Araucariaceae

Araucariaceae have been reported from the Triassic about 200 Ma (Chapter 4). In fact, possible araucarian wood (Araucarioxylon) is thought to be related to that of Dadoxylon, a cordaitalean tree abundant during the Carboniferous period, 300 Ma. Today, Araucariaceae are a small family with only three genera and about 40 species (Appendix 1). Araucaria (19 species) is the most diversified genus and is disjunctly distributed throughout the warm southern temperate zone. However, araucarian fossils have been discovered widely in both the northern and southern hemispheres. Beautifully preserved fossil cones of Araucaria have been identified from as long ago as the Triassic and Jurassic periods (Miller 1977,1988;Stockey 1982). Although some Araucaria species today produce abundant resin, often associated with insect damage, Araucaria has not been studied from an ecological perspective. The resin has a complex composition, often admixed with gum. There is relatively little variability in the gum fraction of resin from different species of Araucaria (D. Anderson and Munro 1969); the terpenoid fraction, however, has received little study.

The taxonomy of Agathis remains confused, with about 20 species recognized (Whitmore 1980a, de Laubenfels 1989). The genus may have evolved from Araucaria in the late Jurassic (Miller 1977). It contains by far the most important resin-producing species of Araucariaceae, some of which produce copious quantities of resin (Thomas 1969, Whitmore 1980a). Agathis is the genus of conifers most nearly confined to the tropics; in fact, A. robusta in southern Queensland, Australia (Plate 8), and A. australis in northern New Zealand (Figures 2-2 and 2-3) are the only species of the genus that extend beyond the tropics into the subtropics. Within the tropics, Agathis occurs in a wide range of habitats, for example, those with dry seasons varying in length from one to a few months, lowlands on a diversity of soil types, and at elevations up to 2000-2500 m. Both the timber and resin are of sufficient commercial value that rapidly growing species have been considered for enrichment planting, particularly in Irian Jaya (or West New Guinea), Indonesia (Chapter 11). The very hard (highly polymerized) copal-type resin has an extensive fossil record; researchers have chemically identified Agathis-type resin from the Triassic, 200 Ma (Chapter 4).

Figure 2-3. Agathis australis, towering monarch and copal-producing tree of northern New Zealand. With permission of the Alexander Turnbull Library, National Library of New Zealand, Te Puna Matauranga o Aotearoa (timber industry, logging, reference 6266 1/1).

Agathis australis is the most famous species in the genus, and its Maori vernacular, kauri, has become a common name for the genus in many European languages. It is also commonly referred to as kauri pine, an obvious misnomer since it is not a pine. About 1850, kauri occurred over millions of hectares, but now only about 7000 hectares of virgin forest remain on the northern tip of New Zealand's North Island (Whitmore 1977). Agathis australis is one of the world's forest giants, and trees can form a canopy 40-50 m or more tall. The trees also have vast girth, more than 10 m being common, with clear boles of 10-12 m before the crowns spread (Figure 2-3). Trees self-prune their lower branches as they grow, leaving massive limbs sometimes a meter in diameter in the crowns of older trees. Although the big trees are thought to be 500-800 years old, with a few approaching 1000 years, their precise age is difficult to determine because the trees are often hollow. These giant trees contain a large volume of millable timber and produce enormous quantities of resin. The copal-type resin, used for fine, very durable varnishes, was sufficiently important commercially that it played a role in the establishment of the economy of northern New Zealand (Chapters 6 and 9).

Wollemia nobilis has been discovered relatively recently in a sheltered gorge of temperate rain forest in New South Wales, Australia (Jones et al. 1995). It occurs as an emergent tree in this one population. Morphological characteristics of Wollemia are intermediate between those of Araucaria and Agathis; similar characteristics are known only in fossil taxa such as Podoza-mites, which occurred from the Jurassic to Tertiary periods. Therefore, Seto-guchi et al. (1998) called Wollemia a living fossil. The chemistry of the resin of Wollemia has been studied from several perspectives such as carbon isotope biogeochemistry (Murray et al. 1998) and NMR (Lambert et al. 1999). NMR spectra of Wollemia and Agathis are similar.

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