The Nothofagus

Some 100 million years ago, the ancestors of Nothofagus first appeared on Gondwana. Today the  Nothofagus is common in South America, New Zealand, Antarctica, Australia, New Guinea and New Caledonia. The present distribution of the plant is evidence that these landmasses might once have been joined.

Nothofagus is commonly referred to as the southern beech and is a genus of 35 species of trees.  According to the recent data, the Nothofagacea has four subgenera; the Brassopora, the Nothofagus, Fuscospora and the Lophorzonia. Living specimen from those four subgenus are found in New Zealand; South America; New Guinea; New Caledonia.

Fourteen species of Nothofagus are currently recognised in the taxonomically distinct subsection Bipartitae, occurring in New Guinea from 700 – 3,150 m above sea level (asl), mostly above 1400 m asl., in areas of high rainfall and cool climates, except for the New Guinea low altitude occurrences which are normally cloud-bound (Read and Hope 1989).

All members of sub genera Brassospora are gregarious species, commonly dominating the canopy (Keast 1981; Read and Hope 1989). The large canopy tree can grow to 20-50 m high but rarely grows to 60 m and are flat topped. They have a cylindrical bole (up to 150 cm diameter which is straight for up to 25 m long). The tallest tend to occur at valley bottoms or stable slopes; mid altitude slopes canopy ~ 30-40 and comprise one or two species; however, at very high altitude or in environment that is under suboptimal conditions the tree tends to be stunted and shrubby.

Nothofagus is a monoecious trees, accommodating both the male and the female flowers on the same tree.  The male flowers appear earlier than the female and wind dispersed seed results in very poor and regeneration within a short distance of the tree. In addition due to the seeds being wind pollinated, there is a lot of hybridization and introgression, giving rise to seed capsules that are sterile; furthermore, a large proportion of the seed is destroyed by insect predation or fungal attack (Ash 1982).

Tropical Nothofagus are affected by low temperatures because, the tropical Nothofagus are not exposed to extreme temperatures like the Southern species, as a result are not able to photosynthesize in extreme temperatures. Therefore, the New Guinea showed a lower frost resistance than southern species (Read and Hope 1989; Read et al. 2005) which is related to the geographic and climatic range of these species.  This has implications for the climate change. This tree family will be affected as the world heats up further.

Furthermore, Ash (1988) observed dieback in Nothofagus stands on Mount Wilhelm. The dieback was not related to any drought period (Arentz 1988). A possible explanation reached by Ash (1988) and Arentz (1988) is that even aged must die from stress as a result of, nutrient deficiency or infection by a pathogen. Periods of heavy frost which are often associated with drought may provide an additional trigger for stand-level dieback of Nothofagus. However studies of die backs in Tasmania show that the die back is the result of a pathogen attack.   The tree has also been observed to regenerate from diebacks by lignotubers and epicormic stems that coppice after the die back (Arentz 1988).

Nothofagus is widespread in PNG within their attitudinal range. Due to the widespread nature of the tree there is currently no conservation effort. However, because of its slender and straight bole as well as the characteristic of this tree to grow in even-aged stands it is a good building tree. However, in PNG the tree is not exported in significant numbers because grows in inaccessible slopes in the interior.

The Nothofagus species is a remnant of vegetation which was once on the super continent Gondwana, therefore, it is a legacy from that period in the geological history of the earth.

References

  1. ARENTZ, F. (1988) Stand-level dieback etiology and its consequences in the forests of Papua New Guinea. GeoJournal, 17, 209-215.
  2. ASH, J. (1988) Nothofagus (Fagaceae) forest on Mt Giluwe, New Guinea. New Zealand Journal of Botany, 26, 245 – 256.
  3. READ, J. & HOPE, G. S. (1989) Foliar frost resistance of some evergreen tropical extra tropical Australian Nothofagus species. Australian Journal of Botany, 37, 361-373.
  4. READ, J., HOPE, G. S. & HILL, R. (2005) Phytogeography and climate analysis of Nothofagus subgenus Brassospora in New Guinea and New Caledonia. Australian Journal of Botany, 53, 297-312.
  5. READ, J., JAFFRE, T., MCCOY, S. & HOPE, G. S. (2006) Does soil determine the boundaries of monodorminant rainforest with adjacent mixed rain forest and maquis on ultramafic soils in New Caledonia? Journal of Biogeography, 33, 1055-1065.
  6. VAN VALKENBURG, J. L. C. H. & KETNER, P. (1994) Vegetation changes following human disturbance of mid-montane forest in the Wau area, Papua New Guinea. Journal of Tropical Ecology, 10, 41-54.
  7. HYNDMAN, D. C. & MENZIES, J. I. (1990) Rain Forests of the Ok Tedi Headwaters, New Guinea: An ecological analysis. Journal of Biogeography, 17, 241-273.
  8. KEAST, A. (1981) Ecological biogeography of Australia, Junk bv Publishers, The Hague, Boston,.
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