemic N. fusa, but differs from species of Nothofagus on any other land mass. There was little evidence in the pollen record of the subgenus Nothofagus from places other than near its present range before the Tasmanian discoveries. Macrofossils of Brassosporus, the subgenus producing the most commonly found pollen in the deposits, provide the only known substantial evidence of the gross morphology of this subgenus.
Macrofossils of Nothofagus from the Tasmanian Oligocene have also brought to light a number of problems with the palaeoecological knowledge of Nothofagus from that time. Among these problems are the extinction of N. cethanica in Tasmania, while N. fusca survived at similar latitudes in New Zealand. The extinction of the subgenus Nothofagus in Tasmania but its survival in similar, or possibly more southerly, latitudes in South America. The presence of all 4 subgenera in very close proximity, possibly within the same vegetation. There appear to have been bizarre mixtures of subgenera, such as Brassospora, that presently grows in tropical montane vegetation, with N. gunnii, that is a deciduous shrub or small tree presently growing in alpine or subalpine locations, that has been found at Cethana (Hill, 1984; Carpenter, 1991). The evergreen members of the subgenus Lophozonia appear to have had the ability to evolve substantially, at least in leaf form, while being found in the region until the present, while most other species went extinct. N. gunnii, a winter deciduous species, has survived to the present, while retaining unchanged its gross leaf morphology, while many fossil evergreen species of the subgenus Nothofagus, and 2 other subgenera, have not survived, the members of the 4th subgenus surviving, but with substantially changed leaf morphology.
In the Nothofagus record, the big enigma is the abundance of the subgenus Brassospora-type pollen in the mid-Tertiary of southern Australian and New Zealand, but with a paucity of macrofossils. A small sedimentary unit in southwestern Tasmania has produced 2 distinct types of cupule and leaf of the subgenus Bassospora (Hill, 1987, 1991). In north-central Tasmania, possible leaves and a single cupule, the only conclusive nonpollen record of the subgenus, were found in a more diverse fossil suite, have been found (Carpenter, 1991). Prevailing palaeoclimate analysis, and experiments on the physiological tolerances of extant species, has resulted from the discovery of their co-occurrence with all other subgenera of Nothofagus (Read & Hill, 1989; Read & Hope, 1989; Read, 1990; Read et al., 1990). As a result of the findings of these studies, an hypothesis has been proposed that there were several features of the Oligocene Tasmanian climate that have no modern analogue (Hill, 1990a; Read et al., 1990). These features of the Tasmanian climate during the Oligocene, include mild temperatures with severely restricted extremes, resulting in a relatively frost-free environment. The dense, diverse epiphytic populations of fungi on many leaves indicate high humidity (Hill, 1990a). It has been suggested that this climate probably led to compression of ecological zonation, similar to that seen in extant rainforests of the Ok Tedi headwaters in New Guinea (Hyndman & Menzies, 1990). It is believed that the Brassospora subgenus was probably a component of the canopy trees in Tasmanian rainforests during the Oligocene, allowing juvenile trees of this subgenus to mature in an environment where the adult trees protected them from any climatic extremes. The juvenile and adult trees of other subgenera were exposed to prevailing climatic extremes, as they grew in locations such as ridge tops and the margins of lakes and rivers, developing tolerance of variations in the climate that occurred from time to time. Later in the Tertiary, the climate deteriorated, with temperature extremes widening and rainfall decreasing, and the climate became markedly seasonal. It appears likely that trees of the Brassospora subgenus populations probably gradually decreased as they had not evolved the necessary tolerance to withstand the vagaries of a deteriorating climate, their place in the canopy being taken by trees of other subgenera that had developed the tolerance. As the climate continued to deteriorate, some of these more tolerant species also went extinct, though some species, especially of the subgenus Lophozonia, evolved to tolerate the changing conditions (Hill, 1991).
An alternative hypothesis has been proposed to account for the extinction of the Brassospora subgenus from southeastern Australia. According to the alternative hypothesis, the extinction of Brassospora subgenus was a result of its failure to keep pace with the increasingly pronounced climatic fluctuations that occurred in the region from the Middle Miocene (Read et al., 1990). This was originally proposed as the cause of the extinction of the subgenus from New Zealand (Wardle, 1968). These hypotheses are consistent with earlier physiological research involving extant species that occur across the latitudinal range.
It has also been suggested that Nothofagus spp. were favoured by the high frequency of wide-scale disturbance in the Oligocene (Hill, 1987), as many of them live in disturbance-based environments (e.g., Veblen & Ashton, 1978; Veblen et al., 1981; Read et al., 1990). The extinction of these species have been associated with the lower frequency of disturbance in later times. It has also been suggested the competitive ability of the component taxa in the Tasmanian rainforests during the Oligocene may have been affected by the CO2 atmospheric level changes, but data is not available to determine if this was a factor in the decline.
Most of the fossil record of Nothofagus comes from the Cenozoic, resulting in the microfossil record providing little evidence of the evolution of the genus because it is known from the pollen record (e.g.,Dettmann et al., 1990) that most of the evolution of the genus had occurred by the end of the Cretaceous. This is supported by the finding of macrofossils in the early Tertiary deposits, those found often being morphologically similar to extant species. The leaves of the earliest known species of Brassospora, from the Oligocene, had serrated margins and the fruit were enclosed in cupule valves (Hill, 1991), though a cupule has been found in which the valves are much reduced (R.S.Hill). Leaves with serrated margins and large cupule valves may be the ancestral condition to that seen in species of the same subgenus that are extant, that have leaves with finely serrated margins or which have no serrations, and cupules that range from robust and fully enclosing the fruit, to those in which the valves are absent. These fossils are from a time much later than the origins of the subgenus, and it has been suggested that they may be peculiar to the Tasmanian region, being derived forms.
Widespread evidence, including conclusive fossil evidence, indicates that in southeastern Australia, with Tasmania, and probably including New Zealand, evergreen species of the subgenus Lophozonia had leaves with a significantly reduced surface area, that is believed to have been a response to the climatic changes of the Cenozoic. These micrphyllous species dominate the microthermal rainforests that are characteristic of the regions (Hill, 1991). Nothofagus moorei, with very similar leaves to those of the widespread broad-leaved ancestral species, from the early Tertiary, in Australia and possibly New Zealand, is found in isolated high altitude microthermal rainforests in mid-latitudes on the eastern coast of Australia. It has been suggested it may have dispersed across the Tasman Sea to New Zealand from Australia in the Early Tertiary. N. gunnii, endemic in high altitude areas of Tasmania, has retained its general leaf morphology since at least the Early Oligocene (Hill, 1991). It has been suggested that this lack of change in leaf morphology may be the result of the leaves being shed before being exposed to the Tasmanian winters that were increasing in severity as the climate changed (Hill, 2005). It is the only deciduous extant species outside South America.
Nothofagus is a significant plant in the fossil record because it is a climate indicator. Nothofagus pollen is of several types, each of which are produced by a number of species, both living and extinct. In tropical and warm sub-tropical and perhumid conditions with no seasonal aridity, brassii occurs in species requiring these conditions.
Species with fusca and menziesii pollen type are produced in cool temperate species which can cope with little dryness. The earliest pollen to be found in the fossil record was Nothofagadites senectus pollen type. It was originally associated with brassii type. It is now thought to be an ancestral type, differing from any other pollen group.
No species of Nothofagus can survive long dry spells. As Australia moved northward and dried out, Nothofagus became confined to refuges where its preferred conditions still prevail or migrated into new areas or into the mountains of New Guinea when they were arose.
Seed production of Nothofagus cunninghamii varies from year to year (Adam, 1994), germination rates being much higher in years of heavy seed production than in years of low production (Hickey et al., 1983). In an old field studied by Read & Hill (1983), they found that following the pioneer shrub stage, N. cunninghamii regenerated only at the boundary between the field and undisturbed forest. The poor dispersal of the species is believed to have been the main reason for the low invasion rate of the field, as well as the requirement of competition-free establishment sites. It was suggested that as the few N. cunninghamii trees that successfully invaded the field matured to the stage at which seed was produced the increased potential for seeding would lead to increasingly more rapid colonisation (Read & Hill, 1983). Studies have been undertaken of cool temperate rainforests in the absence of disturbance, in N. cunninghamii forests, as well as a smaller number of studies in forests of N. moorei (Howard, 1981; Read, 1988; Read & Hill, 1985a,b). A frequent component of N. cunninghamii forests is Atherosperma moschatum. It has been suggested that A. moschatum is more shade tolerant then N. cunninghamii, as it can regenerate beneath a closed canopy (Gilbert, 1959). The stands he described in the Florentine Valley, Tasmania, displayed little evidence of regeneration, suggesting that A. moschatum would probably replace N. cunninghamii progressively if there was little or no disturbance. Since his study, the area was cleared, so his conclusions cannot be tested for this area (Read & Hill, 1985b). Accepting that Atherosperma had greater shade tolerance than Nothofagus, the succession model (Noble & Slatyer, 1980, 1981) predicted that Atherosperma would dominate Tasmanian rainforests in the absence of disturbance. Most stands comprised a mixture of N. cunninghamii and A. moschatum, indicating that some level of disturbance must be occurring to explain the persistence of Nothofagus (Noble & Slatyer, 1979). N. cunninghamii forests have been described by other authors as self-regenerating by both vegetative regrowth and seeding of gaps in the canopy (Howard, 1981; Read & Hill, 1985a). Compared to the growth of species in tropical and subtropical rainforests, the persistence of supposedly shade-intolerant Nothofagus without disturbance is considered to be anomalous (Adam, 1994).
The shade tolerance of Nothofagus was confirmed to be less than that of Atherosperma (Read, 1985). In N. cunninghamii, the highest photosynthetic rates occurred under full sunlight, with N. cunninghamii displaying relatively better growth in intermediate shade than other species examined by Read (1985). Both species show predominantly clumping in gaps in the canopy (Read, 1985; Read & Hill, 1985a; Ellis, 1985).
The requirement of gaps for the regeneration by seed of N. cunninghamii and the superior Atherosperma seedling shade growth suggest the model proposed, according to which, in the absence of disturbance, A. moschatum would replace N. cunninghamii in the long term (Noble & Slatyer, 1979, 1980, 1981) is considered to be plausible (Adam, 1994). Field observations have found little evidence of this process occurring. It was suggested (Read, 1985) that low seed viability of A. moschatum could explain the failure of A. moschatum to replace N. cunninghamii (Hickey, 1983), poor seedling establishment was also proposed as a reason (Read & Hill, 1985a). Regeneration of A. moschatum is mostly by vegetative growth of sprouts from the stem bases, permitting its persistence, while limiting its spread throughout the forest.
Seedlings of N. moorei show similar photosynthetic characteristics to those of N. cunninghamii (Read & Hill, 1985b), but regeneration characteristics of the 2 species have been suggested to differ somewhat (Howard, 1981; read & Hill, 1985b).
Apart from Mount Nothofagus, on the New South Wales-Queensland border, the most northwestern site of its distribution, seedling establishment is rare below N. moorei (Howard, 1981; Adam, 1987b). Continuous regeneration by vegetative regrowth is indicated at some sites by size-class distribution of stems (Read & Hill, 1985a). It has been suggested that N. moorei would be replaced by the understorey species where there is a well-developed undercanopy of species such as Ceratopetalum apetalum, Doryphora sassafras, Orites excelsa, and at Mount Banda Banda, Sloanea woollsii, as it will not regenerate (Read & Hill, 1985a). It has been shown that seedlings of C. apetalum and D. sassafras are shade tolerant, so would be capable of establishing beneath canopies of N. Moorei.
Based on these data, it has been suggested that vegetative growth will retain relatively pure strands of N. moorei, though N. moorei would be replaced by other species if the area is invaded by them. N. moorei seedlings grow vigorously in disturbed situations, such as the edges of tracks, which makes it is difficult to explain the apparent failure of to establish in gaps (Read & Hill, 1985a). Invasion of eucalypt woodland at high altitude has been observed of the Barrington Tops (Turner, 1976).
In some stands of N. moorei, based on size class and species composition, the evidence has been interpreted as indicating that Nothofagus is being replaced. If this is the case, it needs to be determined if this situation is of recent origin, such as a response to changing climate, as has been suggested (Turner, 1976). It has also been suggested that it may be part of a recurrent cycle, major disturbance promoting the regeneration of Nothofagus (Adam, 1994).
Nothofagus outside Australia
In both Chile and New Zealand, Nothofagus spp. are an important component of temperate rainforests. In New Zealand, they are not often found competing with other species on fertile lowland soils, though they are common in disturbed sites on infertile soils at high altitude (Wardle, 1983). In Chile, it is the dominant tree found at high altitude and high latitude, where the more shade-tolerant species are absent, regenerating continuously (Veblen et al., 1981), as occurs with N. cunninghamii in Australia. Nothofagus is gradually replaced by more shad-tolerant species on mid-latitude lowlands. The disturbances occurring in Chile, as a result of the region being tectonically active, events such as landslides opening sites for regeneration of shade-intolerant Nothofagus. These infrequent catastrophic disturbances are essential for the long-term survival of Nothofagus in lowland and mid-altitude sites (Veblen & Ashton, 1978; Veblen et al., 1981). Nothofagus does not regenerate by seedling in lowland forests where there is no major disturbances. This also applies to relatively large gaps in the canopy formed by the falling of very large old trees (Veblen et al., 1980; Veblen et al., 1981). Studies have been undertaken in which the photosynthetic characteristics of Nothofagus species were compared. The results suggested that there was little difference between Nothofagus on the 2 continents (Read & HIll, 1985b), though in Tasmania, N. cunninghamii had no problems regenerating in such gaps. The differences in the regeneration in gaps are thought to be related to properties of the associated flora. Atherosperma, the most shade-tolerant of Tasmanian trees, rarely replaces Nothofagus, as it regenerates poorly. Under most stands of Nothofagus in Australia, the understorey is not well developed. In this situation, when a gap in the canopy appears, Nothofagus seedlings are less likely to have competition for the open space than they would if there was a better developed understorey (Read et al., 1990a). The situation is different in Chile, there the understorey is richer, many seedlings of shade-tolerant species are all waiting for a gap to form, so compete vigorously with the Nothofagus seedlings, the worst possible situation for seedlings of Nothofagus. At higher elevations, it is the bamboos, Chusquea spp., that compete for the open space in the canopy (Veblen et al., 1981). Nothofagushas has the same problems in New Guinea, where there is also a rich understorey, as well as lower canopy flora (Read et al, 1990a).
Nothofagus regenerate following large-scale disturbance in Chile. In Australia, fire is the most likely natural cause of disturbance in temperate rainforests. N. cunninghamii can be maintained after fire, but only if the fire frequency is low enough and seeds are available for regeneration after the fire (Gilbert, 1959). Available evidence indicates that fire has caused the regression of rainforests (Jackson, 1968, 1978).
An unusual feature of Australian rainforests is that a canopy species with pioneer characteristics can be maintained, even in the absence of major disturbance. Establishment of shade-intolerant species in small gaps is permitted by the absence of understorey and climax species. Persistence of the canopy species is also assisted by their a propensity for coppicing. Where true climax species establish beneath Nothofagus, it can be expected that it will replace the Nothofagus to form a canopy (Read & Hill, 1985a).
Relative shade intolerance appears to be a general feature of the genus Nothofagus, though the species differ from each other in their photosynthetic physiology. Disturbance, in some form, is apparently a requirement for successful regeneration of all members the genus. If the fossil record of Nothofagus in Australia is interpreted as the genus being a component of a mixed forest, as opposed to islands of specialised habitat, that occurred within an otherwise widespread diverse forest, does its persistence indicate regular disturbance on a large scale (Hill, 1987). The nature of any large-scale disturbances that would be required to allow the regeneration of Nothofagus throughout the Tertiary is no known (Adam, 1994). In Tasmanian rainforests, the rainforest conifer, Athrotaxis selaginoides is also a pioneer species, depending on open spaces for regeneration in evergreen forests. In forests where Nothofagus gunnii, a deciduous species, is a dominant, with greater light penetration to the forest floor, A. selaginoides regenerates continuously, even in the absence of disturbance (Cullen, 1987). A similar situation is found in other Tasmanian rainforest conifers (Read, 1988).
The distribution of the cool temperate Nothofagus moorei rainforests is discontinuous, mostly occurring at an altitude of above 800 m, though occasionally, in some places it is found at 500 m. Apart from at the highest altitudes, at which the stands are mostly pure, such as at Barrington Tops in central New South Wales, it is often associated with coachwood, Sassafras, small-leaved laurel (Cryptocarya foveolata), and prickly ash (Orites excelsa) as well as tree ferns, especially the soft tree fern. Tree ferns are found in all the cooler rainforests types. An epiphytic orchid found in these beech forests is the beech orchid (Dendrobium falcorostrum), which grows on negrohead beech trees. The flowers of this orchid are white with purple markings and very fragrant, with up to 20 individual flowers on a single raceme.
Very large trees with gnarled moss-covered trunks dominate mature forests, with multiple trunks formed from suckers of various ages. There is a lack of seedlings on the forest floor beneath such forests, the floor being carpeted with a thick layer of golden and rust-coloured leaves. The appearance of the huge trunks being illuminated by rays of sunlight is often described as having the appearance of a cathedral. A similar multi-stemmed habit is found in plumwood.
At about 900 m, on Barrington Tops, the rainforest dominated by Nothofagus merges with cool subtropical rainforest. Where the rainforest types merge there are many other tree species, such as prickly ash (Orites excelsa), crab apple , Shizomeria ovata, and rosewood, Dysoxylum fraserianum. One plant that stands out against the green background is a restricted shrub, the broad-leaved pepperbush, Tasmannia purpurescens, found only in the area of Barrington Tops area, in rainforest communities and, at higher altitude, within eucalypt forest. They have red and green leaves and clusters of purple berries.
In areas such as the upper Forbes River valley to the north, and to the west of Port Macquarie, along the New England Escarpment, at Mt Banda Banda, coachwood is commonly associated with Nothofagus. It also commonly occurs with Nothofagus to the west of Coffs Harbour, in the gullies of the Dorrigo Plateau. Subalpine woodland occurs adjacent to Nothofagus in the Barrington Tops on the Dorrigo Plateau. Snow grass, Poa spp, and snow gum, Eucalyptus pauciflora occur in these woodland areas.
Cool temperate rainforests differ from other types of rainforest in having a low diversity of fauna. In the fauna, few of the species are restricted to cool temperate rainforests in New South Wales. These forests produce very few fleshy fruit, so they are devoid of the fruit pigeons that are found in other types of rainforest. The edges of the rainforest usually have the densest, with more diverse plant communities, as a result of the increased sunlight, making these places the best places to observe birds. Among the birds are the rufous scrub-bird, Atrichornis rufescens, a secretive bird found in the undergrowth, it occurs in isolated populations at higher altitudes between Barrington Tops and Mt Mistake over the Queensland border. Other birds are White's thrush, Zoothera dauma, rose robin, Petroica rosea, pink robin, P. rodinogaster, olive whistler, Pachycephala oloivacea. The reptiles and amphibians are rather limited, loveridge's frog, Kyarmanus loveridge, K. kundagungan, hip pocket frog, Assa darlingtoni. This species is unique among Australian frogs in that the male carries the eggs and larvae in pouches on either side of their flanks.
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